Chen Jf

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.

Initial in vivo tests of an electrohydraulic actuated total artificial heart

The authors are involved in developing a total artificial heart (TAH) for permanent human use. This device was designed to fit human anatomy, and it has housings made of carbon fiber-epoxy composite and titanium. Tissue valves and protein coating of blood contacting surfaces minimize the need for anticoagulants. A continuously reciprocating electrohydraulic actuator is packaged between two alternately ejecting and passively filling ventricles. The control system varies the pump rate to maintain average left ventricular filling at 90%. This TAH in vivo successively progressed through 1, 5, 9, and 45 day implants in calves of 84, 94, 82, and 82 kg preoperative body weights. The operating modes include automatic and fixed rate. The chronic and acute effects of varying the right pump displaced stroke volume indicated the need for it to be limited to 85% of that of the left for stable hemodynamics at maximum flow. The pump exhibited afterload insensitive and preload sensitive performance. Pump output ranged from 4.0-9.5 L/min at left atrial pressures of 7-16 mmHg at pump rates of 80-160 beats/min in these four experiments. These data suggest that this device will meet clinical hemodynamic requirements; it has the potential for total implantable cardiac replacement.

A biolized implantable ventricular assist device compatible with IABP console.

A low pressure pneumatic pusher plate blood pump was developed for temporary right, left, or biventricular assist. Important features of this pump are its 1) driveability by the standard, easily available intraaortic balloon pump (IABP) console; 2) gelatin coated internal surface for blood compatibility; 3) essentially flat disc shape, 3 cm thick and 11 cm in diameter, for optimal anatomic fit; and 4) unique pusher plate guide mechanism to ensure linear motion without deflections of the diaphragm, and consequent uniform flow distribution into the pump. The guide telescopes into itself to avoid a housing protrusion for easy implantability; this controlled movement also provides a number of performance, control, and diagnostic benefits. The pumps 60 ml displacement gives up to 4.7 L/min at 80 bpm and 6.7 L/min at 120 bpm outputs in a mock loop. This VAD has been implanted in two calves for 43 to 84 days, continuously driven by a Datascope IABP console. An average 5 L/min pump output has been observed in both synchronous and fixed rate modes. No anticoagulation was required. We expect extensive clinical use of this VAD, based on its reliability, low cost, and simplicity.