Am. J. Respir. Crit. Care Med., Vol 151, No. 6, Jun 1995, 1815-1820.
Dependency on the rate of change in PaO2 of the ventilatory response to progressive hypoxia
T Igarashi, M Nishimura, S Kobayashi, K Miyamoto and Y Kawakami
First Department of Medicine, Hokkaido University School of Medicine, Sapporo, Japan.
The biphasic nature of the ventilatory response to sustained hypoxia (<
1 h) is thought to occur as a result of combined effects of stimulation and
depression with hypoxia. If the depressant effect of hypoxia on ventilation
occurs later than the stimulatory effect, the magnitude of the ventilatory
response to progressive hypoxia may be different according to the time
required for a given fall in PaO2 during the test. In this study, we
measured, in 10 healthy adult volunteers, ventilatory responses to
isocapnic progressive hypoxia (HVR) using three different protocols (4 min,
6 min, and 15 min for SaO2 to decrease from the baseline to 80%) with or
without pretreatment using theophylline (300 mg twice a day), an adenosine
receptor antagonist, in a 2-d, single-blind crossover design. The slope
values of HVR with the placebo were 0.31 +/- 0.04 (SE) (L/min/% fall of
SaO2) in the 4-min protocol, 0.26 +/- 0.04 in the 6-min protocol, and 0.18
+/- 0.04 in the 15-min protocol. The HVR for the 15-min protocol was
significantly lower than that for the 4-min or 6-min protocol. The HVR with
theophylline was 0.46 +/- 0.08 for the 4-min protocol, 0.54 +/- 0.09 for
the 6-min protocol, and 0.66 +/- 0.11 for the 15-min protocol, among which
there were no significant differences. The dependency of HVR on the rate of
change in PaO2, that was seen with a placebo run, disappeared after
pretreatment with theophylline.(ABSTRACT TRUNCATED AT 250 WORDS)
