James
E. Kennedy
September,
1990, Unpublished Manuscript
Abstract: Understanding and application of various respiratory
practices are impeded by the many interacting physiological and psychological
variables. Yoga techniques may offer
insights into useful breathing practices and control of important
variables. This review integrates
relevant data from (a) the psychophysiological/psychological literature, (b)
the physiological/medical literature, and (c) studies of yoga. The available data indicate that yogic slow
breathing practices promote dominance of the parasympathetic system, can help
control stress, and can contribute to treatment programs for some chronic
diseases. Basic research is needed on
yogic rapid breathing and alternate nostril breathing techniques. Yogic claims about nasal airflow laterality
and cognitive laterality have partial support.
Psychological factors such as anxiety and distraction, as well as the
physical details of breathing techniques, are important variables in
psychophysiological research on respiratory practices.
NOTE OF MAY, 1994: Several lines of research have progressed
since this unpublished manuscript was prepared four years ago. These include: (a) several new studies of
yoga breathing techniques have been reported, but they do not significantly
alter the conclusion in this manuscript, and (b) the effects of deep breathing
on the autonomic system and the effects of hyperventilation appear to be more
complicated and/or variable than was recognized when the manuscript was prepared.
--------------------------------------------------------------
Various respiratory patterns and maneuvers can provide
striking influences on the autonomic nervous system and may exacerbate or
reduce adverse responses to stressors.
For example, increased breathing rate is a typical response to stressful
situations (Grossman,
1983; Magarin, 1982). This tendency can lead to breathing in
excess of metabolic needs (hyperventilation), which causes reduced blood carbon
dioxide concentrations. The reduced
carbon dioxide causes psychophysiological and psychological effects that
include (a) enhanced arousal and anxiety, and (b) decreased cerebral and
coronary blood flow, which can lead to a variety of clinical symptoms including
dizziness, poor performance, headache, chest pain, cardiac abnormalities, and
sleep disturbance
(Brown, 1953; Fried, 1987; Grossman, 1983; Lum, 1976; Magarin, 1982). Certain
other respiratory patterns that modestly elevate blood carbon dioxide
concentration appear to promote the opposite effects, including reduced anxiety
and increased or well maintained cerebral and coronary blood flow (Grossman, 1983).
However, practical applications of breathing techniques
are hindered by the lack of understanding and control of the many interacting
variables. A recent review of
physiological mechanisms for respiratory influences on the cardiovascular
system described a maze of interwoven and dramatically interacting control
mechanisms (Daly, 1986). As
indicated above, psychological factors can strongly interact with these
physiological mechanisms. With the
present state of knowledge, the psychophysiological effects of novel
respiratory practices cannot be reliably predicted and replications of basic experiments
are often inconsistent due to uncontrolled variables (several examples are
given in following sections).
Yoga breathing practices may provide insights into
valuable respiratory techniques and control of important variables. These practices are intended to maintain
optimum health--with particular emphasis on stress reduction--but have received
little scientific attention. According
to yoga tradition, the practices were developed by extensive personal
experimentation and keen introspection of the results. The breathing practices, or pranayama, are
one component of hatha yoga, which is intended to give one a healthy body and
mind.
Reduction of hypertension (Irvine, Johnston, Jenner, & Marie, 1986; Patel,
Marmot & Terry, 1981; Patel & North, 1975) and dramatic improvement of heart disease (Ornish et al., 1979; 1983; 1990) have resulted from integrated treatment programs
that included yoga breathing practices.
However, the roles of individual treatment components have not been
delineated in these studies. A review
of the scientific information related to yoga breathing practices may be useful
for evaluating the role of breathing practices in these programs and for
improving the practices or adapting them to special cases.
According to yoga tradition, certain breathing practices
induce relaxation and calmness, whereas others are invigorating and
arousing. In addition, certain
practices are claimed to influence cognitive functioning of the brain
hemispheres.
This article is intended to (a) describe basic yoga
breathing practices, (b) summarize the available scientific information
relevant to the effects of these practices, and (c) identify topics needing
further research. Health threats from
potential misuse of certain powerful respiratory techniques are also
noted. The techniques are discussed
individually in the sequence they are commonly practiced. Studies that combined several practices
without isolating the effects of individual breathing techniques are included
in the final discussion and conclusions section. The review focuses on the common basic breathing techniques, with
emphasis on beginning to intermediate levels.
Less common practices and extremely advanced practices are beyond the
scope of this review.
Diaphragmatic Breathing
Yoga Practice
The basic mode of respiration used in many yoga practices
and recommended for normal daily activities is slow, smooth breathing using the
diaphragm rather than the respiratory muscles of the chest (Christensen, 1987, p. 136;
Samskrti & Veda, 1985, p. 10). This breathing pattern is sometimes referred
to as abdominal breathing, although, as noted below, the abdominal muscles may
play a minor role. Breathing is through
the nose rather than the mouth.
Scientific Information
The diaphragm is the dominant respiratory muscle for
quiet breathing in awake healthy adults, but increased use of chest muscles and
increased breathing rate are common results of stress and may become
habitual. Slow diaphragmatic breathing
appears to reduce adverse effects of stress and promote parasympathetic cardiovascular
dominance. The opposite effects are
induced by more rapid breathing using the chest muscles. Before discussing the available data, a
brief review of the respiratory process may clarify the nature of these modes
of breathing and the methodological issues in their investigation.
The Respiratory Process
Three muscle groups can be used in breathing: (a) the
diaphragm, (b) the muscles of the rib cage, and (c) the abdominal muscles. This summary of the roles of these muscles
is based on Collett, Roussos, and Macklem (1988); Grassio
& Goldman (1986); Guyton (1986); and Troyer
and Loring (1986).
The diaphragm is the most important muscle for
inhalation. It is a thin sheet of
muscle separating the chest and abdominal cavities. When relaxed the diaphragm forms an open-bottomed cylinder that
extends up into the lower part of the rib cage along the sides of the rib cage,
and forms a dome on top. Diaphragm
contraction shortens the cylindrical portion and pulls the dome down. This movement expands the lungs by pulling
them down, which creates a partial vacuum that causes inhalation if the airway
is open. When the diaphragm relaxes,
the elastic recoil of the lungs pulls it upward, causing exhalation. The downward pressure on the abdominal
viscera from contraction of the diaphragm forces the abdominal wall to extend
forward and/or the lower rib cage to expand to the sides. The term abdominal breathing derives from
this easily observed movement of the abdominal wall, but can also refer to the
use of abdominal muscles described below.
Although upper chest movement is relatively inconspicuous
in quiet breathing for a relaxed person, some thoracic muscles play a
role. The external and parasternal
intercostals (joining adjacent ribs) and the scaleni (connecting the shoulder
area and spine) are activated during inspiration to hold the ribs in an
expanded position that compliments the force of the diaphragm. However, the exact roles of each of the
muscles are not yet resolved. The
minimal chest movement combined with the fact that some chest displacement
could be a result of diaphragmatic action have contributed to the difficulty in
resolving this question. The internal
intercostals may sometimes play a role in exhalation.
