Influence of arterial hypoxia on cardiac and coronary dynamics in the conscious sinoaortic-denervated dog

Arterial hypoxia was produced in 10 conscious, chronically instrumented, tracheostomized dogs by allowing them to breathe 7.5% O₂ in N₂ for 10 min. Hypoxia (Pa(o₂)=28±0.7 (SE) Torr) caused significant increases in coronary blood flow (+196%), left ventricular dP/dt max (+60%), aortic blood flow (+48%), heart rate (+50%), and left ventricular systolic (+12%) and aortic (+10%) pressures. Left ventricular end-diastolic pressure and stroke volume were unchanged, while systemic (-30%) and coronary diastolic (-66%) vascular resistances declined significantly. When equivalent levels of arterial hypoxia were produced in four of these dogs after chronic sinoaortic denervation, the coronary, cardiac, and systemic hemodynamic responses were not significantly different, with the exception that the small arterial pressure response was abolished. Thus the peripheral chemoreflexes are not essential for the normal coronary vasodilator and cardiac adjustments to occur during hypoxia in the conscious dog. The data support the hypothesis that a large part of the cardiac adjustments to hypoxia is initiated outside the sinoaortic reflexogenic zones, probably within the central nervous system.