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Left ventricular dysfunction in early stage of regional myocardial ischemia

Li Yunxia, Yang Luhua, Lei Xiaoguang, Cheng Liren

Department of Physiology, Hunan Medical College. Hunan, China

Abstract

Acute regional myocardial ischemia was produced in seven open-chest anesthetized dogs by occlusion of the, left anterior descending artery (LAD) at the point just below the origin of its first branch. In order to assess the regional myocardial function, two mercury-filled length gauges were sutured on the epicardium in both the ischemic and the non-ischemic areas, respectively. The segmental myocardial length (SL), the first derivative of length change (dL/dt), the pressure-length (P-L) loop, and other left ventricular function parameters were recorded on an 8-channel polygraph and an oscilloscope. The stroke work of the segmental myocardium (SM) was calculated, based on the P-L loop. In all the experiments, the LVEDP and SM end-diastolic length increased significantly after the onset of LAD occlusion and at the point when the -dP/dt-max decreased to its nadir at the fifth second. At this time, the non-ischemic SM (n=8) work increased, however, the phasic configurations of the length curve, the dL/dt curve and the P-L loop were unchanged, but the ischemic SM (n=16) work decreased rapidly and even became negative. During the late ejection and early. Relaxation period, there was an ,abnormal SM elongation, the normal .anti-clczckwise rectangular P-L loop changed to an,8-shaped loop or even in a clockwise pattern. Furthermore, under the control condition, at the point of-dP/dt-max, the rate of SM shortening (dL/dt) reached its maximum (dL/dt-max). After, LAD occlusion, when the -dP/dt-max decreased and reached its nadir, the dL/dt-max decreased gradually and finally became a negative value (-dL/dt-max). Afterward, the -dL/dt-max became larger, but did not correlate with the -dP/dt-max, and preceded the -dP/dt-max. These results indicate that the abnormal movement of ischemic myocardium first appears in the isovolumic relaxation period. This might be a reasonable explanation for the decrease in -dP/dt-max and left ventricular dysfunction during the early stage of ischemia.

Key words: Pressure-length loop;Length gauge;;;

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Citing This Article：

Li Yunxia, Yang Luhua, Lei Xiaoguang, Cheng Liren. Left ventricular dysfunction in early stage of regional myocardial ischemia. Acta Physiol Sin 1985; 37 (1): (in Chinese with English abstract).