Urodynamics Voiding Position: Potential for Misdiagnosis of Atonic Bladder

Objectives: We explored position change effects on observation of bladder contractions during urodynamic study (UDS). We investigated whether absence of detrusor contraction in a urodynamic chair was observed when patients assumed a more normal voiding position and surface. We hypothesized that patients without demonstrable bladder contractions on the UDS chair after permission to void may be able to mount a bladder contraction after changing to a more normal voiding position.

Methods: We conducted a retrospective cohort study analyzing UDS performed from 1/2022 to 1/2024. Urodynamic reads were screened for positional changes from the UDS chair to either the commode or standing position when patients were unable to void in the UDS chair. Studies with positional changes after permission to void were analyzed by two neurourologists in a blinded fashion. Data collected included: time spent attempting to void in the UDS chair, whether a bladder contraction was present in the UDS chair, pdet Qmax and Qmax if voiding occurred, time spent attempting to void after moving, presence of a bladder contraction in the new position, and the new pdet Qmax and Qmax.

Results: Of the 503 UDS performed, 94 patients were identified to have moved to commode or standing position due to unsatisfactory or absent void on the UDS chair. Of these, 81/94 (86.2%) studies were deemed interpretable. The average time spent attempting to void on the UDS chair was 8.41 minutes +/- 4.1. Once in the new position, the patients took an average of 2.29 +/- 1.9 minutes to void. Of the 81 patients identified with an unsatisfactory or absent void on the UDS chair, 69/81 (85.2%) demonstrated a bladder contraction in the new position. Agreement between blinded providers on presence of a bladder contraction in the UDS chair showed that 91.4% were congruent (k=0.78). Provider reads for the presence of a bladder contraction on the commode/standing showed that 88.9% were congruent (k=0.42). Of these studies that were congruent (N=44/55), we demonstrated that 80% of the patients unable to demonstrate a bladder contraction on the UDS chair were then able to demonstrate a bladder contraction when moved to the commode or standing. If a contraction was present, we compared the pdet Qmax and Q max on the UDS chair to the pdet Qmax and Q max in the new position. The average pdet Qmax on the UDS chair was 6.86 +/- 11.8 cm H2O versus the average pdet Qmax in the new position was 25.9 +/- 17.9 cm H2O (p= < 0.001).

Conclusions: Atonic bladder (and some cases of hypotonic bladder) can be misdiagnosed based on measuring voiding only in a padded UDS chair. Moving to a more natural seating surface such as a floor level commode or standing can improve measurement of detrusor function.