Journal of Applied Physiology, Vol 46, Issue 6 1171-1177, Copyright © 1979 by American Physiological Society
Hypopnea consequent to reduced pulmonary blood flow in the dog
R. W. Stremel, B. J. Whipp, R. Casaburi, D. J. Huntsman and K. Wasserman
The ventilatory responses to diminished pulmonary blood flow (Qc), as a
result of partial cardiopulmonary bypass (PCB), were studied in
chloralose-urethan-anesthetized dogs. Qc was reduced by diverting vena
caval blood through a membrane gas exchanger and returning it to the
ascending aorta. PCB flows of 400--1,600 ml/min were utilized for durations
of 2--3 min. Decreasing Qc, while maintaining systemic arterial blood gases
and perfusion, results in a significant (P less than 0.05) decrease in
expiratory ventilation (VE) (15.9%) and alveolar ventilation (VA) (31.0%).
The ventilatory decreases demonstrated for this intact group persist after
bilateral cervical vagotomy (Vx), carotid body and carotid sinus
denervation (Cx), and combined Vx and Cx. The changes in VE and VA were
significantly (P less than 0.001) correlated with VCO2 changes, r = 0.80
and r = 0.93, respectively. These ventilatory changes were associated with
an overall average decrease in left ventricular PCO2 of 2.1 Torr; this
decrease was significant (P less than 0.05) only in the intact and Cx
groups. Decreasing pulmonary blood flow results in a decrease in
ventilation that may be CO2 related; however, the exact mechanism remains
obscure but must have a component that is independent of vagally mediated
cardiac and pulmonary afferents and peripheral baroreceptor and
chemoreceptor afferents.
