Frequency response of implantable blood pressure telemetry systems

1. Measurement of blood pressure via telemetry in a variety of animal species has become an indispensable part of cardiovascular physiology, drug development and safety pharmacology. 2. These telemetry systems use fluid-filled catheters, which differ from commonly encountered indwelling catheters by virtue of their short length, high durometer, variable inner diameter and the use of a gel interface at the distal tip. 3. Despite the widespread use of blood pressure telemetry, there is little information describing the frequency response of these systems. The frequency response is of importance because it determines how well the waveform dynamics, such as pulse pressure, are captured. 4. For this reason, we measured the frequency responses of commonly used telemeters manufactured by Data Sciences International (St Paul, MN, USA; namely PA-C10, PA-C40 and PA-D70) and Telemetry Research (TR43P). The mean (+/- SEM) -3 dB frequencies measured for the PA-C10, PA-C40, PA-D70 and TR43P telemeters were 57 +/- 2 Hz, 40 +/- 6 Hz, 32 +/- 2 Hz and 173 +/- 3 Hz, respectively. 5. Simulation of the devices' dynamic performance by applying their frequency responses to a high-fidelity recording of arterial pressure demonstrated that the devices have sufficient bandwidth to accurately record arterial waveform dynamics. Experiments were also performed to determine how routine laboratory use and maintenance of the catheter affects the frequency response of the telemeters. Provided no air bubbles were introduced, these showed that the telemeters' frequency responses were robust to the maintenance procedures of tip removal and gel application. 6. The frequency response measurements, combined with simulation results, demonstrate that the systems tested have adequate dynamic performance to record arterial pressure.