Low flow after global ischemia to improve postischemic myocardial function and bioenergetics*

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Abstract
In this study, we test the hypothesis that a period of low flow perfusion before full reperfusion improves ventricular function and bioenergetics. Prospective, randomized, controlled animal study. Research laboratory. Sprague-Dawley rats. Hearts were perfused with Krebs-Henseleit buffer at 85 mm Hg. The protocol consisted of 10 mins of baseline flow, 15 mins of global ischemia, 5 mins of low flow ischemia, and 30 mins of reperfusion. Groups received 10% or 1% of baseline flow during the low flow period. A control group received 0% low flow (20 mins of global ischemia). Left ventricular function was continuously measured. Hearts were freeze-clamped at various time points, and metabolites were measured. At 10% flow, following global ischemia, both left ventricular function and bioenergetics improved compared with 0% flow and 1% flow. At 1% flow, no changes in function were seen and adenosine 5'-triphosphate concentrations decreased during reperfusion, compared with no flow (9.4 +/- 1.0 vs. 13.2 +/- 1.0 micromol/g of dry weight, p <.01). Following global ischemia but before full reperfusion, a period of low flow improves postischemic myocardial function and energetic recovery, only if a certain level of low flow is met. Very low flow may further reduce bioenergetic recovery without improvement in postischemic function, compared with continuous global ischemia.