Thank you for the very interesting letter about our paper. Data quality was ensured by checking subtraction after every void and also every hour during the test. Because of the high level of supervision and the 20-cm length of urethral catheter inserted, none of the studies was rejected due to inadequate data quality. The multiple analyses of the bladder pressures were carried out blinded, which would, hopefully, remove bias.
We agree that the intra- and inter-observer reliability of every method of assessment needs to be evaluated. The most important message about our study evaluating asymptomatic women is that ambulatory traces should be interpreted with the woman present. This is no different from the interpretation of laboratory urodynamic studies where the woman's symptoms are crucial to the evaluation of a urodynamic trace. ‘A loss of objectivity’ may occur but this is probably the only method by which urinary symptoms can be fully incorporated into the evaluation of a trace.
Most differences between the two transducers were due to pressure rises not seen in both bladder lines. This is more than likely to be due to the transducer coming into contact with the wall of the bladder. The artefacts seen in the rectal line are not as important as those seen in the bladder line. Bladder line artefacts suggest detrusor instability but rectal line artefacts do not. We have not evaluated two rectal pressure measurements simultaneously or their effect on the diagnostic accuracy of ambulatory urodynamics.
We feel that video urodynamics should still be considered the ‘gold standard’, against which ambulatory urodynamic monitoring should be compared in women with urinary symptoms. Ambulatory urodynamic monitoring is not designed to replace subjective analysis of urodynamic traces. The only method of objective analysis is to use automated systems, which have not been shown to be of value due to the large number of artefacts.