Analysis of Blood Flow Pattern of Superior Vena Cava in Hypertensive Heart Comparison with that of Acute pressure Overloading in Normal Subjects

The pattern of blood flow velocity (BFVP) of superior vena cava (SVC) in hypertensive patients with significant left ventricular hypertrophy was examined non-invasively using pulsed Doppler echocardiography, and results were compared with those obtained during acute pressure overloading in normal subjects. Forty-two normal subjects [N], and twenty hypertensive patients [HT] were included in this study. In fourteen subjects of N, we infused angiotensin-II (0.5-4μg/min) to create acuty pressure overloading [N (A-II)]. The image of the SVC was obtained by orienting the sector plane parallel to the SVC from the right supraclavicular fossa on supine position. The Doppler sample volume in SVC was placed at 7-9 cm from the transducer, and flow velocity signal was recorded at 100mm/sec with a carrier frequency of 3.5MHz and a pulse repetition frequency of 6 KHz during resting end-expiration. At rest, BFVP in SVC was characterized by a small reversed flow during active atrial contraction period (A wave), and forward flows during ventricular systole (S wave) and during ventricular diastole (D wave). Between S and D waves, close-by the second heart sound, BFVP was transiently diminished (O wave). In N, during acute pressure overloading, A, S, O and D waves occured significantly earlier then those at control rest, while in HT, only S wave was present significantly earlier than that in N at rest. In HT, peak flow velocity of S wave was significantly less and that of D wave was increased compared with those in N at rest, so that D/S ratio was significantly increased in HT. These findings suggest that in HT, in spite of the left heart disease, the reserve function of the right atrium (RA) might be diminished and angiotensin may lead the increment of smooth muscle activity of SVC, RA and the right ventricle, which may result in decrease in cavity compliance. However, in HT, the compliance of the SVC might not be decreased, compared with N.