Distension reduces the vasoreactivity of the internal mammary artery

Although the vasoreactivity of internal mammary artery grafts is beneficial in the long term, after mobilisation, vasospasm reduces flow through the vessel. This may be overcome and flow improved by distension. To assess the effects of distension on the vasoreactivity of the artery we have measured changes in isometric tension in rings of distended and undistended human internal mammary artery. For an equivalent wall tension, the diameter of the distended artery was 1922 microns (CL 1858 to 1986) and undistended 1684 microns (CL 1628 to 1739), (P < 0.001). In response to 25 mM potassium the increase in isometric tension, as a percent of resting tension, was 35% (CL 31 to 39) in undistended and 5% (CL 3 to 6) in distended segments (P < 0.001), with 10 microM noradrenaline increases were 57% (CL 47 to 66) and 3% (CL 2 to 5), respectively (P < 0.001). The reduction in developed tension in segments contracted with potassium and relaxed with 1 microM acetylcholine was 65% (CL 47 to 83) in undistended, and 15% (CL -1 to 32) in distended (P < 0.01). With 10 microM glyceryl trinitrate relaxation was 96% (CL 87 to 105) and 17% (CL -9 to 43), respectively (P < 0.01). Similarly, after contraction by noradrenaline, with acetylcholine, undistended segments relaxed by 50% (CL 44 to 55) and distended by 14% (CL 8 to 21) (P < 0.01), with glyceryl trinitrate relaxation was 90% (CL 80 to 99) and 7% (CL -4 to 19), respectively (P < 0.001). Distension produces a profound reduction in vasoreactivity of the internal mammary artery which is not due to endothelial damage alone.