Hypoxic pulmonary vasoconstriction and gas exchange in acute canine
pulmonary embolism.
Delcroix, Marion, Christian Melot, Francoise Vermeulen, and Robert
Naeije.
Laboratory of Cardiovascular and Respiratory Physiology, Erasme
University Hospital, Brussels, Belgium
APStracts 2:0532A, 1995.
Hypoxic pulmonary vasoconstriction (HPV) is inhibited in several
models of acute lung injury. Whether HPV is preserved in pulmonary
embolism is unknown. We investigated the effects of a reduction in
the fraction of inspired O2 (FIO2) on pulmonary hemodynamics and gas
exchange in anesthetized dogs before and after autologous blood clot
pulmonary embolism. In a first group of 14 dogs, stimulus-response
curves for HPV were constructed as pulmonary artery pressure (Ppa)
versus FIO2 varied between 1.0 and 0.06 at a cardiac output (Q) kept
constant at 3.5 l.min-1.m-2. Gas exchange was evaluated using the
multiple inert gas elimination technique at the FIO2 of 1.0, 0.4 and
0.1. Embolism decreased the relative magnitude of HPV, expressed as
the gradient between Ppa and pulmonary artery occluded pressure
(Ppao) in hypoxia divided by (Ppa - Ppao) at the FIO2 of 1.0, from
1.8 to 1.2 (P<0.05). Retention minus excretion gradients for
sulfur hexafluoride and ethane were increased by decreased FIO2
(P<0.005 and P<0.05 respectively) before but not after
embolism. Hypoxia-induced deterioration in gas exchange before
embolism was related to the amount of base line very low
ventilation/perfusion (VA/Q) ratios. Similar results were obtained in
a second group of 7 dogs with Q decreased to maintain Ppa at the same
average value as before embolism. However, gas exchange was not
affected by inspiratory hypoxia before as well as after embolism in
this group which presented with a lesser amount of base line very low
VA/Q. In both groups of dogs, increasing the FIO2 from 0.4 to 1.0 did
not affect gas exchange. We conclude that (1) pulmonary embolism is
associated with a partial inhibition of HPV, (2) HPV does not
contribute to preserve gas exchange in pulmonary embolism, and (3) a
strong HPV may deteriorate gas exchange in severe hypoxia in the
presence of minor very low VA/Q inequality.
Received 31 May 1995; accepted in final form 16 November 1995.
APS Manuscript Number A566-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95