Blood pressure levels and variance assessed by ambulatory monitoring: optimal parameters.

We obtained multiple ambulatory blood pressure monitoring (ABPM) records over five years from two trained, normotensive subjects experienced in wearing the apparatus. The resulting time series data on systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were used to suggest optimal parameters for monitoring by two instruments (Colin Medical Instruments ABPM-630 and Del Mar Avionics Pressurometer) and to compare two indirect methods (auscultatory and oscillometric). A 10-min sampling interval day and night provided sufficient density of data to support spectral analysis for ultradian rhythms in the frequency range of one cycle per hour to one cycle per 9 h on a 24-h record. Rhythms with major periods of approximately 3, 6, and 9 h were variously found in 94 normotensive subjects, aged 20 to 95 years, including the two trained subjects. When the monitoring period was extended to 72 h, the circadian (approximately 24 h) rhythm could be more sharply defined, as well as a 12-h harmonic. In some studies the two trained subjects wore two monitors, one on each arm, set to read simultaneously. From the simultaneous measurements on both arms, it was shown that averaging across three points (30 min of record) reduced the coefficient of variation between the two simultaneous records to 6% or less. Auscultatory and oscillometric methods were equally reliable. Echocardiographic data were obtained in five normotensive subjects and compared to their ABPM data. The ABPM records provided additional information about cardiovascular function not merely duplicating that obtained by acute stress tests, such as exercise or cold pressor responses, or echocardiography. Standards for ABPM are suggested.