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An attempt was made to develop a tracheal or bronchial stent for nonsurgical implantation using a bronchoscope. Titanium-nickel alloy composed of 50% by weight of each metal has unique thermal shape-memory properties, with a transition temperature of 20 degrees C. Each stent consists of one wire with a diameter of 0.9 mm. It is 30 mm long with a cross-sectional profile resembling a horseshoe. The stent is designed to sustain the airway only at the cartilage rings. Tracheal cartilages of dogs were broken to make a tracheomalasia model, and 10 stents were implanted in 10 animals. The stents were made straight by cooling in liquid nitrogen and then inserted into the region of tracheomalasia. Once in place, they were warmed and recovered their initial shape. The animals were killed between 1 week and 6 months after implantation, and then examined. Nine of the ten stents were located in the implanted area. In one dog, the stent had been displaced into the bifurcation. Microscopic observation showed that the wires were gradually covered with epithelium. At 6 months, 58% were covered with epithelium.

In a retrospective study of 330 animals with total artificial hearts (TAH), 103 (31%) had microbially infected thrombi (MIT). The incidence of MIT approximated 75% in the animals surviving more than 100 days. The most common pathogen isolated from animals with MIT was Pseudomonas. Most thrombi appeared to have originated from valve junctions and connectors. Methods to prevent MIT should be aimed at eliminating thrombus formation by improved design and materials and controlling the route of bacterial colonization. These findings suggest that bacterial interaction with the thrombus, device-related bacterial colonization, host immunomodulation, and gut barrier function after TAH implantation need further study.

To clarify further the extent, pathways, and significance of convective transport during peritoneal dialysis, acute transport studies were conducted in which five continuous ambulatory peritoneal dialysis (CAPD) patients underwent 6 hr dialyses (2 L infusate with 2.25% dextrose) on 2 successive days, with multiple sampling of both blood and peritoneal dialysate. Concentrations of permeants (urea, creatinine, uric acid, beta 2 microglobulin, and apolipoprotein A) and a radiolabeled marker (125I-polyvinyl pyrollidone [PVP]) were determined at 20-30 min intervals in dialysate and every 90 min in plasma. Intraperitoneal volumes and lymphatic flows were calculated from rates of dilution and disappearance of 125I-PVP. Intratreatment lymphatic flow rate averaged 76 +/- 15 ml/hr. Although lower than observed in small animal models and reported by some clinical groups, this level of lymphatic drainage was still sufficient to decrease net patient weight loss by approximately 50% and to resorb approximately 15% of metabolites in the peritoneal cavity, independent of molecular weight. Transcapillary ultrafiltration ranged from 7.4 +/- 1.5 ml/min at 10 min into the exchange to 1.3 +/- 1.5 ml/min at 345 min. Reverse ultrafiltration, from the peritoneal cavity back through capillary vasculature to the patient, was not observed in any patient in this study.

Fifteen patients with acute deterioration of liver function, high serum ammonia, and an average coma level of 3.9 (of 4) were treated for 8-12 hrs daily with a system that uses the membranes of a cellulosic plate dialyzer to pump blood through a single access at 200-225 ml/min, and includes a sorbent suspension as dialysate. Neurologic status of the patients was declining before treatment, but significantly improved during each treatment and over the course of 1-12 (average, 4) treatments. Diastolic blood pressure and pulse rate normalized. For half the patients, treatment with the BioLogic-DT system served as a bridge to liver transplant or liver recovery.

Continuous monitoring of pump performance is essential and effective for optimal driving of a pulsatile blood pump. The authors contrived a practical method for continuous estimation of blood volume in a pump by measurement of electrical impedance (Z). This method was evaluated with the air-driven, diaphragm type pump. The pump was made from polyurethane and had two metal connectors at the inlet and the outlet ports. Z was measured by charging the alternating current (50 kHz, 0.4 mA) between two connectors as electrodes. In in vitro tests, Z reached maximum value during full-empty and minimum value at full-fill. The blood volume calculated by an empirical equation of Z was linearly related to the real blood volume (r = 0.99). In in vivo tests with goats, pump output estimated by this method was linearly related to pump output measured with an electromagnetic flowmeter and effectively evaluated pump performance. For calibration, this method needed only to measure Z at full-fill. This method was useful as a controller of a full-fill to full-empty drive. It was concluded that this method is a practical estimate of pump performance, even if implantable diaphragm type pumps are used, and easily applicable to any kind of pulsatile pump.

