INHALED ANESTHETICS ALTER THE DETERMINANTS OF CORONARY COLLATERAL BLOOD-FLOW IN THE DOG

Background: Whether coronary steal is induced by inhaled anesthetic ag ents remains controversial in part because multiple factors determine collateral blood flow. Methods: We used an established model to determ ine how halothane, isoflurane, and desflurane affect the hemodynamic d eterminants of coronary collateral blood flow. Twelve dogs were studie d 4-5 weeks after ameroid constrictor implantation. Retrograde flow dr aining from the occluded artery was measured as an index of collateral flow after antegrade embolization. Pressure in the supplying artery a t the origin of the collaterals was estimated with a stop-flow techniq ue. These techniques allow calculation of collateral segment resistanc e and the resistances of the supply artery upstream and downstream fro m the origin of the collaterals. Results: None of the inhaled anesthet ics affected collateral segment resistance. Downstream (arteriolar) re sistance of the supplying artery was decreased by desflurane (-45%), i soflurane (-35%), and halothane (-15%), lowering pressure at the origi n of the collaterals, an effect that was partially offset by a decreas e in upstream resistance. Retrograde flow was unaffected by isoflurane and halothane but decreased by about 20% during desflurane administra tion. Conclusions: Inhaled anesthetics have many effects on segmental resistance and pressure in the coronary circulation. These findings he lp explain conflicting results from previous studies and provide a use ful model for investigating the effects of inhaled agents on small cor onary arteries.