Journal of Applied Physiology, Vol 73, Issue 2 465-472, Copyright © 1992 by American Physiological Society
Changes in respiratory muscle activity in conscious cats during experimental dives at 101 ATA
H. Burnet, P. Lenoir and Y. Jammes
Laboratoire de Physiologie, 1330 Centre National de la Recherche Scientifique, Faculte de Medecine Nord, Marseille, France.
The rationale for the present study was to test the hypothesis that
increased work of breathing during experimental deep diving may lead to
respiratory muscle fatigue. For this purpose, electromyograms (EMGs) of
respiratory and skeletal muscles, plus electrocardiogram and
electroencephalogram (EEG) derivatives, were continuously recorded in
conscious cats. In each muscle group, the ratio of power in a high (H) to
that in a low (L) band of EMG frequencies was computed. Direct
diaphragmatic stimulation in selected animals produced a mass action
potential to obtain the muscle fiber conduction velocity (MFCV). The
maximal pressure was 101 ATA (1,000 msw) with a maximal duration of 72 h.
Four cats breathed an He-O2 mixture and five others a ternary mixture (10%
N2 in He-O2). Inspired O2 partial pressure was 350 Torr. With the He-O2
mixture, all the animals died within 2-54 h during the study at maximal
depth. EEG signs of high-pressure nervous syndrome (HPNS) were present in
all cats, and low-frequency (11-14 Hz) hyperbaric tremor discontinuously
contaminated all EMG tracings. The H/L ratio computed from diaphragmatic
and intercostal muscle EMGs increased after 12 h at 101 ATA. With the
He-N2-O2 mixture, the cats survived until the end of the sojourn at 101
ATA, during which no hyperbaric tremor was detected from EMG tracings, and
EEG signs of HPNS were weak or absent. From 31 ATA, the H/L ratio decreased
significantly in respiratory but not in skeletal muscles; this was
associated with decreased MFCV in the diaphragm after several hours at
maximal depth.(ABSTRACT TRUNCATED AT 250 WORDS)
