[Neural influences on pulmonary vasomotility in man]

In man, the extent, the physiological role and even the existence of neural influences on the pulmonary vasomotility are not defined. A major obstacle to these evaluations is passive adaptation of the lung vessels to changes in flow, making it hard to separate the active from the passive component of vasomotion during adrenergic activation. In this study, which was carried out in 8 patients during diagnostic procedures, the inflation of a balloon in the inferior vena cava was utilized to reduce blood flows through the lungs and to buffer its changes consequent to stimulation of the adrenergic system. Neural activation was obtained with the mental arithmetic and the cold pressor tests. When venous return was unimpeded, cardiac output rose by 2,060 ml during the former and remained stable during the latter test, and arteriolar resistance in the pulmonary circuit was significantly reduced and slightly increased, respectively. Under vena cava obstruction, cardiac output decreased in the baseline by 600 ml; it rose by 925 ml during the arithmetic test and again remained stable during the cold test; pulmonary arteriolar resistance was unchanged since before obstruction in the baseline and was significantly augmented by both test. These observations support the view that lung blood vessels in man are sensitive to adrenergic influences and the vasoconstrictor component of these becomes effective in circumstances in which the flow through the lungs reduced. The physiological importance of these influences remains unclear.