Acta physiologica Scandinavica
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Acta Physiol. Scand. · Mar 2000
No apparent effect of nitric oxide on the local matching of pulmonary perfusion and ventilation in awake sheep.
The respiratory tissue in the lung receives nitric oxide (NO) from two sources; NO produced in upper airways, and NO produced in lung parenchyma. It has been hypothesized that optimal local matching of ventilation and perfusion (which is necessary for effective gas exchange) is ensured because well-ventilated lung tissue has a higher concentration of NO and thereby higher blood flow owing to the vasodilatory effect of NO. To test this hypothesis, we simultaneously measured the distributions of local (regions of approximately 1.5 cm3) blood flow (radioactive microspheres) and local ventilation (fluorescent aerosol) in five tracheostomized, awake and standing sheep. ⋯ These changes in vertical distribution of perfusion can be explained by the effect of variable NO concentrations on pulmonary arterial pressure and cardiac output. Variable access to NO had no effect on arterial blood gases. We conclude that NO is important for the vertical distribution of pulmonary perfusion, but has no apparent effect on the local matching of ventilation and perfusion within horizontal layers of the lung.