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 again observed when patients assumed a more normal voiding position and surface. We hypothesized that patients without demonstrable bladder contractions during UDS on the UDS chair after permission to void may be able to mount a bladder contraction after changing to a more normal voiding position.

We conducted an IRB-approved retrospective cohort study analyzing video urodynamics performed at a single academic center from January 2022 to January 2024. Urodynamic reads were screened for positional changes from the UDS chair to either the commode or standing per patient preference when patients were unable to void in the UDS chair. All attempts to void were initially started on Sonesta Urology Exam Chair, Model 6210 where patients were given permission to void, lights were turned down, faucet water was turned on, and the exam chair was tipped forward to optimize voiding position. The urodynamicist remained out of view behind a curtain during the attempt to void. If no void occurred, the urodynamicist would leave the room for 5 minutes. If still no void occurred, all patients had the opportunity to change voiding position keeping the UDS catheters in place and adjusting transducer height. Patients either moved to a hard-surface commode or stood to void according to their preference. Studies with positional changes after permission to void were reanalyzed by two neurourologists: the original present in the room, and a second (late in fellowship) 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 Q max and Q max when voiding occurred, time spent attempting to void after moving to the commode or standing, presence of a bladder contraction in the new position, and pdet Q max and Q max in the new position. 

Analysis was performed to determine whether position change affected observation of a bladder contraction on UDS. Agreement between the two neurourologists’ interpretations were analyzed using Cohen’s Kappa statistic and Bland Altman plots. Paired T tests were used to evaluate the change in pdet Q max and Q max in all genders and BOOI and BCI in males.

Of the 503 UDS performed over the two-year time frame, 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 by both urodynamicists during the UDS chair and commode/standing voiding attempts.  

The average time spent attempting to void on the UDS chair was 8.41 minutes +/- 4.1 with a mean difference of 0.14 minutes +/- 2.9 between providers. Once in the new position, the patients took an average of 2.29 +/- 1.9 minutes to void with a mean difference of 0.51 +/- 2.3 minutes between providers.   

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). Of these studies that were congruent, 7 were male. 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, 11 were male. 

Out of the urodynamicists’ reads which 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.  Additionally, if contraction was present, we compared the pdet Q max and Q max on the UDS chair to the pdet Q max and Q max in the new position. The average pdet Q max on the UDS chair was 6.86 +/-  11.8 cm H2O versus the average pdet Q max in the new position was 25.9 +/- 17.9 cm H2O (p=<0.001). The mean Q max on the UDS chair was significantly lower than the mean Q max in the new position (2.2 +/- 2.8 ml/s vs 11.11 +/- 7.6 ml/s; p =<0.001).  

13/81 patients were men. The mean bladder outlet obstruction index for males on the chair was 13.3 +/- 14.4 with a mean difference 2.08 +/- 7.1 between providers. The mean bladder outlet obstruction for males on commode or standing was 38.3 +/- 28.6 with a mean difference 8.4 +/- 10.3 (p=0.002). The mean bladder contractility index for males on the UDS chair was 13.6 +/- 15.1 with a mean difference 0.8 +/- 8.6, and 61.7 +/- 31.6 with mean difference 3.6 +/- 10.1 on commode or standing (p<0.001).

80% of patients who demonstrated no or ineffective bladder contraction on the UDS chair demonstrated an adequate contraction on the commode/standing. Given the agreement between the providers performing the UDS reads, we have demonstrated that evaluation of a bladder contraction may be limited by the artificial environment of performing the study on a UDS chair, and those with suspicion of atonic/hypotonic bladder may demonstrate more normal detrusor function on a more familiar voiding surface and position.

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.