To investigate the effects of gaps between the wire pitches of a shape memory Nitinol alloy intravascular endoprosthesis (IVEP), 42 stents with and without gaps were implanted transluminally into the infrarenal abdominal aortae of 11 normal and 10 atherosclerotic rabbits. Digital subtraction angiography was done every 4 weeks to examine the restenosis rate and major side branch patency. Restenosis rates within IVEPs with gaps were significantly lower than in stents without gaps in both normal and atherosclerotic rabbits. The side branch patency rate was significantly higher with IVEPs having gaps. These results suggest that the placement of gaps between wire pitches reduced the restenosis rate within IVEPs, and prevented the obstruction of major side branches.

Angioplasty, Balloon↗

PubMedDate not supplied

Study of heat dissipation to the lung from a thermal ventricular assist system.

The thermally powered left ventricular assist system (LVAS) requires that heat be dissipated to surrounding lung tissue and blood. This acute study was conducted in three anesthetized calves (weighing 84.3 +/- 14.3 kg) to evaluate the mechanisms involved in the dissipation of heat to the lung tissue. The heaters were placed in contact with the left lung surface and skeletal muscle tissue. Compared to the muscle tissue, heat flux to the lung was approximately three times higher for the same surface temperatures. For a constant heat flux, lung interface temperature tended to vary inversely with the cardiac output and ventilatory flow. This preliminary study demonstrated that the level of heat generated by the thermal LVAS can be effectively dissipated to the lung, with the convection mechanisms of airflow and blood flow playing a major role.

Animals↗

PubMedDate not supplied

Methods for volume assessment of an air filled compliance chamber.

The air-filled (120 ml) compliance chamber employs a Dacron covered Hexsyn-butyl bilaminar diaphragm to minimize gas diffusion. Finite permeability dictates the need for a means to detect the remaining air volume and a refill port for gas addition. X-ray studies were used to detect radiopaque chamber markers in cadavers. Tangential X-ray cinematography enabled detection of chamber volumes less than 100 ml and diaphragm center deflection predicted volume to within +/- 6 ml of the actual volume. An electrically driven left ventricular assist pump (90 cc) was used to evaluate motor current (MC) and intracompliance pressure (IP) as indicators of low compliance volume. Peak MC was a function of both hemodynamic output power and compliance volume. Thus, if the peak current for a given hemodynamic output is known, variances may be indicative of low compliance volumes. The cyclic minimum IP vs. volume was +1, -3, and -13 mmHg for compliance volumes of 120, 90, and 80 cc, respectively. Ejection velocity did not significantly affect IP. In conclusion, X-ray studies and MC are useful as noninvasive means of assessing the need for compliance refill. IP, though measured invasively, is the most sensitive volume-dependent parameter.

Cineradiography↗

PubMedDate not supplied

Compliance effect on patency of small diameter vascular grafts.

The compliance mismatch hypothesis as a cause of failure of small diameter grafts was investigated using 4 mm internal diameter, 5 cm long Biolized polyurethane grafts. The luminal surface of 0.5 mm thick Biomer sponge grafts was covered with 100 microns of crosslinked gelatin. Compliance matched, and noncompliant grafts had in vivo compliance values of 13.5 +/- 2.89 and 1.0 +/- 0.7 X 10(-2%) per mmHg, respectively. In vivo compliance defined as 2 X dD/dP X 1/Do was measured in situ using the ultrasonic Hokanson probe. Compliance values of compliant grafts equaled that of the canine carotid artery at 100 mmHg mean arterial pressure. Grafts were implanted using an end-to-end anastomosis in 14 dogs for 6 wk. Patency rates for compliant vs. noncompliant grafts were 64% (9/14) and 50% (7/14). Compliance values for compliant grafts decreased to a mean of 7.14 X 10(-2%) per mmHg. Anastomotic intimal hyperplasia at the proximal and distal ends of compliant and noncompliant grafts measured 239.9 +/- 128, 197 +/- 129 microns, 338.9 +/- 273.6, and 304.3 +/- 179.3 microns, respectively. There were no significant differences in localized anastomotic intimal hyperplasia at either graft end for either graft type. This study did not show any positive effects of graft compliance.

Anastomosis, Surgical↗

PubMedDate not supplied

An intrathoracic left ventricular assist system: utilization of results from a development program.

An intrathoracic, electrohydraulically actuated, left ventricular assist system (LVAS) was subjected to formal device readiness testing. Endurance testing was initiated on eight systems before testing was halted due to failure of four of the systems. Three failed due to environmental leakage. Solutions were straightforward, involving gasket changes and o-ring resizing. The fourth failure involved a magnetic coupling piston swelling and seizing. The failure was attributed, after long investigation, to hydrogen adsorption by the samarium-cobalt magnets. An unknown number of coupling magnets were affected in this fashion, necessitating complete replacement of magnets to resolve the problem. However, this was beyond the scope of the program, and no further endurance testing was accomplished. The test experience of the Nimbus/CCF LVAS has demonstrated all functional aspects of the complete LVAS, both in vitro and in vivo, and the endurance and reliability potential is indicated as well. Although the LVAS program is currently inactive, its legacy of technical innovations continue to drive the development of other medical devices.

Animals↗

PubMedDate not supplied

Systemic and local effects of heat dissipation in the thermally powered LVAS.

A thermally powered left ventricular assist system (LVAS) requires 20 W of heat dissipation either to the blood or to the surrounding tissues, such as the lung subcutaneous tissues. Postoperative systemic and local effects of heat dissipation were studied in 5 thermally powered LVASs and 2 heated blood pumps implanted in calves, and compared with 10 pneumatically powered left ventricular assist devices (LVADs). Postoperative mean temperatures of the heat dissipation group were as follows: 1. rectal (RT), 39.1 x 0.4 degrees C (NS versus control); 2. Lung interface, 41.6 +/- 0.6 degrees C (P less than 0.01 versus RT); 3. tissue interface, 40.2 +/- 1.2 degrees C (P less than 0.01 versus RT); and 4. blood, 39.2 +/- 0.8 degrees C (NS versus RT). There was no significant postoperative change in heart rate, respiratory rate, or rectal temperature between the two groups. No difference was shown between the two groups in hematologic parameters, plasma free hemoglobin, liver and renal function, fibrinogen levels, or coagulation processes at the same postoperative time. Heat dissipation to the pump-blood interface promoted a thinner neointima when compared with the nonheated surface. Angioneogenesis was observed in the tissue capsule adjacent to the heat dissipating surface. These results indicated that the thermal LVAS induced no deleterious local or systemic effects on recipient animals.

Air↗