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Inhaled CO2 and progressive hypoxia: Ventilatory response in a yearling and a newborn harbor seal
Life Sciences Vol. 12, Part II, pp . 52?-533, 1973 Printed in Great Britain
Pergamon Press
INHALED COy AND PROGRESSIVE HYPOXIA: VENTILATORY RESPONSE IN A YEARLING AND A NEWBORN HARBOR SEAL Cedric R . Bwinton Departments of Anesthesia and Physiology, University of California School of Medicine, San Francisco, California 94122 Robert Elsner Scripps Institute of Oceanography, University of California at San Diego, Lo Jolla, Colifaniw 92037 Richard C . Mattkiews Scripps Institute of Oceanography, University of Califomia at San Diego, La Jolla, Califomia 92037
(Received 30 October 1972, in final form 7 April 1973) Summary These studies indicate that despite the extreme tolerance of seals to lowered arterial Pay (Paoy) and elewted arterial Pcoy (Pacoy) during a dive, both a yearling harbor seal and a pup can have sizeable ventilatory rosponse to these chemical stimuli when not diving . Our pup had had no previous diving experience . He also differod from the yearling in having lower rosting alveolar Pco~ (PAcoy) and more regular breathing . It is interosting to theorize that these differonces from those of the yearling are due to lack of diving experience . Introduction In a compulsory dive, the seal can simultaneously tolerate 130 mm Hg CCh and 8 mm Hg Ch in arterial partial prossure without initiating broathing .l Since this extraordinary ability far exceeds man's tolerance for these rospiratory stimuli during voluntary breath-holding 2, it is conceivable that either these chemical stimuli to ventilation aro weak, with little influence on vantilatory control in the seal,or active but inhibited during diving by the potent diving reflex . Although the rosponse to inhaled C41, maintwining a corutant C1y level, has been studied by Robin et a1 .4 in young harbor seals, their reaction to progrossive hypaxia with a constwnt alveolar Pcoy has not been investigated . Neither of these chemical stimuli to ventilation have been explored in the pup. In the
527
Ventllatory Response in Harbor Seals
528
Vol . 12, No. 12
present study, we had the opportunity to evaluate in detail both ventilatory stimuli in a newborn pup with no diving experience and in a yearling . Methods These studies took place on The Research Vessel (~ Alpha Helix on the 1972 Bering Sea Expedition . Our yearling harbor seal (Photo vitulina ), a female, was captured in Eureka, California, and transporird to Alaska on the Alpha Helix, whereas the pup, a male, was captured on the ice-flow of the Bering Sea . No trace of the mother could be found . The newborn seal, estimated to be 12 hours old at the time of capture was maintained on tube feedings during the observation period . We administered the feedings three to four times daily . The diet consisted of dried milk, water, vegetable and cod liver oil, vitamins, ground fish, squid,and seal liver . The pup's weight increased from 5 .5 to 10 .5 Kg in throe weeks, and he was at all times alert and active . The two seals were immobilized for ventilation studies in canvas jackets, each attached to a board . The head of the yearling was further immobilized by yokes around both neck and rwse, .comfortably arranged with no limitation to respiration . The pup was easily handled without head immobilization . Because he maintained his heavy lanugo fur throughout the period of study, it was necessary to put him on a bag of ice during this interval of inactivity to prevent increase in core temperature . This method maintained the pup's rectal temperature at 38°C or less . Throughout the studies, the animals breathed through rubber rrrâsks (Everseal Equipment Corp .) sealed with KY jelly . The masks were tested for fit and leaks by periodic application of positive pressure . They were each attached to a two-way Rubin valve (Collins Equipment Corp ., Boston) and compressed gas (air, Ny, CC~) was delivered via flow meters 8 inches from the inspiratory valve but directed away from this valve into an open tubular reservoir 5 feet long . No positive pressure was exerted on the inspiratory valve . Total gas flows into the reservoir exceeded 20 liters min . The two animals inspired from this reservoir while expired gas was collected in a water filled Tissot spirometer . We evaluated the ventilatory effect of increased inspired CCs and decreased inspired 01 in separate studies. Increased COz was administered to the seal pup in air .
