We read with interest the paper by Salvatore et al.1. The authors describe the validation of a protocol for ambulatory urodynamic monitoring and have compared their results in asymptomatic volunteers with historical reports of conventional urodynamics. A number of important issues have been raised, however, and we have some reservations regarding the study methodology.
The authors do not describe methods of ensuring data quality and the proportion of studies rejected due to inadequate data quality. Two units with extensive experience of ambulatory urodynamic monitoring have reported a rejection rate of approximately 8%2,3.
Multiple analyses were performed with one and two transducers, both with and without the symptom diary, but no indication has been given whether this process was randomised or blinded to avoid bias. The intra- and inter-observer reliability of any method of assessment should be measured. The authors describe interpretation of the trace in the presence of the woman. Although described as ‘non-directive’, loss of objectivity is clearly a risk for both the clinician and the woman.
When analysing the two vesical transducers, differences in performance between the distal and proximal transducers were not examined. When differences occurred (n= 6), no explanation for the discrepancies was provided. For example, it is possible for one transducer to slip out of the bladder without detection and the subsequent reading to be misinterpreted. In our experience, artefact associated with the rectal transducer is common. As the authors recommend two vesical transducers, have they evaluated the use of two rectal transducers? Furthermore, the data suggest that the addition of a second vesical transducer did not significantly influence the rate of detection of detrusor contractions when the diary was employed (1/26 traces). We suggest that including regular cough tests and intermittent on-line monitoring is central to ensuring high quality data.
The criteria employed for the definition of amplitude and duration of detrusor activity in this study are not clear. Mild, moderate and severe contractions were defined ‘according to Coolsaet’, although the parameters described by the authors are different from those in the quoted reference.
We share the authors' concerns regarding the lack of standardisation in the conduct and interpretation of ambulatory urodynamic monitoring, and also welcome the recent report on standardisation by the International Continence Society. The validation of a protocol for ambulatory urodynamic monitoring, for the assessment of detrusor function, compared with conventional urodynamics, is contentious, since conventional urodynamics as the standard in this context has been recently challenged. The relationship between ambulatory urodynamic monitoring and symptoms is clearly important. However, retrospective analysis of the urodynamic trace in the presence of the woman re-introduces a subjective element to cystometry that ambulatory urodynamic monitoring was designed to avoid. Our experience, and that of others2,3, suggests that measurements of detrusor contractions (amplitude, duration, frequency and bladder volume), combined with the woman's symptoms, may be used to differentiate clinical detrusor instability from detrusor activity which may be regarded as a variation of normal.