Pressure-flow relations in dog arteries.

The propagation of the arterial pressure and flow pulses through the vas-cular beds is characterized by marked changes in shape and magnitude. In order to understand better the mechanisms which account for these changes, instantaneous pressures and flows were measured simultaneously at various sites in the arterial tree of 12 anesthetized dogs, using Statham strain gauges and electromagnetic flowmeters. The data were processed by on-line Fourier analysis and the frequency spectra of pressure, flow and vascular impedance at these sites were evaluated. In these dogs about 101 of the cardiac output was distributed to the head, 14% to the kidney, 35% to the gastrointestinal tract, 14% to the pelvic organs and 6% to the legs. The input impedances of the various beds were frequency dependent, the frequency-dependent components varying between 2 and 45% of the corresponding D-C impedances (peripheral vascular resistance). The viscous losses associated with pulsatile flow were larger than those for corresponding steady flows. The excess losses varied between 9 and 30% of the mean flow losses. The marked decrease in cross section down the aorta lead to considerable acceleration of the mean blood velocity and corresponding pressure losses despite the drainage through aortic branches. Comparisons of measured flows with those predicted from Womersley's theory showed satisfactory agreement for short vascular segments. However the theory underestimates the losses occurring in the nonuniform arterial tree. On the basis of anatomic measurements, the space dependence of resistance, in-ertance and vascular distensibility was evaluated. ADDITIONAL KEY WORDS vascular geometry elastic tapering frequency spectra of arterial pressure and flow vascular impedance on-line Fourier analysis distribution of mean flow arterial models energy losses in blood flow anesthetized dogs • Theoretically it is possible to calculate dynamic blood flows from instantaneous pressure measurements if the physical properties of the blood and blood vessel walls are known. Hamilton and Remington 1 were among the first to make systematic use of such a possibility for the determination of cardiac output. Their approach is based on Frank's Windkessel theory 2 and requires only the measurement of a pressure pulse at one site. More refined theories predicting flow in terms of the pressure gradient have recently been advanced by Womersley 8 and by others (see reference 4 for review). However, all theories depend upon simplifying assumptions relating to geometry of the blood vessels, visco-elastic properties of the vessel walls and rheology of the blood itself. The primary purpose …