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The local control of coronary blood flow

Xu, Xiao Fang 1992 , 'The local control of coronary blood flow', PhD thesis, University of Tasmania.

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The mechanism of local metabolic regulation of coronary blood flow is still
unclear. It is still unknown which control system- an "open-loop feedback control"
or a "close-loop control" - operates in the coronary circulation and whether common
mechanisms exist in this control. To separate the putative chemicals proposed to be
physiological regulators in the coronary bed, the time courses of coronary resistance
change in response to either increased cardiac work or hypoxia have been examined,
before and after a, ß and adenosine inhibition.
An acute open-chest sheep model was used for this investigation. The sheep
were anaesthetised with sodium pentobarbitone and instrumented for circumflex
coronary artery and pulmonary artery flows, left ventricular, proximal aortic and
coronary sinus pressure. Continuous coronary sinus oxygen saturation was measured
by a fibre optic technique. Blood samples from coronary sinus and proximal aorta
were analysed for blood gases, Na+ and K+. An occluding band was placed around
the proximal aorta to produce variable increments of aortic pressure for variable
periods. Low oxygen gases (5%02, 5%C02 and 90%N2) were used to produce
systemic hypoxia. Phentolamine, propranalol and 8-phenyltheophylline were used as
a, ß and adenosine blockers respectively, and nonadrenaline and isoprenaline
(injected into left ventricle) and intra-coronary injection of adenosine were used to test
the efficacy of the blockers. Continuous coronary resistance was calculated
throughout each intervention.
The recovery of coronary resistance to normal after the change of the afterload
of the left ventricle had a constant half life of 4.7±0.2 seconds. The half life was not
related to either the degree or the duration of increased work. a, ß and adenosine
inhibitors did not alter the half life, but produced more profound changes in coronary
resistance due to increased cardiac work. The half life of exogenous adenosine was
about 26 seconds.
During the increase of aortic pressure the coronary sinus oxygen saturation
varied significantly both above and below the steady state unpredictably, but with
systemic hypoxia there was vasodilation during which the oxygen level in the
coronary sinus was closely linked to coronary resistance with a small "hysteresis"
when the hypoxia was reversed. After adenosine blockade, the coronary resistance
and oxygen supply were more closer linked.
The results suggest an open loop control system with a short acting mediator
whose half life is the same for varying periods and degrees of increased work, but
very much shorter than that of adenosine. The metabolic control of coronary flow is
not dependent on the oxygen requirements of the muscle. Multiple factors may
involved in the local coronary vasoregulation. Current data do not support adenosine
as the common factor in metabolic vasodilation.

Item Type: Thesis - PhD
Authors/Creators:Xu, Xiao Fang
Keywords: Blood, Coronary circulation
Copyright Holders: The Author
Copyright Information:

Copyright 1992 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1994. Includes bibliographical references (leaves 195-214)

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