Jp. Praud et al., VAGAL AND CHEMORECEPTOR INFLUENCES ON ABDOMINAL MUSCLE-ACTIVITY IN AWAKE LAMBS DURING HYPOXIA, Journal of applied physiology, 74(4), 1993, pp. 1689-1696
The ventilatory response to hypoxia is a complex phenomenon involving
several control mechanisms. We designed this study to examine the dyna
mic control of abdominal muscle expiratory electromyogram (EMG) activi
ty during room-air breathing and hypoxia and then to analyze the relat
ive contribution of the chemoreceptors and vagal afferents. We studied
12 11- to 22-day-old awake nonsedated lambs, six intact and six vagot
omized. To assess the dynamic influence of peripheral chemoreceptors o
n abdominal muscle expiratory activity, we performed transient testing
of peripheral chemoreceptor function (pure O2 and N2 inhalation, KCN
injection). To assess the influence of central chemoreceptor afferents
, we compared results obtained during hypocapnic and isocapnic 15-min
hypoxic runs (fractional concentration of inspired O2 0.08) in each la
mb. We also compared results obtained in intact and vagotomized lambs
so that the importance of vagal afferents could be assessed. We consis
tently observed abdominal muscle expiratory EMG activity in each lamb,
whether intact or vagotomized, during baseline room air breathing; fu
rther recruitment was observed during hypoxia. We also consistently ob
served abdominal musele expiratory recruitment during hypocapnic hypox
ia in each lamb, although it was significantly less marked than during
isocapnic hypoxia. Our transient testing of peripheral chemoreceptor
function showed, furthermore, that peripheral chemoreceptor afferents
dynamically modulate abdominal muscle expiratory activity. Thus, durin
g hypoxia in 11- to 22-day-old awake nonsedated lambs, increased affer
ent information from peripheral chemoreceptors forcefully enhances abd
ominal muscle expiratory activity. This hypoxia-related recruitment pe
rsists, although attenuated, in the presence of hypocapnia with or wit
hout vagal information.