Respiration Physiology (1975) 24, 163-17 1; North-Holland Publishing Company, Amsterdam
VENTILATORY
RESPONSE OF GOATS TO TRANSIENT CO2 AND O2 DURING ACUTE HYPOXIA
CHANGES
IN
CURTIS A. SMITH and RALPH H. KELLOGG Department of Physiology, University of California, San Francisco, California 94143, U.S.A.
Ahstnct. The authors assessed the relative sensitivity of the peripheral chemoreceptors of 4 goats to a transient decrmsc in inspired CO2 using a 2-breath test. This test provides a steady-state background of hypoxia and hypercapnia and then, for 2 breaths, an equally hypoxic gas mixture containing no CO1. Another type of 2-breath test, providing 2 breaths of a hyperoxic gas mixture against a background of hypoxia, was used to establish the time course of a response known to come from peripheral chemoreceptors. Seven human subjects were studied in a similar fashion to establish the validity of the procedure. Except for 2 responses, the author’s human data agree with those reported previously by others. All 4 goats resembled man in responding to removal of hypoxia with a significant decrease in ventilation, but 3 of the 4 goats, unlike man, showed no significant decrease in ventilation when CO2 was removed. The authors conclude that the peripheral chemoreceptors of goats are commonly insensitive to transient changes in inspired CO, during acute hypoxia. Carotid bodies Chemical regulation Goats
Peripheral chemoreceptors Two-breath test Ventilatory response
The goat has long been used for respiratory studies (Held et al., 1964; Tenney and Brooks, 1966; Fencl et al., 1966; Pappenheimer, 1967). Its ventilatory responses to CO2 inhalation during acute and chronic hypoxia have been well characterized (Mines and Srarensen, 1970; Lahiri et al., 1971X but there is little information concerning the contribution of the peripheral chemoreceptors to the CO, response. The presence of positive interaction between the responses to hypoxia and CO2 in the studies of Lahiri et al. ( 1971) suggest that the peripheral chemoreceptors of goats may be sensitive to CO, (or pH), whereas the lack of such interaction in the studies of Tenney and Brooks (1966) and of Mines and Sorensen (1970) suggests the contrary. Sorensen and Mines (1970) also demonstrated that chronic carotid denervation can affect the steady-state CO2 response of goats, but they did not study the acute Accepted for publication 18 March 1975.
C. A. SMITH AND R. H. KELLOGG
164
responses of the peripheral chemoreceptors to COz. Clearly, a knowledge of such responses would be useful in interpreting respiratory data from this species. The purpose of this study was to ascertain the existence of a peripherally mediated response to transient changes in CO, (and the associated changes in arterial pH) during acute hypoxia in the awake goat.
Materials and methods
We used a two-breath test as described by Cunningham et al. ( 1965, 1973) and Miller er al. (1974), which is based on the single-breath test of Dejours er al. (1958). In this test, the goat is presented with a gas mixture that makes it both hypoxic (end-tidal oxygen, PETIT, about 40 mm Hg) and hypercapnic (Ptzrco, about 50 mm Hg). Abruptly the inspired gas is switched, for two breaths, to an equally hypoxic mixture that contains no COz (‘removal of CO,‘) and is then returned to the original mixture. The advantages of this method over other methods of presenting a transient change in CO2 stimulus have been discussed by Miller et al. (1974). Of course, CO2 stimulates central chemoreceptors as well. It is therefore necessary to know the time course of a peripheral response so that it can be distinguished from the central effects. To accomplish this, another type of two-breath test (‘removal of hypoxia’) was used, in which two breaths of a hyperoxic gas (PIN, about 670 mm Hg) were given against a steady-state background of hypoxia (PETE, about 40 mm Hg) (Cunningham et al., 1965, 1973; Miller et al., 1974). Since acute hypoxia is directly sensed only by peripheral chemoreceptors and since its on-transient in cats (Black er al., 1966) is known to be somewhat slower than the off-transient for CO1 both in cats (Black et al., 1966) and in human subjects (Cunningham et al., 1973), one may presume that any peripherally mediated decrease in ventilation due to COz removal would occur no later than that due to increased PoL. In these experiments, responses were compared by calculating the mean single breath ventilation(%‘~)for three breaths prior to the two-breath change in inspired gas and for eight breaths following the onset of this change. The following formula was used:
VE (I/min) =
VT -:(1) .-.-~. [60 secjmin] breath duration (set) 1
This calculation was performed for each breath in every test. Mean ventilations were calculated by averaging each breath (numbered from the change of inspired gas) from 7 to 52 such tests. Control ventilation was considered to be the mean of the means of the three breaths prior to the change in inspired gas. All data were measured and recorded by the same person. A change in ventilation was considered significant if it was more than two pooled standard errors from the control mean (Dixon and Massey, 1969). Since the silent, remote-controlled valve that we used to change gas mixtures had never before been used in experiments, we chose to test it and our recording system
165
VENTILATORY RESPONSE OF COATS
by trying to reproduce the human experimental data of Miller et al. (1974). Seven human volunteers were tested. The protocol was similar to that described for the goats except that in the hypoxic portions the PET,, was approximately 65 mm Hg rather than 40 mm Hg. TABLE 1 Physical characteristics of the goats -. Weight
Goat
.__~._. 1088 1778 1298 1299
(kg)
Sex
-.--
.~..
