Journal of Applied Physiology, Vol 78, Issue 3 914-920, Copyright © 1995 by American Physiological Society
Flow pulsatility does not increase mean microvascular pressure or filtration in zone 3 rabbit lungs
O. Saito, W. J. Lamm, J. Hildebrandt and R. K. Albert
Department of Medicine, University of Washington, Seattle 98195, USA.
We previously reported that mean pulmonary arterial pressure (Ppa) during
pulsatile flow exceeded that for steady flow when flow was greater than the
normal resting value and speculated that this was due to irregularities of
the flow profiles in precapillary vessels, mainly the larger arteries. From
this we hypothesized that neither mean microvascular pressure nor the rate
of fluid filtration would be affected by flow pulsatility. We therefore
compared the effects of steady vs. pulsatile flow on the double-occlusion
pressure (Pdo) and on edema formation (rate of weight gain) in zone 3
rabbit lungs. Excised left lungs (n = 19) were perfused with Tyrode
solution and ventilated with an end-expiratory pressure of 2.5 cmH2O. A
diaphragm pump generated pulsatile flow with a stroke volume of 1.0 ml
(approximately 0.8 the normal resting value for rabbit left lung).
Nonpulsatile flow was generated by raising an arterial reservoir. Flow rate
was set at 100 or 400 ml/min (approximately 0.4 or 1.6 x the normal resting
cardiac output, respectively). Vascular pressures (referenced to the bottom
of the lung) were measured after ventilation, at end expiration, was
interrupted. Pdo values were obtained in random order at 15 time points
that were evenly distributed within the pulse cycle, averaged across pulses
to obtain the mean capillary pressure profile, and then averaged over time.
At the lower flow of 100 ml/min, mean Ppa and Pdo were slightly lower
(3-4%) during pulsatile compared with nonpulsatile conditions. At the
higher flow of 400 ml/min, mean Ppa was higher under pulsatile conditions
(13%), whereas downstream the mean Pdo values were equal.(ABSTRACT
TRUNCATED AT 250 WORDS)
