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mise à jour
27 janvier 2002
 Behavioural and Neural Biology
1987;48:382-393
Yawning : No effects of 3-5% CO2,
100% O2 and exercice
RR Provine, BC Tate, LL Gelmacher
Department of Psychology University of Maryland Baltimore
 
Autres articles de R. Provine et R. Baenninger
Chat-logomini
Resume : the present research found no support for the popular hypothesis that yawning is a response to elevated CO2 or depressed O2 levels in the blood.
 
Yawning is a common and probably species-typical human behavior (Provine, 1986) that is performed throughout the life span (Gesell, l928). It is characterized by a gaping of the mouth accompanied by a long inspiration followed by a shorter expiration. Yawning is a stereotyped behavior that is evoked by unknown physiological stimuli or released by observed yawns or y awn-related stimuli (Provine, 1986). Yawns are easily triggered; even reading about or thinking about yawns stimulates them. Yawning is most frequent during the 'hour before 'bedtime and afterwaking (Provine, Hamernik,& Curchack). People also yawn when watching.uneventful stimuli or participating in repetitious, uninteresting tasks (Provine & Hamernik, 1986). The temporal proximity of yawning to bed and waking times and other occasions of low arousal is probably the basis for yawning as a paralinguistic signal for drowsiness.
 
Yawning is of medical importance because it is symptomatic of pathology such as brain lesions and tumors, hemorrhage, motion sickness, chorea, and encephalitis (Barbizet, 1958, Graybiel & Knepton, 1976; Heusner, 1946, Jurko & Andy, 1975). Yawning is also therapeutic in preventing postoperative respiratory complications (Cahill, 1978) and in adjusting the air pressure in the middle ear (Laskiewicz, 1953).
 
There is much popular opinion but little empirical evidence about the physiological cause and function of yawning. The unsupported hypothesis that yawning is a respiratory maneuver that somehow increases the oxygenation or decreases the CO, level of blood is often repeated in the popular and scientific literature (i.e., Abarbanel, 1964; Brody, 1984; Montagu, 1962; Redican, 1982). The present studies evaluated the effect of elevated levels of CO2, 02, and exercise on human yawning. These interventions alter blood levels of these gases and breathing rates (Comme, 1965). If yawning either increases or decreases in response to O2, CO2 or exercise, some form of the CO2/O2 hypothesis is supported and a respiratory role for yawning is suggested.
 
EFFECTS OF CO, AND O2 ON YAWNING
 
The prescent study tested the hypothesis that yawning is facilitated by higher than normal blood levels of CO, or lower than normal blood levels of O2 by observing the effect on yawning of breathing compressed air, 100% O2, and gas mixtures with higher than normal levels of CO2(3 or 5% CO2). (The normal composition of air is 20,95% O2, 79.02% N2 and inert gases, and 0.03% CO2). If yawning is a response to heightened blood CO2 levels, breathing gases high in CO2 should increase yawning rate and/or duration. If low blood O2 levels produce yawning, breathing 100% O2 should inhibit yawning. The effects of breathing gases with subnormal levels of O2 were not investigated because of concern about stressing the subjects.
 
Method : Subjects. The 18 subjects (3 males, 15 females) were 17 to 21 year old college freshmen who volunteered to earn experiment participation credit for an introductory psychology class. All subjects who began the study completed all four experimental conditions.
 
