Vol. 280, Issue 4, H1875-H1881, April 2001
Helium inhalation enhances vasodilator effect of
inhaled nitric oxide on pulmonary vessels in hypoxic dogs
Masaki
Nie1,
Hirosuke
Kobayashi2,
Motoaki
Sugawara3,
Tomoyuki
Tomita2,
Kuniyoshi
Ohara1, and
Hirokuni
Yoshimura1
1 Department of Thoracic and Cardiovascular Surgery and
2 Department of Medicine, Kitasato University, Kitasato 1-15-1,
Sagamihara, Kanagawa 228-8555; and 3 Department of
Cardiovascular Sciences, Tokyo Women's Medical University, Tokyo
162-8666, Japan
There are theoretical and
experimental indications that the presence of He as a balance gas
markedly increase the diffusion velocity of other gases contained in a
gas mixture. We allowed dogs with pulmonary vasoconstriction induced by
hypoxia to inhale a mixture of 5 parts per million (ppm) of nitric
oxide (NO) and O2 balanced with He (NO in He) instead of
N2 (NO in N2). The dilating effect of NO in He
and NO in N2 on the pulmonary artery was evaluated by
determining conventional pulmonary hemodynamic parameters, mean
pulmonary artery (PA) pressure (MPAP), and pulmonary vascular resistance indexed to body surface area (PVRI), pulmonary impedance (Z), and the recently developed hemodynamic index,
time-corrected wave intensity (WI). The main findings in this study
were as follows: 1) hypoxia increased MPAP, PVRI,
Z at 0 Hz (Z0), Z at the
first harmonics, characteristic impedance (Zc),
the reflection coefficient (
), and the first peak of WI;
2) NO in N2 reduced Z0
and ; and 3) NO in He reduced the first peak of WI and
reduced Z0 and more than NO in
N2. The enhanced vasodilatory effect of NO in He might be
associated with facilitated diffusion of NO diluted in the gas mixture
with He. In conclusion, increased efficacy of NO in He offers the
possibility to reduce the inhaled NO concentration.
diffusion; pulmonary hypertension; impedance; wave
intensity
