Quantitative estimation of compliance of human systemic veins by occlusion plethysmography with radionuclide--methodology and the effect of nitroglycerin.

Volume-pressure relationship and compliance of human systemic veins were estimated quantitatively and noninvasively using radionuclide. The effect of nitroglycerin (NTG) on these parameters was examined. Plethysmography with radionuclide (RN) was performed using the occlusion method on the forearm in 56 patients with various cardiac diseases after RN angiocardiography with 99mTc-RBC. The RN counts-venous pressure curve was constructed from (1) the changes in radioactivity from region of interest on the forearm that were considered to reflect the changes in the blood volume of the forearm, and (2) the changes in the pressure of the forearm vein (fv) due to venous occlusion. The specific compliance of the forearm veins (Csp.fv; (1/V).(delta V/delta P] was obtained graphically from this curve at each patient's venous pressure (Pv). Csp.fv was 0.044 +/- 0.012 mmHg-1 in class I (mean +/- SD; n = 13), 0.033 +/- 0.007 mmHg-1 in class II (n = 30), and 0.019 +/- 0.007 mmHg-1 in class III (n = 13), of the previous NYHA classification of work tolerance. There were significant differences in Csp.fv among the three classes. The systemic venous blood volume (Vsv) was determined by subtracting the central blood volume, measured by RN-angiocardiography, from total blood volume, measured by the indicator dilution method utilizing 131I-human serum albumin. Systemic venous compliance (Csv) was calculated from Csv = Csp.fv.Vsv. The Csv was 127.2 +/- 24.8 ml.mmHg-1 (mean +/- SD) in class I, 101.1 +/- 24.1 ml.mmHg-1 in class II and 62.2 +/- 28.1 ml.mmHg-1 in class III. There were significant differences in Csv among the three classes. The class I Csv value was calculated to be 127.2 +/- 24.8 ml.mmHg-1 and the Csv/body weight was calculated to be 2.3 +/- 0.7 ml.mmHg-1.kg-1 of body weight, which was very close to the values for Csv reported previously by other investigators in animal experiments. The administration of NTG caused the RN counts - venous pressure curve to become steeper and shift upward. It increased Csv significantly in all cases.