Reflex control of vascular capacitance during hypoxia, hypercapnia, or hypoxic hypercapnia

Mongrel dogs anesthetized with sodium pentobarbital and paralyzed with veruronium bromide

Exposure to hypoxia (PaO2 = 38 mmHg), hypercapnia (PaCO2 = 72 mmHg), or hypoxic hypercapnia (PaO2 = 41; PaCO2 = 69 mmHg) with intact cardiovascular reflexes

Exposure to the same gas mixtures with reflexes blocked (hexamethonium and atropine), systemic arterial pressure supported with a constant infusion of norepinephrine, and mean circulatory filling pressure restored toward control with 5 mL/kg blood

Mean circulatory filling pressure (an index of venous tone) and cardiac outputsurrogate