Procedure. All subjects began with a 30-min baseline condition in which they breathed normal room air. Three other 30-min experimental sessions were spaced at least 1 day apart. The order of presentation of all but the initial baseline condition was counterbalanced. The baseline session acclimated subjects to the experimental procedures without the additional novelty of breathing through a mask as in later conditions. During each of the next three 30-min sessions subjects breathed one of four gas mixtures: (a) 1 00% 02; (6) 3% C02, 21% 02, balance N2; (C) 5% CO2, 21% O2, balance N2; and (d) normal compressed air (20-95% O2 0,03%c CO2, 79.02% N, and inert gases). After observing no apparent effect of the 3% CO, mixture on the yawning of the first six subjects, the next 12 subjects were presented the 5% CO2 mixture. The compressed gases were fed into a 60 liter Douglas bag that acted as a reservoir from which subjects breathed using a small, hand held (Vital Signs) mask that covered the nose and mouth. The small mask was hand held by subjects to avoid their possible concern about having the mask strapped on. The reservoir (Douglas) bag technique for gas presentation was chosen instead of a demand regulator because the bag was more likely to produce a normal breathing pattern. Breathing was monitored with a chest bellows transducer and recorded with a Grass oscillograph. All gases were obtained from the Puritan-Bennett Corp. The gas mixtures with enhanced CO2 were guaranteed to be accurate within +-0.5% but were usually accurate within +- 0,1%. All conditions except baseline were counterbalanced in order and involved breathing gases through a hand held mask. The baseline condition during which subjects breathed room air was always first and served as a training session. For these reasons, the counterbalanced compressed air (air) condition that involved mask breathing is the best control condition with which to contrast the results for O2 and CO2.
 
Each subject was seated at a table in a well-lighted, fan-ventilated, sound-attenuating chamber with floor dimensions of 2.5 m X 3.1 m. After being seated, the participant was joined by the experimenter who took a seat across the table and explained the objectives and procedures of the study. All subjects were read the following information: "In this first part of a four-part study, we will be examining the naturally occurring frequency and duration of yawns. Your breathing rate will be monitored by a belt-like device that will be wrapped around your chest. You will be recording your own yawning behavior. Yawning is easy. It.is important hat you relax. and do net force yawns. It.will be unnecessary; most people can yawn by simply thinking of it. When you start to yawn, push down the button of the event recorder and keep it depressed until the yawn is complete. Consider the yawn to end when you finish exhaling. You will record the duration of each yawn until the end of the half-hour session. It is important to record your yawns as accurately as possible because other than the responses that you record, you will not be observed in any way. You will have complete privacy in the sound proofed booth. I will demonstrate how to respond to a yawn." (The experimenter demonstrated a typical yawn and the appropiate reonse to it). "Think about yawning and you can produce a real yawn. Now you try a practice yawn. Do you have any questions? After I leave the room, relax and think about yawning throughout the session and record your yawns, when they occur. You will be notified when the time is up".
 
After the first baseline session, each session was preceded with instructions about the use of the face mask used to supply the gas mixtures. Subjects were told, "In this part of the study, we will bc examining the effects of breathing one of threc gas mixtures on the naturally occurring frequency and duration of yawns. You will probably be unable to distinguish any difference between the gases. You will breathe the gas through a small mask that you will hold over vour mouth and nose. Do not alter your normal pattern of breathing while using the mask. Breathe naturally. The gases are safe to breathe and should produce no distressing sensations, but if you feel uncomfortable in any way, you may remove the mask for a few seconds. You may also quit the session at any time and.still receive credit for participating. The rest of the procedures are the same as in the first session. As before, your breathing rate will be measured by a belt-like device that will be wrapped around your chest. Your task is to think about yawning throughout the half-bour session and to record your yawns when they occur. When you start to yawn, push down the button of the event recorder and keep it depressed until the yawn is complete. Consider the yawn to end when you finish exhaling. If you think that the mask is inhibiting your yawning movements, you may remove the mask until the yawn is complete. Do von have any questions? After I leave the room, relax and think about yawning throughout the session and record your yawns when they occur. You will be notified when the time is up.
 
