Arterial occlusive disease: a function of vessel bifurcation angle.

A clinical observation that patients with aortoiliac occlusive disease have a high aortic bifurcation serves as the stimulus for this study. A review of 100 consecutive abdominal aortograms revealed that patients with occlusive disease had an average bifurcation angle of 38 degrees and those with normal studies or aneurysmal disease had an average angle of 52 degrees. A flow visualization system was constructed to study shear stress using eight Pyrex models with varying bifurcation angles (20 to 90 degrees). The perfusate consisted of a 35% sucrose solution with anion-exchange beads to serve as flow particles. The bifurcations were photographed at three different flow rates. The length of each tracer particle was measured to determine its velocity. Velocity profile curves were constructed and shear stress calculated by the formula shear stress = mu x dv/dr, where mu is viscosity, v is velocity, and r is radius. Results of the study suggest that more acute angles cause a greater shear stress on the inner wall of the bifurcation and decreased shear stress on the outer wall. Two theories of atheroma predilection, high shear stress and low shear stress, are applied to patients with high acute aortic bifurcations.

Suture resistance to infection.

The emergence of both absorbable and nonabsorbable synthetic materials has been primary among the many new developments in suture materials. This is a study of 16 types of natural and synthetic suture materials and their resistance to both gram-positive and gram-negative infections. Four hundred and twenty suture inplants were made in the Edlich mouse model. The 16 different sutures were compared to appropriate controls and graded by the degree of infectibility. Synthetic sutures were superior in all areas. The monofilament sutures performed better than the multifilament sutures. Lubricating coatings had no effect on infectibility. Natural sutures performed poorly and should not be used in wounds that are potentially susceptible to infection.

Pyrolytic carbon-coated Dacron grafts.

A new pyrolytic carbon surface (ULTI) was tested on a loosely knitted dacron substrate in dogs. Patency was 97.5% as compared with a control of 33%. Physical properties of the dacron were not altered by the ULTI carbon deposition process. This modified pyrolytic carbon on a dacron substrate is a very promising vascular biomaterial for small vessel replacement.

Thrombogenic potential of dacron grafts after prior exposure to whole blood, plasma, or albumin.

On hundred forty six (146) vascular graft insertions have been examined to determine the best exposure media, the mode of exposure, and the time of exposure required to change the TP of knitted dacron fabric. Whole blood, plasma, albumin, and Ringer's lactate (as control) were the media used. The mode of exposure was by either simple soaking or physiological perfusion with the appropriate media. The time of exposure was from one hour to 7 days. Simple soaking in species-specific albumin was found to be highly effective in lowering the TP of knitted dacron and we advocate this as the initial step in preclotting dacron grafts. This step is equally critical in the smaller vascular replacements and should lead to improved patency of these dacron vascular grafts.

Thromboresistance of pyrolytic carbon grafts.

This study reports in vivo testing of ULTI carbon coated dacron grafts in the dog's 4 mm carotid artery, and showed 97.5% patency at 21 days in 40 grafts compared to 33% in 6 control grafts. Physical properties of the dacron substrates were not altered after ULTI carbon deposition. The carbon coated grafts must be carefully cleaned and maintained in that condition. This initial study with the modified pyrolytic carbon adds a new dimension to vascular prosthetics and artificial organ development.