55 61 45* 45*
161 212 113 95
castrate castrate castrate castrate
male male male male
* estimated.
h
! ,
Fig. I. A typical record from a CO1 removal experiment with a goat. The signal bar in front of the arrowhead indicates the duration of the two-breath change of inspired gas composition. VE is recorded directly from the pneumotachograph. VT is the integral of VE. Pc,, is recorded on a compressed scale (to show zero) and also on an expanded scale. PET,, % 40 mm Hg.
166
C. A.
SMITH AND R. H. KELLOGG
Four mixed breed, short haired, castrated male goats were prepared with chronic tracheostomies by the method of Thilenius and Vial (1963). Surgery was performed under methoxyflurane or halothane anesthesia. The goats had been born and reared at low altitudes. Their physical characteristics are listed in table 1. After a month for recovery from surgery the goats, were subjected to several practice sessions in the laboratory to accustom them to the procedure. They stood in a stanchion and were intubated through the tracheostomy with an endotracheal tube with inflatable cuff. During an experiment, the endotracheal tube was connected to a low dead space respiratory valve designed to allow remote-controlled and silent switching between two gas mixtures (Smith and Kellogg, 1975). The gas mixtures were adjusted to appropriate concentrations by means of a double set of Matheson flowmeters. Each gas mixture was mixed in a large manifold half tilled with water for partial humidification and then piped directly to the respiratory valve. The expired gas passed through 1arge:bore respiratory tubing to a heated f3 Fleisch pneumotachograph. The pneumotachograph signal was electrically integrated to give expired tidal volume for each breath (fig. 1). Volume corrections for temperature and pressure were considered unnecessary for this study. Airway Pco, was continuously recorded from an infrared CO2 meter (Beckman LB-l), and end-tidal Po, was intermittently sampled manually for analysis in an oxygen electrode (Radiometer). The order in which the experiments were performed was varied randomly from day to day. Panting was prevented by cooling the goats with an electric fan and by sponging their flanks with water when necessary. Results of a test were accepted only if the goat did not defecate, urinate, cough, pant, or move about and the tidal volumes of both breaths of altered inspired gas were greater than twice the dead space determined for that goat. Seven human volunteers were studied (table 2). All were natives and residents of low altitudes and gave informed consent. The experimental apparatus was similar to that used with the goats except that the human subjects breathed through a mouthpiece, were seated in a comfortable chair, and were encouraged to read and/or TABLE 2 Physical characteristics of the human subjects Subject
RC RF RK SK CS IS ss
Height
Weight
Age
(4
(kg)
(Yd
75
30 23 54 33
190 188 179
82 79 72
170 I75
80
26
170
55
26
I67
54
27
Sex
male male male male male female female
167
VENTlLATORY RESPONSE OF GOATS
listen to recorded music. Human tests were accepted only cough or move about and the tidal volumes of both breaths were greater than twice the predicted dead space (values Subjects consistently stated afterwards that they were unaware of the changes in inspired gas.
