Development of a novel intra-vaginal transducer with improved dynamic response

Design and validation of an automated dual-arm instrumented intravaginal dynamometer

AIMS

(1) To present the design of a novel intravaginal dynamometer (IVD) capable of measuring vaginal closure force on both the anterior and posterior arms, (2) to use bench testing to validate the force, speed of arm opening, and positional accuracy of load measurement along the IVD arms, and (3) to present in vivo force measurements made with this device, comparing forces measured by the anterior and posterior arms.

METHODS

IVD load measurements were validated against an Instron® Universal Tester, arm opening speeds were validated using video analysis, and position-load accuracy was validated against calibration weights. In vivo IVD data were acquired from female volunteers during passive opening and pelvic floor muscle contraction tasks. Anterior and posterior IVD arm force outcomes were compared.

RESULTS

Forces measured by the IVD and Instron® exhibited a strong linear relationship with excellent model fit. The speed control system was valid when tested under physiological loading conditions, however smaller antero-posterior opening diameters (25 and 30 mm) exhibited some error. The loading position along the IVD arms had no effect on force outcomes. In vivo data exhibited differences between force outcomes measured at the anterior and posterior aspects of the vagina during active contraction and passive elongation of the pelvic floor muscles.

CONCLUSIONS

This IVD design demonstrates valid load measurement and speed control during bench testing. Active and passive forces measured are consistent with the literature. With dual instrumented arms, this device allows for further investigation into the source of measured vaginal closure forces.

Design Synthesis and Preliminary Evaluation of a Novel Tool to Noninvasively Characterize Pressurized, Physiological Vessels

A prolonged increase in intra-abdominal pressure (IAP) is life-threatening, yet commonly seen in intensive care units (ICUs). Despite this, existing clinically accepted IAP measurement techniques are invasive and not inter-rater reliable. As such, it is the effort of this research to develop a direct, noninvasive, handheld tool to measure internal pressures in pressurized, physiological vessels. The novel device uses a localized known pressure (namely, aspiration) to measure resulting tissue deformation, from which internal pressures can be divulged considering the extended Hencky solution. Two male participants were tested with the device to confirm feasibility of the theoretical device function for IAP measurement. Participants' Young's moduli of the abdominal wall were calculated with measured IAP values. Results were consistent with participant body mass indices and overall health. Average measured IAP was 0.42 kPa and 0.46 kPa at supine and inclined positions, respectively. Average measured abdominal wall elasticity was 14.91 kPa and 23.09 kPa at supine and inclined positions, respectively. These preliminary findings suggest the potential use of the device described herein as a measurement system for pressurized vessels, whereas the system will be tested on a larger sample size before recommending clinical use.

Effects of walking speeds and carrying techniques on intra-abdominal pressure in women

INTRODUCTION AND HYPOTHESIS

Walking speed and carrying technique affect intra-abdominal pressure (IAP) in women. In this study, we tested the feasibility of monitoring IAP outside the laboratory environment and compared IAP while study participants were (1) carrying 13.6 kg (similar to a 3-month old in car seat) in six different ways while walking 100 m; and (2) while walking 400 m at self-selected slow, normal, and fast paces.

METHODS

Forty-six healthy women between 19 and 54 years completed the walking and lifting activities; the order for each was randomized. IAP was monitored with an intravaginal pressure transducer that wirelessly transmitted pressure data to a portable base station. We analyzed maximal peak IAP and area under the curve (AUC) IAP.

RESULTS

Monitoring IAP outside of the laboratory was feasible. Mean maximal IAP during walking increased as pace increased: 42.5 [standard deviation (SD) 10.2], 50.5 (10.9), and 62.0 (12.1) cmH2O for slow, medium, and fast speeds, respectively: p < 0.0001 by mixed-model analysis of variance (ANOVA). The corresponding AUC of IAP for walking decreased as pace increased. The awkward carry, side carry, and front carry activities each resulted in higher mean maximal IAP [65.8 (10.6), 67.7 (12.8), and 77.3 (13.1) cmH2O, respectively] than the carry-in-backpack activity [55.5 (11.4) cmH2O; p < 0.0001].

CONCLUSION

Subtle variations in walking speed or method of carrying a toddler-size load can produce significant changes in IAP. Whether these changes increase the risk of pelvic floor disorders is not yet clear. However, these data suggest that further inquiry into optimal methods and appliances to assist women in carrying may create a lower IAP profile.

More complicated than it looks: the vagaries of calculating intra-abdominal pressure

Activities thought to induce high intra-abdominal pressure (IAP), such as lifting weights, are restricted in women with pelvic floor disorders. Standardized procedures to assess IAP during activity are lacking and typically only focus on maximal IAP variably defined. Our intent in this methods article is to establish the best strategies for calculating maximal IAP and to add area under the curve and first moment of the area as potentially useful measures in understanding biologic effects of IAP. Thirteen women completed a range of activities while wearing an intravaginal pressure transducer. We first analyzed various strategies heuristically using data from 3 women. The measure that seemed to best represent maximal IAP was an average of the 3, 5, or 10 highest values, depending on activity, determined using a top-down approach, with peaks at least 1 second apart using algorithms written for Matlab computer software, we then compared this strategy with others commonly reported in the literature quantitatively using data from 10 additional volunteers. Maximal IAP calculated using the top-down approach differed for some, but not all, activities compared with the single highest peak or to averaging all peaks. We also calculated area under the curve, which allows for a time component, and first moment of the area, which maintains the time component while weighing pressure amplitude. We validated methods of assessing IAP using computer-generated sine waves. We offer standardized methods for assessing maximal area under the curve and first moment of the area for IAP to improve future reporting and application of this clinically relevant measure in exercise science.

