Long-term changes in urodynamic studies of voiding in the elderly.

Urodynamic studies were conducted in 80 incontinent elderly patients (27 men and 53 women; mean age, 77 years) and repeated 2-4 weeks later after patients had been subject to interventions. Interpretable voiding studies were performed in 84% of sessions. Interpretable initial and repeat studies were performed in 74% of patients. For detrusor pressure at maximum flow the intra-individual, between-sessions variability was +/- 11.7 cm H2O (SD) and the initial-repeat correlation coefficient was 0.61. For maximum flow rate the corresponding figures were +/- 4.7 ml/s and 0.44. Mean residual urine volume was 195 ml, with a between-sessions variability of +/- 113 ml (SD). These results suggest that there is substantial long-term variability in voiding function, including urethral resistance. Of the mean, 5% showed a change in obstruction classification (unobstructed/obstructed) between sessions. This variability and the modest proportion of interpretable studies should be taken into account when assessing urethral obstruction and designing clinical trials.