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Reflexes Controlling Circulatory, Ventilatory and Airway Responses to Exercise

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Abstract

The sections in this article are:

1 Reflex Cardiovascular Responses to Muscular Contraction in Anesthetized and Decerebrate Animals
1.1 Sensory Innervation of Skeletal Muscle
1.2 Reflex Autonomic Responses to Stimulation of Muscle Afferents in Anesthetized Animals
1.3 Discharge Properties of Group III and IV Muscle Afferents
1.4 The Site of the First Synapse—The Dorsal Horn
1.5 Role of Spinal Neurotransmitters and Neuromodulators in the Exercise Pressor Reflex
1.6 Pathways Ascending from the Dorsal Horn
1.7 The Ventrolateral Medulla
1.8 Other Central Neural Structures
1.9 Final Common Pathways
1.10 Interaction Between the Arterial Baroreflex and the Exercise Pressor Reflex in Anesthetized and Decerebrate Animals
2 Evidence for the Exercise Pressor Reflex in Humans and Conscious Animals
2.1 Feedback from Contracting Limb Skeletal Muscle in Humans and Conscious Animals
2.2 The Nature of the Stimulus Evoking the Exercise Pressor Reflex
3 Contribution of Peripheral Afferents to the Exercise Hyperpnea
3.1 Afferents from the Exercising limbs
3.2 The Carotid Chemoreceptor Afferents
3.3 Role in Hyperventilation During Heavy Exercise
3.4 The Pulmonary Afferents
3.5 Cardiac Afferents
3.6 Respiratory Muscle Afferents
3.7 Mediation of the Exercise Hyperpnea by Multiple Mechanisms
4 Summary and Conclusions
4.1 Peripheral Afferent Contribution to Circulatory Responses to Exercise
4.2 Peripheral Afferent Contribution to Ventilatory Responses to Exercise
Figure 1. Figure 1.

Records of tidal volume, arterial blood pressure, and dorsal root compound action potential from three periods of static hindlimb contraction in a chloralos‐anesthetized cat. From above downward are shown a control period of exercise; a period of exercise that commenced 3 1/2 min after application of a few drops of 0.125% lidocaine solution to the dorsal roots. Note that this period of contraction produced no pressor or ventilatory response, although the A‐wave of the compound action potential was little, if at all, reduced; and in the bottom set of records, a further control period of exercise begun some minutes after the lidocaine had been washed away with warm saline.

Reprinted with permission from McCloskey and Mitchell
Figure 2. Figure 2.

Recordings of renal sympathetic nerve activity (RSNA) in a chloralose‐anesthetized cat showing changes in RSNA evoked by intermittent tetanic contractions of the triceps surae. This maneuver synchronized the sympathetic activity such that each increase in muscle tension caused a large burst of RSNA before but not after dorsal root section.

Reprinted with permission from Victor et al.
Figure 3. Figure 3.

Discharge patterns of four thin fiber muscle afferents that responded to static contraction. Contraction period depicted by black bar. A, Group III fiber (conduction velocity 17.8 m/s) discharged vigorously at onset of contraction, but then its firing rate decreased even though muscle continued to contract. B, Group III fiber (conduction velocity 9.6 m/s) discharged vigorously at start of contraction, adapted, and then fired again during contraction. C, Group IV fiber (conduction velocity 1.3 m/s) started to fire 10 s after onset of contraction and then gradually increased its firing rate during contraction period. Note that firing of fiber slowed even though muscle continued to contract. D, Group IV fiber (conduction velocity 1.1 m/s) fired irregularly 4 s after onset of static contraction.

Reprinted with permission from Kaufman et al.
Figure 4. Figure 4.

