AGE-ADJUSTED NORMAL CONFIDENCE-INTERVALS FOR HEART-RATE-VARIABILITY IN HEALTHY-SUBJECTS DURING HEAD-UP TILT

Purpose: Aging leads to a decline in autonomic nervous system function . In this study, designed to assess the influence of age on neuroauton omic regulation of cardiac activity, heart rate variability was measur ed by power spectral analysis and normal ranges were determined in a p opulation of healthy subjects. Patients and methods. In 83 healthy vol unteers (42 men and 41 women; age range 25-85 years) autonomic nervous system function was assessed by autoregressive spectral analysis of h eart rate variability in clinostatism and after passive orthostatic lo ad (head-up tilt). The analysis considered two spectral components rel evant to the study of the autonomic nervous system - high-frequency po wer (approximate to 0.25 Hz) and low-frequency power(approximate to 0. 10 Hz)- and the ratio between them. Low-frequency spectral components, in particular the ratio between low- and high-frequency spectra, refl ect sympathetic activity; high-frequency components reflect parasympat hetic activity. Results. For data comparison, the study group was subd ivided into three age groups: 25 subjects (12 men and 13 women) under 44 years of age; 28 (15 men and 13 women) aged 44-64 years; and 30 (15 men and 15 women) over 64 years of age. The natural logarithms and no rmalized units of low- and high-frequency power, and the low-to-high p ower ratio were used to calculate 95% confidence intervals. Power spec tral analysis at baseline and after postural tilt showed significantly higher low-frequency power of heart rate variablity (P < 0.05), natur al logarithm of power (P < 0.001) and normalized units (P < 0.001) in the two younger groups than in the oldest group. The two younger age-g roups also had significantly increased high-frequency power (P < 0.05) and natural logarithm of power (P < 0.05). The oldest age group had s ignificantly increased high-frequency power analyzed in normalized uni ts (P < 0.001). Conclusion: The age-related lowering observed in nearl y all the spectral frequency components of heart rate variability conf irms in healthy subjects that autonomic nervous system function declin es with age.