Laryngeal reflex apnea is blunted during and following hindlimb
muscle contraction in sheep.
P., Haouzi, C. Beyaert, J. P. Gille, B. Chalon, F. Marchal.
Laboratoire de Physiologie, Facult[acute]e de M[acute]edecine de
Nancy, INSERM Unit[acute]e 14
APStracts 3:0211R, 1996.
This study was carried out on seven chloralose anesthetized sheep, and
was designed to investigate the role of muscular afferent fiber
stimulation on the duration of reflex apnea triggered by laryngeal
stimulation (LS). In six animals, injection of distilled water onto
the laryngeal mucosa provoked a 15.7 +/- 1.0 sec (mean +/- SEM) apnea
associated with a rise in systemic blood pressure (+7 +/- 0.8 Torr).
Electrically induced contractions (EIC) of the hindlimb muscles
doubled the metabolic rate and ventilation, and reduced the duration
of the apnea produced by LS to 7.4 +/- 1.0 sec (p<0.01). Apnea
duration was still reduced during the first minute after the
cessation of EIC (7.2 +/- 1.1 sec, p<0.01), but returned to
control after a five-minute recovery period (16.7 +/-?1.6 sec). The
apnea triggered by LS was also reduced during EIC when the venous
return was impeded by occluding the inferior vena cava (5.2 +/- 1.1
sec, P<0.01), despite a profound hypocapnia (20.7 +/- 0.3 Torr).
The duration of apnea was not significantly affected (14.2 +/- 1.4
sec) by breathing a 6 % CO2 -14 % O2 in N2 gas mixture, that roughly
mimicked the alveolar gas composition when the apnea turned off.
These results suggest that chemical drive has a negligible role in
the fast reinitiation of breathing following LS during muscular
stimulation. Stimulation of muscle afferent fibers does however
appear to be a potent source of ventilatory reflexes capable of
counteracting the inhibition of breathing resulting from laryngeal
stimulation. Conversely, it is postulated that any reduction in
somatic afferent traffic during this type of reflex apnea, including
that resulting from the LS induced systemic vasoconstriction, may
delay the termination of apnea.
Received 7 August 1995; accepted in final form 15 May 1996.
APS Manuscript Number R492-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96