Stimulation of group IV muscle afferent (conduction velocity 0.5 m/s) by contraction of gastrocnemius muscle, induced by ventral root stimulation. Filled circle (•) has been placed over each impulse discharge by group IV afferent. A, At onset of muscular contraction, group IV fiber did not fire. B, 8 s after end of A, group IV fiber has increased its firing rate over control level, which averaged 0.6 imp/s. C, 21 s after end of B, fiber is firing at greater rate than in B. D, After the contraction period, which lasted 45 s, fiber discharged. Horizontal bar in AD represents 1 s. Note that chart recorder speed was slower in D than in A–C.

Reprinted with permission from Kaufman et al.
Figure 5. Figure 5.

Effect of ischemia on response to static contraction of a group IV afferent (conduction velocity 0.8 m/s) whose receptive field was in triceps surae. A, Stimulation of afferent by ischemic static contraction (represented by bar). Note maintained stimulation of afferent after end of contraction. B, Nonischemic contraction (represented by bar) had no effect on afferent. C, Recording of impulse activity of group IV afferent during period of time, depicted by bracket with C over it in A.

Reprinted with permission from Kaufman et al.
Figure 6. Figure 6.

Effects of static contraction (A) and arachidonic acid (1 mg in 1 ml) injection into femoral artery (B and C) on discharge of a group IV afferent (conduction velocity 1.1 m/s). ▪, Contraction period in A. Note that B and C are continuous in time. D, Recording of the impulse activity of afferent during period of time depicted by bracket with D over it in B. E, Recording of impulse activity of afferent during period of time depicted by the bracket with E over it in C.

Reprinted with permission from Rotto and Kaufman
Figure 7. Figure 7.

Response of a group III muscle afferent in triceps surae muscles to dynamic exercise. Afferent (conduction velocity 11.7 m/s) was strongly sensitive to exercise. A: Control period before and B, 5‐step cycles during walking evoked by stimulation of MLR.

Reprinted with permission from Pickar, Hill, and Kaufman
Figure 8. Figure 8.

Mean (± SEM) R‐R intervals from one decerebrate cat in response to an increase in carotid sinus pressure at time zero, at rest (•_____•), and during hindlimb contraction elicited by ventral root stimulation at 50 Hz (○—–○). Baroreceptor responses at rest and during contraction were tested in an alternating sequence. The third R‐R interval (marked by asterisk) and subsequent R‐R intervals after sinus pressure elevation were significantly longer at rest than during contraction (P<0.05). No error bar is visible if smaller than the symbol. The period of contraction is denoted by the bar. Neither the initial nor the final carotid sinus pressure were significantly different in the resting and contracting situations; similarly, systolic and diastolic arterial pressures and R‐R intervals immediately before sinus pressure elevation, were not significantly different in the two situations.

Reprinted with permission from McWilliam, Yang, and Chien
Figure 9. Figure 9.

Individual microneurographic record of MSNA, MAP, and HR (beats per minute) responses to 6 min of rhythmic handgrip to 50% of maximum voluntary contraction. In this subject, MSNA increased during 6 min of exercise, and this increase was maintained after exercise when arm cuff was inflated. MAP responses to exercise were similar during exercise in two trials, but MAP was lower during postexercise ischemia (cuff up) after suction. HR responses were similar throughout.

Reprinted with permission from Joyner and Wieling
Figure 10. Figure 10.

Heart rate (a) and systolic arterial pressure (b) at rest and as functions of external workload in the leg positive pressure (•) and control (Δ) conditions, all data referring to steady state. On the abscissa, workloads are given as a percentage of the peak load attained in the control condition, with WL o‐V representing 0%, 23%, 48%, 61%, 87%, and 100% of this load and WL III indicating the highest load that could be managed in the leg positive‐pressure condition. Values are means; (a) n = 7, (b) n = 8. Vertical bars: | SEM. *P<0.05, **P<0.01, ***P<0.001.

Reprinted with permission from Eiken and Bjurstedt
Figure 11. Figure 11.