Subjects were fully informed of the experimental procedures and objectives, although they were not told which gas they were breathing during a given session. Informed subjects were considered to be less likely than uninformed subjects to speculate about their expected behavior and, thus, become more sensitive to possible experimental demand characteristics. The high-amplitude, all-or-none, behavior of yawning makes the yawner more reliable and accurate at discriminating his yawns than an outsider who must respond to sometimes ambiguous cues. The between session reliability of self-reponed yawns is documented in Provine (1986). Also, yawns were self-reported because attempts too bserve subjects directly may reduce yawning frequency because of the social sanctions against public yawning; several subject participating in a pilot study volunteered the comment that they did not like to y awn while being watched. Subjects pressed a button in response to a yawn. Their response was recorded with an Esterline-Angus chart recorder (A 620X) driven at 2.5 mm/s. Yawn duration was the time the subject kept the response button depressed. Yawn duration was measured manually from the event recorder records with a millimeter rule. The above procedures were modeled after those of a previous study. (Provine, 1986).
 
Results
The effects of breathing room air (baseline), compressed air (air), 100% 02, and C02 (3 or 5% C02, 21% 02, balance N2)on breathingrate, yawing rate, and yawning duration were examined. Breathing rate. The study is a factorial design with groups (3% CO, and 5%. C02), conditions (baseline, air, 02, and C02), and time periods (5, 10, 15, 20, 25, and 30. min).- The -.time periods were produced by averaging data from 1 to. 5 min, 6 to 10 min, and so on. The main effect of conditions was first tested in terms of three orthogonal contrasts baseline versus the average of all other conditions, air versus the average of 02 and the C02 mixtures, and 02 versus the CO, mixtures. The main effect of time period (period) was analyzed in terms of polynomial trend across the six 5-min periods. Both 100% 02 and the two CO2 mixtures increased breathing rate. The analysis of breathing rate reveals a highly sighificant (p < .0005) main effect of conditions using both multivariate (F(3,14) =14.94) and univariate (F3,48) = 14.46) tests. The contrast of baseline (room air, no mask) with other conditions is highly significant (F(l ,16) 13.67, p.002), as is the contrast of the air (compressed air) with the O2 and CO2 conditions (F(l, 16) = 31.77, p <.0005). The comparison of O2 with CO2 is marginally significant (F(l, 16) = 4.21, p =.057). The air versus O2 contrast is also significant as is the air versus CO2 contrast. There is no interaction with conditions and groups, either overall or for any of the individual interaction contrasts (all F ratios < 1). The main effect of period and the interaction of period with groups is nonsignificant. The interaction of Condition x Period and the three way interaction of Group X Condition X Period are also nonsignificant.
 
It should be noted that the above analyses yield a very conservative estimate of CO2 effects. Although CO2 produced small but significant increases in breathing rate, previous work from other laboratories has established that respiratory tidal volume almost triples in response to breathing 5% CO2 (Dripp's &-Comroe, 1947). The heavy breathing produced by 5% C02 in the present study was not experienced in response to the other gases.
 
Yawn frequency. Neither 100% 02 nor either of the C02 mixtures influenced the rate of yawning. A multivariate analysis of yawn fiequency revealed no main effects of group condition or period. There was, however, an effect of condition by the univariate test (F(3, 48)= 3.17, p = .033) that was interpretable as a difference between the haseline and the average of the other three conditions (F(l, 16) =4.17, p = .045). The detection of such a difference is not surprising because, as noted above, the baseline training condition was always first and did not involve breathing through a mask. The compressed air (air) condition is, thus, a better control. The interaction of condition and period was also significant (multivariate F(15,2)=42,98, p = ,023) and suggests that the fonctions for the four conditions are diverging over time. However, the 30-min session length is probably adequate to reveal experimental effects if they were present. As noted above, breathing 5% C02 produces dramatic increases in breathing rate and tidal volume: This respcinse is obvious within a few minutes.
 
Yawn duration neither 100% O2 nor either of the CO2 mixtures influenced the duration of yawns. In the analysis of yawn duration, the main effect of period is highly significant by both multivariate (F(5, 12)=7.76, p = .002) and univariate (F(5, 80) 3.34, p = .009) tests. A trend analysis revealed a linear increase in yawn duration over the six 5-min time periods. No other main effects or interactions concerning yawn duration were significant.
 
