REPRODUCIBILITY OF NONINVASIVE MEASUREMENT AND OF SHORT-TERM VARIABILITY OF BLOOD-PRESSURE AND HEART-RATE IN HEALTHY-VOLUNTEERS

1 Spectral analyses of blood pressure and heart rate oscillations are increasingly used to assess the influences of diseases and drugs on the autonomic nervous system. Such influences can only be interpreted in view of the spontaneous variability of these oscillations. We therefore studied the reproducibility of power spectral analyses of blood pressure and heart rate fluctuations measured by a non-invasive finger plethysmographic method in 24 healthy volunteers. 2 Intra-observer reproducibility was assessed from measurements obtained on 3 consecutive days and 1 month later in each subject. Inter-observer reproducibility was assessed by comparing measurements made by two observers on one occasion. 3 There was no significant difference in standard haemodynamic and spectral analysis parameters (low frequency: 60-130 mHz and high frequency: respiration rate +/- 30 mHz) measured on 3 consecutive days and 1 month later in each subject. The standard deviation of differences between systolic blood pressure or heart rate oscillations on different occasions was in the 150-200 and 50-100 mm Hg Hz(-1/2) or beats min(-1) Hz(-1/2) range for low frequency and high frequency oscillations respectively. Similar results were found when inter-observer reproducibility was considered. 4 From these results, we derived a sample-size table giving the number of subjects to be included in studies of cross-over or parallel design in order to detect a nonrandom difference in spectral analysis parameters. For example, detection of a 200 mm Hg Hz(-1/2) difference in low frequency oscillations of systolic blood pressure at an alpha and a beta risk of 0.05 and 0.10 respectively would require the inclusion of approximately 15 subjects in a cross-over design study and 50 subjects in a parallel design study. 5 We conclude that, under our experimental conditions, non-invasive measurements of blood pressure and heart rate oscillations are reproducible. This technique can be used to assess the influences of diseases and drugs on the autonomic nervous system using a reasonably small number of subjects.