NUMBER OF MEASUREMENTS REQUIRED FOR THE ANALYSIS OF DIURNAL BLOOD-PRESSURE PROFILE

The aim of this study was to investigate how frequent blood pressure ( BP) readings need to be obtained to reproduce the diurnal BP profile w ithout loss or distortion of information. The subjects were 97 normote nsives aged 23-84 years. Noninvasive ambulatory BP readings were progr ammed with an interval of 7.5 minutes during the day (from 8 am to 8 p m) and at 15 minutes intervals at night. Readings were stepwise omitte d from the original recordings. For each step the diurnal BP profile w as modelled with five different techniques. The concordance between or iginal and reduced recordings was quantified using the repeatability c oefficient, i.e. twice the standard deviation of the differences betwe en these recordings (expressed as a percentage of the 5th to 95th perc entile range of the parameter under investigation). The concordance be tween original and reduced recordings tended to be better for the leve l of pressure than for the parameters of the diurnal profile. If the s ampling frequency was two readings per hour, concordance for SBP was < 10% for the BP level, 19% for the 24h standard deviation, 12% for the nocturnal fall in BP, 23% for the amplitude of the Fourier curve and 17% for the cusum derived circadian alteration magnitude. Concordance worsened to > 25% for most parameters of the diurnal BP curve when the interval between consecutive measurements exceeded 30 minutes. If rec ordings with readings every 7.5 minutes during the day and every 15 mi nutes during the night are used as a reference frame, BP must be recor ded at least at 30 minute intervals throughout the 24h period in order to estimate most parameters of the diurnal BP profile with a concorda nce within 25% of near maximum variation.