Blood pressure variability and urine flow in the conscious dog.
Nafz, Benno, Heimo Ehmke, Claus D. Wagner, Hartmut R. Kirchheim, and
Pontus B. Persson.
Institut f[umlaut]ur Physiologie der Charit[acute]e, Humboldt
Universit[umlaut]at zu Berlin, I. Physiologisches Institut der
Universit[umlaut]at Heidelberg
APStracts 5:0011F, 1998.
Pressure dependent urine production is considered to be a major factor
in long- term blood pressure control. The phenomenon has been well
characterized for fixed levels of renal perfusion pressure (RPP), but
the influence of physiological fluctuations in RPP and spontaneous
variations in renal blood flow (RBF) on short- term urine flow (UV)
remain unclear. To clarify this issue, we studied the interdependence
of RPP, RBF, and UV in 13 conscious foxhounds during a single step
pressure reduction, under normal conditions, and with induced
pressure changes. Reducing RPP in a single step to 80mmHg revealed
short response times of RBF (0.4+/-0.1sec, N=7) as well as of UV
(8.1+/-0.8sec N=7). Under control conditions, UV was coupled with
spontaneous variations of RBF (r=0.94,P<0.001), in contrast to RPP,
which showed no significant correlation with UV (r=0.09, NS). In
order to discern the pressure and blood flow dependency of UV at a
reduced RPP, we induced 0.9mHz blood pressure oscillations (80+/
-10mmHg) which phase shifted RPP and RBF. Conversely, under these
conditions, UV was dependent on RPP (r=0.95, P<0.001).
These results suggest that spontaneous fluctuations in RBF around a
normal baseline level lead to concomitant changes in urine
production, in contrast to physiological short- term oscillations in
RPP, which are not correlated with changes in UV. However, during
induced oscillations of perfusion pressure the blood flow dependence
was no longer observed and UV was entirely pressure dependent.
Received 4 August 1997; accepted in final form 2 January 1998.
APS Manuscript Number F259-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 28 January 1998