European Journal of Cardio-Thoracic Surgery, Vol 10, 684-689, Copyright © 1996 by European Association for Cardio-thoracic Surgery
Loss of endothelium-mediated vascular relaxation as a response to various clamping pressures
B Gersak, R Trobec, I Krisch and M Psenicnik
Department of Cardiovascular Surgery, Medical Center Ljubljana, Slovenia.
The contraction/relaxation responses of thoracic aortal rings clamped with
two clamping pressures to potassium chloride (KC1), noradrenaline and
carbachol were studied using a scanning electron microscope (SEM) to
ascertain endothelial lacerations. Clamp A had the tip pressure PA = 0.60
N/mm2 and clamp B PB = 5.16 N/mm2. In 15 Wistar albino rats, weighing 328
+/- 19 g (mean +/- SD), the thoracic aorta was occluded for 15 min and then
three vascular rings (2 mm wide) were excised. The proximal unclamped ring
served as a control. The aorta diameter was calculated from the
circumference of distal rings 1.61 +/- 0.01 mm (n = 15, dmin = 1.51 mm,
dmax = 1.70 mm). The rings were challenged with cumulative additions of KC1
(10-80 mmol/l) to measure the contraction. Then cumulative relaxation on
the administration of carbachol (0.01-100 mumol/l) as a response to
noradrenaline precontraction (0.1 mumol/l) was determined. A significant
loss (P < 0.05) of vascular relaxation in all clamped rings (clamped
with PA and PB clamping pressures) was seen. No significant differences (P
> 0.05) were observed for contraction between clamped and control rings
clamped with clamp A, however the rings clamped with clamp B showed
significantly reduction of contraction (P < 0.05). No significant
differences were seen from control rings between groups A and B (P >
0.05), as well as from clamped rings between groups A and B (P > 0.05)
for both the contraction and relaxation parts of the experiments. With SEM,
great endothelial lacerations with complete disruption of the endothelial
layer in the rings clamped with the clamp B were seen, but no disruption in
rings clamped with clamp A. Therefore endothelial vascular layers are much
more susceptible to pressure injuries than was previously believed. The
clamped vessel wall injuries, particularly in endothelial layers, depend on
the momentary peak clamping pressure (MPCP) as well as on the lower
stationary clamping pressure (SCP).
