Head-to-head comparison of pressures during full cystometry, with clinical as well as in-depth signal-analysis, of air-filled catheters versus the ICS-standard water-filled catheters

Abstract

Aims: To compare in vivo differences of two catheter systems for urodynamics to further discover their measurement properties.

Methods: Side-by-side catheterization with two catheters for intravesical and abdominal pressure during full cystometry in 36 prospectively recruited patients with analysis of mean and absolute differences at urodynamic events and post hoc in-depth signal analysis comparing the full pressure traces of both systems.

Results: The mean pressure differences at urodynamic events between air-filled and water-filled systems are small, however, with a large variation, without a systematic difference. The majority of the intersystem differences are significantly larger than 5 cmH₂ O. Further analysis showed that urodynamic event pressure differences of both systems at the start of the test were carried forward throughout the remainder of the test without subsequent or additional tendency to differ. Post hoc whole test signal analysis with pressures equalized from the first sample shows high cross-correlation (>0.981) between the pressure signals per location (rectum and bladder) per test and almost zero-time shift (<0.05 s) of all cystometry pressure samples.

Conclusions: We confirm earlier studies that showed random differences at events between air-filled and water-filled pressures during clinical urodynamic testing and confirm that these are intrinsic but not systematic-and still incompletely explained-offset-baseline differences. We determined on closer full measurement analysis after equalizing, that both systems are similar in displaying urodynamic pressure variations and amplitudes. We also confirm that both systems require awareness of intrinsic measurement properties during urodynamic testing and especially may necessitate adjustment of pressure offsets into a quantitative diagnosis of a urodynamic test.

Figure 1

Our standard water‐filled catheters (WF) cystometry (left‐hand side) and the experimental WF + AF) cystometry (right hand side) with side‐by‐side catheters; AF catheters are both 7F

Figure 2

(A) Cystometry with simultaneous water‐filled and air‐filled pressure recording from top to bottom: PvesW(ater); PabdW(ater); PdetW(ater); PvesA(ir); PabdA(ir); PdetA(ir); Vinf(used); Qura (flowrate) and incontinence in this case; and time in min:s. Full scale vertical for all pressures is 100 cmH₂O. (B) Cystometry with the WF (blue) and the AF pressures over‐projected for 20 Hz signal analysis (saline fill volume on bottom trace). Note that the vertical axes scales differ per pressure. Note the tube knock artifacts in the WF system. Note also that small differences in the intravesical and abdominal pressures add‐up in the detrusor pressure (e.g., at 100 ml, 150 ml, and after 370 ml)

Figure 3

Bland and Altman graphs: (A) pressure differences at FS, (B) pressures at SD (C) pressures at DO and during voiding or DO‐incontinence. Limits of an agreement are indicated, and the tables show the regression coefficients all test‐test differences were not proportional. DO, DO, detrusor overactivity; FS, first sensation

Figure 4

Scatterplot of cystometry P_ves WF versus AF samples of Figure 2a; including the tube knock artifacts. Relatively large differences occur in the low (<10 cmH₂O) pressures (tube knocks) and the pressures >40 cmH₂O, including patients’ moving and coughing. >98% of the 9.000 samples (per system) between 15 and 40 cmH₂O is close around the mean. AF, air‐filled; WF, water‐filled

Figure 5

Examples of a single and a double cough in detail (baselines 3.5 and 5 s) with responses of each system per location and the resulting detrusor subtracted curves