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University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom
Measurement
of the acute hypoxic ventilatory response (AHVR) requires careful
choice of the hypoxic stimulus. If the
stimulus is too brief, the response may be incomplete; if the stimulus is too long, hypoxic ventilatory depression may ensue. The purpose of
this study was to compare three different techniques for assessing AHVR, using different hypoxic stimuli, and also to examine the between-day variability in AHVR. Ten subjects were studied, each on six
different occasions, which were
1 wk apart. On each occasion, AHVR
was assessed using three different protocols: 1) protocol SW, which uses square waves of hypoxia; 2) protocol
IS, which uses incremental steps of hypoxia; and 3)
protocol RB, which simulates an isocapnic rebreathing test.
Mean values for hypoxic sensitivity were 1.02 ± 0.48, 1.15 ± 0.55, and 0.93 ± 0.60 (SD)
l · min
1 · %
1
for protocols SW, IS, and RB, respectively. These
differed significantly (P < 0.01). The coefficients of
variation for measurement of AHVR were 20, 23, and 36% for the three
protocols, respectively. These were not significantly different. There
was a significant physiological variation in AHVR
(F 50,100 = 3.9, P < 0.001), with a
coefficient of variation of 26%. We conclude that there was relatively
little systematic variation between the three protocols but that AHVR varies physiologically over time.
acute hypoxic ventilatory response; ventilation
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