Blood flow with an arteriovenous access is limited by the resistance of the catheters and hemofilters or dialyzers in the extracorporeal system. Resistance data from manufacturers are varied as to the test conditions used, however, making it difficult to select optimum components. Furthermore, the same size catheters may have varying inner diameters, resulting in large differences in flow resistance. The pressure at various flow rates was determined using a water manometer. The pressure/flow relationship for catheters gave a curve, whereas the logarithmic function resulted in a straight line with a slope of 1.48. The pressure/flow relationship for hemofilters and dialyzers was a straight line with an intercept close to the origin. The data in the tables for flow resistance at 50 and 100 ml/min can be used to compare the various components, and to estimate flow in a given extracorporeal system.

To clarify the roles of endothelin (ET: vasoconstrictor) and platelet activating factor (PAF: vasodilator) in hemodialysis (HD), intradialytic changes in those substances were compared by a crossover study between HD with regenerated cellulose (RC) and polymethylmethacrylate (PMMA) membranes using currently developed radioimmunoassay methods. Hemodialysis patients demonstrated higher plasma ET values than normal controls, and hypertensive HD cases showed the highest levels. Although ET decreased significantly during the initial stage of HD with both membranes, the decreasing rates were greater in the group with intradialytic hypotension than those in the normotensive group. Plasma PAF did not differ among normal controls, hypertensive HD, and normotensive HD patients. Platelet activating factor tended to increase during HD in both hypotensive and normotensive groups; however, the increasing rates were greater in HD with RC than those with PMMA. These results indicate that the decrease in ET may partially contribute to the initiation of HD induced hypotension. Because PAF is an intracellular mediator, and there is an intradialytic increase in PAF with RC membrane, PAF should be regarded as one of the indices of membrane biocompatibility.

This study was initiated to investigate the use of the Gianturco intravascular stent in prolonging dialysis access graft patency after angioplasty. Stents were placed in 25 patients with follow-up to date of 0.5-8 months. The stent used was 1.5 x 3 cm and consisted of two units connected by a single strut. In Phase 1, the strut was rigid, and the stent had no barbs. The rigidity of the stent and stent migration caused problems. In Phase 2, an articulated strut design was used, and in Phase 3, barbs were added. These modifications solved the previously noted problems. No anticoagulation was used, and clotting was not a significant problem. The duration of patency for the total group was not significantly better than for control groups. However, there were no losses with the modified stent design used in Phases 2 and 3 with follow-up to date of 0.5-5.5 months. Further study of this treatment modality appears warranted.

Ventricular assist devices augment aortic or pulmonary flow while the patient's heart recovers from surgery or infarction. Most are used in the asynchronous full-to-empty mode, but they also may be used in a synchronous counter-pulsation mode. This study examines which assist mode optimally reduces myocardial oxygen consumption (MVO2). Eighteen pigs were instrumented with pulmonary artery, carotid artery, and coronary sinus catheters for determination of MVO2. Pierce-Donachy Ventricular Assist Devices (VAD) were used in left, right, or biventricular assist mode. Fifteen minute periods each of control, synchronous, and asynchronous bypass were randomly instituted. The mid-left anterior descending coronary artery was then ligated, and the sequence repeated. At the end of each period, MVO2 was determined. In comparison with controls, MVO2 was statistically significant in the BIVAD asynchronous mode only. Synchronized counterpulsation did not decrease MVO2. When ventricular assist devices are used to aid in cardiac recovery postoperatively or postmyocardial infarction, biventricular assist should be used.

Fluid velocities were measured with a two-component laser Doppler anemometry system in the regurgitant jet regions of Bjork-Shiley Delrin monostrut tilting disc valves mounted within a Plexiglas model of the 70 cm3 Penn State electric left ventricular assist device. At each measurement location, 250 instantaneous velocity realizations were collected at times when regurgitation through the valves occurred. The maximum Reynolds shear and normal stresses were calculated after filtering the data. Results show that Reynolds shear and normal stresses proximal to the mitral valve were elevated to magnitudes of 9,000 dynes/cm2 and 20,000 dynes/cm2, respectively. The peak Reynolds stresses near the mitral valve occurred during early systole, when regurgitant jet velocities reached magnitudes as high as 440 cm/sec. The Reynolds shear and normal stresses proximal to the aortic valve reached magnitudes of 9,900 dynes/cm2 and 20,500 dynes/cm2, respectively. The peak Reynolds stresses near the aortic valve occurred during early diastole, when regurgitant jet velocities were as high as 280 cm/sec. These high Reynolds stresses created by turbulent regurgitant flow have the potential to cause significant blood damage.