Xb. Mou et al., A PROTOCOL FOR DETERMINING THE SHAPE OF THE VENTILATORY RESPONSE TO HYPOXIA IN HUMANS, Respiration physiology, 101(2), 1995, pp. 139-143
The ventilatory response to isocapnic hypoxia is biphasic, which makes
any experimental assessment of the relationship between the acute (pe
ak) ventilatory response and the level of hypoxia difficult. This stud
y explored whether one particular protocol could be useful for determi
ning this relationship. The protocol consisted of exposing subjects to
seven different levels of isocapnic hypoxia, each of which lasted 50
sec. In order to test whether the order of the hypoxic exposure had an
y effect on the outcome, the steps were performed both in increasing a
nd decreasing severity of hypoxia, and the ventilatory responses compa
red. Twelve subjects were studied, and each test was repeated four tim
es in each subject. PET(CO2) was held at 2 mmHg above resting througho
ut. The ventilations obtained at the lowest level of PET(O2) employed
were clearly different between the two protocols. However, provided th
at these ventilations were excluded, no significant differences were p
resent between the results from the ascending and descending exposures
(ANOVA). This finding suggests that the rate of change of P-O2 in the
se protocols was sufficiently slow for a full ventilatory response to
develop, but also sufficiently fast to prevent significant ventilatory
depression from occurring.