Flowpatterns in the Peripheral Circulation of the Anesthetized Dog

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Abstract
To evaluate the distribution of cardiac output as well as the physiological range of the pulsatile pressure and flow patterns, instantaneous pressures and flows were measured in 31 anesthetized dogs. The measurements were carried out simultaneously by means of Statham strain gauges and electromagnetic flowmeters at at least 4 of the following sites ascending, descending, upper and lower abdominal aorta, superior mesenteric, femoral and carotid artery, portal vein, abdominal and thoracic inferior vena cava and superior vena cava. The data were processed by means of Fourier analysis. It was found that about 30% of the aortic flow was directed to the forepart of the body, 30% to the gastrointestinal system, 15% to the kidneys and 20% to the hindpart of the body. The proportion of hepatic outflow increased hypovolemia and subsequent reinfusion of blood, while the fraction of the cardiac output carried by the superior vena cava increased after reinfusion of blood and during the infusion of norepinephrine. The relation between cardiac output and body mass was evaluated on the basis of data obtained from the literature. This correlation is inadequate for the prediction of the cardiac output of individuals within 1 species. No correlation was found between cardiac output and arterial pressure, but the flow through the mesenteric artery and the portal vein were markedly pressure-dependent. The decrease in cardiac output observed after thoracotomy was found to be time-dependent. More than 95% of the frequency content of the arterial flow and pressure pulses were contained within a frequency band of 0-20 cps. The magnitudes of the low frequency components of the arterial pressure pulse increased toward the periphery, while the corresponding components of the flow pulse decreased. The frequency dependent part of the vascular impedance represented only a fraction of the peripheral vascular impedance, however, this fraction increased steadily from the ascending aorta toward the periphery (with the exception of the femoral artery). The implication of these findings for the work of the heart are discussed. Venous flow is only pulsatile in the central veins, where the flowpattern is strongly influenced by atrlal function and by respiration. Because of differences in the mechanical properties the damping of the pressure and flow pulses in the veins is considerably greater and the wave velocity lower than in the arteries.

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