Baroreceptor control of pressure-flow relationships during hypoxemia.

In the absence of peripheral chemoreceptors, the effects of graded hypoxemia on the carotid sinus control of central and regional hemodynamics were studied in anesthetized mongrel dogs. Baroreceptor stimulation was effected by carotid sinus isolation and perfusion under controlled pressure. Blood flows were measured in the aorta and the celiac, mesenteric, left renal, and right iliac arteries. Carotid sinus reflex set-point pressures were well maintained until hypoxemia was severe. Carotid sinus reflex set-point gain was maximal during mild hypoxemia. Reflex operating point regional flows were unaffected by hypoxemia. A factorial analysis of overall reflex increases in mean aortic pressure, flow, and power during reduced baroreceptor stimulation showed potentiation by increasing hypoxemia. Corresponding effects of baroreceptor stimulation and hypoxemia on aortic resistance and heart rate were additive. Celiac, renal, and iliac blood flows increased during both hypoxemia and reduced baroreceptor stimulation. Only in the celiac bed were blood flow changes independent of concomitant changes in cardiac output. Thus, at maximum sympathetic stimulation (low carotid sinus pressure) during hypoxemia, the cardiovascular system maintained both central and regional blood flows at high systemic blood pressures independent of the peripheral chemoreceptors.