[Variant of quantitative evaluation of the mechanisms of orthostatic response of central hemodynamics].

This paper describes an approach that can help clarify mechanisms of central circulation of orthostatic men using a mathematical model and noninvasive methods of examinations. Circulation parameters such as peripheral resistance (PR), arterial compliance (Ca), and ratio of vein compliance (Cv) to the pump coefficient of the heart (beta) were determined by the "partial identification" method of the two-component circulation model with the aid of cardiac output and arterial blood pressure measured by tetrapolar thoracic rheography and tachooscillography. The paper also contains physiological interpretation of the above parameters as related to the upright posture of man. Peripheral resistance in the head-up position characterizes both the degree of arterial vasoconstriction and the state of the so-called muscle pump. Blood displacement to the lower body results in an increase of the ratio Cv . beta. The orthostatic reaction of circulation of 28 healthy male subjects was investigated. Blood pooling in the lower body, with venous and cardiac reactions being manifest, led to the fall of arterial pressure and cardiac output to 67% when compared with the pretest level. The change in the properties of resistance vessels (Ca and PR) accelerated the recovery of the arterial pressure value.