Regional Lung Function in Patients with Mitral Stenosis Studied with Xenon133 during Air and Oxygen Breathing*

Abstract

In a normal sitting man, pulmonary blood flow per unit lung volume is greater in the lower than in the upper parts of the lung. In patients with mitral stenosis, the ratio of upper to lower zone blood flow may be markedly increased (Dollery and West, 1962). In this study, the distribution in the lung of inspired and intravenously injected xenon133 was measured by external scintillation counting in 15 patients with mitral stenosis to see if the increase in relative flow to the upper zones is closely correlated with the hemodynamic findings and if the decreased lower zone flow is due to hypoventilation of the lung bases. The relative flow to the upper lung zones was abnormally increased in 14 of the patients. In those with moderate elevation of the pulmonary artery pressure the increase was more marked than in those with severe pulmonary hypertension. There was no consistent evidence of selective hypoventilation of the lower lung zones as assessed either by the distribution of a single breath or by the regional wash-in-time of xenon during closed-circuit equilibration. Breathing 100% O2 for 20 min caused a slight but significant increase in the relative flow to the lower zones. It was concluded that the relative reduction of lower zone blood flow in mitral stenosis is probably not due to regional hypoxia. The results are more consistent with the explanation that vasoconstriction results from elevated pulmonary venous pressure which in early cases is confined to the lower zones owing to the added hydrostatic pressure. In severe pulmonary hypertension there is generalized vasoconstriction and blood flow is even throughout the lung.