Am. J. Respir. Crit. Care Med.,
Volume 164, Number 8, October 2001, 1476-1480
Effects of Chronic Hypoxemia on the Afferent Nerve
Activities from Skeletal Muscle
ERICK
DOUSSET,
PATRICK
DECHERCHI,
LAURENT
GRELOT,
and
YVES
JAMMES
Laboratoire de Physiopathologie Respiratoire (UPRES EA 2 201), Institut Jean Roche, Faculté de Médecine Nord, Université de la Méditerranée,
Marseille, France; and Laboratoire des Déterminants Physiologiques de l'Activité Physique (UPRES EA 3 285), Faculté des Sciences du Sport,
Université de la Méditerranée, Marseille, France
An acute reduction of the oxygen supply to contracting muscles
not only affects their metabolism but also modifies their sensorimotor control through changes in afferent discharge of the group
I and group III-IV nerve fibers, the latter playing a pivotal role in the protective mechanisms against muscle fatigue. The effects of
chronic hypoxemia on the muscle sensitivity are totally unknown. In the present study, group I fibers (mechanosensory afferents) and group III-IV fibers (mechanosensory and chemosensory afferents) from the anterior tibial muscle were recorded in normoxemic and chronic hypoxemic rats. Hypoxemic rats breathed for 45 d
a gas mixture containing 9.5 to 10% O2 in N2. The data were compared with those obtained in normoxemic animals of the same
age. To activate the different muscle afferents, we used different test agents, including electrically induced fatigue (EIF), KCl, lactic acid
injections, as well as tendon vibrations. The conduction velocity of
all nerve fibers was significantly (p < 0.01) higher in hypoxemic
rats than in the normoxemic group. Chronic hypoxemia significantly depressed the response of the group III-IV muscle afferents
to KCl injections and even abolished their response to lactic acid and
EIF. However, the response to tendon vibrations of the group I afferents was similar in hypoxemic and normoxemic rats. These results suggest that chronic hypoxemia markedly alters the chemosensitivity of the group III-IV muscle afferents, which may explain the
higher fatigability of hypoxemic subjects.