Coronary Vascular Effects In Vivo
Halothane has variable effects on coronary blood flow and coronary
vascular resistance in vivo that occur
concomitant with changes in MVO2
.[242]
[243]
[244]
[245]
Decreases in MVO2
cause declines in coronary
blood flow with relative maintenance or modest increases in coronary vascular resistance
during halothane anesthesia.[14]
[246]
[247]
Despite the decreases in coronary blood flow,
halothane increases coronary sinus oxygen tension and decreases oxygen extraction,
[243]
[245]
indicating
that halothane is a relatively weak coronary vasodilator. Like halothane, isoflurane
variably alters coronary blood flow in vivo.[19]
[248]
[249]
[250]
[251]
Isoflurane reduces MVO2
and simultaneously decreases oxygen extraction, indicating direct coronary vasodilation.
[249]
Isoflurane can also produce mild and transient
increases in blood flow independent of changes in MVO2
and autonomic nervous system activity during inhalational induction of anesthesia.
[252]
Perfusion of the left anterior descending
coronary artery with blood previously equilibrated with isoflurane dramatically increases
coronary blood flow,[253]
but only mild coronary
vasodilation occurs after a period of anesthetic equilibration in a similar experimental
model.[250]
Isoflurane-induced increases in coronary
blood flow are not accompanied by epicardial coronary artery dilation, indicating
that isoflurane predominantly dilates small coronary arteries.[254]
However, adenosine, a potent coronary vasodilator, causes considerably greater vasodilation
in coronary microvessels than does isoflurane.[255]
The effects of enflurane on the coronary circulation in vivo are somewhat controversial.
[232]
[238]
[239]
[240]
Enflurane produces greater reductions in
MVO2
than does isoflurane concomitant with metabolically determined declines in coronary
blood flow.[256]
[257]
However, isoflurane produces more profound decreases in myocardial oxygen extraction
than does enflurane, indicating that isoflurane is a more potent coronary vasodilator
than its structural isomer.[257]
The influence of the new volatile anesthetics on coronary blood
flow in the intact cardiovascular system has been incompletely examined. Desflurane
and isoflurane caused similar increases in the ratio of oxygen delivery to consumption
and decreases in oxygen extraction, consistent with coronary vasodilation.[258]
However, the increases in coronary blood flow produced by desflurane, but not isoflurane,
are attenuated by pharmacologic blockade of the autonomic nervous system, suggesting
that isoflurane causes greater direct coronary vasodilation in vivo than does desflurane.
[16]
Sevoflurane does not appear to produce any
significant degree of coronary vasodilation,[46]
[241]
[259]
[260]
[261]
in contrast to the findings with other volatile
agents.
