Cardiac Autonomic Control Reflects Sympathovagal Changes Associated With Withholding Urination.
Level 4 - case-series / case-control
Single-arm pre-post physiological study without a control group
PubMed 40575945 · doi:10.1002/nau.70105
What was done
Electrocardiogram recordings (5-minute continuous, supine) were obtained in 11 apparently healthy young males before and approximately 3.5 hours after withholding urination to evaluate heart rate variability (HRV). Measured parameters included heart rate, total power, standard deviation of RR intervals (SDNN), percentage of successive RR differences ≥50 ms (pNN50), low-frequency normalized units (LFnu), high-frequency normalized units (HFnu), and the LF/HF ratio. Paired t-tests on log10-transformed data were performed on participants who completed measurements on both occasions.
What was found
Withholding urination did not significantly change heart rate (from 80.0 ± 4.1 to 84.5 ± 3.1 bpm, p = 0.135). It significantly 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). It significantly increased LFnu (from 57.3 ± 5.3 to 65.1 ± 4.5, p = 0.029) and the LF/HF ratio (from 1.77 ± 0.73 to 2.42 ± 0.47, p = 0.047).
Why it matters
Bladder distention accompanied by an urge to urinate shifts cardiac autonomic control toward sympathetic dominance. This demonstrates that bladder fullness is a physiological confounder that should be standardized during clinical and autonomic HRV testing.
Limits
The sample size is very small (n = 11 enrolled, with paired data analyzed in only half of participants). The study included only young, healthy males, limiting generalizability across sexes, age groups, and clinical populations. There was no control group, and actual bladder volume was not objectively measured.
Cited by
- context Urination induces vagal withdrawal, resulting in an elevation in heart rate.