if the subject did not of altered inspired gas from Comroe, 1974). of the timing or nature
Results The data are summarized in fig. 2 and table 3. In general, the human subjects transiently decreased their breathing following the transient removal of hypoxia and following the transient removal ofC02 with average latencies of 12.1 and 10.7 seconds respectively, agreeing reasonably well with the observations of Miller et al. (1974). The exceptions were that subject JS showed no significant response to removal of hypoxia and subject SS showed no significant response to removal of CO,. The latencies were longer following removal of hypoxia than following removal of CO? TABLE 3 Latency of response Hypoxia removal
CO2 removal
(M
N
(=I
N
Goat
Background Pmo,=40 mm Hg
2 breaths Pto,=700 mm Hg
Background Pm,,=40 mm Hg Ptrrco,=50 mm Hg
2 breaths Paro,=40 mm Hg &,,=O mm Hg
1088 1778 1298 1299
6.7 *0.7* 6.4kO.2 10.1kO.7 6.7 f 0.5
50 52 16 10
no response no response no response 6.1 kO.2
48 50 19 11
mean
7.4
Subject
Background PFT,, = 65 mm Hg
2 breaths Pto, g 700 mm Hg
Background Pxro,=65 mm Hg Pmco,=50 mm Hg
2 breaths F%ro,=65 mm Hg b,=O mm Hg
RC RF RK SK CS JS ss
13.6kO.4 9.1 kO.5 17.5kO.6 10.9kO.4 10.5+0.1 no response 10.7* 1.3
10 7 12 19 21 15 18
12.9kO.2 8.8 f 0.2 14.150.1 11.9kO.2 8.7kO.l 7.9* 1.1 no response
10 20 14 20 18 19 19
mean
12.1
* mean f standard error.
10.7
168
Fig. 2. Mean ~ntiI~tiun
C. A. SMITH AND R. H, KELLOGG
by breath number. The vertical bar represents one standard error on either side of the mean.
in each individual subject except SK. The four goats studied all showed a significant decrease in breathing after removal ofhypoxia with latencies generally shorter than in man, but only goat 1299 showed a significant decrease in breathing in response to CO2 removal. In that case, the latency
VENTILATORY
RESPONSE
OF GOATS
169
following removal of hypoxia was longer than that following removal of C02. and the significantly decreased breath appears somewhat aberrant compared to adjoining breaths (fig. 2). Discussion The results of the human experiments satisfied us that our apparatus and techniques were capable of reproducing the observations of Miller et al. (1974). Removal of hypoxia produced a prompt decrease in breathing in all but one human subject and in all four goats. Removal of COz produced a prompt decrease in breathing in all but one human subject; but we could not detect such a response in 3 of the 4 goats. Thus the usual pattern of response is clear: peripheral chemoreceptor responses to acute changes in oxygen are typical ofboth man and goat, whereas peripheral chemoreceptor responses to acute changes in CO2 are typical of man but not of the goat. Since the experiments of Sorensen and Mines (1970) indicate that the aortic bodies of goats provide little or no ventilatory stimulus in response to hypoxia, these response characteristics can be attributed to the carotid bodies of goats. What about the exceptions? The one human subject who failed to respond to removal of hypoxia happened to be female, but there is no reason to think that such failure is typical of females in view of the clear response shown by the other female subject in this study and the female studied by Dejours et al. (1958). It has long been known that a small minority of normal sea-level residents have little or no ventilatory response to acute hypoxia (Horvath et al., 1943; Dripps and Comroe. 1947; Brown, 1956). Our subject may be another example of this. We do not know whether there is a similar occasional failure of the peripheral CO1 response among the normal human population, since relatively few have been tested in this way. In any case, the test of significance used by Miller et al. (1974) and therefore used here for comparability, represents a criterion of significance or P value of about 0.05. That means that in an extensive series of tests such as this about 1 in 20 would deviate ‘significantly’ from the mean just by chance variations. Furthermore, the one goat that seemed to respond to removal of COz was the goat from which the data are least reliable because of the relatively scanty number of observations available. Thus we do not feel justified in drawing any conclusions from the ‘exceptions’, although it is possible that some goats do show carotid body responses to COz while others do not, just as some human subjects lack acute responses to hypoxia. Our conclusion from this study, that goats differ from man in that they typically lack peripheral chemoreceptor responses to removal of COz, must be compared with evidence from chronic carotid de,nervation in goats. Sorensen and Mines (1970) reported that chronic carotid sinus nerve section depressed the steady-state ventilatory response to both hyperoxic and hypoxic COz administration in some of their goats and suggested that this might be due to elimination of that part of the CO, stimulus mediated by the carotid bodies. We cannot, of course, rule out the possibility that the carotid bodies of goats mediate a very slow response to CO2