Ventilatory Response in Harbor Seals
Vol . 12, No. 12
529
Response to hypoxia was evalwted at constant Pq c~ (50 mm Hg) in both yearling and pup. In order to proserve the arteries for concurrent studies to be undertaken by other investigators, arterial blood studies were not conducted . All our studies included analysis of end expiratory gas for Pq c~ . In addition, during the hypoxia experiments, we evaluated this gas for Pq~ . End expiratory gas was sampled from a point diroctly subsequent to the expiratory valve, aspirated continuously through a Beckman infrared CC~ analyzer, and then rotumed without volume change to the spirometer . In contrast, end expiration sampling for Pq~ was performed manually . We aspirated 1-2 cc of gas from the sampling port on clasuro of the expiratory valve in several successive breaths . These samples wero measured for Pop in a Radiometer oxygen electrode . We used a breath-by-breath record of alveolar Pcop to calculate a mean resting Pqc~ in the animals during one minute intervals . During periods of apnea at rost (Fig .l), which aro typical for harbor seals as young as four months of age 3, we proceeded on the assumption that there was a linear increase in Pq c~ from the beginning to the end of the apneic period .
~s PAC02 ss mmHp
35 30 s~c .
FIG. 1 Typical pattern of periodic broathing observed in yearling seal in the resting state breathing ambient air . The yearling seal was studied in fasting condition . The pup, however, was given frequent feedings and studied one hour past-feeding and then for up to 2 hours or until he became rostless . We strapped him to the board, fixed the mask in place, and permitted the baby animal to stabilize for 10 to 15 min . In assessing the rosponse to inhaled CC>z, we allowed 10 min for CC~ equilibration and subsequently collected expired gas for at
Venülatory Response in Harbor Seals
530
Vol . 12, No. 12
least two 5 min periods . Equilibration time for differont levels of P~q~ during progrossive hypoxia was limited to 5 min . The yearling seal could tolerate continuous inhalation of low inspired oxygen for up to 3 hours, wheroas the pup was limited to 1/2 hour exposuro at the lowest level of inspired aocygen or highest inspired
CCal . At such time the pup became restless and was
returned to ambient air . Results and Discussion Table 1 prosents the respiratory parameters of our seal pup and the yearling . The pup clearly reveals an increase in alveolar ventilation (mean PA c~ 42 mm Hg), rospiratory frequency, and metabolic rate/rcg when these values are compared to those of our yearling and to those reported by Robin et al .4for young seals 20-30 kg in weight . We further observed that the typical periodic breathing of our yearling seal (see Fig . 1) was raroly seen in the pup. these differonces (apparontly due to age discrepancy) are inexplicable in other terms, but it is interostirg to speculate that elevated P,4cop and periodic broathing are acquired by the seal as a rosult of the diving experience . TABLE 1 Pulmonary Gas Exchange in the Harbor Seal, Phoca vitulina , Yearling and Pup ~ PA c Respiratory ~ Seal Wt . R .Q . /K9 Froquency mm ~ c~min (S'r~2 Per min cc min (nom) 50 f 3
22 f 2
235 f 22 (8)
.89 f .04
5.5
42 f 3
32 f 2
76 (2)
.75
10 .5
41 t 3
32 t 2
Yearling 30 .5
7 .2
Pup 1 Day 18 Days
122 f I 1 (b)
13 .9
.88 f .03 11 .2
Values for PA c~ and rospiratory froquency are mean f S .D . of average values which occurred during ans minute observation periods . Values for app and R .Q . (rospiratory quotient) aro mean f S .D . We found that in the yearling seal, the stimulus of either incroased Pcap or low Pop almost totally eliminated periodic broathing . This observation was utilized in pragrossive hypoxia studies to maintain constant levels of alveolar Pcop and Pot . Regular broathing at
Vol. 12, No. 12
Ventllatory Response in Harbor Seals
53 1
constant P,gc ~50 did not lake place in the yearling until PAop was lowered to 55 mm H8 . For this reason, the effects of decreased PA S at constant PA c~ wero examined in the yearling only at a PA S of 55 mm Hg and below . As shown in Fig . 2, a definite stimulus to ventilation occurred at this level of PA S in the yearling .
Vl:
L/m in BTPS
PA
02
FIG . 2 Resting ventilation during air-broathing and ventilatory response to a PA S of 55 mm Hg and below at constant PA c~ (50 mm Hg) in yearling seal . Lines connect data For four separate days . In the pup, a moro progrossive fall in PA S could be established since periodic broathing was raroly seen . As in the yearling, a clear incroase in VE was observed at a PAS of 55 mm Hg (Fig . 3) . Below this level, ventilation was in some instances depressed . Interprotation of this fall in ventilation is difficult, since this was usually associated with obvious rostlessness . We cannot exclude the possibility, however, that it may reprosent a true adaptation to the hypoucic stimulus a, alternatively, may be the rosul.t of obntral
53 2
Ventüatory Response in Harbor Seals
Vol . 12, No . 12
nervous system deprossion . These findings will require further study .
