Hemodynamic basis of oscillations in systemic arterial pressure in conscious rats. Janssen, Ben J. A., Jan Oosting, Dick W. Slaaf, Pontus B. Persson, Harry A. J. Struijker-Boudier. Departments of Pharmacology and Biophysics, Cardiovascular Research Institute Maastricht, University of Limburg, Maastricht, The Netherlands; Department of Physiology, Humboldt University (Charit[acute]e), Berlin, Germany.
APStracts 2:0039H, 1995.
Janssen, Ben J.A., Jan Oosting, Dick W. Slaaf, Pontus B. Persson, and Harry A.J. Struijker-Boudier. Hemodynamic basis of oscillations in systemic arterial pressure in conscious rats. Am. J. Physiol. XXX (Heart Circ. Physiol. XX): HHHH-HHHH,XXXX. Indices of blood pressure and heart rate variability are currently explored as prognostic tools in cir culatory pathophysiological states. However, the hemodynamics under lying the various fluctuations in these signals, especially those at low frequency, are not well understood. Using spectral analysis techniques, we compared in conscious resting rats the hemodynamic fluctuations in systemic mean arterial pressure (MAP) with those in cardiac output and those in blood flow in three major peripheral beds. To this end two groups of rats were instrumented for compu terized beat-to-beat measurement of either cardiac output or of blood flow through the renal, mesenteric, and hindquarter vascular bed. Spon taneous oscillations (lability) in MAP were observed in frequency bands centered about 1.6 Hz (high:HF), 0.4 Hz (mid:MF), and 0.13 Hz (low:LF). However, they were mainly confined within the LF ( nearly equal to 8 s) band. Lability of cardiac output, on the other hand, showed primary HF oscillations, which relied predominantly on respiration -synchronous fluctuations in stroke volume and to a lesser degree on heart rate. Following calculating of the transfer functions with MAP as input and regional flows as output, admittance gains were >/=1 across all frequencies for all vascular beds, indicating the absence of autoregulation. LF oscillations in regional blood flow were i) of greater amplitude than MF oscillations, ii) most prominent in the mesenteric and renal vascular bed, and iii) showed negative phase angles with MAP, whereas those between MAP and hindquarter blood flow were positive. Cross correlation analysis indicated that approximately 2 s following a LF change in MAP, LF changes in mesenteric and renal blood flow occurred opposite to those of MAP. Changes in hindquarter flow were negatively correlated with those in MAP about zero time delay. This hemodynamic pattern suggests that myogenic mechanisms predominantly control mesenteric and renal blood flow in a non-autoregula tory but rather superregulatory manner, while autonomic mechanisms regulate hindquarter blood flow. Thus, in conscious resting rats, spontaneous fluctuations in systemic arterial pressure predominantly exhibit slow ( nearly equal to 8 s) oscillations, which do not arise from fluctua tions in cardiac output, but originate from regionally specific myogenic oscillatory mecha nisms contributing to resistance to flow. 

Received 17 October 1994; accepted in final form 3 February 1995.
APS Manuscript Number H931-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.