A bio-telemetric device for measurement of left ventricular pressure–volume loops using the admittance technique in conscious, ambulatory rats

Abstract

This paper presents the design, construction and testing of a device to measure pressure volume loops in the left ventricle of conscious, ambulatory rats. Pressure is measured with a standard sensor, but volume is derived from data collected from a tetrapolar electrode catheter using a novel admittance technique. There are two main advantages of the admittance technique to measure volume. First, the contribution from the adjacent muscle can be instantaneously removed. Second, the admittance technique incorporates the nonlinear relationship between the electric field generated by the catheter and the blood volume. A low power instrument weighing 27 g was designed, which takes pressure-volume loops every 2 minutes and runs for 24 hours. Pressure-volume data are transmitted wirelessly to a base station. The device was first validated in thirteen rats with an acute preparation with 2-D echocardiography used to measure true volume. From an accuracy standpoint, the admittance technique is superior to both the conductance technique calibrated with hypertonic saline injections, and calibrated with cuvettes. The device was then tested in six rats with a 24-hour chronic preparation. Stability of the animal preparation and careful calibration are important factors affecting the success of the device.

Miniature implantable telemetry system for pressure-volume cardiac monitoring

“…In Loeffler's work, she decreased the transmission power and increased the weight compared to [24], however, her implementation was tested in large rats. As with [24] and unlike Raghavan [23], Loeffler's device operated in the 915 MHz band.…”

“…In order to generate accurate PV loops it is essential to measure both pressure and volume data at the same time, thus a dual sensor approach is required. Limited research has been completed on implantable PV telemetry systems in literature, where only four systems have been developed [23][24][25]90], a detailed review of these systems along with other relevant works is provided in the following chapter. These devices are all limited by their size, weight, power consumption, and battery life to be implanted for long periods of time.…”

“…ronment and may affect the measurement results [23]. The solution to this would be to create a wireless implantable system similar to implantable pressure systems described in the previous section but incorporate blood volume sensors as well.…”

“…Raghavan [23] improved this initial research by designing an admittance based telemetry system using analog circuit techniques, and a printed circuit board (PCB) whose size and weight are 17.67 cm 2 and 27 g, respectively, Fig. 2.19.…”

“…Although, improved over [90], there are still drawbacks and areas of improvement. This device was tested in large rats [23] and the size and weight of More recently, Loeffler et al [25,26] designed an admittance based telemetry system with a volume of 5.92 cm 3 and a weight of 7.2 g, Fig. 2…”