volumes and body weight in mammals. Am. J. Physiol. 215(3): 704-715. 1968.-Left and right ventricular end-diastolic (EDV), endsystolic (ESV), and stroke volumes, heart rates, cardiac output, total peripheral resistance (TPR), and other cardiovascular variables have been measured in the control state in nine species of mammals varying 1,790-fold (rat to horse) in body weight. The log-log relationships between these variables and bodyweight (BW), body surface, metabolic rate, heart weight, and ventricular weight have been determined and are described bypower law equations. On the basis of these results relationships for each ventricle are described by equations in which ventricu lar volumes are related to BW1-0, heart rate to BW °-20, cardiac output to BW075, and TPR to BW"0-75. Evidence is presented that in the control state the heart rate of mammals is a function of metabolic rate per unit body weight, and left ventricular stroke work per unit body weight is constant. It is concluded that the EDV, ESV, and stroke volumes of mammals are linear functions of body weight and not of body surface or metabolic rate; and that cardiac output is a linear function of metabolic rate'and not a linear function of body surface area. It is sug gested that ventricular volumes be reported as volume per unit body weightheart; cardiovascular equations; heart-body weight functions; cardiac outputIn the wide range of mammals that have been studied (bat to elephant) body weight is inversely related to heart rate (3, 25) and directly related to blood volume and heart weight (3, 4, 10). There is considerable evidence that cardiac output, which is the product of stroke volume and heart rate, is related to metabolic rate (13). For more than 100 years basal metabolism has been related to body surface (16), and since the studies of Grollman (12) relating cardiac output to body surface area, it has become the practice to report the cardiac output of man in terms of flow per square meter of body surface (28). In 1932 Kleiber (21, 22) and later Brody (2) in a study of the metabolism of a wide variety of mam mals ranging from the mouse to the elephant, showed that basal metabolic rate was not related to body surface, which is a function of the two-thirds power of body weight, BW2", but is related to the 0.74 =fc 0.01 power. On the basis of these studies Kleiber suggested that, in ore r for data on the metabolism of mammals of different body sizes to be useful for the study of mammals in general, basal metabolic rate should be reported as a function of BW3/4. If the reporting of cardiac output per square meter of body surface is based on the assumption jhat cardiac output is related to metabolic rate, then it would appear more desirable to report cardiac output per BW"1 than per body surface area (13). The primary reason, however, for reporting cardiac output as a func tion of any power of body weight should rest on -peri-" mental evidence obtained in mammals extending over a wide range of body size.Assuming cardiac output to be a function of m...

In anesthetized open-chest and closed-chest dogs subjected to plethora and hemorrhage, pressures were measured simultaneously in the right atrium, right and left ventricles, and the pleural and pericardial spaces. It was found that an increase in ventricular end-diastolic pressure above approximately 1 mm. Hg was associated with a rise in pericardial pressure of nearly the same amount. Thus, the practice of defining "effective" ventricular end-diastolic pressure as the difference between the ventricular and intrapleural pressure gives erroneous values when ventricular end-diastolic pressure is greater than a few mm. Hg. The true ventricular transmural pressure is the difference between ventricular end-diastolic and pericardial end-diastolic pressure and has a value of no more than 2 or 3 mm. Hg under all except the most abnormal circumstances. When ventricular end-diastolic pressure is greater than a few mm. Hg, the pericardial pressure at the end of systole is likewise elevated, but to a lesser degree. Thus, when ventricular end-diastolic pressure is elevated, the measured ventricular end-systolic pressure is greater than the pressure developed by ventricular muscular contraction because end-systolic pressure is the algebraic sum of the pressure developed by ventricular muscular contraction and the pressure in the pericardial space. This error in ventricular systolic pressure may be relatively large for the right and small for the left ventricle. Pericardial pressure decreases during ventricular systole, lowers the pressure on the outside of the atria, and thus, tends to draw blood into the right atrium during ventricular systole.

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The diameters of the aorta and venae cavae at various points throughout their lengths, the diameters of their major branches, and the lengths of various aortic and vena caval segments were measured in plastic corrosion casts of the arterial and venous systems of the normal adult mouse, rat, rabbit, dog, goat, horse, and cow, extending over a body weight range of 38,000-fold (arterial) and 1,100-fold (venous). It is shown that the diameters and lengths of these vessels are described by power-law equations relating the particular diameter or length to body weight (BW) raised to a particular diameter or length to body weight (BW) raised to a particular power, i.e., diameter = a BWb. Equations for the diameters and lengths of the vessels are given for slightly distended vessels and for vessels distended in the physiological range.

A dye dilution and an electric conductivity method for measuring end-diastolic volume and stroke volume of the left ventricle are described, and equations for the calculation of stroke volume are given. When dye is injected "instantaneously" into the left ventricle during diastole, the aortic dye concentration-time curve obtained is a step-like curve and not a smooth curve. The ventricle empties itself in a "fractional" manner, approximately 46 per cent of its end-diastolic volume being ejected with each stroke and 54 per cent remaining in the ventricle at the end of systole.