Analysis of subcutaneous fluid in rats.

Subcutaneous implantation in rats is a commonly used model for biomaterial calcification studies. Although this model is frequently used, its components have not been characterized with respect to calcification. Exudate from the subcutaneous spaces of 18 young rats was collected using diffusion chambers. These chambers consisted of polymethylmethacrylate tubes with 0.22 micron pore filters covering each end allowing fluid, but not cells, to enter the chambers. Glutaraldehyde treated bovine pericardial strips were implanted subcutaneously, inside the chambers and outside the chambers, to test the calcification inducing abilities of the various environments. The animals were killed on postoperative day 10, and the exudate and materials were collected. The exudate was analyzed for ionic calcium, total calcium, inorganic phosphorus, and albumin, and for cells by a differentiated cell smear. The materials were analyzed for calcification by radiography, histology, and atomic absorption. Calcification was present in the materials inside the chambers where no cells were present and in the materials that were not in chambers. The distinct features of the exudate were elevated ionic calcium, a high Ca x P product, and elevated phosphorus.

Heat from an implanted power source is mainly dissipated by blood perfusion.

Heat dissipation and its effects on tissue and blood interfaces are common problems associated with the development and increased use of artificial hearts, because all of the implantable actuators for artificial hearts generate waste heat due to inefficiencies of energy conversion. To determine the mechanisms of heat dissipation from artificial hearts, heated disks producing constant heat fluxes of 0.08 watts/cm2 were implanted adjacent to the left lung and the latissimus dorsi muscle in calves for 2 weeks, 4 weeks, and 7 weeks. At the end of each experiment, a series of acute studies was performed in which blood perfusion to the heated tissue was decreased or stopped to observe the contribution of blood perfusion to heat dissipation. The cooling effect of ventilation was also examined to determine its relative contribution to heat dissipation in lung tissue by decreasing the minute ventilation volume. The importance of blood perfusion for heat dissipation was demonstrated by the temperature rise after cessation of blood perfusion to the heated tissue. The contribution of ventilation to heat dissipation in the heated lung tissue was minimal. Contribution of total blood perfusion to heat dissipation was increased with time in the muscle tissue, which has relatively low resting blood perfusion, but not in the lung tissue, which has relatively high blood perfusion. In the heated muscle tissue, the in vivo adaptive response to chronic heat was functionally shown by the increased perfusion. In conclusion, blood perfusion was the main mechanism of heat dissipation from tissues that were adjacent to an implanted power source.

Platelets are deposited early post-operatively on the leaflet of a mechanical heart valve in sheep without post-operative anticoagulants or antiplatelet agents. A scanning electron microscopic observation of the pyrolytic carbon surface in a mechanical heart valve.

Pyrolytic carbon has been used for mechanical heart valves as a thromboresistant, wear resistant, and fatigue resistant material. Thrombosis and thromboembolism, however, remain major mechanical heart valve associated complications and may frequently occur during the early post-operative period. In depth morphologic studies on blood-pyrolytic carbon surface interactions are limited. The purpose of this study was to evaluate the blood compatibility of the pyrolytic carbon surface of St. Jude Medical mechanical heart valves that were implanted in the mitral position of sheep without the administration of post-operative anticoagulants or antiplatelet agents for 2, 4, and 6 weeks. Almost the entire leaflet and orifice ring surfaces were observed by scanning electron microscopy. Although the surfaces appeared clean macroscopically, when observed by electron microscopy, the surface were mottled, mainly by solitary platelets and aggregations. There were only a few leukocytes or red blood cells observed. No fibrin clots were observed on the leaflets. The density of platelet deposition was higher in the vicinity of the pivots and near the edges of the leaflets. The sizes of the platelet aggregations decreased with longer duration. The outer surfaces of the pivot guards were covered by various amounts of deposition composed of platelet aggregations and thrombi. Thus, the administration of antiplatelet agents is recommended during the early post-operative period after mechanical heart valve implantation.

Assessment of circulating blood volume in calves with a total artificial heart.

Measurement of the circulating blood volume (CBV) is essential to a proper understanding of the hemodynamic performance of total artificial hearts (TAHs). Recently, the authors employed CBV measurements using indocyanine green dye in calves with a TAH. The advantages of this method over previous methods using radionuclides include simplicity, low cost, and the capability of repeated and frequent measurements. Reproducibility of the measurements was demonstrated in three normal calves with a relative standard deviation of 3.9 +/- 2.4%. CBV was measured in eight calves with the Cleveland Clinic-Nimbus TAH and compared with that of seven calves that underwent mitral valve replacement. Small standard deviations in pre operative values in both TAH and mitral valve replacement groups demonstrated the precision of CBV measurements. Although there was no change in CBV in the mitral valve replacement group, CBV in the TAH group increased to more than twice the pre operative value after 2 weeks. Although the right atrial pressure increased similarly after TAH implantation, there was no correlation (r = 0.08) between the right atrial pressure and CBV, which suggested a possible inaccuracy in estimating CBV from the right atrial pressure. A negative correlation between the hematocrit value and CBV suggested that hemodilution might be one of the causes of anemia observed in our TAH animals.

Quantification of the edge effect in calcified bioprosthetic tissues.

In bioprosthetic tissue samples that had been implanted in the subcutaneous space of rats, and recurring pattern of calcification was observed. In this pattern, which we call the edge effect, the interior of the tissue is calcified and is surrounded and separated from the subcutaneous fluid by a zone that is free from calcification. The edge effect has been qualitatively described in the literature for subcutaneous implants and for valve leaflets, and it may be related to the mechanism of calcification for these materials. The thickness of the calcification free outer layer was quantified for glutaraldehyde treated bovine pericardium, glycerol treated bovine pericardium, glutaraldehyde treated human dura mater, and glycerol treated human dura mater. The edge effect values were found to be unique and consistent for each material type, and they were inversely related to the shrinkage temperatures and the calcium contents of the materials. It was determined that the chemical treatment was more important than the tissue type in determining the edge effect value.