We assessed the OSCILL-IT ambulatory blood pressure (BP) recorder (FIGI sr1, Rome, Italy) according to the performance criteria set out by the British Hypertension Society (BHS) protocol. The OSCILL-IT is a portable, noninvasive recorder that uses a process that correlates systolic, mean, and diastolic areas, identified on the oscillations, to the cuff absolute pressure. According to the recommendations of BHS, a large heterogeneous population (100 subjects: 52 men aged from 19 to 79--median 44 and 48 women from 19 to 74--median 54) was recruited in order to assess accuracy and to analyze, in addition, the effects of observer agreement and BP level on the observer-device differences. With reference to BP level, we suggest also a new graphic approach. Four sets of sequential, same arm, comparative BP measurements were obtained, performed by the OSCILL-IT recorder and two skilled clinicians using a mercury column, for each subject. We used a linear combination for the statistical evaluations. We confirmed the observer agreement through the frequency distribution of BP as a function of the observer and through the differences between observers. We compared OSCILL-IT with sphygmomanometric readings: the differences were not significant. A visual inspection, with the addition of regression lines, showed that there were no variations in differences at the changing of BP level. The difference between observers and OSCILL-IT was 0.2 +/- 5.3 mm Hg and 0.2 +/- 5.8 mm Hg both for systolic BP (SBP) and diastolic BP (DBP). The level of agreement, according to BHS criteria, showed that 64% of all systolic and 70% of all diastolic readings obtained by the OSCILL-IT were within 5 mm Hg of the sphygmomanometric determinations. Therefore, the grade is C for SBP, even if 93% of SBP and 95% of DBP obtained by the OSCILL-IT were within 10 mm Hg of the sphygmomanometric determinations. These analyses demonstrate that the OSCILL-IT satisfies the accuracy parameters and the additional linear regression yields graphics more immediate.

This study analyzes some methods of evaluating the effects of antihypertensive drugs on blood pressure circadian rhythm. We reviewed four different approaches: hourly averages, trough-to-peak ratio, cosinor method, and Fourier series applied to the same data to prove the time course of the effects of isradipine administered once daily. A total of 141 patients of both sexes (mean age 53 years, range 30-76) with mild to moderate essential hypertension were enrolled in this multicenter trial after a 2-week placebo run-in. Treatment with isradipine SRO 5 mg/day administered between 8 and 9 AM was started. Each patient underwent ambulatory BP monitoring at the time of entry and after 6 weeks of treatment. Calculation of hourly averages showed decreases after 4 AM, and from about 8-9 AM, when the drug was administered, and the decreases practically did not vary until about 10 PM. Subsequently, the decreases became smaller and indicated reduced drug activity. However, this hypothesis no longer held after 4 AM. The trough-to-peak ratio was calculated including hourly averages after the dose divided by the lowest hourly average. Both systolic and diastolic blood pressure showed constant reduction from 3 PM (time of peak) to 11 PM. However, after 11 PM, higher trough-to-peak ratios paradoxically occurred due to a major reduction obtained with placebo, and the negative percentages just before the next dose cannot be attributed to treatment. Applying the cosinor method, maximal values were greatly underestimated, nocturnal values were overestimated, and the absolute maximum occurred in proximity to the minimum relating to postprandial dip. The generalized cosinor model, known as Fourier partial series, was always curtailed to the third harmonic. Fourier analysis was able to describe the daily trend of BP both before and after isradipine administration. We used statistical tests to determine if the differences described by the models were significant. The tests indicated significant mean level reductions after therapy and no appreciable amplitude and phase-related variations. The nocturnal and periawakening intervals, in which BP changed linearly, oscillated between 3 and 4 hours. Within these intervals BP rose by 13-16 mm Hg or fell by 14-19 mm Hg. The intervals, ranges, and speed differences were tested and were never significant. The medication tested was effective only at the mean level, the variables used to characterize the time course of its effect remaining unchanged. There was no significant phase shift of the curves, and BP rhythm was preserved.

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