[Evaluation of the effect of ischemic preconditioning using near-infrared spectroscopy]

Ischemic preconditioning (IP) protects the myocardium from subsequent sustained ischemic insults. Temporary occlusion of the coronary artery is indispensable for anastomosing the graft vessel during coronary artery bypass operation without cardiopulmonary bypass. In the canine model of ischemia and reperfusion, we measured myocardial tissue oxygen saturation (SO2) continuously using near-infrared spectroscopy to determine the effect of IP on myocardial oxygen metabolism. Nine dogs underwent occlusion of the left descending coronary artery for three 5-minute periods, followed by three 5-minute periods of reperfusion. The dogs were then subjected to a 20-minutes periods of sustained coronary artery occlusion, followed by prolonged reperfusion. The myocardial SO2 was 82 +/- 2% at the baseline before coronary occlusion and was decreased to 74 +/- 2%, 76 +/- 2%, 77 +/- 3%, 77 +/- 3% at the first, second, third and sustained coronary occlusion, respectively. The increase in the minimum myocardial SO2 value at the second and third coronary occlusion suggested the effect of IP. Near-infrared spectroscopy is a useful method of continuously monitoring myocardial oxygenation and of evaluating the effect of IP during off-pump heart surgery.