Journal of Applied Physiology, Vol 75, Issue 5 2234-2238, Copyright © 1993 by American Physiological Society
Influence of body position on diaphragmatic and scalene activation during hypoxic rebreathing
A. Xie, Y. Takasaki and T. D. Bradley
Sleep Research Laboratory, Queen Elizabeth Hospital, University of Toronto, Ontario, Canada.
We measured electromyographic activity of the diaphragm (EMGdi) and scalene
(EMGsc) during isocapnic progressive hypoxic ventilatory responses in five
normal males in the supine and upright seated positions. The slope of the
regression line relating EMGdi expressed as a percentage of maximum to
percent fall in arterial oxyhemoglobin saturation was 93% steeper upright
than supine (P < 0.005), whereas the slope of EMGdi activity to minute
volume of ventilation was 73% higher upright than supine (P < 0.05). In
addition, the slope of EMGsc activity relative to percent fall in arterial
oxyhemoglobin saturation and minute ventilation was greater upright than
supine (151%, P < 0.001 and 61%, P = 0.056, respectively). Greater EMGsc
activity upright than supine was similar to findings during hypercapnic
rebreathing. However, the greater EMGdi activity upright than supine stands
in contrast to hypercapnic rebreathing where it was previously shown that
EMGdi activity was not affected by a change in body position. We conclude
that during hypoxic ventilatory responses both EMGdi and EMGsc activities
are more pronounced upright than supine. Diaphragmatic activation during
progressive hypoxia in response to a change in body position is different
from that seen during progressive hypercapnia.