Graphs of peak increases in total muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate (HR) caused by static handgrip at 15% MVC (open bars) and at 30% MVC (hatched bars) before curare infusion and by attempted handgrip during a high dose of curare (solid bars). During curare infusion, subjects used near‐maximal effort to attempt sustained handgrip but generated almost no force. Without sustained contraction, the intent to exercise alone (i.e., central command) caused much smaller increases in MSNA and arterial pressure than normally caused by an actual static handgrip at 30% MVC even though the effort was greater with the attempted than with the actual contraction. In contrast, heart rate increased as much with the attempted handgrip as with the actual handgrip at 30% MVC. Entries are mean ±SEM for eight subjects.

Reprinted with permission from Victor et al.
Figure 12. Figure 12.

Responses of forearm muscle cell pH (▪) as determined by 3P‐NMR and of peroneal muscle sympathetic nerve activity (□) during 4 min of rhythmic handgrip (2 min at 30% MVC followed by 2 min at 50% MVC). Data represent mean ±SE for seven subjects (*P<0.05 vs. control).

Reprinted with permission from Victor et al.
Figure 13. Figure 13.

Changes in forearm muscle pH and calf vascular resistance during static forearm exercise at 30% MVC. Base = 5 min of baseline data. Grip 1 and 2 represent each minute of static exercise; PHG‐CA, posthandgrip circulatory arrest, and represents the mean value of 3 min of data; Rec, recovery and represents data during the third minute of recovery. Measurements were made during exercise of dominant and non‐dominant forearms of six individuals. Bars represent ± SEM. This figure demonstrates the roughly inverse relationship between changes in pH and calf vascular resistance during forearm exercise.

Reprinted with permission from Sinoway et al.
Figure 14. Figure 14.

Original records of MSNA in two subjects showing peak responses during static handgrip at 30% MVC and during phases 2 and 3 of a Valsalva maneuver. Whereas MSNA responses evoked by static handgrip were markedly attenuated in the patient with myophosphorylase deficiency, increases in MSNA evoked by the Valsalva maneuver were comparable in the normal subject and patient.

Reprinted with permission from Pryor et al.
Figure 15. Figure 15.

The time course of pulmonary ventilation (VF), oxygen consumption (VO2) and the VF–VO2 and (VFO2) in a neural dog when the hindlimb muscles were induced electrically to contract and the venous blood from the hindlimbs was diverted to a humoral dog.

Reprinted with permission from Kao
Figure 16. Figure 16.

The relationship between pulmonary ventilation (E) and alveolar PCO2 (PACO2) to oxygen consumption (VO2) during voluntary (Δ) and electrically induced muscle contraction (•) in a single awake human subject.

Reprinted with permission from Asmussen and Nielsen
Figure 17. Figure 17.

The pulmonary ventilation (1) end tidal CO2 (PETCO2), the ratio of 1 to metabolic rate (O2), and blood lactate during several intensities of bicycle exercise in human subjects. Open triangles represent data with unobstructed leg blood flow and closed circles represent data when blood flow to the legs was reduced about 20% by increasing pressure around the legs to 50 mm Hg.

Reprinted with permission from Williamson et al.
Figure 18. Figure 18.

The relationship between the ratio of pulmonary ventilation to metabolic rate (F/O2) and the reduction in hand‐grip strength during neuromuscular blockade by tubocurarine. Note that as the degree of block increased the F/2 ratio increased.

Reprinted with permission from Asmussen
Figure 19. Figure 19.

response to two levels of treadmill exercise repeated in one pony on several different days before and 3 weeks after partial lesioning the dorsal lateral spinal columns at the L2 level. The different symbols represent separate days. Note the attenuated exercise hypocapnia following spinal lesioning.

Reprinted with permission from Pan et al.
Figure 20. Figure 20.

Average arterial and end‐tidal CO2 tensions ( and PACO2) respectively, arterial pH, and bicarbonate for control and carotid chemoreceptor‐resected (CBR) asthmatics below (left) and above (right) the anaerobic threshold.

