SPONTANEOUS PRESSURE-FLOW RELATIONSHIPS IN RENAL CIRCULATION OF CONSCIOUS DOGS

Renal pressure-flow (P-F) relationships are usually evaluated by measu ring effects of mechanically induced changes in renal arterial pressur e (AP) on renal blood flow (RBF). We devised a method allowing evaluat ion of renal P-F relationships during normal changes in AP occurring s pontaneously in a conscious animal rather than during artificially ind uced changes in AP. In 18 trials in 6 dogs standing at rest, we measur ed average AP and RBF for each cardiac cycle over periods of approxima tely 35 min (approximately 3,100 cardiac cycles/trial). AP and RBF val ues for each cardiac cycle were expressed as percent change (%DELTA) f rom the 35-min average (beat-to-beat changes). Slope and angle of each consecutive beat-to-beat P-F change were calculated and collated into one of eight zones representing the possible physiological mechanisms responsible for concurrent, spontaneous changes in RBF and AP. In a p redominance of the cardiac cycles (approximately 43%), the spontaneous AP-RBF relationship was consistent with being mediated by arterial ba roreflexes (i.e., increases in AP were accompanied by proportionately greater increases in RBF during 44.4% of cardiac cycles in which AP in creased, and decreases in AP were accompanied by proportionately great er decreases in RBF during 41.4% of cardiac cycles in which AP decreas ed). Blockade of autonomic ganglionic transmission with hexamethonium markedly attenuated this pattern. Our results indicate that renal circ ulation participates in moment-to-moment control of AP via a predomina nt baroreflex-like pattern.