AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 5 868-R874, Copyright © 1986 by American Physiological Society
Peripheral circulatory responses to 96 h of hypoxia in conscious sinoaortic-denervated sheep
J. A. Krasney, K. Miki, K. McAndrews, G. Hajduczok and D. Curran-Everett
Conscious sheep exposed to 4 days of eucapnic hypoxia (arterial PO2 40
Torr, arterial PCO2 33 Torr) respond with sustained increases in heart
rate, cardiac output, and coronary, cerebral, and respiratory muscle blood
flows (Respir. Physiol. 59: 197-211, 1985). In the present investigation,
seven adult ewes were studied during similar levels of hypoxia (arterial
PO2 40 Torr, 4 days) after chronic section of the carotid sinus and aortic
depressor nerves to determine the contribution of the arterial
chemoreceptors to these responses. Ventilation and arterial PCO2 did not
change, indicating that ventilatory acclimation did not occur. O2
consumption decreased by 24%. Cardiac output (thermodilution) increased by
12% for only 24 h, heart rate increased by 44-69% above normoxic levels for
only 72 h, and stroke volume was unchanged. Systemic arterial pressure was
unchanged, whereas pulmonary arterial pressure rose by 56%. Coronary flow
(radio-labeled microspheres) increased from 155 +/- 50.4 (SE) to 299 +/- 81
ml X min-1 X 100 g-1 at 24 h and then declined to normoxic levels by 96 h.
Cerebral flow rose from 62 +/- 6.5 to between 85 +/- 14.4 and 124 +/- 43.5
ml X min-1 X 100 g-1 for 96 h. These results indicate that the arterial
chemoreflexes or reflexes secondary to increased ventilation are
responsible for the continued elevation of heart rate, cardiac output, and
coronary flow during eucapnic hypoxia.
