Basal Cardiac Function and Body Composition With Special Reference to Obesity 1

Abstract

It has been known for many years that the surface area is increased with increasing obesity and that this increase in surface area is accompanied by a proportional increase in basal oxygen consumption (1). Therefore, it has been reasoned that in the presence of obesity cardiac output and cardiac work in the basal state are increased approximately in proportion to the increase in oxygen consumption (2). This reasoning is based on the assumption that the quantity of oxygen carried away by a liter of blood from the lungs (the arteriovenous oxygen difference) is constant in lean and obese individuals.Certain generally accepted facts support this argument. Thus it is generally agreed that basal cardiac output is proportional to surface area and oxygen consumption. The relationship between surface area and cardiac output has been re-examined in a recent publication from this laboratory (3) and it was found that as a first approximation, the cardiac output is directly proportional to surface area. However, the individual differences in surface area accounted for only 40 per cent of the individual differences in cardiac output. Furthermore, it has been found that while resting cardiac output is proportional to oxygen consumption; the individual differences in oxygen consumption account for only 50 per cent of the observed variability in cardiac output (4). It ence of blood flowing through fatty tissues or the rate at which it flows.Precise investigation of the relationships between cardiac function and obesity has been hampered by the inability of the investigator to estimate the relative amounts of fat and other tissue in a given individual. The use of the specific gravity of the body to estimate the relative amount of fat in intact man (6) makes such investigations profitable. It is the purpose of this paper to examine the quantitative relationships between cardiac output, cardiac work and the arteriovenous difference on the one hand and the fat content of the body on the other. SUBJECTS AND CONDITIONSThe subjects used in this investigation were 34 male university students, 18 to 31 years old, who were free of disease detectable by physical examination. Deliberate efforts were made to obtain a scattering of men from very fat to very lean. The men reported to the laboratory in the morning without breakfast or late in the afternoon without lunch. They rested for one half hour before observations were made. All procedures were carried out in an air-conditioned room. Duplicate determinations of cardiac output were made at one sitting. This was followed by a measurement of the intra-arterial blood pressure. The specific gravity of the body and a roentgenogram of the chest were made after the other cardiovascular measurements had been carried out. In 22 of the 34 subjects, duplicate cardiac output determinations were made on two separate days. Intraarterial pressures were obtained on 20 subjects and roentgenograms of the chest on 15. METHODSThe cardiac output measurements were made with the acetylene technic of Grollman. ...

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