Journal of Applied Physiology, Vol 75, Issue 5 2022-2027, Copyright © 1993 by American Physiological Society
Chemical and nonchemical stimuli during breath holding in divers are not independent
D. Courteix, M. Bedu, N. Fellmann, M. C. Heraud and J. Coudert
Laboratoire de Physiologie, Faculte de Medecine, Clermont-Ferrand, France.
In the breath-hold model described by S. Godfrey and E. J. M. Campbell
(Respir. Physiol. 5: 385-400, 1968), chemical and nonchemical stimuli are
independent. Because these two factors are time dependent, the effect of
each could not be measured by breath-holding time (BHT). The aim of this
study is to dissociate chemical and nonchemical stimuli and to assess the
effects of BHT and PCO2 on respiratory center output by measurement of
occlusion pressure (P0.1) and mean inspiratory flow (VI). Nine well-trained
divers (age 36.5 +/- 5.0 yr) took part in the study. Each subject had to
hold his breath at 75% of vital capacity for 30, 50, and 70 s of BHT.
Before each breath hold, the subject inspired successively two vital
capacities of the same CO2-O2 gas mixture. P0.1 and VI were measured during
the first reinspiration after the breath hold. For the same BHT, we
observed good linear relationships between P0.1 or VI and alveolar PCO2.
The slopes of these relationships increased with BHT. For alveolar PCO2 of
> 50 Torr, P0.1 increased linearly with BHT. These results indicate
that, during breath holding, chemical and nonchemical stimuli acted
linearly on respiratory motoneuron activity, but they were not independent.
