Autonomic function in elderly uremics studied by spectral analysis of heart rate

Aging determines an altered response of the autonomic nervous system (ANS) to physiologic stresses. A widespread autonomic damage is well recognized in chronic renal failure (CRF).

We studied 30 CRF patients, aged 19 to 85 years, who were on bicarbonate hemodialysis. Surface electrocardiogram was recorded on lying and 65 degrees head-up tilt standing positions. A dedicated software, using an autoregressive modeling technique, allowed to calculate power spectral analysis (PSA) of heart rate variability, assessing a low-frequency band in the range 0.03 to 0.15 Hz, and a high-frequency band in the range 0.15 to 0.33 Hz. Low-frequency and high-frequency components are regarded, but not invariably, as specific markers of sympathetic and parasympathetic activities, respectively, and the low-frequency/high frequency ratio as an index of sympathovagal balance.

In normal controls, low-frequency band value and low-frequency/high-frequency ratio on standing resulted significantly reduced in the group older than 65 years when compared with those younger than 65 years; an opposite finding was seen in high-frequency band value on standing. In uremic patients, low-frequency band on lying resulted significantly lower only in elderly uremics when compared with elderly controls, whereas low-frequency band on standing was significantly lower in elderly than in younger uremics. Regression analysis showed a significant inverse relationship between aging and most low-frequency band values, especially in uremics. The comparison of linear regression models confirmed that a sympathetic autonomic derangement is greatly present in older uremics, in particular after 50 years of age.

Our data support assertion that combination of aging and CRF increases the chance of autonomic derangement being present.