Hollier, Larry H.

Although some previous experiments have demonstrated encouraging early results with venous vascular prosthesis, the long-term results have not been sufficiently investigated. The late thrombogenicity of 12 autogenous vein grafts and eight polytetrafluoroethylene (PTFE) grafts, three of which had been subjected to endothelial seeding, was evaluated 6 months after implantation in the canine venous system by determination of the survival time of the indium-labelled autogenous platelets and of the light and electron microscopic appearance of the graft-to-blood interface. Twelve dogs receiving autogenous vein grafts had a platelet half-life of 64 ± 13 (mean ± s.d.) hours and a completely thrombus-free internal graft surface covered by a smooth endothelium. The platelet half-life in five dogs with non-seeded PTFE grafts was significantly ( P < 0.01) shorter (44 ± 11h). The PTFE-to-blood interface consisted of a 100- to 170-μm-thick pseudointima with a thrombus-free surface area of 25-90% and substantial endothelial coverage in only two animals. Three dogs receiving endothelial-seeded PTFE grafts had a platelet half-life of 38, 46 and 53h, respectively, a 10- to 80-μm-thick pseudointima covered with typical endothelium, and a thrombus-free surface area of 90-100%. Our results demonstrate that PTFE grafts are still thrombogenic at 6 months following implantation in the canine venous system. Therefore, additional measures are required to maintain graft patency. Our limited experience with endothelial seeding does not allow any definite conclusions, but our findings indicate that this procedure might be beneficial.

A low oxygen tension might contribute to the dermatological changes produced by deep venous insufficiency and venous stasis. Since elastic support is often prescribed for stasis disorders, it would be of value to know whether compression alters the oxygen tension in affected skin. We performed studies in which the transcutaneous Po 2 (TcPo 2 ) was determined for the foot or lower leg in subjects with normal veins (n = 9) or with dermatitis caused by documented deep venous insufficiency (n = 14). Measurements were made using O 2 -sensing electrodes placed 1–2 cm apart; surface temperature was 45°C for one electrode (producing maximal vasodilation of the underlying skin) and 42°C for the other (producing submaximal vasodilation). The vasodilation index (VI = TcPo 2 at 42 °C/TcPo 2 at 45°C) was used as an index of vasomotor tone. In normal limbs, TcPo 2 (mmHg) and VI were affected by the subject's posture (TcPo 2 = 38.8 at 42°C and 61.4 at 45°C when supine; 40.8 at 42°C and 74.6 at 45°C when upright with legs dependent; VI = 0.63 supine and 0.53 upright). In limbs with venous stasis, TcPo 2 and VI were considerably lower (TcPo 2 = 23.6 at 42°C and 51.5 at 45°C when supine; 20.8 at 42°C and 60.5 at 45°C when upright; VI = 0.48 supine and 0.37 upright). Following the application of an elastic wrap to the limbs with stasis, upright values for TcPo 2 and VI were substantially improved (TcPo 2 with compression = 28.8 at 42°C and 62.4 at 45°C; VI = 0.46). We conclude that (1) TcPo 2 is reduced in regions of skin affected by stasis dermatitis, and (2) elastic compression improves TcPo 2 (during upright posture) in limbs with stasis dermatitis.

The authors evaluated the relationship between sympathetic nerve activity and transcutaneous oxygen tension (TcpO 2 ) in normal and ischemic lower extremities. Dorsal foot TcpO 2 was measured by using oxygen-sensing electrodes with surface temperatures of 42 ° C and 45°C; in theory, changes in sympathetic activity should affect vasomotor tone and TcpO 2 in skin beneath an electrode at 42 °C (submaximal vasodilation), but not at 45°C (maximal vasodilation). The vasodilation index (TcpO 2 at 42°C/TcpO 2 at 45°C) was created as an index of vasomotor tone (vasodilation index increases as tone decreases). In normal limbs (n=24) averages for TcpO 2 at 42°C, TcpO 2 at 45°C, and vasodilation index were 30.3 mmHg, 62.1 mmHg, and 0.47, respectively. In subjects (n=5) with quadriplegia and reduced sympathetic tone secondary to cervical cord trauma, TcpO 2 at 42 ° C and vasodilation index were increased (45.0 mmHg and 0.61); TcpO 2 at 45 ° C did not change. When normal subjects (n=7) were chilled for twenty minutes with a cooling blanket at 5 ° C (to increase sympathetic tone) average vasodilation index dropped from 0.50 to 0.29. Among ischemic limbs (n = 34) vasodilation index was highly variable (range: 0-0.77); in general, vasodilation index fell as the ischemia worsened. In a subset of patients with ischemic limbs, the vasodilation index increased after the limb was wrapped in a warm dressing (average vasodilation index=0.25without dressing, 0.37 with dressing). The authors conclude: (1) TcpO 2 can be used to assess the degree of vasomotor tone (and sympathetic activity) in skin; (2) tone generally increases as ischemia worsens; and (3) local warmth can improve cutaneous circulation in ischemic limbs.