Intra-abdominal pressures during activity in women using an intra-vaginal pressure transducer

Strenuous physical activity has been linked to pelvic floor disorders in women. Using a novel wireless intra-vaginal pressure transducer, intra-abdominal pressure was measured during diverse activities in a laboratory. Fifty-seven women performed a prescribed protocol using the intra-vaginal pressure transducer. We calculated maximal, area under the curve and first moment of the area intra-abdominal pressure for each activity. Planned comparisons of pressure were made between levels of walking and cycling and between activities with reported high pressure in the literature. Findings indicate variability in intra-abdominal pressure amongst individuals doing the same activity, especially in activities that required regulation of effort. There were statistically significant differences in maximal pressure between levels of walking, cycling and high pressure activities. Results for area under the curve and first moment of the area were not always consistent with maximal pressure. Coughing had the highest maximal pressure, but had lower area under the curve and first moment of the area compared to most activities. Our data reflect novel findings of maximal, area under the curve and first moment of the area measures of intra-abdominal pressure, which may have clinical relevance for how physical activity relates to pelvic floor dysfunction.

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

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.

Clinical evaluation of a wireless intra-vaginal pressure transducer

OBJECTIVE

To describe the development, feasibility and validity of a wireless intra-vaginal pressure transducer (IVT) which can be used to measure intra-abdominal pressure in real-world settings.

STUDY DESIGN

A feasibility study was conducted in sixteen physically active women to determine retention and comfort of various IVT prototype designs during activity. A criterion validity study was conducted among women undergoing urodynamic testing to determine the accuracy of the IVT prototypes when compared to accepted clinical standards.

RESULTS

A final prototype wireless IVT was developed after four design revisions of the second generation model. The feasibility study found that women reported the final prototype comfortable to wear and easily retained during physical activity. Intra-abdominal pressure measurements from the final prototype IVT compared favorably to standard urodynamic transducers, thus confirming evidence of its utility.

CONCLUSION

We have successfully advanced the design of a wireless, intra-vaginal pressure transducer which provides accurate measures of intra-abdominal pressure. The final wireless IVT is better tolerated by patients and overcomes limitations of traditional urodynamic testing while laying the foundations for intra-abdominal pressure monitoring outside of the clinic environment.

A Gel filled intravaginal transducer for extended measurements of intra-abdominal pressure

Limitations of the standard urogynecological pressure transducers have not adequately provided reliable measurements of intra-abdominal pressure (IAP) during physical activities. A previous novel intravaginal pressure transducer (IVT) was developed in order to overcome the shortcomings in existing technology. The design of the IVT was validated though comparisons with existing pressure transducers in both the clinical and bench top settings. However, a number of improvements were needed to overcome limitations in the previous design. A larger elastomeric capsule with transducer was developed and filled with silicone gel to replace the existing saline filled capsule and to better integrate proposed wireless technology. Impulse response and frequency testing were compared between the saline filled IVT and the new gel filled sensor and were found to be equivalent. Additional testing was performed on the gel filled device including drift and temperature measurements of sensitivity and offset. Results show the temperature coefficient of offset and sensitivity within correctible limitations with our proposed signal conditioner circuits.

Development and testing of a vaginal pressure sensor to measure intra-abdominal pressure in women

AIMS

Elevated intra-abdominal pressure (IAP) may be a potentially modifiable risk factor for pelvic floor disorders. However, limited evidence exists due to the lack of instruments suitable to measure abdominal pressures in real world settings. The aim of this study was to develop and test a vaginal sensor prototype to measure intra-abdominal pressure in women.

METHODS

We developed a non-directional vaginal sensor by housing pressure-sensing circuit boards in 1.2 x 3 cm radially symmetric silicon capsules. We characterized the response in a standardized pressure chamber. Eight women wore a sensor intra-vaginally while undergoing filling cystometry. We compared peak pressures during coughing, valsalva, squatting, and jumping to those obtained using a #10 French rectal balloon urodynamics catheter. We calculated Pearson's correlation coefficients between rectal and vaginal sensors for each event.

RESULTS

The vaginal sensors exhibited linear responses during initial bench testing. Each transducer correlated well with the rectal balloon catheter during coughing, valsalva, and squatting (r = 0.97, 0.94, and 0.97, respectively). However, the rectal balloon catheter recorded higher peak and lower, often negative, trough pressures during jumping. The vaginal sensor showed no such artifact.

CONCLUSIONS

This vaginal pressure sensor can be used as a surrogate for measuring intra-abdominal pressure in women without advanced prolapse. By measuring pressure at the physiological source, the vaginal sensor is less prone to extraneous noise and error than current transducers. Using this prototype, we will next develop a remote wireless version to capture a range of abdominal pressures experienced outside of the laboratory setting.