The abdominal muscles are the most powerful and important
muscles for forced exhalation, but are normally not used in quiet
breathing. Contraction puts inward
pressure on the abdominal viscera, which then push the diaphragm up and reduce
lung volume. In addition, these muscles
may assist expiration by pulling down and deflating the lower rib cage. The important abdominal muscles for
respiration are the rectus abdominous, the transverse abdominous, and the
external and internal obloquies.
Abdominal muscles can contribute significantly to inhalation
by pushing the relaxed diaphragm farther into the rib cage. This action (a) places the diaphragmatic
muscle fibers on a more favorable part of their length-tension curve, and (b)
converts some of the respiratory system expiratory elasticity to inspiratory
forces.
Only about 10 percent of total respiratory capacity is
used on each breath in quiet breathing.
The volume of each exhalation or tidal
volume is about 500 ml for a quiet adult male. Most of this tidal volume goes to lung areas that exchange oxygen
and carbon dioxide with blood, but about 150 ml is dead space from passages that cannot contribute to gas
exchange. Dead space volume is
relatively constant whereas tidal volume varies greatly with physical exercise,
breathing pattern, and other factors.
Thus, larger tidal volumes have a smaller proportion of dead space. Dead space can increase significantly with
lung disorders.
During normal quiet breathing, exhalation is driven by
the elastic forces of the lung. Muscles
used for inhalation contract to slow and control the rate of exhalation. The position of the relaxed diaphragm and
corresponding lung volume after exhalation depend on a balance between the
elastic forces collapsing the lungs inward and the elastic forces expanding the
chest outward. This lung volume at the
end of relaxed expiration is called the functional
residual capacity (FRC).
About one fourth of the respiratory capacity not used
with quiet breathing can be accessed with additional exhalation and three
fourths with additional inhalation. If
abdominal muscles force maximum reduction of lung volume, the expiratory reserve volume of about 1100
ml of air below FRC for an average male is expired. This combines with the tidal volume (500 ml) and the inspiratory reserve volume of about 3000
ml to give a vital capacity of 4600
ml. In addition, a residual capacity of about 1200 ml of air remains in the lung after
maximum exhalation. These values are
typical for a young adult male. The
volumes are about 25 percent less for an average female, and vary with body
size, posture, and physical condition.
Adequate air flow or ventilation
of the lungs can be achieved with slow breathing rate and large tidal volume or
fast rate and small tidal volume. The
ventilation rate is normally set to provide oxygen and remove carbon dioxide in
accordance with metabolic needs.
The abdominal and chest muscles also have important
functions for posture, locomotion, and verbalization that must be integrated
with and may modify respiratory functions.
Thoracic Breathing
In a wide-ranging, extensive review of the literature
related to respiration and stress, Grossman (1983) concluded:
A breathing pattern characterized as rapid, low-tidal
volume, predominantly thoracic ventilation with relatively low alveolar and
blood concentrations of carbon dioxide . . . is associated with psychological
characteristics of anxiety, neurosis, depression, phobic behavior, and high
levels of perceived and objective stressors.
Voluntary performance of this breathing pattern seems to intensify
subjective and physiological indicators of anxiety when exposed to stress. Cardiovascularly, voluntary production of
this ventilatory pattern appears to bring about significant reduced
parasympathetic tone and increased sympathetic dominance, which are expressed
in augmented heart rate and cardiac output, muscle vasodilation, decreased
blood flow and oxygen supply to the heart and brain, reduced [respiratory sinus
arrythmia] and baroreceptor responsiveness, and increased likelihood of major
ECG abnormalities. (p. 293)
Stress causes a tendency for enhanced ventilation with
upper chest breathing patterns that can become habitual in some people. This conclusion is supported by a variety of
studies of stress reviewed by Grossman, by more recent studies of stress (Freeman, Conway & Nixon, 1986) and by studies of hyperventilation (Lum, 1976; Magarin, 1982).
The increased ventilation in response to stress
presumably is in anticipation of physical activity such as a fight or flight
reaction (Grossman,
1983).
However, when little physical activity follows, a tendency to breath in
excess of metabolic needs results. In
this context, the tendency to hyperventilate in response to stress in a
civilized society is not surprising.
The degree of hyperventilation and associated symptoms vary from mild to
severe depending on dispositional and situational factors (Bass & Gardner, 1985; Clark
& Hemsley, 1982; Freeman, Conway, & Nixon, 1986; Wientjes, Grossman
& Defares, 1984).
As noted in the introduction, over breathing causes a
variety of effects, including increased heart rate, arousal and anxiety, and
various clinical symptoms due to decreased blood flow to the brain and
heart. Note that voluntary
hyperventilation usually induces increased arousal and anxiety in normal subjects [1]
(Clark & Hemsley, 1982;
Grossman, 1983; Thyer, Papsdorf, & Wright, 1984). The reduced
carbon dioxide concentration in the blood is a key physiological factor
underlying these effects. The decreased
blood flow to the heart and the heart rhythm abnormalities can pose a
significant risk for those with cardiovascular problems.
Thoracic breathing is symptomatic of habitual or chronic
hyperventilation and may be a potentiating factor (Freeman, Conway & Nixon, 1986; Lum, 1976). Lum (1976) reported that over 99 percent of the 640 patients he
had seen for chronic hyperventilation were thoracic rather than diaphragmatic
breathers. He suggested that some
people with a tendency to respond to stress with thoracic breathing become
habitual over breathers. The result is
that:
The chronic hyperventilator lives much nearer the
frontier of hypocapnic [low carbon dioxide] symptoms and any small additional
stress, whether psychological or physical, may push him over into symptoms
which add to the stress while leaving him mentally and physically less able to
cope. Thus the vicious cycle may be
triggered. (Lum, 1976, p. 214)
Based on clinical
experience and very limited published data, Fried (1987, p. 8)
estimated that incidence of habitual hyperventilation in the general population
may be 10 to 15 percent and perhaps over 20 percent.
Autonomic Effects
Diaphragmatic breathing appears to lead to advantageous
physiological and psychological effects through autonomic nervous system
activity. Grossman (1983) concluded:
A slow, large-tidal-volume, predominantly abdominal
pattern of ventilation . . . is associated at the psychological level with
emotional stability, sense of control over the environment, calmness, a high
level of physical and mental activity, and relative absence of perceived or
objective stressors. Short-term
modification of breathing pattern toward this type seems to cause a reduction
of subjective and physiological indices of anxiety under conditions of stress;
long-term modification seems to produce--with certain clinical populations--a
diminution of psychological difficulties, e.g. neurotic tendencies, chronic
anxiety responses, and psychosomatic symptoms.
