SPONTANEOUS BLOOD-PRESSURE FLUCTUATIONS AND RENAL BLOOD-FLOW DYNAMICS

Two mechanisms operating at 0.03-0.05 and 0.1-0.2 Hz are involved in a utoregulation of renal blood flow (RBF). To examine the behavior of th e faster system, the response of RBF to spontaneous fluctuations of ar terial pressure was assessed in Sprague-Dawley rats anesthetized by is oflurane or halothane. During halothane anesthesia, autonomous oscilla tion of total RBF was observed at 0.10-0.15 Hz, and normalized admitta nce gain became negative at 0.11 +/- 0.01 Hz. During isoflurane anesth esia, there was autonomous power in blood flow in a broad peak between 0.15 and 0.25 Hz, and gain became negative at 0.15 +/- 0.01 Hz. Incre asing inspired isoflurane concentration from 1.4 +/- 0.1% to 2.2 +/- 0 .1% reduced pressure by 22 +/- 2 mmHg but did not alter blood flow or the transfer function, indicating that the operating frequency was not changed. In another experiment, changing from isoflurane to halothane increased peak power in the autonomous blood flow oscillation fivefol d and reduced its frequency from 0.18 +/- 0.01 to 0.14 +/- 0.01 Hz. Ga in became negative at a higher frequency (0.16 +/- 0.01 Hz) during iso flurane than halothane anesthesia (0.12 +/- 0.01 Hz). The results show that the 0.1-0.2 Hz system is reliably detected under unforced condit ions and provides modest attenuation of pressure fluctuations at less than or equal to 0.1 Hz. Its operating frequency under isoflurane anes thesia is consistent with previous estimates from barbiturate-anesthet ized rats, whereas it operates significantly slower under halothane an esthesia.