[Recognition of actual periods of nocturnal rest from 24-hour heart rate profile].

UNLABELLED: Inability to delineate exactly periods of nocturnal sleep and diurnal wakefulness during 24-hour blood pressure (BP) monitoring causes reporting of erroneous BP values for these periods. We suggested a simple mathematical algorithm for detection of periods of nocturnal rest determined as period of low values of cardiac rhythm using data of BP monitoring itself. AIM: To compare novel method of recognition of periods of sleep with 2 standard techniques: use of fixed time interval between 23 and 7 hours (1), or period of sleep according to patient's diaries (2). Reproducibility of nocturnal BP lowering between two 24-hour intervals during 48-hour blood pressure monitoring was used as a measure of precision of determination of diurnal/nocturnal BP. METHODS: Ambulatory 48-hour BP monitoring was carried out in 33 patients with uncomplicated stage II hypertensive disease. Automatic analysis of BP monitoring data was performed with the use of specially designed computer application. Standard deviation (SD) of differences (SDD) between pairs of nocturnal BP lowering during 48 hours was used as a measure of reproducibility. RESULTS: Reproducibility of values obtained with novel algorithm (SDD for systolic/diastolic BP 6.7/8.2 mm Hg) was substantially better than those obtained with standard methods (1) and (2) (SDD 13.0/14.8 and 13.5/18.3 mm Hg, respectively). CONCLUSION: The proposed method of recognition of the period of nocturnal rest substantially improved precision of automatic analysis of 24-hour BP monitoring.