Collateral vessel development after chronic bilateral common carotid artery occlusion in the dog.

The functional response to occlusion of arteries supplying the head has been found to be much less severe in th dog than in man, indicating that a more significant collateral development occurs in the dog. To document the anatomic response to chronic occlusion of vessels supplying the head, patterns of collateral vessel growth and development were studied by corrosion casting in adult mongrel dogs 8 weeks after bilateral ligation of the common carotid artery. Dissection of the casts revealed two consistent and bilateral anastomotic connections: (i) internal carotid artery to maxillary artery (anastomotic artery) and (ii) internal carotid artery to ascending pharyngeal artery. Also present in all of the casts was a connection between one common carotid artery and both vertebral arteries, which has been designated as the deep collateral vessel. Significant collateral connections did not occur between the orbital vessels or between analogous vessels of the right and the left sides.

Collateral vessel development, following unilateral chronic carotid occlusion in the dog.

Because much of the data base describing the physiology of cerebral circulation is based on experiments using the dog as a model and because the functional response to occlusion of arteries supplying the head have been shown to be different in man than in dogs, it is important that the growth and development of the extracerebral collateral circulation in dogs be documented. Using the techniques of corrosion casting, collateral vessel development was evaluated in adult mixed-breed dogs, following 4- and 8-week periods of unilateral ligation of the common carotid artery or the external carotid artery. Neurologic deficits or severe ischemia was not observed in any of the dogs during the postoperative period. Extensive collateralization occurred between the ipsilateral vertebral artery, regardless of the occlusion site. In addition, numerous collateral connections developed between the same vessel from the contralateral side. Two main patterns of collateral vessel organization consistently developed. Initially, a collateral network of highly tortuous superficial vessels predominated. With longer survival times after occlusion, deeper and more uniform-diameter direct-collateral vessels developed.

Effects of therapy on maximal walking time following femoral ligation in the rat.

Maximal walking times at a constant rate of 10 m/min were compared in normal rats, normal rats that had been exercised daily for 6 weeks, and rats that had undergone bilateral femoral artery ligation followed by 6 weeks of either an oral vasodilator, absence of sympathetic impulses to the extremities, cold exposure, or daily exercise. Rats maintained on the vasodilator could walk no farther than untreated, ligated rats. Both chronic cold exposure and sympathectomy significantly increased maximal walking distances of ligated rats and daily exercise increased maximal walking distances 7-fold. Rats that had received 6 weeks of exercise training following femoral artery ligation could walk longer than normal untrained rats; therefore, the increased exercise tolerance could not be explained solely by the restoration of normal large artery conductance by enlargement of collaterals bypassing the femoral occlusion.

Role of sympathetics in the response to acute venous occlusion.

The effect of venous ligation and subsequent blockade of alpha receptors on hindlimb venous pressure, vascular resistance, oxygen extraction and carbon dioxide removal was evaluated in mongrel dogs with use of constant-flow perfusion of the extremity bed. Perfusion, metatarsal vein, femoral vein, and central vein pressures, and changes in paw and thigh circumference were recorded in mongrel dogs in which the hindlimb was perfused at a constant flow. Arterial, metatarsal venous, and femoral venous blood gases were drawn and analyzed for arteriovenous oxygen and carbon dioxide differences. Measurements were repeated following extensive ligation of veins and after subsequent alpha-receptor blockade with Dibenzyline. Findings indicated that ligation of extremity veins resulted in an active increase in total limb resistance upstream from the ligation, and an increase in volume of the limb. Following alpha-adrenergic blockade with Dibenzyline, limb volume increased and oxygen extraction decreased below control levels. The reflex constriction following ligation of veins protected against the detrimental effect of excessive accumulation of fluid in tissue spaces.

Anatomic response of canine hindlimb vasculature to chronic venous occlusion.

Total limb (iliac) flow, small-vein pressure, and total small-vessel and venous resistances were measured in the fully dilated bed 2 h, 2 wk, and 8 wk after extensive ligation of veins. Values were compared to similar measurements in the contralateral unoccluded extremity. Wall thickness, lumen size and distensibility of noncollateral veins, and enlargement of collateral veins were evaluated 8 wk after venous ligation. Two hours after ligation, anatomic vascular resistance was twice normal, and venous resistance was increased sevenfold. Eight weeks later, total limb anatomic resistance had decreased to a value slightly less than normal, suggesting an "overcompensation" in anatomic resistance. Wall thickness of noncollateral veins was greater than normal at 8 wk postligation, and lumen size and distensibility were less than normal in spite of a return of supine venous pressure to normal levels.

Acute response to venous distention in the extremity of the dog.

Aortic and vena caval pressures, right and left iliac flows. and pedal small artery and small vein pressures were recorded in mongrel dogs prior to and for 90 min following ligation of the right iliac, femoral, medical saphenous, and lateral saphenous veins. Total, arterial, small vessel and venous resistances were calculated. Measurements were repeated following alpha-receptor blockade (phenoxybenzamine) and perfusion of the extremities with a calcium chelator (EGTA). Results indicated that venous ligation resulted in constriction of small vessels in both the occluded and contralateral extremities and constriction of veins in the occluded extremity only. Relative responses of right and left vascular bed to alpha-blockade and EGTA perfusion suggested that small vessels were constricted bilaterally by enhanced sympathetic stimulation and that veins and small vessels were constricted on the occluded side in response to a local myogenic stimulus.