Abstract
Diabetic cardiovascular autonomic neuropathy (CAN) carries an increased risk of mortality.
The early detection and characterization of CAN has traditionally been based on the
results of autonomic reflex tests (AFTs). A variety of different measures to quantify
24-hour heart rate variability (HRV) have recently been introduced, but their normal
ranges, reliability, and validity in patients with CAN have not been adequately studied.
We established the normal ranges of statistical (SDNN index, CV, SNN50, RMSSD), geometric
(triangular index (TI), triangular interpolation (TINN), top angle index [TAI]), frequency
domain (spectral power in the VLF, LF, and HF bands, LF/HF ratio, LF in normalized
units [NU]), and non-linear measures (CV1 and CV2 of the Poincaré plot) of 24-hour
HRV in 94 healthy control subjects. Day-to-day reproducibility was evaluated on two
occasions in 17 healthy subjects and 9 diabetic patients. The parameters of HRV were
computed over time periods representing the day (6:00 - 24:00 hours), night (00:00
- 6:00 hours), and 24 hours in total. The results of all indexes, except for the LF/HF
ratio and LF-NU, declined significantly with increasing age (p < 0.05), but were independent
of sex and BMI. The statistical, geometric, and non-linear measures (p < 0.05), but
not the frequency-domain parameters decreased significantly with increasing heart
rate. Since the HRV data showed log normal distribution, log transformation was used
to define the age-related lower limits of normal at the 2.5th centile. Intraindividual
reproducibility was highest for the geometric measures. The nonlinear and statistical
parameters also showed high reliability, except for the SNN50. The repeatability of
the frequency domain measures was somewhat lower but still satisfactory. Reproducibility
was lower in the diabetic than in the control group, higher during the day than during
the night, and better than that reported previously for the AFTs. In conclusion, in
healthy subjects the measures of 24-h HRV are not related to sex or BMI, but strongly
dependent on age and heart rate, the latter except for the frequency domain measures.
The majority of the HRV measures, in particular the geometric parameters, show a relatively
high intraindividual reproducibility which underlines their suitability for the use
in prospective studies.
Key words
Heart Rate Variability - Holter ECG - Normative Data - Reliability - Age - Diabetic
Cardiovascular Autonomic Neuropathy