Cardiovascularly, this breathing pattern appears independently to
produce relatively high [parasympathetic] tone and low sympathetic activation,
which manifest as low heart rate, increased supply of blood and oxygen to the
heart and the brain, and enhanced [respiratory sinus arrythmia] and
baroreceptor responsiveness. (p. 292)
Of particular relevance, Grossman noted that the four
studies investigating the effect of paced slow respiration in stressful
situations "uniformly indicate that mere voluntary changes of respiration
rate by subjects under stressful circumstances serve to modify the subjective
perception of anxiety" (p. 292). A more recent study by Cappo and Holmes (1984) also supports this conclusion. Several studies have also found paced slow
respiration reduces autonomic reactivity as measured by skin resistance (but
not heart rate) (Cappo
& Holmes, 1984; Harris, Katkin, Lick, & Habberfield, 1976; McCaul,
Solomon, & Holmes, 1979).
Similarly, slow diaphragmatic breathing has consistently
proven successful therapy for persons with hyperventilation stress responses
that reached clinical severity (Bonn, Readhead, & Timmons, 1984; Clark, Salkovskis & Chalkley,
1985; Grossman, de Swart, & Defares, 1985; Hegel, Abel, Etscheidt,
Cohen-Cole, & Wilmer, 1989; Hibbert & Chan, 1989; Kraft & Hoogduin,
1984; Lum, 1976). Grossman (1983) cites various
studies suggesting that slow breathing causes blood carbon dioxide
concentrations to be in the upper normal range, which promotes
psychophysiological effects generally opposite to those of hyperventilation.
Grossman (1983) notes that respiratory
sinus arrythmia (increased heart rate during inspiration) is a useful index of
parasympathetic tone and is largest during slow deep breathing. He also cites evidence suggesting that
normal parasympathetic tone promotes good health and may serve a protective
function for the heart, whereas decreased parasympathetic tone may be related
to heart disorders. He further suggests
that the relative balance between the parasympathetic and sympathetic nervous
systems may be important in determining responses to stress. More recent studies support the hypothesis
that parasympathetic dominance has protective value for the cardiovascular
system (Beere, Glagov,
& Zarins, 1984; Jennings &
Follansbee, 1985; Muranaka, et al.,
1988).
Physical Effects
Diaphragmatic breathing has traditionally been considered
the most efficient mode of quiet breathing (e.g., Miller, 1954; Sharp et al., 1974). Because
tidal volume is typically larger in diaphragmatic breathing, the proportion of
ventilation wasted as dead space is minimized.
In addition, enhanced ventilation to the lower lungs increases
efficiency of gas exchange because gravitational forces cause much higher blood
flow in the lower lungs
(West, 1988). Diaphragmatic-abdominal breathing can cause higher air flow to
the lower lungs than thoracic breathing (Fixley, Roussos, Murphy, Martin, & Engel, 1978;
Roussos et al., 1977; Sampson & Smaldone, 1984); however,
this effect was not found in other studies (Bake, Fugl-Meyer, & Grimby, 1972; Grassio, Bake,
Martin & Anthonisen, 1975; Grimby, Oxhoj, & Bake, 1975; Sackner, Silva,
Banks, Watson, & Smoak, 1974) and
apparently depends on details of respiratory muscle action and perhaps
experimental methodology
(see, Roussos et al., 1977).
Pressure on the abdominal viscera from diaphragmatic
motion also contributes to venous blood return to the heart (Grossman, 1983; Permutt &
Wise, 1986), which is an important
determinant of cardiac output and efficiency (Guyton, 1986).
Diaphragmatic breathing has historically been recommended
for persons with chronic obstructive lung disease (Barach, 1955; Frownfelter, 1987; Miller, 1954). However,
efforts to quantify the benefits have given mixed results (Jones, 1974; Rochester &
Goldberg, 1980). A detailed review of the literature is
needed, but is outside the scope of the present paper. Potential psychophysiological and
psychological benefits should be considered in addition to the usual measures
of lung function.
Nasal Breathing
Nasal breathing is the best means of warming and
humidifying inhaled air in preparation for the lungs. Available information on the function and evolution of the human
nose is consistent with a primal purpose of conserving moisture and heat (Cole, 1988; Franciscus &
Trinkaus, 1988). In a temperate climate, the estimated energy
expenditure to condition inhaled air can be equivalent to about one sixth of a
person's daily energy output; however,
about 30 to 40 percent of this energy is recovered by exhaling through the nose (Cole, 1982, 1988). Higher
efficiencies of heat and moisture recovery occur in cold and/or dry
environments.
The nose also filters incoming air (Guyton, 1986, p. 477), has irritant receptors that trigger protective
reflexes (Widdicombe,
1986), and, of course, provides the
sense of smell. The resistance to air
flow in nasal breathing may be an efficient passive means of slowing air flow
to provide adequate gas exchange at low ventilation rates (Hairfield, Warren,
Hinton, & Seaton, 1987; Jackson, 1976;
McCaffrey and Kern, 1979a).
Nasal breathing is the normal and preferred mode of quiet respiration.
The
intriguing hypothesis that nasal respiration plays an important role in
controlling brain temperature may have important implications for brain
functioning and psychological states (Dean, 1988; Zajonc, Murphy, & Inglehart, 1989). However,
the basic mechanisms and effects of brain cooling have not yet been resolved (Wheeler, 1990).
Further Research
Role
of abdominal muscles. Both the yoga and scientific literatures
have focused on comparing diaphragmatic-abdominal breathing with thoracic
breathing, but have little discussion of the specific role of the abdominal
muscles. The abdominal muscles may
shift the expiratory end volume, alter the rib cage shape, or play no
role. Differing use of the abdominal
muscles may be a factor in the inconsistent replications of certain respiratory
findings. One yoga master recommends
that abdominal muscles not be used once diaphragmatic breathing is established (Samskrti & Veda, 1985 p. 10). Research
may be of particular value on the following topics:
1. Abdominal
breathing may help stretch and relax the diaphragm in persons who manifest
stress by excessive tonic diaphragm contraction. Some individuals have increasing contraction and immobilization
of the diaphragm as stressful topics are discussed (Faulkner, 1941; Holmes, Goodell,
Wolf, & Wolff, 1950, p. 49; Wolf, 1947). The prevalence of excessive
tonic diaphragm tension, both acute and chronic, and the effects of abdominal pressure
on the diaphragm in these cases may merit further investigation.
2. Diaphragmatic
and abdominal breathing cause rhythmic pressure on and movement of the
abdominal organs, which could affect the functioning of those organs. In fact, a yoga breathing exercise of
pulling in the abdominal muscles during
exhalation is claimed to create perfect digestion (Rama, 1988, pp. 191-192). Digestion
and slow diaphragmatic breathing are both associated with parasympathetic
activity and therefore may be both autonomically and mechanically coupled. Similarly, the stress response of thoracic
breathing with a relatively inactive diaphragm may provide minimal mechanical
stimulation of the abdominal organs and appears consistent with reduced
gastrointestinal activity during sympathetic arousal and anticipated physical
activity. The potential interaction
between the gastrointestinal system and the respiratory system deserves
investigation, particularly with regard to the effects of psychological factors
such as stress.
