Variable Inhibition by Falling CO2 of Hypoxic Ventilatory Response in Man

摘要

Acute hypoxia stimulates an increase in ventilation but the resulting hypocapnia limits the magnitude of the increase. Thus, the hypoxic ventilatory response is usually measured during isocapnia, but this may not reflect events at high altitude. Possibly the degree of inhibition by hypocapnia might depend on individual ventilatory response to C02 and thus vary between persons. if so, it might be useful to compare between individuals an isocapnic hypoxic ventilatory response (PAC02 maintained by C02 addition) with a response in which C02 was not added and the PACO2 fell to a variable extent (poikilocapnic hypoxia). We found in 14 healthy persons that, although the poikilocapnic hypoxic ventilatory response positively correlated with the isocapnic hypoxic response, the relation was improved by a multiple regression which included the negative association with the normoxic hypercapnic response. Thus the magnitude of the difference between the isocapnic and the poikilocapnic hypoxic responses related to the hypercapnic response (p less than .001). In those subjects with small hypercapnic responses, a falling C02 during hypoxia had little depressant effect on the hypoxic ventilatory responses.