Journal of Applied Physiology, Vol 72, Issue 6 2128-2133, Copyright © 1992 by American Physiological Society
Influence of airway resistance on hypoxia-induced periodic breathing
F. Series, I. Series, L. Atton and A. Blouin
Centre de Pneumologie de l'Hopital, Sainte Foy, Quebec, Canada.
We studied the effects of changing upper airway pressure on the variability
of the dynamic response of ventilation to a hypoxic disturbance in 11
spontaneously breathing dogs. Supralaryngeal pressure, instantaneous
inspiratory flow, end-expiratory lung volume, and the inspiratory and
expiratory O2 and CO2 concentrations were continuously recorded at baseline
and after a 1.5-min hypoxic stimulus (abrupt normoxic recovery). Arterial
blood gases were obtained at baseline, at the end of the hypoxic period,
and after 1 min of recovery. Airway resistances were modified during the
recovery by changing the composition of the inspired gas (all with an
inspiratory O2 fraction of 20.9%) among four different trials: two trials
were realized with air (density 1.12 g/l), and the other two were with He
or SF6 (respective density 0.42 and 4.20) in random order. There was no
difference between baseline minute ventilation, arterial blood gases, and
supralaryngeal resistance values preceding the trials. The hypoxemic and
hypocapnic levels and the hypoxia-induced hyperventilation reached during
the hypoxic tests were identical for the different hypoxic stimuli. The
supralaryngeal resistance measured at peak flow was dramatically influenced
by the composition of the inspired gas: 8.8 +/- 1.8 and 6.9 +/- 1.7 (SE)
cmH2O.l-1.s with air, 7.2 +/- 2.2 with He, 21.9 +/- 5.5 with SF6 (P less
than 0.05). Ventilatory fluctuations were consistently seen during the
posthypoxic period. They were characterized by a strength index value (M)
(Waggener et al. J. Appl. Physiol. 56: 576-581, 1984).(ABSTRACT TRUNCATED
AT 250 WORDS)