3. The use of
abdominal muscles to drive end expiration below relaxed expiratory position
(FRC) may lead to less efficient gas exchange and to lower cardiac efficiency,
particularly in older persons and persons with lung impairment. The small airways in the lower lung tend to
close with exhalation below FRC (Collet, Roussos, & Macklem, 1988). These airways reopen only when
pressure is sufficient to overcome surface tension. Until inspiration exceeds the needed pressure, air is distributed
to the upper lung, resulting in inefficient gas exchange. For normal young people some airways are
closed at residual capacity (maximum possible exhalation), but most are
open. With age, lower airway closure
increases and may occur with normal exhalation (i.e., at FRC). In addition, respiratory actions that
increase plural pressure (pressure in the thoracic cavity surrounding the heart
and lungs) tend to decrease venous return to the heart (Permutt & Wise, 1986) and thus reduce cardiac efficiency. Exhalation below FRC increases plural
pressure (Collett,
Roussos, & Macklem, 1988) and,
therefore, may reduce cardiac efficiency.
Improved
experimental controls. Studies on the effects of breathing mode
have rarely considered (a) the subjects' responses to the experimental
procedure, and (b) individual differences in pattern of breathing and chronic
stress level. Troyer and Loring (1986, p. 473) note that normal subjects are well known to adopt a
more thoracic breathing mode during respiration experiments. This result is not surprising in light of
the evidence that anxiety leads to a tendency for thoracic breathing. Likewise, the variation in the tendency to
hyperventilate suggests that individual differences are very important
factors. Studies that find thoracic breathing
prevalent in a quiet breathing condition (e.g., Sharp, Goldberg, Druz, & Danon, 1975) raise questions about the effects of the
experimental procedure and subject pool.
Careful attention should be given to subject pool and the subjects'
reactions to experimental procedures and personnel.
Complete Breath
Yoga Practice
The complete breath
technique, also called three part breathing, slowly fills and empties the
entire lung capacity (Christensen, 1987, p. 137; Samskrti &
Veda, 1985, p. 173; Satchidananda, 1970, p. 142). A smooth maximum inhalation is
accomplished by first expanding the abdomen and lower rib cage, then expanding
the middle rib cage, and finally expanding the upper rib cage. The abdomen naturally withdraws as the chest
is fully expanded. The arms are
sometimes slowly raised overhead to help expand the chest. A slow maximum exhalation follows in the
reverse order--sinking the upper chest, then the middle chest, and finally
pulling in the abdomen. The complete
breath may be done in either a sitting or a standing position. The mind is focused on the breath and the
release of tension during breathing.
This technique is often done three to five times at the
beginning of hatha yoga sessions or at the beginning of the yoga breathing practices. Yoga texts recommend this technique at other
times to counter stress and refresh the mind and body.
Scientific Information and Further Research
The summary of scientific information and suggestions for
further research are combined because very little relevant scientific work has
been done on this technique. (As
discussed below, the technique has been used in studies that combined various
breathing and physical relaxation practices.)
Autonomic Effects
Because the complete breath is the extreme case of slow
deep breathing, the psychophysiological effects discussed for diaphragmatic
breathing may possibly be extrapolated to this technique. However, such an extrapolation would go
beyond the range of available data as no studies were found that used this
specific sequence for full breathing capacity.
For example, Hirsch and Bishop (1981) found that
respiratory sinus arrythmia (a good index of parasympathetic tone) consistently
increased as tidal volume increased, but, the maximum tidal volume studied was
only half vital capacity and the sequence of breathing was not specified.
The complete breath passes through a range of changing
autonomic reflexes so the net effects are difficult to predict. Lung volume or stretch reflexes, for
example, decrease parasympathetic activity at moderate lung inflations, which
in turn causes increased heart rate due to increased sympathetic
dominance. At large lung volumes,
however, autonomic reflexes cause decreased heart rate (Daly, 1986). Basic
research on the psychophysiological effects of the complete breath remains to
be carried out.
Physical Effects
The complete breath gently contracts and stretches all
respiratory muscles. This presumably is
beneficial, particularly for sedentary persons who may not otherwise exercise
some respiratory muscles. Research on
release of muscle tension accumulated during stressful activities might be
fruitful.
The full inhalation of the complete breath should provide
maximum opening of the collapsed lower airways, which may be of particular
value to older persons and those with lung impairment. However, the full exhalation will also
provide maximum collapsing of airways.
For maximum airway opening, the complete breath practice should end
after an inhalation, rather than after a full exhalation.
Rapid Breathing
Yoga Practice
Two rapid breathing techniques are used in basic yogic
practices (Samskrti
& Franks, 1978, p. 158; Satchidananda, 1970, pp.145-146). One
technique is a quick short forced exhalation using the abdominal muscles,
followed by a slower automatic diaphragmatic inhalation as the abdominal
muscles are relaxed. The volume of air
is smaller than normal tidal volume.
The other technique has the same short forced exhalation, but the
inhalation is also short and forced using the diaphragm and extending the
abdomen. These two techniques will be
referred to here as automatic inhalation
and forced inhalation,
respectively. The automatic inhalation
technique is more common. Both
techniques use nasal breathing and are done in a sitting position. The mind is focused on breathing,
particularly the abdominal contractions.
For both techniques, beginners repeat about ten to twenty
of the inhalation-exhalation cycles at a rate of about one cycle per
second. One complete breath technique
is usually done very slowly after the series of rapid cycles. After a short rest, the series of cycles and
complete breath may be repeated once or twice.
Over a period of several weeks or months the practioner may work up to
two to three cycles per second for a series of one hundred or even several
hundred cycles. In the advanced stages,
breathing may be very vigorous and the breath is held after a series of rapid
cycles (see section on breath holding below).
Most
yoga manuals and instructors state that a person should stop and rest if any
sensations of dizziness or light headedness occur during rapid breathing. Also, rapid breathing should not be done
within about two hours after a meal. In
more advanced, vigorous practice, the stomach, bladder and bowels should be
empty.
The common yoga terms for the basic rapid breathing
techniques are kapalabhati and bhastrika;
however, some authors use kapalabhati for an automatic inhalation
technique whereas others use it for forced inhalation. The term bhastrika has similar variations in
use, but usually indicates a more advanced practice that includes breath
holding.
Scientific Information
Yoga practioners describe rapid breathing as
invigorating. As discussed below, mild
arousal may be caused by gentle, controlled hyperventilation and/or significant
exercise of the respiratory muscles.
The information presented in this section is based on data for rapid
breathing without breath holding.
Breath holding is discussed in a separate section below.
Rapid Breathing and Hyperventilation
Rapid breathing such as one breath per second normally
causes hyperventilation and can be used for hyperventilation provocation tests (e.g., Freeman, Conway, &
Nixon, 1986). As discussed above, hyperventilation causes arousal and
sympathetic dominance.