Vl: L/m in BTPS
FIG. 3 Ventilstory rosponse of seal pup to decroasing alveolar PoZ . Pq c~ was maintained constant at 50 mm H8 throughout the experiment . Lines connect data of individual studies . The pup demorutrated daily variations in overall level of ventilation . This level increased with age in days . Ventilstory rosponse to inhaled CC~ is also quite clear in the pup (Fig . 4), which has a slope of approximately .2 liter;/min/mm Flg COt . This is comparable to that reported by Robin et a1 .4 for young seals (.3 liters/min/mm H8 CCt~ . Cur findings indicate that Goth pup and yearling seals have sizeable ventilatory responses to hypoxia and hypercapnea, suggesting the animal's remarkable tolerance for extromes of these two chemical stimuli during a dive is not due to weak or absent responses but rather to probable suppression of these responses bY the diving roflex . The latter situation may be mae favorable to the seal, since recognition of Paol is undoubtedly critical to both termination of the dive and to actual survival .
Vol. 12, No . 12
Ventllatory Response in Harbor Seals
533
10
8
VE
6
L/min BTPS
4
2
i
50
i 60
70
80
PA cot
FIG.4 Ventilstory response of seal pup to COz in air . Lines connect data of individual studies . An overall increase in ventilation occurred with age in days . Acknowledgements This study was supported in part by a National Science Foundation grant to the Scripps Institute of Ocearwgraphy for operation of the Alpha Helix Research Program and by Public Health Service Grant HE08323 . Dr . Bainton is the recipient of Public Health Service Career Development Award 5K04 GM42390-04 .
References 1 . R .ELSNER, J .T .SHURLEY, D .D . HAMMOND, and R .E .BROOKS, Resp . Physiol . 9 , _ 287-290 (1970) . 2 . L .HILL and M . FLACK, J . Physiol ., London, 37, 77-111 (1908) . 3 . L .IRVING, O .M .SOLANDT, D .Y .SCILANDTand K .C .FISHER, J .Cell Comp . Physio . 7-8, 137-151 (1935-1936) . 4. E .D .ROBIN, H .V .MURDAUGH,JR ., W .PYRON, E .WEISS and P .SOTERES, Am . J . Physiol ., 205, 1175-1177 (1963) .
Pergamon Press
INHALED COy AND PROGRESSIVE HYPOXIA: VENTILATORY RESPONSE IN A YEARLING AND A NEWBORN HARBOR SEAL Cedric R . Bwinton Departments of Anesthesia and Physiology, University of California School of Medicine, San Francisco, California 94122 Robert Elsner Scripps Institute of Oceanography, University of California at San Diego, Lo Jolla, Colifaniw 92037 Richard C . Mattkiews Scripps Institute of Oceanography, University of Califomia at San Diego, La Jolla, Califomia 92037
(Received 30 October 1972, in final form 7 April 1973) Summary These studies indicate that despite the extreme tolerance of seals to lowered arterial Pay (Paoy) and elewted arterial Pcoy (Pacoy) during a dive, both a yearling harbor seal and a pup can have sizeable ventilatory rosponse to these chemical stimuli when not diving . Our pup had had no previous diving experience . He also differod from the yearling in having lower rosting alveolar Pco~ (PAcoy) and more regular breathing . It is interosting to theorize that these differonces from those of the yearling are due to lack of diving experience . Introduction In a compulsory dive, the seal can simultaneously tolerate 130 mm Hg CCh and 8 mm Hg Ch in arterial partial prossure without initiating broathing .l Since this extraordinary ability far exceeds man's tolerance for these rospiratory stimuli during voluntary breath-holding 2, it is conceivable that either these chemical stimuli to ventilation aro weak, with little influence on vantilatory control in the seal,or active but inhibited during diving by the potent diving reflex . Although the rosponse to inhaled C41, maintwining a corutant C1y level, has been studied by Robin et a1 .4 in young harbor seals, their reaction to progrossive hypaxia with a constwnt alveolar Pcoy has not been investigated . Neither of these chemical stimuli to ventilation have been explored in the pup. In the
527
Ventllatory Response in Harbor Seals
528
Vol . 12, No. 12
