European Journal of Cardio-Thoracic Surgery, Vol 10, 26-31, Copyright © 1996 by European Association for Cardio-thoracic Surgery
Distension reduces the vasoreactivity of the internal mammary artery
GJ Cooper and TJ Locke
Department of Cardiac Surgery, Northern General Hospital, Sheffield, UK.
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.