However, the yoga rapid breathing techniques cause only
slight or no excess ventilation.
Several lines of evidence support this conclusion. (a) As noted in the description of the
practice, dizziness and other symptoms of significant hyperventilation are
specifically avoided. (b) Wenger and
Bagchi (1961) reported that the pattern of heart rate, finger
temperature and pulse volume was different during automatic inhalation rapid
breathing ("kapalabhati") than during hyperventilation. However, the observed pattern could be
consistent with slight excess ventilation. (c) Mean carbon dioxide
concentrations of alveolar air (where gas exchange with blood occurs in the
lungs) after automatic inhalation rapid breathing were similar to resting
levels, not lower as occurs with hyperventilation (Kuvalayananda &
Karambelkar, 1957a; 1957b; 1957c). The
eight experienced practitioners breathed at about 2 cycles per second. (d) The average arterial carbon dioxide
partial pressure was slightly (14 percent) reduced but within the normal range
during a predominantly thoracic variation of (apparently) forced inhalation
rapid breathing at nearly four cycles per second (Frostell, Pande, & Hedenstierna, 1983).
The small volume of each breath makes very inefficient
respiration that prevents excess ventilation.
Available data indicate average tidal volumes during automatic
inhalation rapid breathing of about 35 to 55 percent of the average resting
tidal volume (Frostell,
Pande & Hedenstierna, 1983; Gore & Gharote, 1987; Karambelkar &
Bhole, 1988; Karambelkar, Deshapande, & Bhole, 1982; Miles, 1964). The net effect can be seen
from a hypothetical example consistent with these data. Typical respiration of 15 breaths per minute
at 500 ml tidal volume gives 7,500 ml per minute total ventilation, of which
5,250 ml (70%) goes to lung areas with gas exchange, assuming 150 ml dead
space. For comparison, 120 breaths per
minute at 215 ml tidal volume gives 25,800 ml per minute total ventilation, of
which 7,800 ml (30%) goes to gas exchange areas.
[2]
(As discussed below, oxygen consumption may
increase by a factor of 1.5 during rapid breathing due to the extra work of
respiration.) Because total ventilation
increases more than carbon dioxide production, carbon dioxide concentration in
expired air is lower during yogic rapid breathing than during normal breathing
(Karambelkar, Deshpande & Bhole, 1982, 1984a).
Heart Rate
Heart rate increases during yogic rapid breathing. Average heart rate increased from a baseline
of 77 beats per minute to 86 beats per minute for 12 subjects performing
automatic inhalation rapid breathing at about 120 breaths per minute (Bhole, 1982). Likewise,
Wenger and Bagchi
(1961) found that average heart rate for
five yogis increased from about 77 to about 90 beats per minute while
performing automatic inhalation rapid breathing ("kapalabhati"). Average respiration rate was not reported,
but the example record showed about two breaths per second. Average heart rate of 64 beats per minute at
rest increased to 94 beats per minute during thoracic forced inhalation
breathing at about 4 cycles per second for three highly trained subjects (Frostell, Pande, &
Hedenstierna, 1983).
The degree of heart rate increase varies with the intensity
and perhaps type of rapid breathing.
Heart rates of 120, 120 and 157 beats per minute were found in three
males during "vigorous" forced inhalation rapid breathing (Hoffman & Clarke, 1982). The subject
with the rate of 157 had regularly practiced yogic breathing for over four
years, whereas the other two subjects had less experience. Corresponding heart rates during
"gentle" forced inhalation rapid breathing were 100, 100, and 121
beats per minute and during resting conditions were 78, 74 and 70. For all subjects, heart rate accelerated
during the first 20 to 40 seconds of rapid breathing and then leveled off at
the faster rate. Specific respiration
rates were not reported, but comments indicate rates of 1.5 to 2 breaths per
second.
Physical Effects
Yogic rapid breathing provides significant exercise for
the respiratory muscles with only a mild to moderate overall body work
output. Overall physical work is
measured by comparing oxygen consumption during exercise with consumption while
sitting quietly. Oxygen consumption
increases by a factor of two for walking at two miles per hour and factors of
eight or more for intense exercise such as running (deVries, 1986, p. 349). (For
comparison, practices such as certain types of meditation are called hypometablolic because oxygen
consumption is lower than while normally sitting quietly [Wallace, Benson,
& Wilson, 1971].)
The average oxygen consumption rates during automatic
inhalation rapid breathing have been 1.1 to 1.8 times higher than while sitting
quietly (Gore &
Gharote, 1987; Karambelkar & Bhole 1988; Karambelkar, Deshapande &
Bhole, 1982; Miles, 1964). These figures are for the overall average in
each study. Karambelkar and Bhole (1988) reported that average oxygen consumption increased
as duration of rapid breathing increased from one to five minutes.
Other rapid breathing techniques that use more respiratory effort have higher oxygen consumption. Frostell, Pande, and Hedenstierna (1983) estimated that the forced inhalation thoracic breathing at about 4 breaths per second (that was maintained continuously for 30 to 60 minute periods) increased oxygen uptake compared to sitting quietly by a factor of three, which was about 23 percent of maximal aerobic capacity and an over 200-fold increase in respiratory work. Likewise, the high heart rates observed by Hoffman and Clarke (1982) during forced inhalation breathing are consistent with moderate rather than mild work loads. [3]
Persons subject to adverse reactions to exercise should
use caution with rapid breathing. For
example, elevated serum muscle enzyme activity from vigorous breathing
exercises during an asthmatic episode may have exacerbated and prolonged the
attack in one susceptible patient (Tamarin, Conetta, Brandstetter & Chadow, 1988).
Further Research
Autonomic
and psychological effects.
Other than heart rate, autonomic effects of yogic rapid breathing have
received very little study. Wenger and
Bagchi (1961) reported decreased average finger temperature and
increased skin conductance during rapid breathing, which is consistent with the
expected increased sympathetic activity.
Further study is needed, particularly on effects on the cardiovascular
system. Likewise, investigations of
possible effects of rapid breathing on arousal, performance, anxiety, stress
response, etc. are needed.
Air flow responses.
Potential psychophysiological
responses to air flow during rapid breathing deserve investigation. Stimulation of air flow receptors in the
nose may activate reflexes that reduce the drive to breath (Widdicombe, 1986). Other
studies suggest that nasal air flow receptors may stimulate electrical activity
in the brain (Kristof,
Servit & Manas, 1981; Servit, Kristof, & Kolinova, 1977; Servit &
Strejckova, 1976; Ueki & Domino, 1959).
Cardiac
arrhythmias. The potential for
rapid breathing to stabilize and stimulate heart beat merits study for clinical
applications. When heart rate and
breathing were synchronized, which occurred at about 110 to 115 cycles per
minute, heart rate showed reduced variability in three healthy subjects (Hoffman & Clarke, 1982). In two case
reports, nodal premature beat cardiac arrhythmias disappeared after automatic
inhalation rapid breathing (Monjo, Gharote, Bhagwat, 1984). One patient used about 120 breaths per
minute and stimulated heart rate to 105 beats per minute. The other patient had severe ischemic heart
disease and used only 60 breaths per minute.
