Journal of Applied Physiology, Vol 54, Issue 1 262-266, Copyright © 1983 by American Physiological Society
Pulmonary vascular tone is a determinant of basal lung perfusion in normal seated subjects
B. Nemery, W. Wijns, L. Piret, F. Cauwe, L. Brasseur and A. Frans
In the human upright lung the downward increase in lung perfusion reverses
in the lower third, thus giving rise to a zone of reduced basal perfusion
(zone 4). The flow in zone 4 is regulated by the extra-alveolar vessels,
the diameter of which is determined by lung volume, perivascular
interstitial pressure, and vasomotor tone. To estimate the role of
pulmonary vascular tone in the formation of zone 4, we infused
nitroprusside (NTP), a potent pulmonary vasodilator, in six normal seated
subjects. We measured their regional perfusion distribution using 133Xe in
control conditions and at two dose levels of NTP (20.8 and 52.1
micrograms/min). Regional perfusion distribution was measured similarly and
according to the same protocol in six subjects receiving only a placebo
solution. In four of the six subjects receiving NTP, right-heart
catheterization allowed simultaneous estimations of cardiac output and
pulmonary arterial pressure to be made. NTP slightly decreased the
perfusion of the nondependent parts of the lungs and markedly increased the
perfusion of the lung bases, thus reducing the extent of zone 4. No changes
were observed in the placebo experiments. Cardiac output and indices of
ventilation and gas exchange did not change significantly. Peripheral and
pulmonary arterial pressure fell slightly but significantly during NTP
infusion. We attribute the observed changes in basal perfusion to the
vasodilatory effects of NTP on the extra-alveolar vessels. Our findings
thus support the hypothesis that in normal subjects zone 4 is partly
created by the pulmonary vascular tone.