In summary, both 100% O2 and the combined CO2 groups (3 and 5%) produced significantly greater breathing rates than the baseline or the compressed air control and the higher breathing rate of the CO2 compared to the O2 group approached significance. In contrast, breathing CO2 and O2 had no significant impact on yawning rate or duration when compared to either baseline or compressed air controls. The hypotheses that yawning is a response to a high blood level of CO2 or a low level of O2 were not confirmed.
 
EFFECT OF EXERCISE ON YAWNING
If yawning serves a respiratory function, yawning and breathing may share common regulatory mechanisms or be influenced by similar stimuli. The present study examined the effect of exercise on yawning rate and duration. Exercise increases breathing rate. If yawning either increases or decreases during exercise, a relationship between yawning and respiration is indicated. If no relation is found between the response to exercise of yawning and breathing separate and independent mechanisms control the rates of the two behaviors.
 
Method Subjects. The 19 subjects (7 males, 12 females) were 17 to 21 year old college freshmen who volunteered to earn experiment participation credit in an introductory psychology class.
 
Procedure. Subjects were seated alone in the small, sound-attenuated experimental chamber described previously, and were instructed to think about yawning. Subjects reported their yawns by pressing the button on a small box held in their right hand that activated an event recorder. This procedure was the same as that used in the first study. Breathing rate was detected with a small thermister probe that was clipped to the subject's left nostril and recorded using a Grass oscillograph. After 10 min of baseline data had been collected from seated subjects in a resting condition, the experimenter entered the chamber and instructed the subject te exercise by stepping up and down a 25.4 cm step at a rate of approximately on step cycle every 2 s. Subjects were also instructed to continue thinking about yawning and to record their responses. After 10 min.in the exercise condition, the experimenter again entered the chamber and instructed the subjects to be seated, but to continue thinking about and recording yawns. The experiment was terminated after this second 10 mn baseline period. Average breathing and yawning rates were tabulated for every 1min interval. Yawn duration was not analyzed because of potential problems that subjects may have had in recording yawn duration in a comparable manner while sitting in the control condition and stepping in the exercise condition. Such potential problems would be unlikely to influence the all-or-none recording of yawn occurrence, the variable of primary interest.
 
Results The effect of moderate exercise on breathing and yawning rates is shown.in Fig 4. During the 10-min exercise period, breathing rate rapidly increased until it was almost twice that of the preceding 10-min baseline period. Breathing rate declined rapidly toward preexercise levels during the recovery period. Significant differences in breathing rate were detected among all three conditions (baseline A; exercise, and baseline 13) using a multivariate test (F(2, 17) = 42.711, p < .0005) and a univariate repeated measures test (F(2, 36) = 69.73, p < .0005). Both the exercise versus baseline contrast and the contrast between the two baseline conditions were significant (FI, 18).- 90.02 and 18.55, respectively, p < .0005). Yawning rate declined across the three conditions of the experiment and no effect of exercise was detected. A multivarlate test of the effect of conditions was significant (F(2, 17) = 5.36, p = .016). The corresponding F ratio from a repeated measures ANOVA was also significant (F(2, 36) = 5.67, p = .007). An evaluation of univariate contrasts indicated that the number of yawns produced in the exercise condition was not different from the average number in the two baseline conditions. The two baseline conditions were, however, significantly different from each other (F(I, 18) = 11.35, P = .003). These two contrasts are equivalent to quadratic and linear trends, respectively. Thus, yawn frequency declined in a systematic linear manner across the three conditions (time periods) of the experiment. The fallure to detect a significant effect of exercise on yawning rate was not due to the inadequacy of exercise to produce a substantial physiological effect on subjects; exercise produced a significant effect on one simultaneously recorded behavioral variable, breathingy rate.
 