Regional
distribution of air. Preferential
distribution of air to the upper lungs could contribute to the inefficient
ventilation and the absence of excessive ventilation during yogic rapid
breathing; however, air distribution has not been studied for small tidal
volume, diaphragmatic rapid breathing.
The rapid thoracic breathing studied by Frostell, Pande and Hedenstierna (1983) strongly shifted air flow to lung regions with low
gas exchange rates.
Alternate Nostril Breathing
Yoga Practice
Alternate nostril breathing consists of slow deep quiet
breaths using one nostril at a time (Samskrti & Franks, 1978, pp. 159-161; Satchidananda,
1970, pp. 143 & 149). The thumb or ring finger are used to close
off the other nostril. Three variations
exit, depending on when the nostrils are switched. In one variation, the active nostril is switched after each inhalation. In the second variation, exhalation is
through one nostril and inhalation through the other. After a few cycles, the inhalation and exhalation nostrils are
reversed. The third variation switches
nostrils after several breaths. For all
three techniques, each breath is as slow as comfortable using full lung
capacity as in the complete breath. A
sitting position is used.
Beginners attempt to make the duration of inhalation and
exhalation equal and do only about six single nostril breaths between
rests. With practice, the duration of
exhalation is slowly extended to twice the duration of inhalation and the
practice is continued for several minutes.
The mind is focused on the slow deep breathing in a manner similar to
meditation. The advanced practice
continues for 10 to 20 minutes or longer with the breath held after inhalation
and/or exhalation. Yoga writings use a
variety of terms for alternate nostril breathing, including nadi shodhanam,
nadi suddhi and sukha purvaka.
Scientific Information
Existing research efforts have focused on understanding
the psychophysiology of nasal functioning.
This work is important background for understanding the potential
effects and significance of the alternate nostril breathing technique, but
basic direct research on the technique remains to be done. As discussed below, research has verified
the yoga claims that nasal air flow is usually greater in one side of the nose
than the other, and that the open side switches every few hours. The available data relevant to the yogic
claim that this asymmetric nasal air flow is related to lateral brain
functioning are inconsistent and difficult to interpret.
Autonomic Effects
Average heart rate increased from 71 to 78 beats per
minute and blood oxygen, carbon dioxide, and pH did not change significantly
after ten minutes of alternate nostril breathing (Pratap, Berrettini, & Smith, 1978). The ten
subjects had two to five years experience with the technique. Average respiration rate was 2.7 breaths per
minute during the last minute of alternate nostril breathing. The breath was not held except very briefly
to move the hands while switching closed nostrils. (Data from an investigation of advanced alternate nostril
breathing is presented in the later section on breath holding.)
Background on Nasal Dominance
According to yoga tradition, alternate nostril breathing
improves the functioning, coordination and balance for two modes of cognitive
activity that are reasonably similar to current concepts of right and left hemispheric
brain functioning
(Rama, Ballentine & Ajaya, 1976). Ancient yoga writings claim that the modes
of mental activity are related to which nostril is dominant or most open to air
flow. Mental capabilities corresponding
the left hemisphere dominate when the right nostril is more open. Likewise, right hemispheric mental
capabilities dominate when the left nostril dominates. Equal air flow through both nostrils
represents a balance of the two mental modes.
Yoga tradition also claims that nostril dominance and
corresponding cognitive mode alternate approximately every one (Bhole & Karambelkar, 1968) or two hours (Rama 1986, p.89). According to these writings, the cycle
becomes erratic with emotional disturbance, irregular eating or sleeping
habits, and various other life style factors.
Nasal Airway Resistance
The airways of the nose are lined with erectile tissue
that swells when engorged with blood.
The swelling increases congestion and resistance to air flow, which
enhances humidifying and warming of inhaled air (Cole, 1982, 1988) and may be an efficient passive mechanism for braking the respiratory
system elasticity during periods of low ventilation (Hairfield, Warren, Hinton,
& Seaton, 1987; Jackson, 1976; McCaffrey and Kern, 1979a; 1979b).
Nasal airway resistance changes in response to changing
air flow or air conditioning needs.
Nasal congestion (a) decreases (vasoconstriction) with exercise or with
elevated carbon dioxide levels from breathing carbon dioxide, rebreathing with
a bag, or holding the breath, and (b) increases (vasodilation) with
hyperventilation or breathing cold air (Cole, Forsyth, & Haight, 1983; Cole, Haight, Love,
& Oprysk, 1985; Dallimore & Eccles, 1977; Forsyth, Cole, &
Shephard, 1983; Hasegawa & Kern, 1978; McCaffrey & Kern, 1979b;
Richerson & Seebohm, 1968; Takagi, Proctor, Salman, & Evering, 1969;
Tatum, 1923). Nasal resistance can vary greatly among subjects and over time (Holmes, Goodell, Wolf, & Wolff,
1950; Takagi et al., 1969).
Psychological factors such as stress, fear, and
frustration can apparently affect nasal resistance. Eccles
(1982) noted that adrenaline, which is
released during stress, causes decreased nasal resistance. Clinical observations of patients with
chronic or recurrent nasal congestion found that congestion increased during
periods of anxiety or conflict with frustration, resentment and guilt (Holmes et al., 1950; O'Neill &
Malcomson, 1954; Wolff, 1950), but
decreased during fear and panic (Holmes et al., 1950, pp. 58 & 114). Holmes et al. (1950, p. 140) suggested that increased nasal congestion was
associated with a passive, withdrawing response to stressors, whereas decreased
congestion occurred in preparation for heightened respiration of an active
fight or flight response.
Sympathetic nerves control nasal congestion whereas
parasympathetic nerves control nasal secretion with some associated influence
on blood flow and congestion (reviewed in Eccles, 1982). Reduced nasal sympathetic vasoconstrictor
tone causes congestion, whereas increased sympathetic activity causes
decongestion. Reduced parasympathetic
tone causes reduced nasal secretion and reduced congestion, whereas increased
parasympathetic tone causes increased nasal secretion and increased congestion. These conclusions are supported directly by
experiments with animals and are consistent with the effects of surgical and
chemical nerve blockade in humans (e.g., Chandra, 1969; Golding-Wood, 1973; Haight &
Cole, 1986; Millonig, Harris, & Gardner, 1950; Richerson & Seebohn,
1968).
Nasal Dominance
Numerous studies consistently show that one side of the
nose usually has higher airway resistance in most people and that the
asymmetric resistance switches sides after a few hours (e.g., Clarke, 1980; Eccles, 1978;
Gilbert & Rosenwasser, 1987; Hasegawa & Kern, 1977; Heetderks, 1927;
Keuning, 1968; Stoksted, 1952, 1953).
