Compliance of human pulmonary "venous" system estimated from pulmonary artery wedge pressure tracings. Comparison with pulmonary arterial compliance.

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Abstract
To evaluate the reservoir function of the pulmonary vascular bed for the left ventricle, the compliance of the pulmonary "venous" system (Cp''v'') (consisting of the pulmonary veins and the left atrium) and that of the pulmonary arterial system (Cpa) were sequentially estimated in each of 31 subjects by using Hirakawa''s and Engleberg''s methods, respectively. In control cases (n = 6), Cpa was 6.68 .+-. 3.52 (mean .+-. SD) ml/mmHg and Cp''v'' was 15.81 .+-. 6.85 ml/mmHg. In patients with mitral stenosis (MS) of Class I (previous classification of NYHA) (n = 7), Cpa was 4.05 .+-. 2.71 ml/mmHg and Cp''v'' was 13.15 .+-. 4.51 ml/mmHg. In patients with MS of Class II (n = 13), Cpa was 2.81 .+-. 1.05 ml/mmHg and Cp''v'' was 8.40 .+-. 2.95 ml/mmHg. In MS Of Class III (n = 5), Cpa was 1.54 .+-. 0.80 ml/mmHg and Cp''v'' was 7.10 .+-. 1.91 ml/mmHg. These results indicate that both systems become less compliant as the cardiac functional capacity deteriorates. The ratio of Cp''v'' to Cpa (Cp''v''/Cpa) was 2.7 .+-. 1.1 in control cases, 3.9 .+-. 1.4 in MS of Class I, 3.4 .+-. 1.6 in MS of Class II and 5.3 .+-. 2.1 in MS of Class III. When one compared these results with the compliance in the systemic circulation, i.e., 118 ml/mmHg in the veins and 2.5 ml/mmHg in the arteries, giving the ratio of 118/2.5 .**GRAPHIC**. 50, it is obvious that the compliance of the pulmonary arterial system shares a sizable portion of the total compliance in the pulmonary vascular bed. The relationship between Cp''v'' and the internal pressure, namely the mean pulmonary artery wedge .**GRAPHIC**. pressure, was expressed with a regression equation of, Cp''v'' = 1/(0.003 .**GRAPHIC**. + 0.080), indicating that Cp''v'' is inversely related to the internal pressure. In 12 of patients with MS, sublingual nitroglycerin shifted the Cp''v'' - .**GRAPHIC**. pressure plots upwards and to the left, roughly alongthe Cp''v'' .**GRAPHIC**. regression curve for the entire groups of MS.

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