170
C. A. SMITH AND R. H. KELLOGG
that would be missed by our study but effective in their steady-state measurements. We think it more likely, however, that denervation, by eliminating the normal background input from the carotid bodies, allowed breathing to diminish and perhaps led to some sort of ‘acclimatization’ that both shifted the CO2 response curves of their goats to the right and diminished their slopes. *Another indication that carotid bodies are sensitive to CO, might be sought by comparing the slopes of the CO, response lines under hypoxic and hyperoxic conditions, since at least part of the increase in slope in other animals during hypoxia is usually attributed to a positive interaction between the hypoxic and CO2 stimuli in the peripheral chemoreceptors. The studies of Tenney and Brooks (1966) and of Mines and Sorensen (1970) show no positive interaction in most goats, although Lahiri et al. (1971) have described a typical ‘fan’ of CO* response lines in goats as Po, is varied. Our results are in accordance with a lack of positive interaction, at least at a peripheral site, and suggest that positive interaction, where it is found, may occur in goats which do not lack carotid body responses to COz or may be produced centrally rather than in the carotid bodies. Acknowledgements We wish to extend our thanks to our subjects and to Miss ,Margareta Nilsson for her technical assistance. This investigation was supported in part by the National Institutes of Health research grant number LH-13841 from the National Heart and Lung Institute. C. A. Smith was a predoctoral trainee supported by the National Institutes of Health training grant number GM-00927 from the National Institute of General Medical Sciences. References Black, A. M. S., D. I. McCloskey and R. W. Torrance (1966). The responses of peripheral chemoreceptors to s&den changes of hypercapnic and hypoxic stimuli. J. Physiol. (London) 185: 67P-68P. Brown, J. H. U. (1956). Failure of the respiratory response to low oxygen tension. J. Aviation Med. 21: 460-461. Comroe, J. H., Jr. (1974). Physiology of Respiration. Chicago, Year Book Medical Publishers, p. 13. Cunningham, D. J. C., B. .B. Lloyd, J. P. Miller and J. M. Young (1965). The time course of human ventilation after transient changes in PA,,, at two values of PACT.J. Physiol. (London) 179: 68P-70P. Cunningham, D. J. C., S. B. Pearson, R. H. K. Marsh and R. H. Kellogg (1973). The effects of various time patterns of alveolar CO2 and O2 on breathing in man. Acta Neurobiol. Exptl. 33: 123-138. Dejours, P., Y. Labrousse, J. Raynaud, F. Girard and A. Teillac (1958). Stimulus oxygtne de la ventilation au repos et au tours de l’exercice musculaire, g basse altitude (50 m), chez l’homme. Rev. Franc. k’tud. Clin. Biol. 3: 105-123. Dixon, W. J. and F. J. Massey (1969). Introduction to Statistical Analysis. New York, McGraw-Hill, pp. 156-l 58. Dripps, R. D. and J. H. Comroe, Jr. (1974). The effect of the inhalation of high and low oxygen concentrations on respiration, pulse rate, ballistocardiogram and arterial oxygen saturation (oximeter) of normal individuals. Am. J. Physiol. 149: 277-291.
VENTILATORY
RESPONSE OF GOATS
171
Fencl, V., T. B. Miller and J. R. Pappenheimer (1966). Studies on the respiratory response to disturbances of acid-base balance with deductions concerning the ionic composition of cerebral interstitial fluid. Am. .I. Physiol. 210: 459-472. Held, D., V. Fencl and J. R. Pappenheimer (1964). Electrical potential of CSF. J. Neurophysiol. 27: 949-959. Horvath, S. M., D. B. Dill and W. Corwin (1943). Effects on man of severe oxygen lack. Am. J. Physiol. 138: 659-668. Lahiri, S., N. S. Cherniak, N. H. Edelman and A. P. Fishman (1971). Regulation of respiration in the goat and its adaptation to chronic and life-long hypoxia. Respir. Physiol. 12: 388403. Miller, J. P., D. J. C. Cunningham B. B. Lloyd and J. M. Young (1974). The transient respiratory effects in man of sudden changes in alveolar CO1 in hypoxia and high oxygen. Respir. Physiol. 20: 17-31. Mines, A. H. and S. C. Sorensen (1970). Ventilatory response of awake goats during acute and chronic hypoxia. .I. Appl. Physiol. 28: 826-831. Pappenheimer, J. R. (1967). The ionic composition of cerebra1 extracellular fluid and its relation to the control of breathing. Haroey Lectures 61: 71-94. Sorensen, S. C. and A. H. Mines (1970). Ventilatory responses to acute and chronic hypoxia in goats after sinus nerve section. J. Appl. Physiol. 28: 832-835. Smith, C. A. and R. H. Kellogg (1975). A respiratory valve for rapid switching between two gas mixtures. J. Appl. Physiol. 38: 181-182. Tenney, S. M. and J. G. Brooks, III (1966). Carotid bodies, stimulus interaction, and ventilatory control in unanesthetized goats. Respir. Physiol. 1: 211-224. Thilenius, 0. G. and C. B. Vial (1963). Chronic tracheostomy in dogs. .I. Appl. Physiol. 18: 4394lO.
