Autonomic nervous system activity assessment by heart rate variability in experimental bladder outlet obstruction

A syndrome with urgency, with or without associated urine incontinence and usually accompanied by higher urinary frequency and nocturia has been named "overactive bladder; OAB". OAB is an entity with complex pathophysiology, involving both myogenic and neurogenic (afferent / efferent bladder innervation) disturbances. OAB symptoms accompany benign prostatic hypertrophy--BPH ("obstructive OAB"). The aim of the study was to estimate the autonomic nervous system activity (ANS) in the experimental bladder outlet obstruction (BOO) which was an animal model of the human BPH. The study was conducted using 30 female rats, divided into two groups: BOO animals (n=15), with surgically induced BOO (by partial ligation of the proximal urethra) and control ones (n=15), which underwent sham procedure (without urethral ligation). Two weeks after the surgery, in both groups, ANS activity was estimated using time- and spectral analysis of the heart rate variability recordings. The bladder overactivity in BOO animals was confirmed using urodynamic recordings and bladder histological assessment, juxtaposed against the results of the control group. The key finding of our study was the development of autonomic disturbances in bladder outlet obstruction (BOO) rats. Our study revealed that BOO animals were characterised by diminished rMSSD and spectral HRV parameters: TP, LF and HF, in comparison with the control group. The normalised nLF and nHF parameters did not differ significantly in both groups, although slight changes in the nLF (increased) and nHF (decreased) were noted in BOO group. The absolute VLF value was almost the same in both studied populations, however, the percentage part of this component in the appropriate HRV spectrum differed considerably in both studied groups. In BOO animals, VLF percentage amounted to about 90%, whereas in control animals this parameter reached only about 53% of the total power spectrum. Thus, to sum up, our findings suggest autonomic imbalance with decreased global autonomic tension and diminished parasympathetic activity with relatively sympathetic overactivity.