However, the widely used term nasal cycle may not be technically correct because there is little
evidence that the changes in nasal resistance have reasonably constant periods. As noted by Gilbert and Rosenwasser (1987), most nasal cycle studies have observed subjects for
only a few hours on one day whereas much longer or repeated study periods are
needed for relevant time series statistical analysis. Changes of nasal dominance during these short periods cannot be
assumed to be a continuing cyclic (i.e., fixed period) process. In one of the few studies to attempt
replicate testing, Hasegawa and Kern (1977) noted
"of the five subjects who had second studies, none had reproducible
findings" (p. 33). Likewise,
failure to observe nasal resistance alternations in these short study periods
does not mean they do not routinely occur in a subject.
Longer studies have given mixed evidence for regular
cycles. Obvious regular shifts about
every three hours were found for one subject examined for 18 hours (Principato & Ozenberger, 1970). Regular
shifts about every one to two and half hours were found for two subjects
examined for seven days
(Eccles, 1978). However, for eight subjects studied for one
month, the alternations in nostril dominance did not have regular
periodicities, except for some very weak daily patterns found by averaging over
the month (Clarke,
1980; Funk & Clarke, 1980). Most subjects in these latter studies also had
one side dominant more often than the other.
Factors Affecting Nasal Dominance
Asymmetric or unilateral pressure on the chest,
shoulders, trunk or buttocks can shift nasal dominance. The pressure triggers vasomotor reflexes
that increase nasal resistance on the side of the pressure and decrease it on
the other side (Bhole
& Karambelkar, 1968; Cole & Haight, 1984, 1986; Davies & Eccles,
1985; Haight & Cole, 1984, 1986; Rao & Potdar, 1970; Singh, 1987;
Takagi & Kobayasi, 1955). These reflexes cause (a) the readily
observed congestion in the lower nostril and decongestion in the upper nostril
when people lie on their sides, (b) the ancient yoga observation that placing a
crutch or yoga-danda under one arm while upright leads to ipsilateral
nasal congestion and contralateral decongestion, and (c) in at least some
persons, nasal dominance shifts due to asymmetrical weight distribution while
seated (Haight &
Cole, 1986). The widely varying time periods between nasal dominance shifts
are not surprising if asymmetrical weight distribution can cause the
shifts. Haight and Cole (1989) report that 37 of 42 subjects showed a nasal
response to unilateral pressure.
Increased ventilation demands can also alter nasal
dominance. Nasal resistance can become
low and nearly symmetric during exercise, rebreathing with a bag, and probably
breath holding
(Dallimore & Eccles, 1977; also supported by the example in Ohki, Hasegawa,
Kurita, & Watanabe, 1987). The amplitude of nasal resistance
fluctuations is less while standing compared to sitting (Cole & Haight, 1986).
The hypothesis that anxiety and other life style factors
cause shifts in nasal dominance is conceptually consistent with the evidence
noted above that psychological factors affect nasal resistance, but specific
studies of psychological factors and nasal dominance have not been
reported. Eccles (1978) suggested that uncontrolled environmental factors
may normally obscure the regular nasal cycles observed in his seven day
laboratory study.
The neural mechanisms controlling nasal resistance are
primarily ipsilateral, but some evidence suggests possible contralateral
effects in some people. Unilateral
sympathetic efferent severance or blockade in humans caused pronounced ipsilateral
nasal congestion, and no apparent effect on contralateral nasal resistance and
responses in several studies (Fowler, 1943; Haight & Cole, 1986; Holmes, et al., 1950, pp.
113-119). However, during unilateral sympathetic blockade, slight increases
in contralateral resistance that may have been related to the blockade occurred
in one study (Stoksted
& Thomsen, 1953) and reduced
contralateral nasal responses to exercise occurred in another study (Richardson & Seebohm, 1968). Unilateral
parasympathetic severance has resulted in less secretion and less congestion on
the side of severance in several hundred patients surgically treated for
excessive nasal secretion
(Golding-Wood, 1973; Jarvis, Marais, & Milner, 1970; Millonig, Harris,
& Gardner, 1950). The immediate unilateral effects were followed
by contralateral effects about two weeks after surgery in about one third of
the cases. The factors causing the
unpredictable contralateral effects in a minority of the patients are not
known.
Ultradian Rhythms
Shannahoff-Khalsa with various others have suggested that
the nasal dominance alternations reflect an underlying endogenous cycle of
shifting right-left dominance in the brain and autonomic system. They report lateral changes in brain wave
activity (Werntz,
Bickford, Bloom & Shannahoff-Khalsa, 1983) and peripheral catecholamines (Kennedy, Ziegler, & Shannahoff-Khalsa, 1986) tightly coupled with nasal dominance. In addition, they cite a variety of studies
suggesting ultradian (less than a day) cycles in psychophysiology and
performance with periods of about 80 to 150 minutes. In particular, the report by Klein and Armitage (1979) of 90 to 100 minute cycles in verbal and spatial
performance that were 180 degrees out of phase supports the hypothesis of
alternating lateral processing. These cycles
are proposed to be an extension of alternating lateral dominance in rapid eye
movement and nonrapid eye movement sleep stages.
Unfortunately, there are few noncontroversial findings in
ultradian-laterality rhythm research.
Replication of the Klein and Armitage (1979) study failed
to find cycles of lateral cognitive processing (Kripke, Fleck, Mullaney & Levy, 1983). Some
recent writers have strong arguments for doubting the basic hypothesis that
rapid eye movement/nonrapid eye movement sleep cycles reflect reciprocal shifts
in lateral brain activity
(e.g., Antrobus, 1987; Armitage, Hoffman, Loewy, & Moffit, 1989). The
integrated total EEG measure used by
Werntz et al. (1983) and in several previous studies of lateral brain
activity primarily reflects alpha activity, whereas lower amplitude higher
frequency activity may be more important indicators of lateral cognitive
processing (Armitage,
1989; Ray & Cole, 1985). The situation is compounded because Werntz
et al. used the opposite interpretation than is traditional for this measure
(i.e., they hypothesized that higher amplitude EEG [i.e., alpha activity]
indicated more mental activity instead of less).
Convincing conclusions about rhythms of lateral
physiological functioning will probably require extensive further
research. This is a very difficult research area--the number of
potentially important variables and methodological details are vast, as are the
speculations about inconsistent findings.
Single Nostril Breathing and Brain Laterality
A recent experiment found evidence that performance on
left hemispheric (verbal) and right hemispheric (spatial) tasks were affected
by single nostril breathing, but the results provided little support for the
specific predictions from yoga (Block, Arnott, Quigley, & Lynch, 1989). The results
were contrary to the yoga predictions for males, and in the predicted direction
for females on only the spatial task.
For the spatial task, males performed significantly better during right
nostril breathing than during left nostril breathing, whereas females had the
opposite result. For the verbal task,
males performed significantly better during left nostril breathing than during
right nostril breathing, whereas females showed no difference in
performance. Nasal air flow was not
measured in this study. Single nostril
breathing began five minutes before the tasks.
