The digital blood flow, arterial pressure, and vascular resistance in arterial hypertension and in coronary thrombosis

Abstract

Methods for the measurement of the digital blood pressure and flow have been described in a previous report (1). The calculation of the blood flow from calorimetric observations has since been modified, and a method developed for calculating the digital vascular resistance. With these methods, studies have been made on normal subjects and on patients with various types of hypertension. Since a decrease in cardiac output had been found after coronary artery ligation in dogs (2), investigations were also made on patients with coronary occlusion in order to determine whether a consistent change in the digital circulation could be demonstrated. METHODAll measurements were made under standardized conditions. The patient was resting in bed and the measurements were made after warming the body, by placing one arm in water at a temperature of from 430 to 450 C. until sweating became generalized. After this procedure, reproducible digital blood flow measurements are obtainable in the same individual, whether normal or abnormal. Whether the degree of vasodilatation thus obtained represents a complete release of sympathetic tone, however, is still controversial.The digital blood flow was measured by the calorimetric method (1). According to Stewart (3), the specific heat of normal blood is nearer 0.9 than 1.0. The specific heat of tissue, on the other hand, is approximately 0.8. The accuracy of the method was therefore slightly increased by substituting 0.9 for 1.0 as the specific heat of the blood, and by adding the hydrothermic equivalent of the immersed finger tip (volume multiplied by 0.8) to the other hydrothermic equivalents.The exact relationships between blood flow, blood pressure, blood viscosity, and frictional resistance of the vascular bed have not yet been clearly delineated. For practical purposes, however, the relationships proposed by B6ger and Wezler (4) and by Bazett, Cotton, Laplace and Scott (5) may be applied to the digital circulation. According to these workers, if F is the blood flow, P, the effective mean arterial pressure, and R, the so-called