INTRODUCTION:  Understanding the pathophysiology of traumatic vascular spasm in uninjured vascular segments is important in the management of microvascular injuries.  Our study focuses on the details of this process.

METHOD: 40 SD male rats, 250-300g each, were used in this multiple crush injury model: Each rat was anesthetized by intraperitoneal injection of sodium pentobarbital; a 4-cm tail artery was exposed, crushed by two 5-inch needle holders with 3-mm width at 1.5 and 2.5cm from its origin, and clamped for 60 minutes. The skin was closed after clamp was released. All rats’ tail arteries were re-exposed for evaluation after the following intervals and compared to normal controls.

Time (hours)	4	6	8	12	24	48	72	Normal Control (No crush injury)
Number of rats studied	2	2	2	2	8	8	8	8

Evaluation focused on uncrushed vascular segments.  Segments were evaluated by appearance, caliber measurements, strip test, and histological studies, which included light microscopy, and Transmission Electronic Microscopy (TEM.)  The lumen area was  measured by computer imaging system.

RESULTS:    Vascular Spasm and Thrombosis in Uncrushed Segments

Time (hours)	4-12	24	48	72	Normal   Control
Mean caliber (mm)	0.40	0.40	0.40	0.40	0.70
Thrombosis	None	Microthrombus adherent to endothelium wall	One third of lumen blocked by clots	Complete blockage of lumen	None
Mean lumen size (μm2)			8187.5		13622.7
Endothelial injury (shown by TEM)	Squeezing and  vacuoles seen after 4 hours	Partial discontinuity in endothelium	Partial rupture of elastic membrane	Internal elastic membrane disrupted	Normal

CONCLUSIONS:  1. Vascular spasm in uninjured segments secondary to crush injury is insidious and permanent if injured segments are not removed.   2. Vascular spasm lasting four hours in uninjured segments will lead to endothelial damage: the longer the spasm, the more serious the damage.  3. Injured vascular segments should be aggressively debrided, and medications to reduce vascular spasm should be initiated as early as possible.