Journal of Applied Physiology, Vol 54, Issue 6 1673-1680, Copyright © 1983 by American Physiological Society
Hemodynamic responses during prolonged sitting
E. Shvartz, J. G. Gaume, R. T. White and R. C. Reibold
Eight young men (group A) underwent 5 h of quiet sitting, preceded by 30
min of recumbency, 20 min of standing, and 20 s of walking, and five other
young men (group B) underwent 70 min of sitting, preceded by recumbency
only, to determine the effects of prolonged sitting and previous posture on
hemodynamic responses (measured by impedance plethysmography). Group A
showed more calf blood pooling and a decrease in thigh blood flow during
sitting in comparison with the control group, but after 1 h of sitting
hemodynamic responses of the two groups were similar. Sitting for 5 h (1st
vs. 5th h) resulted in an increase in calf venous pooling (17%) and a
decrease in calf BF (13%), a reduction in gravitational pooling in the
thigh (corresponding to increased pooling in the calf), increases in
diastolic and mean arterial pressures (6 and 7.3 mmHg, respectively), and
minor changes in heart rate, stroke volume, and cardiac output. The results
show that it is necessary to sit for 1 h before hemodynamic responses can
be assessed in this position, regardless of the posture maintained
previously. The main effect of prolonged sitting is pooling in the calf,
which is compensated for by an increase in peripheral resistance.
