The Journal of Thoracic and Cardiovascular Surgery, Vol 78, 236-243, Copyright © 1979 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Effects of phenylephrine on transmural distribution of myocardial blood flow in regions supplied by normal and collateral arteries during cardiopulmonary bypass
JD Sink, RC Hill, WR Chitwood Jr, R Abriss and AS Wechsler
Cardiopulmonary bypass is frequently accompanied by decreased peripheral
vascular resistance with resultant hypotension that is unresponsive to
increased flow rates. Alpha adrenergic agonists are routinely used to
increase peripheral vascular resistance and augment blood pressure. In this
study, the effects of the alpha adrenergic stimulant phenylephrine on blood
flow distribution during cardiopulmonary bypass in myocardium supplied by
normal and collateral arteries were studied in eight mongrel dogs.
Microsphere determinations of blood flow were made following augmentation
of perfusion pressure with phenylephrine and were compared with
intraoperative normotensive and hypotensive control levels. With systemic
flow rates held constant, phenylephrine was infused in doses adequate to
raise perfusion pressure to normotensive levels following hypotension. In
the normal region (NR), blood flow was returned to normotensive control
levels with flow favoring the subendocardium. In the region supplied by
collateral vessels (CR), however, phenylephrine infusion failed to return
flow to the normotensive control level in the subendocardial layer, and the
flow imbalance present during hypotension was not corrected. An analogue
model of the calculable resistances in the CR is presented, which indicates
that phenylephrine increased resistance in the collateral vessels.
Associated with this inflow restriction is decreased resistance or
vasodilatation of the intramyocardial vessels supplied by collateral
coronary arteries.
