FREQUENCY-DOMAIN OF RENAL AUTOREGULATION IN THE CONSCIOUS DOG

The dynamic range in which renal blood flow (RBF) autoregulation occur s was determined in eight conscious foxhounds chronically catheterized in the abdominal aorta and implanted with a transit-time flow probe o ver the renal artery. Sinusoidal driving pressures (amplitude of 10 mm Hg) were forced on the renal arterial pressure at different frequencie s by a servo-control device, and transfer functions were calculated. O nly one frequency range was found below which the gain of the transfer function declined and in which the phase angle increased (n = 8). Thi s indicates the presence of a potent mechanism for renal autoregulatio n in the examined frequency range between 0.0031 and 0.08 Hz, which bu ffers changes in blood flow < 0.02 Hz. After furosemide treatment, one indicator for autoregulation (phase shift of transfer function) was s ignificantly blunted at low frequencies (n = 6). Furosemide, however, did not reduce the phase shift to zero, suggesting that some autoregul ation still remained in the frequency range between 0.04 and 0.08 Hz. In conclusion, autoregulation of RBF during sinusoidal changes in driv ing pressure between 0.0031 and 0.02 Hz is mediated by a single mechan ism, which can be blocked by the acute administration of furosemide. T he residual phase shift between arterial pressure and RBF in the trans fer function observed during sinusoidal changes in driving pressure be tween 0.04 and 0.08 Hz suggests the presence of a second mechanism for RBF autoregulation.