present study, we had the opportunity to evaluate in detail both ventilatory stimuli in a newborn pup with no diving experience and in a yearling . Methods These studies took place on The Research Vessel (~ Alpha Helix on the 1972 Bering Sea Expedition . Our yearling harbor seal (Photo vitulina ), a female, was captured in Eureka, California, and transporird to Alaska on the Alpha Helix, whereas the pup, a male, was captured on the ice-flow of the Bering Sea . No trace of the mother could be found . The newborn seal, estimated to be 12 hours old at the time of capture was maintained on tube feedings during the observation period . We administered the feedings three to four times daily . The diet consisted of dried milk, water, vegetable and cod liver oil, vitamins, ground fish, squid,and seal liver . The pup's weight increased from 5 .5 to 10 .5 Kg in throe weeks, and he was at all times alert and active . The two seals were immobilized for ventilation studies in canvas jackets, each attached to a board . The head of the yearling was further immobilized by yokes around both neck and rwse, .comfortably arranged with no limitation to respiration . The pup was easily handled without head immobilization . Because he maintained his heavy lanugo fur throughout the period of study, it was necessary to put him on a bag of ice during this interval of inactivity to prevent increase in core temperature . This method maintained the pup's rectal temperature at 38°C or less . Throughout the studies, the animals breathed through rubber rrrâsks (Everseal Equipment Corp .) sealed with KY jelly . The masks were tested for fit and leaks by periodic application of positive pressure . They were each attached to a two-way Rubin valve (Collins Equipment Corp ., Boston) and compressed gas (air, Ny, CC~) was delivered via flow meters 8 inches from the inspiratory valve but directed away from this valve into an open tubular reservoir 5 feet long . No positive pressure was exerted on the inspiratory valve . Total gas flows into the reservoir exceeded 20 liters min . The two animals inspired from this reservoir while expired gas was collected in a water filled Tissot spirometer . We evaluated the ventilatory effect of increased inspired CCs and decreased inspired 01 in separate studies. Increased COz was administered to the seal pup in air .
Ventilatory Response in Harbor Seals
Vol . 12, No. 12
529
Response to hypoxia was evalwted at constant Pq c~ (50 mm Hg) in both yearling and pup. In order to proserve the arteries for concurrent studies to be undertaken by other investigators, arterial blood studies were not conducted . All our studies included analysis of end expiratory gas for Pq c~ . In addition, during the hypoxia experiments, we evaluated this gas for Pq~ . End expiratory gas was sampled from a point diroctly subsequent to the expiratory valve, aspirated continuously through a Beckman infrared CC~ analyzer, and then rotumed without volume change to the spirometer . In contrast, end expiration sampling for Pq~ was performed manually . We aspirated 1-2 cc of gas from the sampling port on clasuro of the expiratory valve in several successive breaths . These samples wero measured for Pop in a Radiometer oxygen electrode . We used a breath-by-breath record of alveolar Pcop to calculate a mean resting Pqc~ in the animals during one minute intervals . During periods of apnea at rost (Fig .l), which aro typical for harbor seals as young as four months of age 3, we proceeded on the assumption that there was a linear increase in Pq c~ from the beginning to the end of the apneic period .
~s PAC02 ss mmHp
35 30 s~c .
FIG. 1 Typical pattern of periodic broathing observed in yearling seal in the resting state breathing ambient air . The yearling seal was studied in fasting condition . The pup, however, was given frequent feedings and studied one hour past-feeding and then for up to 2 hours or until he became rostless . We strapped him to the board, fixed the mask in place, and permitted the baby animal to stabilize for 10 to 15 min . In assessing the rosponse to inhaled CC>z, we allowed 10 min for CC~ equilibration and subsequently collected expired gas for at
Venülatory Response in Harbor Seals
530
Vol . 12, No. 12
least two 5 min periods . Equilibration time for differont levels of P~q~ during progrossive hypoxia was limited to 5 min . The yearling seal could tolerate continuous inhalation of low inspired oxygen for up to 3 hours, wheroas the pup was limited to 1/2 hour exposuro at the lowest level of inspired aocygen or highest inspired
CCal . At such time the pup became restless and was
