Hypoxic response is inversely related to degree of exercise hyperventilation

The Dejours hyperoxic test has been used to quantitate peripheral chemoreceptor contribution to the hyperpnea of exercise. The strength of this drive, measured by the percent reduction in ventilation, varies among individuals and is lacking in chemodenervated humans, who also fail to manifest a hyperventilatory response in heavy exercise. We reasoned that greater hyperventilation in exercise above the anaerobic threshold ought to be associated with greater hypoxic (carotid body) drive. The present study tested this hypothesis. In 17 naive subjects, carotid body O2 chemosensitivity was tested repeatedly during exercise above the ventilatory anaerobic threshold (VAT) using 2 breaths of O2. The response to these transients was quantitated by the percentage change in ventilation, and exercise hyperventilation was quantitated by VE in excess of VCO2 predicted from the slope of delta VE/delta VCO2 below VAT in incremental exercise. Contrary to expectations, there was an inverse relation between the degree of exercise hyperventilation and the percentage reduction in exercise ventilation in response to O2. The significance of this observation and its integration with current thinking of the role of the peripheral chemoreceptor in mediating hyperventilation of heavy exercise is discussed.