Reprinted with permission from Wasserman et al.
Figure 21. Figure 21.

The temporal pattern of the change in alveolar PCO2 (ΔPACO2), pulmonary ventilation (Δ1), tidal volume (ΔVT), and breathing frequency (Δf) in a dog before (full lines) and after carotid chemodenervation (dashed line).

Reprinted with permission from Flandrois, Lacour, and Eclache
Figure 22. Figure 22.

The change in ) between rest and six levels of steady‐state treadmill exercise in carotid body intact and denervated ponies plotted against heart rate used as an index of work intensity. Note the inverse linear relationship between work intensity and ΔPaCo2, and that the exercise hypocapnia is accentuated by CBD.

Reprinted with permission from Pan et al.
Figure 23. Figure 23.

The effect on pulmonary ventilation (1) of reducing PCO2 at the carotid chemoreceptors (unilateral by 7.2 or 13.1 mm Hg in dogs). The perfusion to the carotid chemoreceptors on one side was isolated and PCO2 was reduced (time 0) using an extracorporeal exchange mechanism. Note that carotid chemoreceptor hypocapnia has a rapid and substantial depressant effect on breathing.

Reprinted with permission from Smith et al.
Figure 24. Figure 24.

Relationships between pulmonary ventilation (E) and rates of pulmonary CO2 excretion (CO2) and o2 uptake (o2) in awake sheep. Changes in CO2 and o2 were produced by removing CO2 from and adding O2 to venous blood through membrane lungs. Solid lines are calculated linear regressions; dashed lines are lines of identity.

Reprinted with permission from Phillipson, Duffin, and Cooper
Figure 25. Figure 25.

Effect of treadmill exercise on arterial PCO2 (Paco2) in five ponies before (closed symbols) and 2–4 weeks after (open symbols) hilar nerve denervation (HND). Note that the Paco2 responses to all three exercise protocols was not altered by HND.

Reprinted with permission from Flynn et al.
Figure 26. Figure 26.

Mean values for two 30 sec periods prior to and following the start of voluntary (continuous lines), and electrically (dotted lines) induced muscle contractions in the three patient groups (normal, heart transplant, and heart‐lung transplant). 1, ventilation; , oxygen consumption; , cardiac output, expressed as percentage change from the first resting value. The vertical bars indicate the Fisher's least‐significant difference at the P<0.05 level in each case.

Reprinted with permission from Banner et al.
Figure 27. Figure 27.

Pulmonary ventilation (1) and of goats at rest and during one level of mild treadmill exercise. The left panel was obtained with the goats wearing a conventional mask for obtaining V1 and the right panel was obtained with addition of 250 ml external dead space (D). Closed symbols are prior to drug treatment, while open symbols are after methysergide administration, which is an antagonist of serotonin. Note that methyserside attenuated 1 response to increased D resulting in exercise hypercapnia.

Reprinted with permission from Buch, Lutcavage, and Mitchell


Figure 1.

Records of tidal volume, arterial blood pressure, and dorsal root compound action potential from three periods of static hindlimb contraction in a chloralos‐anesthetized cat. From above downward are shown a control period of exercise; a period of exercise that commenced 3 1/2 min after application of a few drops of 0.125% lidocaine solution to the dorsal roots. Note that this period of contraction produced no pressor or ventilatory response, although the A‐wave of the compound action potential was little, if at all, reduced; and in the bottom set of records, a further control period of exercise begun some minutes after the lidocaine had been washed away with warm saline.

Reprinted with permission from McCloskey and Mitchell


Figure 2.

Recordings of renal sympathetic nerve activity (RSNA) in a chloralose‐anesthetized cat showing changes in RSNA evoked by intermittent tetanic contractions of the triceps surae. This maneuver synchronized the sympathetic activity such that each increase in muscle tension caused a large burst of RSNA before but not after dorsal root section.

Reprinted with permission from Victor et al.


Figure 3.

