[Factors regulating venous return: analysis based on the respiratory variations of superior vena caval flow]

Characteristics of venous return and its determining factors were observed using pulsed Doppler echocardiography. Superior vena caval (SVC) flow was regarded as representing venous return. Ten healthy subjects and 23 patients with chronic pulmonary disease were studied. 1. In the healthy subjects, the forward flow was biphasic with dominant systolic (S) wave. Among 23 patients, 18 had normal SVC flow patterns (Group I), while in the remaining 5, SVC flow showed disappearance of the diastolic (D) wave, or both the D and S waves (Group II). 2. The healthy subjects and Group I patients had negative pleural pressures during inspiration and expiration. Consistent findings in Group II patients included positive pleural pressures during expiration and reduction in FEV1.0%. In the normal subjects and Group I patients, right atrial (RA) pressure was less than the pressure of the subclavian vein (ScV) during an entire respiratory phase. However, in Group II, RA pressure was equal to or greater than ScV pressure during expiration, resulting in disappearance or reversal of the S and D waves. 3. Respiratory variation in pleural pressure correlated significantly with that of the S wave (r = 0.77) (p < 0.005), D wave (r = 0.80) (p < 0.005), x descent of RA pressure (r = 0.77) (p < 0.005), and y descent of RA pressure (r = 0.82) (p < 0.005). The present study clearly confirmed that the superior vena caval flow patterns were closely correlated with right heart hemodynamics and truly reflected the effects of pleural pressure.