Effects of urination process on heart rate variability.

Purpose: Heart rate variability (HRV) is used for the assessment of activity of the autonomic nervous system (ANS). As urination is also under the control of the ANS, this study aimed to investigate the usefulness of HRV in the assessment of ANS during the peri-urination period. The psychological effects of sitting on a chair or on the toilet during pre- and post-urination periods were also assessed.

Methods: Electrocardiogram was used to measure HRV in male participants (n = 40, aged 18-30). They were allowed to drink water to ease urination. At the stage close to voiding, six measurements (each for 90 s) were taken sequentially in sitting position (pre-urination chair, pre-urination toilet, urination, post-urination toilet, post-urination chair, and basal post-urination chair). HRV indices included standard deviation of R-R intervals (SDNN), root mean square of successive differences in R-R intervals (RMSSD), percentage of successive R-R intervals differing more than 50 ms (pNN50), total power (TP), very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) bands together with the ratio of LF/HF.

Results: HR, SDNN, TP, LF, and LF/HF increased during urination process (P < 0.05), whereas RMSSD, pNN50, and HF increased before urination on toilet (P < 0.05) compared to sitting on a chair before and after urination.

Conclusion: HRV indices dynamically reflected the physiological stages of urination. Parasympathetic activity (revealed by pNN50, RMSSD, and HF) increased before urination, whereas sympathovagal balance (revealed by LF/HF) increased during urination. Thus, HRV appears to be a suitable technique for studying physiological and pathological aspects of urination.