Discharge patterns of four thin fiber muscle afferents that responded to static contraction. Contraction period depicted by black bar. A, Group III fiber (conduction velocity 17.8 m/s) discharged vigorously at onset of contraction, but then its firing rate decreased even though muscle continued to contract. B, Group III fiber (conduction velocity 9.6 m/s) discharged vigorously at start of contraction, adapted, and then fired again during contraction. C, Group IV fiber (conduction velocity 1.3 m/s) started to fire 10 s after onset of contraction and then gradually increased its firing rate during contraction period. Note that firing of fiber slowed even though muscle continued to contract. D, Group IV fiber (conduction velocity 1.1 m/s) fired irregularly 4 s after onset of static contraction.

Reprinted with permission from Kaufman et al.


Figure 4.

Stimulation of group IV muscle afferent (conduction velocity 0.5 m/s) by contraction of gastrocnemius muscle, induced by ventral root stimulation. Filled circle (•) has been placed over each impulse discharge by group IV afferent. A, At onset of muscular contraction, group IV fiber did not fire. B, 8 s after end of A, group IV fiber has increased its firing rate over control level, which averaged 0.6 imp/s. C, 21 s after end of B, fiber is firing at greater rate than in B. D, After the contraction period, which lasted 45 s, fiber discharged. Horizontal bar in AD represents 1 s. Note that chart recorder speed was slower in D than in A–C.

Reprinted with permission from Kaufman et al.


Figure 5.

Effect of ischemia on response to static contraction of a group IV afferent (conduction velocity 0.8 m/s) whose receptive field was in triceps surae. A, Stimulation of afferent by ischemic static contraction (represented by bar). Note maintained stimulation of afferent after end of contraction. B, Nonischemic contraction (represented by bar) had no effect on afferent. C, Recording of impulse activity of group IV afferent during period of time, depicted by bracket with C over it in A.

Reprinted with permission from Kaufman et al.


Figure 6.

Effects of static contraction (A) and arachidonic acid (1 mg in 1 ml) injection into femoral artery (B and C) on discharge of a group IV afferent (conduction velocity 1.1 m/s). ▪, Contraction period in A. Note that B and C are continuous in time. D, Recording of the impulse activity of afferent during period of time depicted by bracket with D over it in B. E, Recording of impulse activity of afferent during period of time depicted by the bracket with E over it in C.

Reprinted with permission from Rotto and Kaufman


Figure 7.

Response of a group III muscle afferent in triceps surae muscles to dynamic exercise. Afferent (conduction velocity 11.7 m/s) was strongly sensitive to exercise. A: Control period before and B, 5‐step cycles during walking evoked by stimulation of MLR.

Reprinted with permission from Pickar, Hill, and Kaufman


Figure 8.

Mean (± SEM) R‐R intervals from one decerebrate cat in response to an increase in carotid sinus pressure at time zero, at rest (•_____•), and during hindlimb contraction elicited by ventral root stimulation at 50 Hz (○—–○). Baroreceptor responses at rest and during contraction were tested in an alternating sequence. The third R‐R interval (marked by asterisk) and subsequent R‐R intervals after sinus pressure elevation were significantly longer at rest than during contraction (P<0.05). No error bar is visible if smaller than the symbol. The period of contraction is denoted by the bar. Neither the initial nor the final carotid sinus pressure were significantly different in the resting and contracting situations; similarly, systolic and diastolic arterial pressures and R‐R intervals immediately before sinus pressure elevation, were not significantly different in the two situations.

Reprinted with permission from McWilliam, Yang, and Chien


Figure 9.

Individual microneurographic record of MSNA, MAP, and HR (beats per minute) responses to 6 min of rhythmic handgrip to 50% of maximum voluntary contraction. In this subject, MSNA increased during 6 min of exercise, and this increase was maintained after exercise when arm cuff was inflated. MAP responses to exercise were similar during exercise in two trials, but MAP was lower during postexercise ischemia (cuff up) after suction. HR responses were similar throughout.

