Contributions of pulmonary perfusion ( ) and ventilation () to the
heterogeneity in measured by pet.
Treppo, Steven, Srboljub M. Mijailovich, and Jos[umlaut]a G. Venegas.
Department of Anesthesia (Bio-engineering), Massachusetts General
Hospital and Harvard Medical School, Boston MA 02114
APStracts 3:0560A, 1996.
To estimate the contributions of the heterogeneity in and to that of
we have refined techniques using Positron Emission Tomography (PET)
to image local distributions of and , per unit of gas volume content
( and ), and ratios in dogs. was assessed in two ways: 1) the washout
of 13NN tracer after equilibration by rebreathing () and, 2) the
ratio of an apneic image following a bolus IV infusion of 13NN-saline
solution to an image collected during steady state IV infusion of
tracer (). was systematically higher than in all animals and there
was a high spatial correlation between and in both body positions
(mean correlation was 0.69 prone and 0.81 supine) suggesting
ventilation to well perfused units was higher than to those poorly
perfused . In the prone position, the spatial distributions of , and
were fairly uniform with no significant gravitational gradients,
however, in the supine position these variables were significantly
more heterogeneous due mostly to significant gravitational gradients
(15, 5.5 and -10 %/cm respectively) accounting for 73%, 33% and 66%
of the corresponding COV2s. We conclude that in the prone position,
gravitational forces in blood and lung tissues are largely balanced
out by dorso-ventral differences in lung structure. In the supine
position, effects of gravity and structure become additive resulting
in substantial gravitational gradients in and , with the higher
heterogeneity in caused by a gravitational gradient in , only
partially compensated by that in .
Received 22 February 1996; accepted in final form 12 November
1996.
APS Manuscript Number A315-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996