[Influence of measurement duration and frequency on ambulatory blood pressure monitoring].
OBJECTIVE
Most studies of ambulatory blood pressure monitoring have involved taking measurements every 15-30 minutes over a 24-hour period. We investigated the effect of measurement duration and frequency on the diagnostic blood pressure values obtained by ambulatory monitoring.


METHODS
The study involved 1450 hypertensive patients and a control group of 378 normotensive volunteers. Blood pressure was measured at 20-minute intervals from 07:00 to 23:00 and at 30-minute intervals at night for 48 consecutive hours. Data were subdivided in such a way as to generate different series of data that were collected at 1-, 2-, 3-, or 4-hour intervals over the 48-hour period. In addition, two data series at the original measurement frequency were derived for the first and second 24-hour periods. The correspondence between the mean blood pressure values derived from the original data series and those from the different subdivided data series was assessed.


RESULTS
Variability in the estimated mean blood pressure increased progressively as the measurement frequency decreased: the error range grew from 11 mmHg for hourly data to 28 mmHg for 4-hourly data. The error range was even greater (i.e., 36 mmHg) for data divided into 24-hour series at the original sampling rate.


CONCLUSIONS
This study demonstrates that the reproducibility of mean blood pressure values depends more on measurement duration than measurement frequency. The findings indicate that monitoring blood pressure for only 24 hours may be insufficient for diagnosing hypertension, identifying a dipper circadian pattern, or assessing treatment efficacy.
Hermida
Ramón C
RC
Laboratorio de Bioingeniería y Cronobiología, Universidad de Vigo, Campus Universitario, Vigo, Spain. rhermida@uvigo.es
Ayala
Diana E
DE
Fernández
José R
JR
Mojón
Artemio
A
Calvo
Carlos
C
D001794:Blood Pressure / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory / Q000379:methods* / Q000706:statistics & numerical data; D002940:Circadian Rhythm / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006973:Hypertension / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013997:Time Factors