Development of a wireless intra-vaginal transducer for monitoring intra-abdominal pressure in women

Abstract

Pelvic floor disorders (PFD) affect one of every four women in the United States. Elevated intra-abdominal pressure (IAP) during daily activity or strenuous physical activity has been identified as a risk factor in the prevalence of PFD. However, the relationship between IAP and physical activity is poorly understood and oftentimes activity restrictions are prescribed by physicians without clinical evidence linking various activities to elevated IAP. There are currently no pressure transducers capable of monitoring IAP non-invasively out of a clinical environment. To overcome this shortcoming, a novel intra-vaginal pressure transducer (IVT) was developed to continuously monitor IAP. Improvements were made to the first generation IVT by incorporating wireless capability to enhance the device's mobility while creating a more robust IAP monitoring system. To ensure the changes maintained the functionality of the original device design, comparison testing with standard clinical pressure transducers in both bench top and clinical settings was conducted. The wireless device was found to have high linearity, robust signal transmission, and dynamic response that outperforms the clinical standard rectal transducer and is similar to the original first generation non-wireless design. The wireless IVT presented here is a mobile wireless device capable of measuring, storing and transmitting IAP data during various physical activities.

Fig. 1

Photograph of circuit boards and main features for wireless Gen2 circuitry. The IMD side A (A) contains the piezoresistive pressure sensor, ZMD signal processor and battery contacts. IMD side B (B) contains the MSP430 microcontroller and eight connection pads for linking the IMD board to the RF board. RF side A (C) contains the Zarlink wireless chip and connection pads. RF side B (D) contains four communication lines for programming and calibration and battery contacts

Fig. 2

Assembly drawing of electronic package. The battery is held in place by the four battery contacts. The contact protector at each end prevents the battery contacts from interfering with the IMD and RF circuit boards. Absent from this drawing are the shrink tubing, coaxial cable, and interboard communication wires

Fig. 3

Photograph displaying a cross section of the wireless intravaginal transducer. A coin cell battery is sandwiched between the IMD and RF circuit boards. The clear battery holder houses the electronics and battery in place supported by brass battery contacts. Four programming wires allow for programing and calibration. These wires are removed after calibration and prior to final device assembly. The tether is used for device retrieval and serves as an atmospheric vent. An coaxial cable allows attachment of an external antenna

Fig. 4

Dynamic response test setup. All three pressure transducers were sealed in the pressure chamber. (from left to right: reference transducer, rectal balloon catheter and wireless Gen2 IVT)

Fig. 5

Calibration curve for wireless Gen2 IVT

Fig. 6

Results of three transducers during an impulse response test

Fig. 7

Swept sine wave frequency plot for three transducers

Fig. 8

IAP measurement while subject coughs 4 times

Fig. 9

IAP measurement while subject performs a Valsalva maneuver