Decreased ventilatory response to hypoxia during acute polycythemia in the calf

Abstract

Increase in ventilation in response to acute hypoxia is mediated by stimulation of systemic arterial chemoreceptors. Probably the stimulus is intracellular hypoxia resulting from a reduction m the amount of oxygen delivered to the chemoreceptor tissue. If oxygen transport were increased, then the ventilatory response to hypoxia might be reduced. This hypothesis was examined in nine calves. Blood oxygen carrying capacity was increased by the infusion of packed red cells sufficient to increase the hemoglobin concentration from 11.4 to 15.7 g/100 ml, which increased systemic oxygen transport by 37%. Lowering the arterial oxygen tension from 60 to 40 mm Hg increased ventilation 141% prior to transfusion, but only 76% in the presence of polycythemia (p < .005). However, polycythemia did not alter significantly the ventilatory response to hypereapnia in the absence of hypoxia. It is postulated that in the presence of a given degree of arterial hypoxemia, polycythemia augments oxygen transport to lessen chemoreceptor tissue hypoxia and thereby reduce the stimulation of ventilation.