Determination of the force necessary for the propagation of tears in ostrich and calf pericardium.

The durability of prosthetic heart valve leaflets made of biological materials is limited. A tear in the biomaterial accelerates their early failure, but microtearing of the collagen fibers may be responsible for their medium-term failure. We studied the force necessary to propagate tearing in two biomaterials: ostrich and calf pericardium. One hundred twenty samples of each tissue were tested in an Elmendorf pendulum capable of measuring the force required to tear a tissue in which a predefined slit had been made. The forces required to produce tears, ranging between 2.5 and 0.25 cm in length, were determined. For ostrich pericardium, this force ranged between 67.67 and 4.80 newton, while that required to tear the same lengths of calf pericardium ranged between 70.67 and 4.70 newton. The function that relates the tearing force to the length of the tear was expressed as follows: y = 20.62x + 1.77x(2) (R(2) = 0.923) for ostrich pericardium and y = 45.57x - 7.21x(2) (R(2) = 0.936) for calf pericardium, where y is the force in newton and x is the length in centimeter. Calf pericardium was found to have a greater resistance to tearing. However, these results should be interpreted with caution owing to the fact that the thickness of the majority of the samples of ostrich pericardium was significantly less than that of calf pericardium. A more careful selection and utilization of adult ostrich pericardium would probably improve these results.

Resistance to tearing of calf and ostrich pericardium: Influence of the type of suture material and the direction of the suture line.

The tearing of the valve leaflet of a cardiac bioprosthesis can cause early failure of this device, which is employed to replace a diseased native valve. This report involves the study of the behavior of 312 tissue samples (152 of calf pericardium and 160 of ostrich pericardium) treated with glutaraldehyde and subsequently subjected to tear testing. The samples were cut in the two principal directions: longitudinally, or root to apex, and transversely. They included a series of control samples that were left unsutured, and the remaining samples were repaired with the use of two different suture techniques: a running suture in the direction of the load and a telescoping suture perpendicular to the load. Four commercially available suture materials were employed: Pronova, nylon, Gore-Tex, or silk. The unsutured control samples of both types of pericardium exhibited a similar anisotropic behavior in the tear test. The mean resistance to tearing of the calf pericardium was 24.29 kN m in samples cut longitudinally and 34.78 kN m in those cut transversely (p =.03); the values were 28.08 kN m and 37.12 kN m (p =.002), respectively, in ostrich pericardium. The series repaired with the telescoping suture always exhibited greater resistance to tearing, with values that ranged between 44.34 and 64.27 kN for the samples of calf pericardium and from 41.65 to 47.65 kN for those obtained from ostrich. These assays confirm the anisotropic behavior of calf and ostrich pericardium treated with glutaraldehyde when subjected to tear testing, as well as the loss of this behavior in ostrich pericardium after suturing. Suturing techniques, such as the telescoping model, that provide a greater resistance to tearing should be studied for use in the design of the valve leaflets of cardiac bioprostheses made of biological materials.

Antioxidant effect of gamma-tocopherol supplied by propofol preparations (Diprivan) during ischemia-reperfusion in experimental lung transplantation.

Free radicals are involved in ischemia-reperfusion injury and inflammatory processes. The commercial formulation of the anesthetic propofol contains gamma-tocopherol and delta-tocopherol, which may exert antioxidant effects during transplantation. Animals were randomly assigned to a control group or experimental groups for lung transplantation after 3 and 24 h of ischemia. Individual tocopherols, malondialdehyde, biochemical indices, and hemodynamic, blood gas, and ventilatory parameters were determined during reperfusion. Results showed that administration of commercially available propofol provoked a time- and dose-dependent increment in serum gamma-tocopherol and delta-tocopherol in control animals and in the group receiving lungs subjected to 3 h of ischemia, but not in the group with 24 h of ischemia. Malondialdehyde levels increased during reperfusion and did not differ significantly between the two experimental groups, which did not differ with respect to lung function either. gamma-Tocopherol, supplied by the anesthetic, may act as an antioxidant that is consumed during reperfusion. This potential effect could be relevant to the choice of anesthetic agents in situations where free radical damage to tissues is expected.