Abstract
The durability test for a newly developing axial-flow ventricular assist device (VAD) with hydrodynamic bearings was conducted under pulsatile flow condition for six months to obtain a long-term reliability. A mock circulation was consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance and simple-layout flow paths that were made of polymer or titanium. The VAD was installed behind the diaphragm pump submerged in saline solution. A blood analog fluid was saline added with glycerin whose viscosity coincided with that of blood at the temperature of 37 ℃. The pulsatile flow condition was set within the flow rate range to realize positive flow rate and positive head at the impeller rotational speed obtaining the flow rate of 5 L/min and the pressure of 100 mmHg. The pump characteristics were monitored for flow rate, pressure head, impeller rotational speed, and so on. The mock circulation characteristics were maintained for fluid temperature, fluid density and pulse rate of the diaphragm pump, and so on. The mock circulation realized the pulsatile flow rate to achieve 0±1 L/min at the systolic phase, 9.5±1 L/min at the diastolic phase and 5±1 L/min in average at the pulse rate of 72 bpm. The durability tests were conducted for eight axial-flow VADs. For six months, the experimental conditions have been maintained that were the average flow rate of 4.4 (± 0.2) ± 0.05 (± 0.04) L/min, the diastic flow rate of 0.1 (± 0.1) ± 0.1 (± 0.1) L/min, the systolic flow rate of 10.9 (± 0.2) ± 0.1 (± 0.03) L/min, the average head of 80 (± 3) ± 2 (± 2) mmHg, the pulse rate of 72.1 (± 0.3) ± 0.2 (± 0.1) bpm, the fluid temparature of 37.2 (± 0.2) ± 0.2(± 0.1)℃, the fluid viscosity of 3.2(±0.1)±0.3(±0.1) cP, in which the value in the bracket means individual device differences. The metal components were hardly detected in the working fluids. The long-term durability of the developing axial-flow VAD for six months was confirmed.
