EFFECTS AND INTERACTIONS OF NITROUS-OXIDE, MYOCARDIAL-ISCHEMIA, AND REPERFUSION ON LEFT-VENTRICULAR DIASTOLIC FUNCTION

The effects of nitrous oxide on left ventricular diastolic function an d its potential interactions with ischemia-induced diastolic dysfuncti on have not been described. Accordingly, we investigated the effects o f nitrous oxide in ischemic and remote nonischemic myocardium during b aseline, 90 min severe low-flow myocardial ischemia (systolic bulge), and reperfusion in 11 open-chest dogs. Anesthesia was maintained with fentanyl infusion (2 mu g . kg(-1) . min(-1)), animals were ventilated with 60% nitrogen in oxygen, and hemodynamic variables were recorded prior to and after the replacement of nitrogen by 60% nitrous oxide. D uring baseline, nitrous oxide moderately increased chamber stiffness ( +10%), myocardial stiffness (+33%), and unstressed length (+4%) and de creased the peak lengthening rate (-10%). Moreover, nitrous oxide decr eased regional contractility during baseline (-12% at apex, -8% at bas e) as well as in nonischemic myocardium during myocardial ischemia (-9 %) and reperfusion (-8%). However, nitrous oxide did not modify ischem ia-induced systolic or diastolic dysfunction in ischemic myocardium du ring ischemia and reperfusion. Myocardial ischemia (+45%) and reperfus ion (+57%) were associated with an increase in myocardial stiffness of nonischemic myocardium regardless of the anesthetic technique used. T his study is the first to demonstrate that in addition to its well est ablished negative inotropic effect, nitrous oxide affects regional dia stolic function.