VENTILATORY
RESPONSE OF GOATS TO TRANSIENT CO2 AND O2 DURING ACUTE HYPOXIA
CHANGES
IN
CURTIS A. SMITH and RALPH H. KELLOGG Department of Physiology, University of California, San Francisco, California 94143, U.S.A.
Ahstnct. The authors assessed the relative sensitivity of the peripheral chemoreceptors of 4 goats to a transient decrmsc in inspired CO2 using a 2-breath test. This test provides a steady-state background of hypoxia and hypercapnia and then, for 2 breaths, an equally hypoxic gas mixture containing no CO1. Another type of 2-breath test, providing 2 breaths of a hyperoxic gas mixture against a background of hypoxia, was used to establish the time course of a response known to come from peripheral chemoreceptors. Seven human subjects were studied in a similar fashion to establish the validity of the procedure. Except for 2 responses, the author’s human data agree with those reported previously by others. All 4 goats resembled man in responding to removal of hypoxia with a significant decrease in ventilation, but 3 of the 4 goats, unlike man, showed no significant decrease in ventilation when CO2 was removed. The authors conclude that the peripheral chemoreceptors of goats are commonly insensitive to transient changes in inspired CO, during acute hypoxia. Carotid bodies Chemical regulation Goats
Peripheral chemoreceptors Two-breath test Ventilatory response
The goat has long been used for respiratory studies (Held et al., 1964; Tenney and Brooks, 1966; Fencl et al., 1966; Pappenheimer, 1967). Its ventilatory responses to CO2 inhalation during acute and chronic hypoxia have been well characterized (Mines and Srarensen, 1970; Lahiri et al., 1971X but there is little information concerning the contribution of the peripheral chemoreceptors to the CO, response. The presence of positive interaction between the responses to hypoxia and CO2 in the studies of Lahiri et al. ( 1971) suggest that the peripheral chemoreceptors of goats may be sensitive to CO, (or pH), whereas the lack of such interaction in the studies of Tenney and Brooks (1966) and of Mines and Sorensen (1970) suggests the contrary. Sorensen and Mines (1970) also demonstrated that chronic carotid denervation can affect the steady-state CO2 response of goats, but they did not study the acute Accepted for publication 18 March 1975.
C. A. SMITH AND R. H. KELLOGG
164
responses of the peripheral chemoreceptors to COz. Clearly, a knowledge of such responses would be useful in interpreting respiratory data from this species. The purpose of this study was to ascertain the existence of a peripherally mediated response to transient changes in CO, (and the associated changes in arterial pH) during acute hypoxia in the awake goat.
Materials and methods
We used a two-breath test as described by Cunningham et al. ( 1965, 1973) and Miller er al. (1974), which is based on the single-breath test of Dejours er al. (1958). In this test, the goat is presented with a gas mixture that makes it both hypoxic (end-tidal oxygen, PETIT, about 40 mm Hg) and hypercapnic (Ptzrco, about 50 mm Hg). Abruptly the inspired gas is switched, for two breaths, to an equally hypoxic mixture that contains no COz (‘removal of CO,‘) and is then returned to the original mixture. The advantages of this method over other methods of presenting a transient change in CO2 stimulus have been discussed by Miller et al. (1974). Of course, CO2 stimulates central chemoreceptors as well. It is therefore necessary to know the time course of a peripheral response so that it can be distinguished from the central effects. To accomplish this, another type of two-breath test (‘removal of hypoxia’) was used, in which two breaths of a hyperoxic gas (PIN, about 670 mm Hg) were given against a steady-state background of hypoxia (PETE, about 40 mm Hg) (Cunningham et al., 1965, 1973; Miller et al., 1974). Since acute hypoxia is directly sensed only by peripheral chemoreceptors and since its on-transient in cats (Black er al., 1966) is known to be somewhat slower than the off-transient for CO1 both in cats (Black et al., 1966) and in human subjects (Cunningham et al., 1973), one may presume that any peripherally mediated decrease in ventilation due to COz removal would occur no later than that due to increased PoL. In these experiments, responses were compared by calculating the mean single breath ventilation(%‘~)for three breaths prior to the two-breath change in inspired gas and for eight breaths following the onset of this change. The following formula was used:
VE (I/min) =
VT -:(1) .-.-~. [60 secjmin] breath duration (set) 1
This calculation was performed for each breath in every test. Mean ventilations were calculated by averaging each breath (numbered from the change of inspired gas) from 7 to 52 such tests. Control ventilation was considered to be the mean of the means of the three breaths prior to the change in inspired gas. All data were measured and recorded by the same person. A change in ventilation was considered significant if it was more than two pooled standard errors from the control mean (Dixon and Massey, 1969). Since the silent, remote-controlled valve that we used to change gas mixtures had never before been used in experiments, we chose to test it and our recording system
165
VENTILATORY RESPONSE OF COATS
by trying to reproduce the human experimental data of Miller et al. (1974). Seven human volunteers were tested. The protocol was similar to that described for the goats except that in the hypoxic portions the PET,, was approximately 65 mm Hg rather than 40 mm Hg. TABLE 1 Physical characteristics of the goats -. Weight
Goat
.__~._. 1088 1778 1298 1299
(kg)
Sex
-.--
.~..