Reprinted with permission from Joyner and Wieling


Figure 10.

Heart rate (a) and systolic arterial pressure (b) at rest and as functions of external workload in the leg positive pressure (•) and control (Δ) conditions, all data referring to steady state. On the abscissa, workloads are given as a percentage of the peak load attained in the control condition, with WL o‐V representing 0%, 23%, 48%, 61%, 87%, and 100% of this load and WL III indicating the highest load that could be managed in the leg positive‐pressure condition. Values are means; (a) n = 7, (b) n = 8. Vertical bars: | SEM. *P<0.05, **P<0.01, ***P<0.001.

Reprinted with permission from Eiken and Bjurstedt


Figure 11.

Graphs of peak increases in total muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate (HR) caused by static handgrip at 15% MVC (open bars) and at 30% MVC (hatched bars) before curare infusion and by attempted handgrip during a high dose of curare (solid bars). During curare infusion, subjects used near‐maximal effort to attempt sustained handgrip but generated almost no force. Without sustained contraction, the intent to exercise alone (i.e., central command) caused much smaller increases in MSNA and arterial pressure than normally caused by an actual static handgrip at 30% MVC even though the effort was greater with the attempted than with the actual contraction. In contrast, heart rate increased as much with the attempted handgrip as with the actual handgrip at 30% MVC. Entries are mean ±SEM for eight subjects.

Reprinted with permission from Victor et al.


Figure 12.

Responses of forearm muscle cell pH (▪) as determined by 3P‐NMR and of peroneal muscle sympathetic nerve activity (□) during 4 min of rhythmic handgrip (2 min at 30% MVC followed by 2 min at 50% MVC). Data represent mean ±SE for seven subjects (*P<0.05 vs. control).

Reprinted with permission from Victor et al.


Figure 13.

Changes in forearm muscle pH and calf vascular resistance during static forearm exercise at 30% MVC. Base = 5 min of baseline data. Grip 1 and 2 represent each minute of static exercise; PHG‐CA, posthandgrip circulatory arrest, and represents the mean value of 3 min of data; Rec, recovery and represents data during the third minute of recovery. Measurements were made during exercise of dominant and non‐dominant forearms of six individuals. Bars represent ± SEM. This figure demonstrates the roughly inverse relationship between changes in pH and calf vascular resistance during forearm exercise.

Reprinted with permission from Sinoway et al.


Figure 14.

Original records of MSNA in two subjects showing peak responses during static handgrip at 30% MVC and during phases 2 and 3 of a Valsalva maneuver. Whereas MSNA responses evoked by static handgrip were markedly attenuated in the patient with myophosphorylase deficiency, increases in MSNA evoked by the Valsalva maneuver were comparable in the normal subject and patient.

Reprinted with permission from Pryor et al.


Figure 15.

The time course of pulmonary ventilation (VF), oxygen consumption (VO2) and the VF–VO2 and (VFO2) in a neural dog when the hindlimb muscles were induced electrically to contract and the venous blood from the hindlimbs was diverted to a humoral dog.

Reprinted with permission from Kao


Figure 16.

The relationship between pulmonary ventilation (E) and alveolar PCO2 (PACO2) to oxygen consumption (VO2) during voluntary (Δ) and electrically induced muscle contraction (•) in a single awake human subject.

Reprinted with permission from Asmussen and Nielsen


Figure 17.

The pulmonary ventilation (1) end tidal CO2 (PETCO2), the ratio of 1 to metabolic rate (O2), and blood lactate during several intensities of bicycle exercise in human subjects. Open triangles represent data with unobstructed leg blood flow and closed circles represent data when blood flow to the legs was reduced about 20% by increasing pressure around the legs to 50 mm Hg.

Reprinted with permission from Williamson et al.


Figure 18.

