Causes of autonomic dysfunction in idiopathic recurrent kidney stone formers.

BACKGROUND

A higher prevalence of hypertension and adverse cardiovascular outcomes has been reported in kidney stone formers (KSF). We performed this study with the purpose of evaluating the autonomic nervous system (ANS) activity in KSF.

METHODS

We performed a 70° head-up tilt test in 30 idiopathic recurrent KSF aged 45.6 ± 12.1 years old (17 men: 13 women) and 30 healthy controls aged 42.0 ± 12.4 years old (17 women: 13 men). Thirteen KSF were hypertensive, and 17 were normotensive. Blood pressure (BP) and heart rate variability (HRV) were used for the non-invasive assessment of the efferent activity of the ANS. Discrete wavelet transform (DWT) was used to quantify the low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.4 Hz) components during several periods of tilt.

RESULTS

The results showed significantly higher HR and BP in KSF, in both supine and tilt positions. DWT revealed diminished HRV in the kidney stone patients during head-up tilt, with no increase in the LF and greater decrease in the HF components. The differences in the HF component of HRV were associated with obesity and hyperuricosuria, but the abnormalities of the LF component were independent of the explanatory variables. The LF component of systolic BP was significantly higher in KSF and was associated with hypertension.

CONCLUSIONS

Several factors may contribute to the presence of autonomic dysfunction in patients with recurrent nephrolithiasis. This abnormality has significant implications in cardiovascular risk assessment and treatment planning.