Latency of the ventilatory chemoreflex response to hypoxia in humans

Latencies for the ventilatory response to hypoxia have been estimated from data from experiments in which square waves of isocapnic hypoxia (periods 30 sec and 60 sec) were presented to 5 subjects. Distorted steps were excluded from the analysis, and the remaining steps were time-aligned relative to the step and then averaged. For the 30 sec data, the median latency for the response to the step into hypoxia was 1 breath or 5.1 sec (time to mid-point of first significantly different breath) and for the step out of hypoxia was 1 breath or 4.7 sec. The number of transients analyzed averaged 87 per subject per transition type. For the 60 sec data, the median latency for the step into hypoxia was 2 breaths or 6.8 sec, and for the step out of hypoxia was 2 breaths or 6.0 sec. The number of transients analyzed averaged 40 per subject per transition type. These latencies are generally shorter than those reported previously and suggest that the ventilatory variability may have served to lengthen the measured latency of response in previous studies.