Biomedical subjects

N Ramasamy

Publications and source records attributed to N Ramasamy.

21 records · Page 2Linked to original sources

PubMedDate not supplied

In vitro and in vivo testing of a totally implantable left ventricular assist system.

The totally implantable Novacor LVAS is being tested under NIH auspices to demonstrate safety and efficacy before clinical trials. Twelve complete systems (submerged in saline at 37 degrees C) are being tested, with an NIH goal of demonstrating 80% reliability for 2 year operation with a 60% confidence level. The systems, which are continuously monitored, are diurnally cycled between two output levels by automatically varying preload and afterload. Currently, 14.3 years of failure-free operation have been accumulated, with a mean duration of 14 months. Using an exponential failure distribution model, the mean time to failure (MTTF) is greater than 8.8 years, corresponding to a demonstrated reliability (for a 2 year mission time) of 80% (80% confidence level). Recent ovine experiments with VAS subsystems include a 767 day volume compensator implant, a 279 day pump/drive unit implant and a 1,448 day BST implant. The last 12 chronic pump/drive unit experiments had a mean duration of 153 days (excluding early postoperative complications). This compares favorably with the NIH goals for complete systems (5 month mean duration). Complete system experiments are currently underway.

Animals↗

PubMedDate not supplied

Bioprosthetic valve calcification and pseudoneointimal proliferation in bovine and ovine models.

Both porcine (PX) and bovine pericardial (BP) valves have been used in the implantable Novacor left ventricular assist system (LVAS). Results from 58 chronic LVAS implants of greater than 7 days in calves and adult sheep are presented: the PX valve was used in 41 and the BP in 17. With PX valves, the maximum and mean assist durations were 161 and 54 days, respectively, in the calf and 279 and 129 days, respectively, in the sheep. The maximum and mean durations for BP valves were 93 and 38 days (calf) and 153 and 69 days (sheep). In bovine studies with PX valves, severe obstructive pseudoneointimal (PNI) proliferation in the Dacron inflow conduit was the primary cause for termination; valves exhibited moderate calcification. With BP valves, both PNI proliferation and severe valve calcification contributed to a declining pump output, leading to termination. In contrast to the bovine experience, PNI proliferation was not observed in ovine implants. BP valves still became calcified, as evidenced by a progressive decline in pump output (from about twelve weeks) and confirmed at termination. Valve calcification was minimal with the PX valves, even at 236 days. These results favor the adult ovine animal model for extended implants.

Animals↗

PubMedDate not supplied

Evaluation of an implantable ventricular assist system for humans with chronic refractory heart failure. Device explant protocol.

An explant protocol was developed to investigate the effects of implantation of a left ventricular assist system (LVAS) manufactured by Novacor Division, Baxter Healthcare Corporation on the function of end organs (such as the brain, the kidney, the liver), with particular interest in examining possible complications due to LVAS support. Emphasis was placed on an analysis at the time of device removal and/or autopsy of 1) the local LVAS-host interface; 2) remote cardiovascular and end-organ effects; and 3) the impact of chronic circulatory support on the native heart. To accomplish these objectives, tissue and device samples must be obtained in an appropriate fashion to ensure photographic documentation, microscopic examination, microbiologic and biochemical assays, and compliance with regulatory and manufacturer requirements. This article describes the techniques and protocol that were proposed to ensure the quality of device explant and tissue analysis.

Autopsy↗