Frequency dynamics of arterial autoregulation.

In anesthetized dogs the low-frequency input impedances (0.001 to 0.1 Hz) of different arterial beds were measured. The following arteries were perfused with blood by a servocontrolled pump in different experiments: Femoral, renal, superior mesenteric, and circumflex branch of the left coronary artery. Step and sinusoidal flow changes were used as input patterns. Furthermore, in the femoral artery the high-frequency input impedance was calculated from pulsatile pressure and flow. The pressure reactions to flow changes were interpreted by assuming a lead-lag autoregulatory control system consisting of two opposing components. The time constants of the two components were found to have characteristic values in different arterial beds and may vary depending on the condition of the experiment. The magnitude of the response usually depends on the mean perfusion pressure, indicating a nonlinear behaviour of the system. Furthermore in the renal artery a characteristic delayed pressure increase was observed after short flow impulses. It is interesting to compare the general pattern of the pressure reaction to the input flow with the force response to stretch which, according to the literature, can be observed in certain striated muscle preparations. The mechanisms underlying the autoregulatory reactions described in this study appear to be, at least in part, a general feature of contractile tissues.