55 61 45* 45*
161 212 113 95
castrate castrate castrate castrate
male male male male
* estimated.
h
! ,
Fig. I. A typical record from a CO1 removal experiment with a goat. The signal bar in front of the arrowhead indicates the duration of the two-breath change of inspired gas composition. VE is recorded directly from the pneumotachograph. VT is the integral of VE. Pc,, is recorded on a compressed scale (to show zero) and also on an expanded scale. PET,, % 40 mm Hg.
166
C. A.
SMITH AND R. H. KELLOGG
Four mixed breed, short haired, castrated male goats were prepared with chronic tracheostomies by the method of Thilenius and Vial (1963). Surgery was performed under methoxyflurane or halothane anesthesia. The goats had been born and reared at low altitudes. Their physical characteristics are listed in table 1. After a month for recovery from surgery the goats, were subjected to several practice sessions in the laboratory to accustom them to the procedure. They stood in a stanchion and were intubated through the tracheostomy with an endotracheal tube with inflatable cuff. During an experiment, the endotracheal tube was connected to a low dead space respiratory valve designed to allow remote-controlled and silent switching between two gas mixtures (Smith and Kellogg, 1975). The gas mixtures were adjusted to appropriate concentrations by means of a double set of Matheson flowmeters. Each gas mixture was mixed in a large manifold half tilled with water for partial humidification and then piped directly to the respiratory valve. The expired gas passed through 1arge:bore respiratory tubing to a heated f3 Fleisch pneumotachograph. The pneumotachograph signal was electrically integrated to give expired tidal volume for each breath (fig. 1). Volume corrections for temperature and pressure were considered unnecessary for this study. Airway Pco, was continuously recorded from an infrared CO2 meter (Beckman LB-l), and end-tidal Po, was intermittently sampled manually for analysis in an oxygen electrode (Radiometer). The order in which the experiments were performed was varied randomly from day to day. Panting was prevented by cooling the goats with an electric fan and by sponging their flanks with water when necessary. Results of a test were accepted only if the goat did not defecate, urinate, cough, pant, or move about and the tidal volumes of both breaths of altered inspired gas were greater than twice the dead space determined for that goat. Seven human volunteers were studied (table 2). All were natives and residents of low altitudes and gave informed consent. The experimental apparatus was similar to that used with the goats except that the human subjects breathed through a mouthpiece, were seated in a comfortable chair, and were encouraged to read and/or TABLE 2 Physical characteristics of the human subjects Subject
RC RF RK SK CS IS ss
Height
Weight
Age
(4
(kg)
(Yd
75
30 23 54 33
190 188 179
82 79 72
170 I75
80
26
170
55
26
I67
54
27
Sex
male male male male male female female
167
VENTlLATORY RESPONSE OF GOATS
listen to recorded music. Human tests were accepted only cough or move about and the tidal volumes of both breaths were greater than twice the predicted dead space (values Subjects consistently stated afterwards that they were unaware of the changes in inspired gas.
