REPEATABILITY OF SPECTRAL COMPONENTS OF SHORT-TERM BLOOD-PRESSURE ANDHEART-RATE-VARIABILITY DURING ACUTE SYMPATHETIC ACTIVATION IN HEALTHY-YOUNG MALE-SUBJECTS

1. Changes in the law-frequency (LF) components of blood pressure and heart rate variability and in the ratio of LF to high-frequency (HF) c omponents of heart rate variability (LF/HF ratio) are used to assess a cute changes in sympathetic control of blood pressure or heart rate an d in sympathovagal balance that occur in response to physiological or pharmacological stimuli, Before these spectral indexes can be used to assess the effects of drug therapy or other clinical interventions on reflex sympathetic activity, their repeatability must be evaluated. 2. Intra-observer repeatability was studied by analysing changes in the LF components (expressed as absolute or normalized units) of cardiovas cular variability and in the LF/HF ratio during sympathetic activation induced by nitroglycerin infusion (n = 10 subjects) or 60 degrees hea d-up tilt (n = 13 subjects) repeated on two occasions, 2 days and 1 we ek apart respectively, in healthy young male volunteers, Repeatability was estimated as recommended by Bland and Altman. 3. Bland and Altman 's plots of the repeatability of changes in the LF components and LF/H F ratio showed that measurements were sufficiently repeatable to be us ed over periods of time of up to 1 week in clinical studies. 4. The sa mple-size tables derived from our results show that expression of spec tral components as normalized units, and use of a cross-over design, m inimize the number of subjects to be included in clinical studies cond ucted using similar designs and LF component changes as endpoints.