Evaluation of Subendocardial Microcirculatory Hemodynamics by High-Speed Needle-Probe CCD Microscope

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This study is to test our hypothesis that enhancement of alpha-receptor sympathetic nerve stimulation improves subendocardial ischaemia by its inhibitory effect on coronary slosh phenomenon adjusting coronary tonus. We, therefore, directly observed pulsatile diameter changes and microcirculation of subendocardial arterioles with our needle type CCD intravital microscope.Open chest mongrel dogs under anaesthesia were used in the experiment. We measured intramural blood flow with a 20 Mhz 80-channeled ultrasound Doppler flowmeter after exposing septal branches of the left coronary artery. The needle type CCD intravital microscope was inserted from the left appendage into the left ventricle via mitral valve and the subendocardial arterioles were observed. To make comparison, epicardial arterioles were observed too. Heart rate was controlled by right ventricular pacing. Coronary perfusion pressure was controlled aortic banding. Under various pacing rates (140,200,250 bpm), observation of e … More ndocardial arterioles were made while measuring intramural blood flow under the following conditions ; 1) basal condition, 2) continuous intravenous injection of norepinephrine (NE,0.25 mug/kg/min), 3) NE plus alpha-receptor blockade (phenoxybenzamine, 0.5 mg/kg).At the rate of 140 bpm, alpha-receptor blockade caused remarkable increase of retrograde flow during continuous administration of NE.Diastolic forward flow did not show any significant change. As for the subendocardial flow volume, it increased at the rate of 140 bpm, did not show any change at the rate of 200 bpm and decreased at the rate of 250 bpm. At any heart rate, there was an increase of significan retrograde flow and slosh ratio by alpha-receptor blockade. Pulsatililty of both subendocardium and subepicardium showed significant charges after alpha-receptor blockade.The needle type CCD intravital microscopy enabled to observe pulsatile diameter changes of subendocardial arterioles of a beating heart under alpha-receptor sympathetic nerve stimulation. It was found that alpha-receptor stimulation inhibited slosh phenomenon and maintained the subendocardial blood flow during tachycardia. Less