if the subject did not of altered inspired gas from Comroe, 1974). of the timing or nature
Results The data are summarized in fig. 2 and table 3. In general, the human subjects transiently decreased their breathing following the transient removal of hypoxia and following the transient removal ofC02 with average latencies of 12.1 and 10.7 seconds respectively, agreeing reasonably well with the observations of Miller et al. (1974). The exceptions were that subject JS showed no significant response to removal of hypoxia and subject SS showed no significant response to removal of CO,. The latencies were longer following removal of hypoxia than following removal of CO? TABLE 3 Latency of response Hypoxia removal
CO2 removal
(M
N
(=I
N
Goat
Background Pmo,=40 mm Hg
2 breaths Pto,=700 mm Hg
Background Pm,,=40 mm Hg Ptrrco,=50 mm Hg
2 breaths Paro,=40 mm Hg &,,=O mm Hg
1088 1778 1298 1299
6.7 *0.7* 6.4kO.2 10.1kO.7 6.7 f 0.5
50 52 16 10
no response no response no response 6.1 kO.2
48 50 19 11
mean
7.4
Subject
Background PFT,, = 65 mm Hg
2 breaths Pto, g 700 mm Hg
Background Pxro,=65 mm Hg Pmco,=50 mm Hg
2 breaths F%ro,=65 mm Hg b,=O mm Hg
RC RF RK SK CS JS ss
13.6kO.4 9.1 kO.5 17.5kO.6 10.9kO.4 10.5+0.1 no response 10.7* 1.3
10 7 12 19 21 15 18
12.9kO.2 8.8 f 0.2 14.150.1 11.9kO.2 8.7kO.l 7.9* 1.1 no response
10 20 14 20 18 19 19
mean
12.1
* mean f standard error.
10.7
168
Fig. 2. Mean ~ntiI~tiun
C. A. SMITH AND R. H, KELLOGG
by breath number. The vertical bar represents one standard error on either side of the mean.
in each individual subject except SK. The four goats studied all showed a significant decrease in breathing after removal ofhypoxia with latencies generally shorter than in man, but only goat 1299 showed a significant decrease in breathing in response to CO2 removal. In that case, the latency
VENTILATORY
RESPONSE
OF GOATS
169
following removal of hypoxia was longer than that following removal of C02. and the significantly decreased breath appears somewhat aberrant compared to adjoining breaths (fig. 2). Discussion The results of the human experiments satisfied us that our apparatus and techniques were capable of reproducing the observations of Miller et al. (1974). Removal of hypoxia produced a prompt decrease in breathing in all but one human subject and in all four goats. Removal of COz produced a prompt decrease in breathing in all but one human subject; but we could not detect such a response in 3 of the 4 goats. Thus the usual pattern of response is clear: peripheral chemoreceptor responses to acute changes in oxygen are typical ofboth man and goat, whereas peripheral chemoreceptor responses to acute changes in CO2 are typical of man but not of the goat. Since the experiments of Sorensen and Mines (1970) indicate that the aortic bodies of goats provide little or no ventilatory stimulus in response to hypoxia, these response characteristics can be attributed to the carotid bodies of goats. What about the exceptions? The one human subject who failed to respond to removal of hypoxia happened to be female, but there is no reason to think that such failure is typical of females in view of the clear response shown by the other female subject in this study and the female studied by Dejours et al. (1958). It has long been known that a small minority of normal sea-level residents have little or no ventilatory response to acute hypoxia (Horvath et al., 1943; Dripps and Comroe. 1947; Brown, 1956). Our subject may be another example of this. We do not know whether there is a similar occasional failure of the peripheral CO1 response among the normal human population, since relatively few have been tested in this way. In any case, the test of significance used by Miller et al. (1974) and therefore used here for comparability, represents a criterion of significance or P value of about 0.05. That means that in an extensive series of tests such as this about 1 in 20 would deviate ‘significantly’ from the mean just by chance variations. Furthermore, the one goat that seemed to respond to removal of COz was the goat from which the data are least reliable because of the relatively scanty number of observations available. Thus we do not feel justified in drawing any conclusions from the ‘exceptions’, although it is possible that some goats do show carotid body responses to COz while others do not, just as some human subjects lack acute responses to hypoxia. Our conclusion from this study, that goats differ from man in that they typically lack peripheral chemoreceptor responses to removal of COz, must be compared with evidence from chronic carotid de,nervation in goats. Sorensen and Mines (1970) reported that chronic carotid sinus nerve section depressed the steady-state ventilatory response to both hyperoxic and hypoxic COz administration in some of their goats and suggested that this might be due to elimination of that part of the CO, stimulus mediated by the carotid bodies. We cannot, of course, rule out the possibility that the carotid bodies of goats mediate a very slow response to CO2
