Life support systems : the journal of the European Society for Artificial Organs最新文献

Textile polymers have been used for the manufacture of synthetic arterial prostheses. The extreme rigidity of these polymers has severely limited the nature of the structures that could be fabricated, so that the mechanical properties and structural form of the prostheses bear little resemblance to those of natural arteries. The variety of chemical structures, of mechanical properties and of means of fabrication make it possible to produce a compliant flexible prosthesis having a more delicate structure, thereby acquiring better tissue and blood compatibility and good long-term durability. These, and an acceptable form that encourages good surgical practice, account for the good performance of the prosthesis. By way of illustration, an electrostatically spun microfibrous arterial prosthesis of small diameter is described. It is made of a polyether-urethane urea (Biomer). We report good two-year patency for arterial prostheses of our design used to replace the common carotid artery in dogs.

Polyurethanes have become the most valuable implantable elastomers for uses requiring toughness, durability, biocompatibility and biostability. They are inherently stable in the body environment. However, physical and chemical changes may be effected by conditions of processing, fabrication, use or interactions with other device components. Most prominent modes of polyurethane degradation include mineralization, environmental stress-cracking and oxidation. While the mechanisms of these forms of degradation are not fully understood, an awareness of their causes and effects can lead to procedures that provide all of the long-term functionality required for the sophisticated polyurethane-based devices of today and tomorrow.

Laminar flow is the condition best suited to the study of platelet thrombi. This type of thrombus is predominant in arteries, in the tubes of cannulas used in artificial circulatory systems, in cardiac valve prostheses and in prosthetic arterial implants. Antiplatelet drugs could, in these cases, reduce the extent of thrombus formation. At present the optimal dose of acetylsalicylic acid (ASA) to achieve the best antithrombotic effect is unknown; some papers show that high doses augment experimental thrombosis. By means of autologous platelets labelled with 111In-oxine, we have quantified the accumulation on different materials used in cardiovascular surgery (woven, knitted and double velour Dacron, Avcothane 51 elastomere and smooth surface and rough surface pericardium). Samples of these fabrics were placed in a laminar flow chamber connected between the right atrium and femoral artery of the experimental animals (dogs). The animals were divided into four groups of eight dogs: Group I: no treatment Group II: animals treated one week earlier with ASA (1 mg/kg/day) Group III: as in Group II, but at a dose of 5 mg/kg/day Group IV: as in Group II, but at a dose of 20 mg/kg/day. The materials upon which the least amount of platelets were accumulated were the smooth, epicardial surface of pericardium (SP) and Avcothane (AV). The least deposition was produced in Group III, with the exception of SP. In the case of this material, there was no difference between Groups I and III. In Group IV, the deposit was greater with respect to the untreated group (Group I), except in the case of AV, in which there was no difference between Groups I and IV.

The dependence of the leaflet motion of bioprosthetic heart valves on the viscosity of the blood analogue fluid was studied in this work. A pericardial and a porcine tissue valve were mounted in a pulse duplicator and high-speed films were taken to record the motion of the valve leaflets. The blood analogue fluids used were physiological saline with a viscosity coefficient of 1.0 cP, and glycerol solution with a viscosity of 3.5 cP. The transvalvular pressure drop and percentage of regurgitation were also measured with the time-averaged flow rate maintained at 6.00 +/- 0.05 litres/min. Our results show that the leaflets did not stiffen with up to 15 days' exposure to glycerol. Also, there was no substantial difference in the time of opening of the leaflets or in the area of opening of the valves with the two blood analogue fluids. However, the leaflets closed substantially later in the cardiac cycle in the case of glycerol solution, owing to the interaction between the leaflets and the viscosity of the fluid. For proper comparison of the flow dynamics past prosthetic valves at comparable Reynolds number and Womersley number, our results suggest that glycerol solution should be used as the blood analogue fluid for tissue valves also.

A porous hydroxyapatite tracheal prosthesis was implanted in rabbits after resection of a 15 mm circular segment of the cervical trachea. Postoperatively the animals were followed by radiography, bronchoscopy, and microscopy at the time of autopsy. The longest survival time was 22 weeks. All the rabbits died of infection at the prosthetic site or of progressive stenosis at the anastomoses. The prosthesis was incorporated by surrounding tissues, but no overgrowth of ciliated epithelium on the luminal surface of the prosthesis was observed. Although a hydroxyapatite tracheal prosthesis is tolerated in rabbits, covering of the luminal surface of the prosthesis with a non-porous layer to prevent infection and to permit mucosal overgrowth is necessary to achieve better long-term results.

The calculation of the effective sodium gradient in dialysis has to consider a membrane potential difference which is generally derived from the Donnan effect. Strictly this is allowed only under equilibrium conditions. This paper considered the effect of the deviation from equilibrium in haemodialysis and haemofiltration. The mathematical analysis is based on the integration of the local transport rate over the membrane area. The local transport rate is calculated from the Nernst-Planck equation using the constant field assumption. Deviation from equilibrium results in a diffusion potential across the membrane. Experimental evidence was presented for part of the theoretical results. The diffusion potential, both in haemodialysis and in haemofiltration, is too small to have any clinical significance. From the theory it follows that better tolerance of haemofiltration in comparison with haemodialysis cannot be explained by a difference in sodium transport. Calculation of the sodium transport in dialysis therapy based on the equilibrium Donnan effect is sufficiently accurate for kinetic considerations in the dialysis routine.