Abstracts: ASAIO Bioengineering/tissue Engineering Abstracts
WATER HAMMER EFFECT ON AN ACCELERATED TESTING MECHANICAL HEART VALVE
The US FDA Replacement Heart Valve Guidance requires artificial heart valve accelerated fatigue tests to have a mean transvalvular pressure of 100 mmHg. Loading forces increase non-linearly with the test rate due to the water hammer effect during the backflow of sudden valve closure.
A 27 mm Medtronic Hall mitral valve placed in a circulatory mock loop was evaluated under physiological conditions for loading force via piezoelectric force measurement ring, compressive wave via SPC 340 Millar catheter, and backflow rate via electromagnetic flowmeter. The results served as references for the same measurements later performed in a single chamber accelerated test system.
Peaks in backflow rate, compressive wave, and loading forces occurred at the instant of valve closure within both test systems. The maximum values rose from 9.7 to 21.3 L/min, 279 to 848 mmHg, and 38 to 102 N, respectively, when the accelerated test rate increased from 70 to 840 bpm. The increase in loading forces far exceeds physiologic range, meaning that accelerated conditions cause additional valve damage. The correlation coefficient between loading force and backflow rate was 0.99, while the loading force is approximately valve orifice area multiplied by twice the peak pressure value. Loading forces can be adjusted by controlling the backflow, making it a suitable parameter during accelerated fatigue testing.Copyright © 2005 by the American Society for Artificial Internal Organs