The complexity of chaotic vasomotion is insensitive to flow and
pressure but can be externally manipulated by feedback control.
Griffith, T. M., D. H. Edwards.
Cardiovascular Sciences Research Group, Departments of Diagnostic
Radiology and Cardiology, University of Wales College of Medicine,
Heath Park, Cardiff, CF4 4XN
APStracts 2:0117H, 1995.
We have previously shown that irregular vasomotion induced by
histamine in isolated rabbit ear resistance arteries is chaotic.
Consistently, in the present study, such activity was found to
respond in a highly unpredictable fashion to changes in flow under
conditions of controlled-flow perfusion although its fractal
dimension, calculated by a standard correlation technique, was
effectively independent of flow rate and remained <4. As this
statistic provides an estimate of the number of control variables
that generate a chaotic time series, flow thus appears to modulate
vasomotion without fundamentally contributing to its genesis.
External modification of the dynamics was attempted by a negative
feedback loop that regulated pump speed through an error signal
derived from perfusion pressure. Irregular responses were converted
to either periodic or steady-state behaviour in 60% of cases with an
associated fall in fractal dimension. Conversely, unsuccessful
control was often associated with an increase in fractal dimension,
reflecting the additional complexity introduced by the feedback loop.
Furthermore, control was more readily achieved in the presence of L
-NAME, when time- and flow-dependent changes in EDRF synthesis would
not be expected to complicate the overall dynamics. The study
suggests that vascular chaos may be economically "controlled"
under both physiological and pathophysiological conditions.
Received 22 November 1994; accepted in final form 15 March 1995.
APS Manuscript Number H1041-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.