170
C. A. SMITH AND R. H. KELLOGG
that would be missed by our study but effective in their steady-state measurements. We think it more likely, however, that denervation, by eliminating the normal background input from the carotid bodies, allowed breathing to diminish and perhaps led to some sort of ‘acclimatization’ that both shifted the CO2 response curves of their goats to the right and diminished their slopes. *Another indication that carotid bodies are sensitive to CO, might be sought by comparing the slopes of the CO, response lines under hypoxic and hyperoxic conditions, since at least part of the increase in slope in other animals during hypoxia is usually attributed to a positive interaction between the hypoxic and CO2 stimuli in the peripheral chemoreceptors. The studies of Tenney and Brooks (1966) and of Mines and Sorensen (1970) show no positive interaction in most goats, although Lahiri et al. (1971) have described a typical ‘fan’ of CO* response lines in goats as Po, is varied. Our results are in accordance with a lack of positive interaction, at least at a peripheral site, and suggest that positive interaction, where it is found, may occur in goats which do not lack carotid body responses to COz or may be produced centrally rather than in the carotid bodies. Acknowledgements We wish to extend our thanks to our subjects and to Miss ,Margareta Nilsson for her technical assistance. This investigation was supported in part by the National Institutes of Health research grant number LH-13841 from the National Heart and Lung Institute. C. A. Smith was a predoctoral trainee supported by the National Institutes of Health training grant number GM-00927 from the National Institute of General Medical Sciences. References Black, A. M. S., D. I. McCloskey and R. W. Torrance (1966). The responses of peripheral chemoreceptors to s&den changes of hypercapnic and hypoxic stimuli. J. Physiol. (London) 185: 67P-68P. Brown, J. H. U. (1956). Failure of the respiratory response to low oxygen tension. J. Aviation Med. 21: 460-461. Comroe, J. H., Jr. (1974). Physiology of Respiration. Chicago, Year Book Medical Publishers, p. 13. Cunningham, D. J. C., B. .B. Lloyd, J. P. Miller and J. M. Young (1965). The time course of human ventilation after transient changes in PA,,, at two values of PACT.J. Physiol. (London) 179: 68P-70P. Cunningham, D. J. C., S. B. Pearson, R. H. K. Marsh and R. H. Kellogg (1973). The effects of various time patterns of alveolar CO2 and O2 on breathing in man. Acta Neurobiol. Exptl. 33: 123-138. Dejours, P., Y. Labrousse, J. Raynaud, F. Girard and A. Teillac (1958). Stimulus oxygtne de la ventilation au repos et au tours de l’exercice musculaire, g basse altitude (50 m), chez l’homme. Rev. Franc. k’tud. Clin. Biol. 3: 105-123. Dixon, W. J. and F. J. Massey (1969). Introduction to Statistical Analysis. New York, McGraw-Hill, pp. 156-l 58. Dripps, R. D. and J. H. Comroe, Jr. (1974). The effect of the inhalation of high and low oxygen concentrations on respiration, pulse rate, ballistocardiogram and arterial oxygen saturation (oximeter) of normal individuals. Am. J. Physiol. 149: 277-291.
VENTILATORY
RESPONSE OF GOATS
171
Fencl, V., T. B. Miller and J. R. Pappenheimer (1966). Studies on the respiratory response to disturbances of acid-base balance with deductions concerning the ionic composition of cerebral interstitial fluid. Am. .I. Physiol. 210: 459-472. Held, D., V. Fencl and J. R. Pappenheimer (1964). Electrical potential of CSF. J. Neurophysiol. 27: 949-959. Horvath, S. M., D. B. Dill and W. Corwin (1943). Effects on man of severe oxygen lack. Am. J. Physiol. 138: 659-668. Lahiri, S., N. S. Cherniak, N. H. Edelman and A. P. Fishman (1971). Regulation of respiration in the goat and its adaptation to chronic and life-long hypoxia. Respir. Physiol. 12: 388403. Miller, J. P., D. J. C. Cunningham B. B. Lloyd and J. M. Young (1974). The transient respiratory effects in man of sudden changes in alveolar CO1 in hypoxia and high oxygen. Respir. Physiol. 20: 17-31. Mines, A. H. and S. C. Sorensen (1970). Ventilatory response of awake goats during acute and chronic hypoxia. .I. Appl. Physiol. 28: 826-831. Pappenheimer, J. R. (1967). The ionic composition of cerebra1 extracellular fluid and its relation to the control of breathing. Haroey Lectures 61: 71-94. Sorensen, S. C. and A. H. Mines (1970). Ventilatory responses to acute and chronic hypoxia in goats after sinus nerve section. J. Appl. Physiol. 28: 832-835. Smith, C. A. and R. H. Kellogg (1975). A respiratory valve for rapid switching between two gas mixtures. J. Appl. Physiol. 38: 181-182. Tenney, S. M. and J. G. Brooks, III (1966). Carotid bodies, stimulus interaction, and ventilatory control in unanesthetized goats. Respir. Physiol. 1: 211-224. Thilenius, 0. G. and C. B. Vial (1963). Chronic tracheostomy in dogs. .I. Appl. Physiol. 18: 4394lO.
