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Detection of 3rd mechanism in renal blood flow via high‐resolution, time‐varying spectral analysis of records subjected to chirp forcing of blood pressure

It is generally agreed that renal autoregulation is mediated by myogenic (0.01–0.3 Hz) and tubuloglomerular feedback (0.02–0.05 Hz) mechanisms. Recently a potential 3rd mechanism that operates at ~0.01 Hz has been reported based upon step response experiments. To begin its characterization, 6 anesthetized, normotensive rats were instrumented for blood pressure (BP) and renal blood flow (RBF) measurements. We forced BP with linearly increasing frequencies (frequency range 0.001 – 0.02 Hz, amplitude ± 7 mmHg). The motivation for using linearly increasing frequencies in BP forcing is that if such a third mechanism exists, it should resonate at its characteristic frequency in the resultant RBF recordings and that RBF power at that frequency should be amplified beyond that in BP. Comparison between the time‐varying spectral amplitudes of BP versus RBF shows that when the BP forcing frequency passed ~0.01 Hz, there was greater spectral amplitude at the same frequency in RBF than in BP. The significance of this increase of spectral amplitude in RBF was verified by testing against white noise signals. Any spectral power above white noise spectral amplitude suggests that such oscillation does exist and not a consequence of some random occurrence. We conclude that a third mechanism contributes to autoregulation of RBF and that it resonates at ~0.01 Hz. Funded by CIHR & NHLBI