Changes in Myocardial Microcirculation Induced by Ischemia and Effects of Drugs on Them.

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Laser Doppler flowmetry (LDF) was applied to measure local myocardial blood flow (MBF) in the beating and arrested left ventricle of anesthetized open-chest dogs. An epicardial and an intramyocardial flow probe were placed in the left anterior descending coronary artery (LAD)-perfused region, and were connected to laser Doppler flowmeters (ALF21) for measurement of epi (EPI)- and endocardial (ENDO)-MBF, respectively. In the beating heart, LDF signals of both EPI- and ENDO-MBF showed beat-to-beat changes. The peak signals of EPI-MBF were observed during systole in 6 out 8 dogs, while those of ENDO-MBF were during diastole in 5 out of 8 dogs. Nitroglycerin (20 mug/kg i. v.), adenosine (0.5 mg/kg i. v.) or partial occlusion of LAD failed to produce significant changes in EPI- and ENDO-MBF, although apparent changes in LAD flow measured with an electromagnetic flowmeter were seen. After complete cardiac arrest induced by KC1, however, signals of MBF invariably fell almost to the electrical zero level. During a long diastole obtained by electrical stimulation of vagus, both MBFs as well as LAD flow linearly declined along with a decrease in aortic pressure (AoP). Thus, each of these diastolic flows showed a linear function of AoP. However, the pressure at zero flow estimated by extrapolation of the regression line in ENDO-MBF was higher than that in EPI-MBF. Moreover, ENDO/EPI flow ratio markedly lessened at a given pressure below 70 mmHg of AoP. Similar results were obtained even when autoregulation was abolished with intracoronary infusion of adenosine. These data suggest that there may be transmurally inhomogeneous extravascular compression as a back pressure to tissue blood flow during diastole. In conclusion, the present study demonstrated that LDF can provide instantaneous and continuous measurement of local perfusion in both the epi- and endocardium in situ.