Investigation of bioimpedance as a method for wearable noninvasive bladder volume measurements in individuals with spinal cord injury or disease: Protocol of a feasibility study

Abstract

Introduction: Neurogenic lower urinary tract dysfunction (NLUTD) is a frequent consequence of spinal cord injury or disease (SCI/D). It can lead to impaired bladder emptying, urinary incontinence, and recurrent urinary tract infections. For those unable to empty their bladder effectively, intermittent catheterization (IC) is the recommended first-line management. Clinical guidelines advise catheterization four to six times daily to prevent bladder overdistension (i.e., bladder volume > 500 ml), yet fixed schedules are often impractical due to fluctuating daily factors. Personalized scheduling is particularly challenging for individuals with SCI/D who lack bladder sensation. Consequently, a noninvasive and unobtrusive method for bladder volume monitoring is needed. Electrical bioimpedance (BI) is a promising solution, as it measures the impedimetric response of tissue to an applied electrical signal and should detect changes related to bladder filling. This may enable continuous, dynamic volume estimation and support individualized bladder management. Methods and Analysis: This multi-center observational feasibility study evaluates a BI sensor for noninvasive bladder volume monitoring across three phases. Phase 1 assesses feasibility in individuals without SCI/D. Phase 2 includes individuals with chronic SCI/D and NLUTD to determine the difference between BI-derived bladder volume and the clinical gold standard (bladder volume determined by catheterization). Effects of abdominal adiposity and muscle activity on BI-signals will also be analyzed. Phase 3 examines the usability of a BI-based wearable during six hours of real-life use in wheelchair users reliant on intermittent catheterization. Sixty participants will be enrolled across all phases. The primary outcome is the difference in bladder volume (mL) between BI measurements and catheterized volumes in individuals with SCI/D. Secondary outcomes include physiological and motion parameters possibly affecting BI measurements. Analyses will be descriptive, focusing on signal quality, feasibility, and measurement agreement. Discussion: This multi-phase feasibility study evaluates whether a BI sensor can measure bladder volume in individuals with SCI/D and NLUTD noninvasively and continuously. By validating BI in controlled and real-life settings, the study aims to determine its feasibility and potential as an alternative to current bladder volume assessment methods.