returned to ambient air . Results and Discussion Table 1 prosents the respiratory parameters of our seal pup and the yearling . The pup clearly reveals an increase in alveolar ventilation (mean PA c~ 42 mm Hg), rospiratory frequency, and metabolic rate/rcg when these values are compared to those of our yearling and to those reported by Robin et al .4for young seals 20-30 kg in weight . We further observed that the typical periodic breathing of our yearling seal (see Fig . 1) was raroly seen in the pup. these differonces (apparontly due to age discrepancy) are inexplicable in other terms, but it is interostirg to speculate that elevated P,4cop and periodic broathing are acquired by the seal as a rosult of the diving experience . TABLE 1 Pulmonary Gas Exchange in the Harbor Seal, Phoca vitulina , Yearling and Pup ~ PA c Respiratory ~ Seal Wt . R .Q . /K9 Froquency mm ~ c~min (S'r~2 Per min cc min (nom) 50 f 3
22 f 2
235 f 22 (8)
.89 f .04
5.5
42 f 3
32 f 2
76 (2)
.75
10 .5
41 t 3
32 t 2
Yearling 30 .5
7 .2
Pup 1 Day 18 Days
122 f I 1 (b)
13 .9
.88 f .03 11 .2
Values for PA c~ and rospiratory froquency are mean f S .D . of average values which occurred during ans minute observation periods . Values for app and R .Q . (rospiratory quotient) aro mean f S .D . We found that in the yearling seal, the stimulus of either incroased Pcap or low Pop almost totally eliminated periodic broathing . This observation was utilized in pragrossive hypoxia studies to maintain constant levels of alveolar Pcop and Pot . Regular broathing at
Vol. 12, No. 12
Ventllatory Response in Harbor Seals
53 1
constant P,gc ~50 did not lake place in the yearling until PAop was lowered to 55 mm H8 . For this reason, the effects of decreased PA S at constant PA c~ wero examined in the yearling only at a PA S of 55 mm Hg and below . As shown in Fig . 2, a definite stimulus to ventilation occurred at this level of PA S in the yearling .
Vl:
L/m in BTPS
PA
02
FIG . 2 Resting ventilation during air-broathing and ventilatory response to a PA S of 55 mm Hg and below at constant PA c~ (50 mm Hg) in yearling seal . Lines connect data For four separate days . In the pup, a moro progrossive fall in PA S could be established since periodic broathing was raroly seen . As in the yearling, a clear incroase in VE was observed at a PAS of 55 mm Hg (Fig . 3) . Below this level, ventilation was in some instances depressed . Interprotation of this fall in ventilation is difficult, since this was usually associated with obvious rostlessness . We cannot exclude the possibility, however, that it may reprosent a true adaptation to the hypoucic stimulus a, alternatively, may be the rosul.t of obntral
53 2
Ventüatory Response in Harbor Seals
Vol . 12, No . 12
nervous system deprossion . These findings will require further study .
Vl: L/m in BTPS
FIG. 3 Ventilstory rosponse of seal pup to decroasing alveolar PoZ . Pq c~ was maintained constant at 50 mm H8 throughout the experiment . Lines connect data of individual studies . The pup demorutrated daily variations in overall level of ventilation . This level increased with age in days . Ventilstory rosponse to inhaled CC~ is also quite clear in the pup (Fig . 4), which has a slope of approximately .2 liter;/min/mm Flg COt . This is comparable to that reported by Robin et a1 .4 for young seals (.3 liters/min/mm H8 CCt~ . Cur findings indicate that Goth pup and yearling seals have sizeable ventilatory responses to hypoxia and hypercapnea, suggesting the animal's remarkable tolerance for extromes of these two chemical stimuli during a dive is not due to weak or absent responses but rather to probable suppression of these responses bY the diving roflex . The latter situation may be mae favorable to the seal, since recognition of Paol is undoubtedly critical to both termination of the dive and to actual survival .
Vol. 12, No . 12
Ventllatory Response in Harbor Seals
533
10
8
VE
6
L/min BTPS
4
2
i
50
i 60
70
80
PA cot
FIG.4 Ventilstory response of seal pup to COz in air . Lines connect data of individual studies . An overall increase in ventilation occurred with age in days . Acknowledgements This study was supported in part by a National Science Foundation grant to the Scripps Institute of Ocearwgraphy for operation of the Alpha Helix Research Program and by Public Health Service Grant HE08323 . Dr . Bainton is the recipient of Public Health Service Career Development Award 5K04 GM42390-04 .
References 1 . R .ELSNER, J .T .SHURLEY, D .D . HAMMOND, and R .E .BROOKS, Resp . Physiol . 9 , _ 287-290 (1970) . 2 . L .HILL and M . FLACK, J . Physiol ., London, 37, 77-111 (1908) . 3 . L .IRVING, O .M .SOLANDT, D .Y .SCILANDTand K .C .FISHER, J .Cell Comp . Physio . 7-8, 137-151 (1935-1936) . 4. E .D .ROBIN, H .V .MURDAUGH,JR ., W .PYRON, E .WEISS and P .SOTERES, Am . J . Physiol ., 205, 1175-1177 (1963) .