Journal of Applied Physiology, Vol 40, Issue 4 491-495, Copyright © 1976 by American Physiological Society
Gas exchange in man during combined +Gz acceleration and exercise
S. A. Nunneley
Gravity and acceleration from head to foot (+Gz) handicap gas exchange by
shifting blood from thorax to dependent veins and creating a
ventilation/perfusion (V/Q) mismatch in the lung. At 1 G leg exercise
improves V/Q matching. Gas exchange was measured in six subjects +1, +2,
and +3 Gz during rest and two levels of exercise, either unloaded pedaling
or 600 kpm/min. The VO2 for pedaling was clearly related to G level, but
work efficiency was unaffected. Acceleration lowered resting Pao2 while
raising VE/VO2, HR, AaDo2, VD, and VD/VT. Unloaded pedaling returned VE/VO2
and HR toward their 1-G values. In contrast, at 3 G each increase in VO2
caused a fall in Pao2 and a rise in AaDo2. The VD showed no further change
with exercise, while VD/VT decreased at all G levels. It thus appears that
only some of the effects of acceleration are counteracted by exercise,
probably by the peripheral muscle pump. Any accompanying rise in VO2 adds
to the stress of acceleration, due to limitations on gas transport.
