A hermetically sealed cardiac dimension transducer for long-term animal implantation.

Pulse transit sonomicrometry is a well-accepted method for assessing cardiac dimensions and function in research animals. Unfortunately, this technique has been hampered in chronic applications by a significant incidence of transducer failure secondary to leakage of corrosive biological fluids into the piezoelectric material. The fluid leakage generally occurred at the interface between the encapsulating epoxy and the bioelectric cable and resulted in progressive functional deterioration with time. In this paper, a new hemispheric ultrasonic dimension transducer is described with a mechanical hermetic seal at the bioelectric cable-transducer interface. The hermetically sealed transducers withstood 400 psi compressed air without leakage, while conventional transducers routinely leaked at 60 psi. The performance characteristics of the new transducers were similar to those previously reported with omnidirectional designs, and no failures have occurred during 3 yr of experience with repeated transducer implantations.