The relationship between the ratio of pulmonary ventilation to metabolic rate (F/O2) and the reduction in hand‐grip strength during neuromuscular blockade by tubocurarine. Note that as the degree of block increased the F/2 ratio increased.

Reprinted with permission from Asmussen


Figure 19.

response to two levels of treadmill exercise repeated in one pony on several different days before and 3 weeks after partial lesioning the dorsal lateral spinal columns at the L2 level. The different symbols represent separate days. Note the attenuated exercise hypocapnia following spinal lesioning.

Reprinted with permission from Pan et al.


Figure 20.

Average arterial and end‐tidal CO2 tensions ( and PACO2) respectively, arterial pH, and bicarbonate for control and carotid chemoreceptor‐resected (CBR) asthmatics below (left) and above (right) the anaerobic threshold.

Reprinted with permission from Wasserman et al.


Figure 21.

The temporal pattern of the change in alveolar PCO2 (ΔPACO2), pulmonary ventilation (Δ1), tidal volume (ΔVT), and breathing frequency (Δf) in a dog before (full lines) and after carotid chemodenervation (dashed line).

Reprinted with permission from Flandrois, Lacour, and Eclache


Figure 22.

The change in ) between rest and six levels of steady‐state treadmill exercise in carotid body intact and denervated ponies plotted against heart rate used as an index of work intensity. Note the inverse linear relationship between work intensity and ΔPaCo2, and that the exercise hypocapnia is accentuated by CBD.

Reprinted with permission from Pan et al.


Figure 23.

The effect on pulmonary ventilation (1) of reducing PCO2 at the carotid chemoreceptors (unilateral by 7.2 or 13.1 mm Hg in dogs). The perfusion to the carotid chemoreceptors on one side was isolated and PCO2 was reduced (time 0) using an extracorporeal exchange mechanism. Note that carotid chemoreceptor hypocapnia has a rapid and substantial depressant effect on breathing.

Reprinted with permission from Smith et al.


Figure 24.

Relationships between pulmonary ventilation (E) and rates of pulmonary CO2 excretion (CO2) and o2 uptake (o2) in awake sheep. Changes in CO2 and o2 were produced by removing CO2 from and adding O2 to venous blood through membrane lungs. Solid lines are calculated linear regressions; dashed lines are lines of identity.

Reprinted with permission from Phillipson, Duffin, and Cooper


Figure 25.

Effect of treadmill exercise on arterial PCO2 (Paco2) in five ponies before (closed symbols) and 2–4 weeks after (open symbols) hilar nerve denervation (HND). Note that the Paco2 responses to all three exercise protocols was not altered by HND.

Reprinted with permission from Flynn et al.


Figure 26.

Mean values for two 30 sec periods prior to and following the start of voluntary (continuous lines), and electrically (dotted lines) induced muscle contractions in the three patient groups (normal, heart transplant, and heart‐lung transplant). 1, ventilation; , oxygen consumption; , cardiac output, expressed as percentage change from the first resting value. The vertical bars indicate the Fisher's least‐significant difference at the P<0.05 level in each case.

Reprinted with permission from Banner et al.


Figure 27.

Pulmonary ventilation (1) and of goats at rest and during one level of mild treadmill exercise. The left panel was obtained with the goats wearing a conventional mask for obtaining V1 and the right panel was obtained with addition of 250 ml external dead space (D). Closed symbols are prior to drug treatment, while open symbols are after methysergide administration, which is an antagonist of serotonin. Note that methyserside attenuated 1 response to increased D resulting in exercise hypercapnia.

Reprinted with permission from Buch, Lutcavage, and Mitchell
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Marc P. Kaufman, Hubert V. Forster. Reflexes Controlling Circulatory, Ventilatory and Airway Responses to Exercise. Compr Physiol 2011, Supplement 29: Handbook of Physiology, Exercise: Regulation and Integration of Multiple Systems: 381-447. First published in print 1996. doi: 10.1002/cphy.cp120110