Journal of Applied Physiology, Vol 46, Issue 1 36-40, Copyright © 1979 by American Physiological Society
Effects of sitting up on pulmonary blood pressure, flow, and volume in man
P. Fournier, J. Mensch-Dechene, B. Ranson-Bitker, W. Valladares and A. Lockhart
Pulmonary vascular pressure, blood flow, and blood volume were measured in
the supine and sitting positions in eight subjects with localized lung
carcinoma associated with moderate airway obstruction. Supine cardiac
output, pulmonary wedge (Ppw) and artery (Ppa) pressure, and pulmonary
vascular resistance (PVR) were normal. Circulatory changes in sitting
position were also normal: heart rate increased 13 +/- 9% (mean +/- SD);
stroke volume fell 21 +/- 15%; cardiac output fell 13 +/- 19%; and
arteriovenous O2 difference increased 37 +/- 21%. Neither the difference
between mean Ppa and mean Ppw nor the rise of PVR from 92 +/- 25 to 122 +/-
49 dyn.s.cm-5 in sitting position were significant. Pulmonary blood volume
(PBV) as measured by a dye-bolus-injection technique fell from 517 +/- 122
ml supine to 360 +/- 43 ml sitting (P less than 0.01). This decrease is
best explained by closure of alveolar vessels in the upper part of the lung
and by the concomitant cessation of flow in corresponding extra-alveolar
vessels, which would prevent distribution of dye in the region.
Circumstantial evidence suggests the latter vessels remain open under the
large expanding stresses that prevail in the upper lung.
