Dynamic pressure-flow curves in the autoregulating kidney vasculature of conscious dogs

Summary In three healthy conscious dogs blood pressure was measured in the abdominal aorta with an implanted miniature transducer. Flow velocity in the left renal artery was recorded by an electromagnetic flowmeter. An appropriate distance between the transducer sites compensated the time-lag introduced by the flowmeter system and allowed records with a negligable foot to foot phase shift between the flow- and the pressure pulse. Pressure-flow curves (I.-P. curves) were obtained recording flow versus pressure beat by beat on an oscilloscope. Electrical stimulation of the right cervical vagus nerve produced I.-P.-curves, which decayed in less than 3 sec down to a blood pressure of 25 mm Hg (dynamic I.-P.-curve). Static I.-P.-curves were recorded by reducing blood pressure within 1 to 2 min to the same pressure level. The following results were obtained:A unique dynamic I.-P.-curve, which follows the power functionI=a·Pⁿ exists for each level of arterial mean pressure i.e. myogenic vascular tone.An increase of arterial mean pressure (i.e. myogenic vascular tone) decreases the exponentn and increases the coefficienta of the power function.The static I. P.-curve, which runs parallel to the pressure axis above 90 mm Hg is actually composed of a family of different dynamic I.-P.-curves.The kidney resistance vessels are rather distensible. The pressure-dependent increase of myogenic vascular tone, which developes at perfusion pressures above 55 mm Hg, decreases the vessel distensibility.A change of mean perfusion pressure causes the kidney resistance vessels to shift from one to another dynamic I.-P.-curve without altering mean blood flow.This study was supported by the Deutsche Forschungsgemeinschaft (S.F.B. 90; Kardiovaskuläres System, Heidelberg).A preliminary report of a portion of this work was presented at the XXV. International Congress of Physiological Sciences, München, July 1971.