LOSS OF ENDOTHELIUM-MEDIATED VASCULAR RELAXATION AS A RESPONSE TO VARIOUS CLAMPING PRESSURES

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).