Estimation of contractility parameters for the urinary bladder

Can we improve our diagnosis of impaired detrusor contractility in women? An ICI-RS 2019 proposal

INTRODUCTION

Widely accepted consensus terminology and calculations of detrusor contractility in females do not exist but may be useful. We report the output of a proposal session at the International Consultation on Incontinence Research Society meeting 2019, addressing the title topic.

METHODS

Three formal presentations and a lively discussion addressed several questions including: which is the optimal cutoff value of female bladder voiding efficiency during uroflow to suspect obstruction or detrusor underactivity? Is there a definition of pure underactive and pure obstructed voiding in females? Is there a place to distinguish those relatively obstructed from those relatively underactive females especially in those cases of equivocal obstruction? Current measures of contractility were reviewed for their usefulness in women.

RESULTS

No recommendation for a specific index or calculation can be made based on current knowledge. "Contractility" may be context-dependent regarding clinical care, clinical prognostication, and physiologic research.

CONCLUSIONS

This group proposes that context-sensitive definitions of "Contractility" deserve attention by international leadership. Cooperative clinical and physiologic expertise will be needed to achieve this goal. Following initial recommendations based on expert opinion, the development of final definitions and measures of contractility should be iterative, based upon validation studies to be considered as part of the definitional process.

The calculation and comparison of the Detrusor Contractility Parameter and Watts Factor

AIMS

To test the significance of association between a validated index of detrusor contractility, v_CE , the Watts Factor, and the Detrusor Contractility Parameter, t_20-80 ; and to test whether t_20-80 depends on outflow tract resistance as indicated by Bladder Outlet Obstruction Index (BOOI).

METHODS

Thirty-seven pressure-flow traces from 20 male and 17 female patients were analyzed and forms of the Watts Factor, t_20-80 and BOOI were compared with v_CE .

RESULTS

The Detrusor Contractility Parameter, t_20-80 , is significantly associated with v_CE for both women and men without a high degree of bladder outlet obstruction. The Watts Factor only had a significant association with v_CE at the point of maximum flow in women.

CONCLUSIONS

The Detrusor Contractility Parameter (DCP) (t_20-80 ), can be measured easily from the pressure flow curves of a urodynamic test. The Watts Factor at maximum urine flow, WF_Qmax , can be readily calculated, but is only applicable to women. In both women and men without a high degree of bladder outlet obstruction, DCP is better associated with true detrusor contractility than any Watts Factor analysis.

Urinary Bladder Contractility Revisited. Correlation of Noninvasively and Invasively Measured Contractility Parameters in Patients Eligible for Transurethral Resection of the Prostate

OBJECTIVE

To validate a noninvasively estimated measure of urinary bladder contractility by correlating it with 3 existing invasive contractility parameters and to compare and correlate those invasive parameters.

METHODS

A group of 74 patients, recruited in 3 different hospitals, and eligible for transurethral resection of the prostate on clinical grounds, were noninvasively studied preoperatively using the condom catheter method. The maximum condom pressure pcond.max measured during a mechanical interruption of flow rate was considered an estimate of urinary bladder contractility and compared to conventional contractility parameters calculated from preoperative (invasive) pressure-flow studies.

RESULTS

The highest correlations were found between the invasive parameters. The correlation between the noninvasive parameter on the one hand and the invasive parameters on the other hand was lower, but mostly significant. In a number of patients, pcond.max underestimated the isovolumetric bladder pressure. The underestimated patients were more obstructed than those who were not underestimated and had a higher (invasively measured) contractility. When the underestimated patients were deselected, the correlation between the noninvasive pcond.max and the invasive parameters in the remaining 52 patients was higher.

CONCLUSION

The 4 tested contractility parameters represent different aspects of urinary bladder contractility. Nevertheless, there was a significant correlation among them supporting the concept of a common basis, that is, detrusor contractility. The invasive contractility parameter bladder contractility index overestimated contractility in patients with lower urinary tract symptoms and/or benign prostatic enlargement. A modified parameter is suggested.

Computer-assisted pressure-flow analysis

Infravesical obstruction can only be diagnosed objectively from a urodynamic pressure-flow study. Analysis of the resulting data is not straightforward. Recently,many methods have been proposed for such analysis. Inevitably most of these methods for pressure-flow analysis are discussed in this contribution, and some results of clinical application of calculated urethral resistance factors are presented.

Contractility parameters of the guinea pig bladder in situ: similarity to human bladder contractility

The parameters P(isv) (active isovolumetric detrusor pressure) and Vmax (maximum shortening velocity), which characterize the contractility of the detrusor muscle, were determined in guinea pigs. To this end it was necessary to develop a method of measuring flow rates in these small animals. The values found were used to calculate the contractility parameter Wmax. Thirteen animals were used. The results found for P(isv) and Vmax were 43.0 +/- 3.7 cm. H2O and 20.2 +/- 3.7 mm. per second, respectively. The latter corresponded to about 0.38 muscle lengths per second, which is similar to values reported for bladder strips from other species. Previous work showed that in vitro P(isv) decreased with increasing bladder volume over a wide range of volumes. In vivo P(isv) seemed to be independent of bladder volume. This suggests that neurogenic stimulation intensifies as volume increases. Vmax also was independent of volume. Wmax appeared to be suitable for detecting differences in the contractility of the bladders of different animals. Values were not significantly different in isovolumetric and nonisovolumetric contractions. Normalized to the size of the bladder, the Wmax values indicated that the power generated by the guinea pig bladder is similar to the power generated by the human bladder.

Comparison of detrusor contractility of guinea pig bladders in situ and strips from these in vitro

To study the relative importance of neurogenic factors in detrusor contractility, active bladder wall stress values were compared in situ and in vitro. Eight male guinea pigs were used. The active stress in the bladder wall in spontaneous micturition contractions was calculated from the results of urodynamic examinations and compared with the active stress developed in response to optimum electrical stimulation in full-thickness bladder wall strips taken from the same bladders. The results indicated that, in normal micturition, the detrusor muscle is not fully stimulated, and the rate of pressure development is not determined by mechanical factors. To identify topological variations of detrusor contractility, the strips were taken from three different locations. It was found that strips from the posterior wall contracted more forcefully than those from the anterior wall.