Two earlier experiments found that breathing through one
nostril did not significantly affect performance on verbal and spatial tasks,
but males and females were not analyzed separately (Klein, Pilon, Posser &
Shannahoff-Khalsa, 1986). In one study, performance was measured
before, during, and after 15 minutes of single nostril breathing. In the other study, performance was measured
before and after 30 minutes of single nostril breathing.
The Klein et al. (1986) experiments
also included measurement of asymmetric nasal air flow and reported equivocal
results correlating air flow with performance on the tasks. Post hoc analyses combining both experiments
correlated the difference between task scores with the degree of asymmetric
nasal air flow. The correlation for the
data collected before the single nostril breathing period gave a suggestive
result (p < .05, uncorrected for multiple post hoc analyses) in the
direction of yoga predictions, but explained less than four percent of the
variance for 114 subjects. A similar
result was obtained for the data collected after single nostril breathing. These results were due primarily to
performance on the spatial task.
Unfortunately, males and females were not analyzed separately. The initial subject pool was 56 percent
female, but some subjects of unspecified sex were excluded. The effect of single nostril breathing on
lateral nasal airflow was not reported.
Another study reported single nostril breathing caused relatively larger total integrated EEG activity contralateral to the open nostril (Werntz, Bickford, & Shannahoff-Khalsa, 1987). The results for the one male and four female subjects were all in the same direction. As noted above, the traditional interpretation for this finding would be relatively more mental activity on the same side as the open nostril, which is counter to the predictions from yoga. After citing a study (Ray & Cole, 1985) suggesting that alpha activity, and by implication total integrated EEG, does not reflect lateral cognitive processing, the authors considered the results ambiguous. [4]
Several physiological studies on animals and humans
indicate that nasal air flow receptors stimulate electrical discharges
predominantly to the same side of the brain as the receptor (Kristof, Servit & Manas, 1981;
Servit, Kristof, & Kolinova, 1977; Servit & Strejckova, 1976; Ueki
& Domino, 1959). Although the studies show that unilateral
nasal hyperventilation can trigger ipsilateral, and to a lesser extent
contralateral, epileptic EEG activity in susceptible subjects, the overall
implications are not clear. Of course,
the very slow air flow rates of the alternate nostril breathing technique should
minimize stimulation of the nasal airflow receptors indicated by these and
other studies
(Widdicombe, 1986).
Taken
together, these studies provide little evidence for the specific cognitive
effects of single nostril breathing that have been hypothesized based on yoga
tradition. However, the specific yogic
alternate nostril breathing techniques apparently were not used in any of these
studies. In addition, any conclusions
appear premature until basic questions about methodology and interpretation are
resolved, and until further replications and explorations are carried out.
Further Research
Autonomic and
psychological effects. Basic
research on the effects of alternate nostril breathing techniques remains to be
done. These techniques are widely held
by practitioners to calm and sooth the mind, and appear ripe for research. Breathing rates near the subjects' limit of
slow breathing may be particularly interesting due to enhanced carbon dioxide
concentrations and minimum stimulation of air flow and olfactory receptors.
Autonomic reflex receptors on the face and in the nose
that could possibly be stimulated by holding one side of the nose closed during
alternate nostril breathing also offer research potential. As discussed in the next section, such receptors
are an important component of the dive response. The receptors respond to water and some other mechanical
stimulation (Daly,
1986; Daly & Angell-James, 1979; Elsner & Gooden, 1983). Medical
procedures such as packing one side of the nose to halt a nose bleed can
apparently activate this reflex (Daly & Angell-James, 1979; Fairbanks, 1986; Jackson, 1976). The related
oculocardiac reflex has similar effects--gentle pressure on the closed eyes
causes heart rate slowing and reduced respiratory drive characteristic of the
dive response (Daly,
1986).
Prolonged
exhalation. Research is needed on
the hypothesis that the prolonged exhalation of alternate nostril breathing and
other yogic slow breathing techniques promotes calmness and parasympathetic
dominance. Heart rate slowing during
exhalation (respiratory sinus arrythmia) is the result of greater
parasympathetic activity during exhalation (Daly, 1986; Grossman, 1983). Likewise, increased alpha EEG
activity (Lehmann &
Knauss, 1976) and theta activity (Lorig, Schwartz, & Herman,
1989) have been reported during
exhalation. Muscle sympathetic activity
has been found to vary with phase of respiration, but inconsistent findings
suggest that variables such as breathing pattern are also important (Eckberg, Nerhed, & Wallin,
1985).
In an initial investigation of prolonged exhalation, Cappo and Holmes (1984) found that slow breathing with prolonged exhalation
resulted in less arousal from threats than breathing with equal durations of
inhalation and exhalation (as used in previous studies), or with prolonged
inhalation. The effect of the prolonged
exhalation treatment was significantly different than for a control group
without paced respiration, but the differences among breathing treatments did
not reach statistical significance.
Nasal dominance. The hypotheses that lateral nasal dominance
is related to lateral brain processing and that unilateral nasal breathing
effects lateral brain activity both need further investigation. If nasal dominance is confirmed to have
significant psychological or psychophysiological effects, then investigation of
the factors controlling nasal dominance becomes important. Because any natural endogenous nasal cycle
in humans is apparently normally overshadowed by exogenous factors, the most
efficient course may be to first focus on the exogenous factors. The pressure points, postures, and weight
distribution that shift nasal dominance due to asymmetric body pressure is an
important and easily researched area.
The finding that weight distribution while sitting can affect nasal
dominance may have significant implications for daily life, but is based
primarily on only two subjects (Haight & Cole, 1986). The hypothesis that stress, depression,
fear, etc. alter nasal dominance and resistance also needs further research.
Theory. Research on nasal dominance is hindered by
the lack of a coherent rationale for the phenomena. The speculation (e.g., Eccles, 1978) that the
alternations of nasal airflow allow one side of the nose to rest from its air
conditioning function offers a testable hypothesis, but provides no obvious
explanation for the important and perhaps dominating effects of asymmetric body
pressure, or for the possible effects on cognitive processing. The hypothesis that nasal respiration
affects brain temperature and brain functioning (Zajonc, Murphy, & Inglehart, 1989) also offers research potential.
Therapy. Friedel (1948) discussed
eleven case reports in which chest pain of angina pectoris and related stress
were greatly relieved by alternate nostril breathing. Alternate nostril breathing was described as an effective means
to obtain the benefits of slow deep diaphragmatic breathing, including
parasympathetic stimulation and elevated blood carbon dioxide concentrations. Prakasamma (1984)
reported that patients with restricted expansion of the lungs due to pleural
effusion had significantly quicker re-expansion after 20 days of alternate
nostril breathing treatment than a control group that followed routine
physiotherapy. The patients reported
that they enjoyed alternate nostril breathing.
Breath Holding
Yoga Practice
During intermediate and advanced practice of rapid br