Relation between progressive decreases in regional coronary perfusion and contractile abnormalities

Abstract

To determine the quantitative relation between partial coronary obstruction and its resultant effects on local contraction, the left anterior descending coronary artery was partially obstructed (while the decrease in both distal pressure and flow were observed) and local tension and len gth were mea sured in 10 open chest dogs. A pressure gradie nt in dex ([AO-COR] /AO) across the obstruction was derived, where AO = mean aortic pressure and COR = mean distal coronary pressure, and was correlated with change in flow ( control flow = 95.3 ± 3.8 ml/100 g). Contractile function of ischemic and nonischemic zones was measured using both Walton-Brodie strain and mercury-in-Silastic segment length gauges. Small pressure gradients (index 0.27 ± 0.03 [mean ± standard error of the mean]) and decreases in distal flow (to 74.2 ± 1.6 ml/100 g) caused no change in tension or length. Further reduction in distal pressure (gradient index 0.52 ± 0.04) and flow (to 50.0 ± 0.8 ml/100 g) produced a decrease in tension to 87.3 ± 3.6 percent of control level ( P < 0.005) and an increase in length to 129.1 ± 4.6 percent ( P < 0.01). The upstroke of the tension curve during the ejection phase persisted despite the decrease in total tension. Additional reduction of pressure (gradient index 0.71 ± 0.03) and flow (27.7 ± 1.3 ml/100 g) caused a marked decrease in tension to 55.5 ± 11.9 percent of control level ( P < 0.01) and an increase in length to 182.0 ± 14.1 percent ( P < 0.001). The tension curve demonstrated loss of ejection tension with a negative slope inscribed during the ejection phase. Total occlusion resulted in no additional decrease in distal pressure and, although flow decreased to 5.0 ± 1.2 ml/100 g, no further change in tension (56.8 ± 9.3 percent) or length (183.3 ± 8.9 percent) occurred. Thus, an acute reduction in coronary pressure and flow of 50 percent or more results in regional contraction abnormalities that are further accentuated as the pressure and flow are reduced by 75 percent or more. Maximal abnormalities produced by total occlusion are similar to those produced by a reduction in flow of 75 percent or more.