Asymmetry in the Ventilatory Response to a Bout of Hypoxia in Human Beings

Abstract

Ventilation rapidly increases initially in response to the sudden imposition of isocapnic hypoxia. Recently there has been interest in the subsequent slow decline in ventilation in the face of sustained hypoxia [9, 7, 2]. The mechanisms behind this decline are still controversial and changes in cerebral blood flow as well as several neuromodulators have been implicated. The return to normoxia or hyperoxia from hypoxia shows a rapid decrease in ventilation followed by a subsequent slow return to the resting level, usually from an undershoot. Examination of the ventilatory responses shows that there are noticeable differences between the response for the transition into hypoxia from the transition out of hypoxia. While the response to the step into hypoxia shows a pronounced overshoot, in comparsion, the response to a step out of hypoxia shows less of an undershoot. We have used curve fitting techniques to fit a mathematical model to ventilatory response data in order to quantify the differences in the response.