Transvalvular left ventricular pressure measurement in the isolated working rat heart

Exercise training preserves coronary flow and reduces infarct size after ischemia-reperfusion in rat heart

The effect of endurance training on the resistance of the heart to left ventricular (LV) functional deficit and infarction after a transient regional ischemia and subsequent reperfusion was examined. Female Sprague-Dawley rats were randomly assigned to an endurance exercise training (Tr) group or a sedentary (Sed) control group. After 20 wk of training, hearts were excised, perfused, and instrumented for assessment of LV mechanical function, and the left anterior descending coronary artery was occluded to induce a transient regional ischemia (1 h) that was followed by 2 h of reperfusion. Throughout much of the regional ischemia-reperfusion protocol, coronary flow rates, diastolic function, and LV developed pressure were better preserved in hearts from Tr animals. During the regional ischemia, coronary flow to myocardium outside the ischemic zone at risk (ZAR) was maintained in Tr hearts, whereas it progressively fell in Sed hearts. On release of the coronary artery ligature, flow to the ZAR was greater in Tr than in Sed hearts. Infarct size, expressed as a percentage of the ischemic ZAR, was significantly smaller in hearts from Tr rats (24 +/- 3 vs. 32 +/- 2% of ZAR, P < 0.05). Mn- and CuZn-SOD protein expression were higher in the LV myocardium of Tr animals (P < 0.05 for both isoforms). Our data indicate that long-term exercise training leads to infarct sparing and better maintenance of coronary flow and mechanical function after ischemia-reperfusion.

Comparison of the alteration of cardiac function by sevoflurane, isoflurane, and halothane in the isolated working rat heart

OBJECTIVES

Despite its widespread use, little is known about sevoflurane's physiologic effects. The direct myocardial effects of sevoflurane were compared with both halothane and isoflurane.

DESIGN

Administration of minimum alveolar concentration (MAC) fractions of anesthetic (0 to 3.0) was systematically varied to decrease the possibility of time-related effects on measured parameters.

SETTING

Isolated rat hearts were perfused using a working heart model where the parameters affecting myocardial work were carefully controlled and monitored.

PARTICIPANTS

To avoid confounding effects of prior anesthetic administration, hearts were removed from rats, after decapitation, in the absence of anesthetic.

INTERVENTIONS

In the first series, isolated perfused rat hearts were exposed to one of the three anesthetics in doses of 0 to 1.5 times MAC. In the second series, hearts were exposed to either sevoflurane or isoflurane in doses of 0 to 3.0 times MAC. The following variables were measured: the rate of change of left ventricular pressure; aortic flow rate; cardiac output; left ventricular end-diastolic pressure; the time constant of isovolumetric relaxation; and coronary vascular resistance. Oxygen consumption was measured during the first series.

MEASUREMENTS AND MAIN RESULTS

In the first series, all systolic variables were reduced in the presence of halothane when compared with either isoflurane or sevoflurane. Halothane affected diastolic function to a greater degree than either sevoflurane or isoflurane, as measured by the rate of relaxation and end-diastolic pressure. In the second series, at a dose of 3.0 times MAC, both sevoflurane and isoflurane decreased systolic and diastolic function, with a greater reduction in cardiac output, and peak aortic flow and higher left ventricular end-diastolic pressures observed with isoflurane. Coronary resistance and oxygen consumption were not affected by any of the anesthetics.

CONCLUSIONS

These data suggest that sevoflurane depresses cardiac function less than either halothane in doses of 1.0 and 1.5 x MAC or isoflurane at doses of 3 x MAC.