Frequency domain analysis of renal autoregulation in the rat

Abstract

The frequency response of renal blood flow was estimated to test our suggestion that autoregulation had one fast and one slow component. Arterial pressure was varied periodically by a pump connected to the distal aorta or aperiodically by stimulating atrial fibrillation. There was only one regulatory mechanism, corresponding to the slow component seen earlier. Two apparent regulators were seen when pressure was measured far from the renal artery (right common carotid), rather than near (superior mesenteric). Simultaneous measurements of pressure in both arteries showed interference of the pressure wave from the heart with pressure waves from the pump in the distal aorta at frequencies near that of the heart rate. Measurements made in the superior mesenteric artery were likely to be correct. The earlier results were in error, and frequency response methods detect only one regulator. Animals made acutely hypertensive behaved similarly. The effect of the regulator appears as a phase shift at frequencies of 0.25 Hz and below and an attenuated flow magnitude at frequencies below 0.1 Hz. This frequency response is consistent with the flow propagation time to the macula densa. We conclude that macula densa feedback was the only flow-regulating mechanism detected.

Mechanisms of renal blood flow autoregulation: dynamics and contributions

“…Results are also the same whether calculated from spontaneous fluctuations of pressure (2,3,9,18,62,116,122,147,161,205,207), from experimentally enhanced variations (41), or from forced oscillations (37,79,81,179,205,206,213). Other studies reported comparable results for parts of the spectrum, although their frequency range was either too high to include TGF (126,159), too low to embrace MR (213), or lower than both mechanisms (126).…”

Long-Term Telemetric Recording of Arterial Pressure and Heart Rate in Mice Fed Basal and High NaCl Diets

“…Simultaneous measurements of MAP from the carotid artery and the aorta indicate that there is no significant difference in the MAP recorded from the 2 sites, suggesting that the pressure wave does not significantly dissipate as it travels to the lower aorta. 11 In the telemetry studies, the MAP recorded by the aortic versus the carotid telemetry probes was consistently lower; this, however, is likely due in part to the small number of animals in the abdominal aorta group and/or the disruption due to the more invasive abdominal surgery and the presence of the probe in the gut.…”

Renal Autoregulation in Health and Disease

“…Studies by Cupples, Bidani, Griffin and colleagues reported the resonance frequency of the myogenic mechanism to be 0.23-0.25 Hz in conscious rats (886,1193), compared with the general finding of 0.18 -0.21 Hz in rats anesthesized with isofluorane or barbiturates (109, 297, 499,597,749,1274,1358,1569,1570,1572). There were similar responses during anesthesia with thiobutabarbital (597, 1274) and pentobarbital (297, 749), but halothane slowed the operating frequency of the myogenic mechanism in SD, SHR, and WKY rats to 0.10 -0.15 Hz (230, 289, 631, 886, 1636).…”

“…Kidneys normally exhibit oscillations in microvascular tone. Transfer function analyses of the gain of renal vascular admittance (the reciprocal of impedance and similar to steady-state conductance that is the reciprocal of resistance) to spontaneous or imposed changes in RPP can distinguish between autoregulatory components in the frequency domain (19,230,297,629,631,722,971,1274,1357,1358,1563,1569,1570). This has been investigated in conscious dogs (753,755,760,1618), mice (668), rabbits (722), and rats (927,1182,1183,1376).…”