Time-frequency and time-scaling analysis of time-varying properties of renal autoregulatory mechanisms

In order to assess the possible time-varying properties of renal autoregulation, time-frequency/time-scaling methods were applied to whole kidney renal blood flow data obtained from normotensive rats and hypertensive rats, under forced blood pressure fluctuations. The time-frequency analyses show that both the myogenic and tubuloglomerular feedback (TGF) mechanisms have time-varying characteristics. Furthermore, Renyi entropy was utilized to measure the complexity of blood flow dynamics in the time-frequency plane in an effort to discern differences between normotensive and hypertensive recordings. The results indicate more complex dynamics in the hypertensive condition. To further evaluate whether the separation of dynamics between normotensive and hypertensive rats is found in the prescribed frequency ranges of the myogenic and TGF mechanisms, we employed multiresolution wavelet transform. Our analysis reveal that exclusively over scale ranges corresponding to the frequency intervals of the myogenic and TGF mechanisms, the widths of the blood flow wavelet coefficients fall into disjoint sets for normotensive and hypertensive rats.