Autonomic nervous system activity during bladder filling assessed by heart rate variability analysis in women with idiopathic overactive bladder syndrome or stress urinary incontinence.

PURPOSE: Idiopathic overactive bladder syndrome is a common disorder, especially in women. Of various pathophysiological factors several studies suggest a specific dysfunction of the autonomic nervous system. To verify this hypothesis we compared heart rate variability parameters, which provide an analysis of autonomic function, in women with idiopathic overactive bladder syndrome to those in a reference population of women with stress urinary incontinence.
MATERIALS AND METHODS: Diseases and medications that can perturb the autonomic nervous system were excluded. We included 7 women with pure stress urinary incontinence and 3 with isolated overactive bladder syndrome. Continuous echocardiogram recording was performed with the bladder emptied and during artificial bladder filling. High frequency variations of instantaneous heart rate represent parasympathetic activity, low frequency variations represent sympathetic activity and the low-to-high frequency ratio represents the autonomic balance.
RESULTS: Heart rate variability parameters did not change significantly during bladder filling in women with stress urinary incontinence. In contrast, sympathetic tone in women with overactive bladder syndrome (low frequency) increased significantly at the end of bladder filling (p = 0.001), in parallel with a decrease in parasympathetic activity (high frequency) and a significant increase in the low-to-high frequency ratio (each p <0.001). Parasympathetic activity with the bladder emptied was significantly higher in the overactive bladder syndrome group (p = 0.017).
CONCLUSIONS: This preliminary study demonstrates the predominance of parasympathetic activity with the bladder emptied and a preponderance of sympathetic activity at the end of bladder filling in women with overactive bladder syndrome. These results suggest dysfunction in the autonomic balance, as implied in idiopathic overactive bladder syndrome. Further studies in a larger population of patients with overactive bladder syndrome with reference to normal subjects free of urinary symptoms are necessary to confirm this hypothesis.