DAY-TO-DAY VARIABILITY OF CARDIAC AUTONOMIC REGULATION PARAMETERS IN NORMAL SUBJECTS

We examined the reproducibility of day-to-day variability in cardiovas cular autonomic nervous function parameters (classical clinical tests and domain analysis of heart rate variability) in four healthy men dur ing a period of 1 working week. The results did not show any significa nt difference in any of the parameters over the five repeated measurem ents. The maximum-minimum difference as percentage of the mean was und er 15% for expiration to inspiration (E/I) ratio, Valsalva ratio, tach ycardia ratio, 30/15 ratio, acceleration index and brake index; about 45% for baroreflex sensitivity for systolic and diastolic blood pressu re and for root mean square difference (RMSSD) of successive R-R inter vals; about 65-85% for low and high frequency bands, total power and m edium to high frequency ratio; and about 125% for medium frequency ban d. The intraclass correlation coefficient (ICC) values showed that the agreement for classical autonomic parameters (except for brake index) was good. ICC for RMSSD, baroreflex sensitivity for systolic blood pr essure and the spectral estimates of heart rate variation were less go od. Coefficient of variation (CV) was 4% for E/I ratio, 2% for 30/15 r atio, 6% for Valsalva, 3% for tachycardia ratio, 4% for acceleration i ndex and 5% for brake index. CV for baroreflex sensitivity and for RMS SD was about 20%. It is concluded that re variation in baroreflex sens itivity is clearly larger than in the classical autonomic nervous func tion parameters. One-minute fixed pace breathing period seems to be to o short to allow reproducible measurement of RMSSD and the spectral pa rameters of heart rate variation. Learning effect could be excluded.