B. Gersak et al., LOSS OF ENDOTHELIUM-MEDIATED VASCULAR RELAXATION AS A RESPONSE TO VARIOUS CLAMPING PRESSURES, European journal of cardio-thoracic surgery, 10(8), 1996, pp. 684-689
The contraction/relaxation responses of thoracic aortal rings clamped
with two clamping pressures to potassium chloride (KCI), noradrenaline
and carbachol were studied using a scanning electron microscope (SEM)
to ascertain endothelial lacerations. Clamp A had the tip pressure P-
A = 0.60 N/mm(2) and clamp B P-B = 5.16 N/mm(2). In 15 Wistar albino r
ats, weighing 328 +/- 19 g (mean +/- SD). the thoracic aorta was occlu
ded for 15 min and then three vascular rings (2 mm wide) were excised.
The proximal unclamped ring served as a control. The aorta diameter w
as calculated from the circumference of distal rings 1.61 +/- 0.01 mm
(n = 15, d(min) = 1.51 mm, d(max) = 1.70 mm). The rings were challenge
d with cumulative additions of KCl (10-80 mmol/l) to measure the contr
action. Then cumulative relaxation on the administration of carbachol
(0.01-100 mu mol/l) as a response to noradrenaline precontraction (0.1
mu mol/l) was determined. A significant loss (P < 0.05) of vascular r
elaxation in all clamped rings (clamped with P-A and P-B clamping pres
sures) was seen. No significant differences (P > 0.05) were observed f
or contraction between clamped and control rings clamped with clamp Al
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 clamp
ed rings between groups A and B (P > 0.05) for both the contraction an
d relaxation parts of the experiments. With SEM, great endothelial lac
erations with complete disruption of the endothelial layer in the ring
s clamped with the clamp B were seen, but no disruption in rings clamp
ed with clamp A. Therefore endothelial vascular layers are much more s
usceptible to pressure injuries than was previously believed. The clam
ped vessel wall injuries, particularly in endothelial layers, depend o
n the momentary peak clamping pressure (MPCP) as well as on the lower
stationary clamping pressure (SCP).