Arteriovenous Bundle Research Articles

The revascularization interface in flap prefabrication: a quantitative and morphologic study of the relationship between carrier size and surviving area.

To make a quantitative assessment of the relationship between size of vascular carrier and surviving area in a prefabricated flap, vascular carriers composed of the superficial epigastric arteriovenous bundles and a surrounding fascial patch with varying sizes were transferred under a 7- x 7-cm bipedicled abdominal skin flap in a rat model. Seven days later, the abdominal flaps were raised as composite island flaps connected only by the superficial epigastric vascular pedicle, transferred, and then sutured back into place. Immediately after replacement, the degree of revascularization was assessed using quantitative skin fluorometry, after intravenous injection of sodium fluorescein. At 7 days after elevation as an island flap, the area of skin flap surviving was recorded and plotted on a map depicting the original flap surface. High levels of fluorescence appeared on the flap surface where the carrier was tacked underneath. The prefabricated island flaps survived with a circular shape up to approximately 4 times the radius of the vascular carrier. When the distance was converted into area, theoretically, an area 13 times the area of the vascular carrier survived, regardless of its size in this experimental model. Histologic examination revealed connections of fine capillaries between the carrier and flap.

Prefabrication of Composite Free Flaps Through Staged Microvascular Transfer

The feasibility of prefabricating free flaps by inducing, through the process of staged reconstruction, an arteriovenous bundle and its surrounding fascia to perfuse a selected block of tissue was investigated experimentally and clinically. Sixteen rat knee joints were wrapped with their ipsilateral superficial inferior epigastric (SIE) fascia. In 8 joints, the composite flaps were resected en bloc and were immediately replaced orthotopically pedicled upon the superficial inferior epigastric vessels. In the remaining joints, the resection and orthotopic transfer were performed 2 weeks later. Only the joints in the latter group, which benefited from the staging period, were found to be perfused. The long finger proximal interphalangeal joint of a child was reconstructed by the staged microvascular transfer of his second toe proximal interphalangeal joint. At the first stage, a temporalis fascia flap was wrapped around the toe proximal interphalangeal joint and revascularized to the dorsalis pedis vessels. Six weeks later, the joint and its temporalis fascia envelope were dissected, and the "prefabricated" joint flap was transferred to the hand and revascularized to the wrist vessels. Bony union progressed uneventfully with excellent recovery of the range of motion. We conclude that regardless of the indigenous vascular anatomy, an unlimited array of composite free flaps can be constructed and transferred based on induced large vascular pedicles.

Countercurrent heat exchange and vascular bundles in sloths.

In the sloth, a few other terrestrial mammals and several aquatic mammals, the limbs and tail are provided with arteriovenous bundles (retes) where 20–40, or sometimes several hundred, small arteries and veins run parallel and intermingled. Obviously, heat exchange must take place in such a structure. The basic temperature relations in a simple countercurrent heat exchange system have been described and verified on a physical model. A striking feature of such a system is the poor conduction of heat and the consequent steep temperature gradient along the line of flow. Temperature measurements in the rete of the sloth revealed gradients sometimes as large as 1 degree/cm, i.e. some 30 times steeper than in a human arm. The gradient immediately decreased when the venous return was reduced, proving the existence of A-V heat transfer. Legs and arms developed steep subcutaneous gradients upon cooling of the body. It took some 4 hours to rewarm a moderately chilled limb to normal temperature. Two other tropical animals (coati and white-faced monkey), without retes, rewarmed their arms after chilling 5 times faster. Hot wire measurements indicated that flow often decreased in the arm rete when a sloth was chilled. At the same time the rete gradient steepened. The sloth is a temperature-sensitive animal which just barely keeps warm in the tropics, and the retes in sloths and other mammals are interpreted as structures which conserve the body heat at the expense of cooling the limbs. Submitted on October 1, 1956