DISCUSSION
The present research found no support for the popular hypothesis that yawning is a response to elevated CO2 or depressed O2 levels in the blood. Neither breathing pure O2 nor gases high in CO2 had a significant effect on yawning although both increased simultaneously recorded breathing rate. Exercise that doubled breathing rate also had no effect on yawning. The increase in breathing rate to elevated CO2, O2, and exercise established that all three interventions had measurable physiological effects. Breathing and yawning share some similar motor processes that produce inspiration and expiration, but the independent variation of yawning and respiration suggested that breathing and yawning are responses to different internal states and are controlled by différent mechanisms. Although it can be argued that other gas concentrations, exposure times, or instructions may have produced different findings, there are no contrary data in the hurnan yawning literature and the prescrit results are a part of a broader pattern of converging evidence.
 
Further evidence that yawning is not primarily a respiratory act comes from an analysis of the routes of inhalation and exhalation during yawning and the relation between yawn duration and inter yawn interval (Provine, 1986; Provine, Hamernik, Tate, & Curchack, 1986). Inhalation and exhalation occur primarily through the mouth and this basic pattern is highly inflexible. It is very difficult, if not impossible, for most people to perform a satisfying yawn with their mouth taped shut even though they are free to respire through their nose and rnove their jaw to a limited extent within their closed mouth. Yawning does not have the degree of behavioral freedom characteristic, of normal breathing. However, oral inhalation by itself is insufficient to produce a satisfactory yawn if the jaws are not free to move. Subjects attempting to yawn with clenched teeth often reported the unpleasant sensation of being stuck in mid yawn and being unable to perform a satisfying yawn although they could inhale and exhale through their teeth. Thus, the yawn is not simply a deep breath. The finding that performers of short yawns do not compensate by yawning more frequently and vice versa is also inconsistent with the yawn as a respiratory event (Provine, 1986).
 
The primary function of the highly stereotyped action pattern of yawning may be some nonrespiratory component of the behavior such as sretching. A precedent exists for the association of yawning and stretching. Subjects who cannot stretch their jaws because their teeth are clenched are unable to perform satisfactory yawns (Provine, 1986), and generalized body stretches often accompany yawns in humans (Provine et al) and other animals (Dourish & Cooper). Neurological case reports of associated movements in human hemiplegics provide further evidence for a correlation between yawning and stretching. Herniplegics often stretch otherwise paralyzed body parts during yawns (Walshe, 1923). Pharmacological evidence for a yawn-stretch relation is provided by the observation that drugs that produce yawning also trigger stretching in a variety of animals (Dourish & Cooper, in press; Gessa, Pisano, Vargiu, Crabai, & Ferrari, 1967; Yamada & Furukawa, 1980). There is also evidence of at least partial autonomy of yawning and stretching. Yawns may be performed without concurrent stretches and vice versa. The circadian patterning of yawns differs from that of stretches; yawning is most frequent shortly before sleeping and after waking, whereas stretching is frequent only immediately after waking (Provine et al).
 
The difference in the temporal distribution of yawning and stretching and the ability to perform elther behavior autonomously suggests that yawning is not simply the facial component of a generalized stretch response. During evolution, yawning may have become emancipated from a generalized stretch response or may have evolved independently but served a furiction homologous to stretching. Stretching has consequences ranging from increases in blood pressure and heart rate to improved flexibility of muscles and joints. If the yawn is a localized stretch of the face and upper body, its consequences may be as diverse and plentiful as those of other types of stretches. However, yawning is unique in having important conseqpences for both groups and individuals. If yawning is assumed to,have a physiological effect on the yawner, the tendency to yawning response to observed yawns produces a behavioral chain reaction among witnesses that synchronizes the physiological state of a group (Provine et al.). Both yawning and its resulting physiology are contagious.
 
Disorders of mental functioning produced by varying the oxygen tension of the atmosphere Barach AL, Kagan J 1940