Cardiac Autonomic Control Reflects Sympathovagal Changes Associated With Withholding Urination

Increased volume of the urinary bladder causes urge to urinate and constricts the sphincter by increasing the tonus of the sympathetic nervous system (SNS). Activity of the autonomic nervous system (or sympatho-vagal balance) can be assessed by heart rate variability (HRV). Current study aimed to test in healthy young male participants whether HRV technique reflects increased sympathovagal balance during bladder distention as revealed by strong urge to urinate.

A total of young and apparently healthy 11 males agreed to participate to the current study. They were asked to provide 5-min continuous electrocardiogram (ECG) recordings in supine position for determination of HRV on two occasions, i.e. before and approximately for 3½ hours after withholding urination. HRV parameters included heart rate (HR, per min), total power (TP, ms²), and standard deviation of RR intervals (SDNN, ms); percentage of successive RR intervals that were different ≥ 50 ms (pNN50), low frequency (LF) and high frequency (HF) bands and their normalized units (LFnu and HFnu, respectively) and their ratios (LF/HF). Half of the students provided samples on both occasions and those data were compared by paired t-test following log10 transformation.

Withholding urination did not change HR (from 80.0 ± 4.1 to 84.5 ± 3.1 per min, p = 0.135) but decreased total power (from 2692 ± 802 to 1605 ± 357 ms², p = 0.008), SDNN (from 50.4 ± 5.8 to 38.7 ± 3.8 ms, p = 0.007) and pNN50 (from 15.6 ± 3.3 to 5.9 ± 2.6%, p = 0.016) and increased LFnu (from 57.3 ± 5.3 to 65.1 ± 4.5, p = 0.029) and LF/HF ratio (from 1.77 ± 0. 73 to 2.42 ± 0.47, p = 0.047).

Increased LF/HF together with decreased SDNN and pNN50 suggest that HRV successfully reflects increased sympathetic tonus over the parasympathetic to help accommodate the urine in the bladder. Moreover, it seems that HRV can be used to assess sympathovagal changes non-invasively during voiding. Additionally, it appears that in all HRV measurements, participants should not have postponed their urination during recording.