Journal of Applied Physiology, Vol 68, Issue 2 611-616, Copyright © 1990 by American Physiological Society
EMG study of respiratory muscles in humans immersed at different water temperatures
M. L. Choukroun, C. Kays and P. Varene
Laboratoire de Physiologie, Universite de Bordeaux II, France.
The electromyograms of the rectus abdominis (EMGra) and of the diaphragm
(EMGdi) have been recorded on human subjects immersed at two bath
temperatures (TW), 25 and 40 degrees C. The recordings were obtained during
a calibrated isometric contraction sustained for 20 s against a closed
stopcock at functional residual capacity (FRC) level for EMGra (expiratory
effort) and at pulmonary volume greater than 90% vital capacity for EMGdi
and EMGra (inspiratory effort). After eliminating the electrocardiographic
artifact, the EMG signal was processed to obtain its root-mean-square (rms)
value and three parameters of its frequency spectrum, total energy (Etot),
centroid frequency (fc), and high-to-low ratio (H/L). The results show that
EMGdi is not modified by TW. On the other hand rms and Etot of EMGra are
always increased at TW = 25 degrees C compared with TW = 40 degrees C,
whereas fc and H/L decrease with temperature during the expiratory effort
at FRC level but do not vary during inspiratory effort at high pulmonary
volume. These results, compared with those previously published for cooled
limb muscles, show that TW can elicit EMG alterations on the superficial
respiratory muscles through two mechanisms, an intrinsic mechanism due to
the local variation in muscle temperature and an extrinsic mechanism acting
upon the control system of the muscle contraction. Linked alterations of
the muscular mechanical activity probably account for the observed effects
of TW on the statics and the dynamics of the pulmonary volumes.
