The overriding influence of physical activity and the diurnal variation during ambulatory blood pressure monitoring (ABPM) has been well demonstrated. We prospectively evaluated the usefulness of electronic activity monitoring for deriving the actual physical activity and the diurnal variation of ABPM.

24-hour ABPM with using an electronic activity monitor was performed on ten normotensive volunteers and fifteen hypertensive subjects. To interpret the ABPM results of the fifteen hypertensive subjects, we obtained the actual awake/sleep periods of every subject with using an electronic activity monitor.

The activity values obtained from the ten normotensive volunteers correlated well with the values of the blood pressure (BP) and the heart rate. In the hypertensives, the nocturnal mean BP derived by the actual period was significantly lower than that derived by the arbitrary period (130±16/81±13 mmHg versus 124±13/77±12 mmHg, respectively, p<0.05). The nocturnal BP fall derived by the actual period was significantly larger than that derived by the arbitrary period (14.9±8.7/11.6±7.5 mmHg versus 21.1±8.6/16.2±7.4 mmHg, respectively, p<0.01). Four among the 7 non-dippers determined by the arbitrary period were re-classified as dippers when the actual period was used. One among the 13 hypertensives, as determined by the arbitrary period, was also re-classified as a non-hypertensive.

The electronic activity monitor was able to determine the actual activity level. The interpretation of ABPM may be altered by the use of the electronic activity monitor. These results suggest that the accuracy and reproducibility of the 24-hour ABPM will be improved by using an electronic activity monitor.