ACTIVITY AND POSITION MONITORING DURING AMBULATORY BLOOD PRESSURE AND HEART RATE MONITORING

P. Gosse(1), P. Guillo(2), M.L. Wetzler(3)

(1) Hopital Saint André, Bordeaux, France
(2) Clinique Saint Yves, Rennes, France
(3) Novacor, Rueil-Malmaison, France

Objectives
The main limitation in the interpretation of ambulatory BP monitoring is linked to high BP variability with activity and position changes. The analysis and quantification of such changes is thus an important objective, especially when assessing the effects of antihypertensive drugs.

Methods
We tested a new device (Quatrholter, Novacor France) allowing both BP and continuous ECG monitoring, equipped with a thorax position sensor and a two direction accelerometer fixed on the patient's thigh. These 2 sensors give continuous information on pt's position and on activity of the legs. 24h monitoring during daily routine was performed twice, 7 days apart, in 18 normal volunteers. BP was measured every 15 ¢ during day and night.

Results
The information from the 2 sensors allowed to classify the activity of the patients in 5 groups: Lying asleep, Lying awake, Sitting, Standing immobile, Walking or running (with information on walking speed). BP and HR were significantly influenced by these 5 conditions. The reproducibility of BP and HR measurements between the 2 recordings was analysed according to these 5 conditions. Results for SBP are summarised in table with mean values for the 2 recordings, standard deviation of differences (SDD) and coefficient of correlation (r). As expected, BP and HR measured when asleep or in sitting position were the most reproducible. BP measured when standing immobile or moving is much more variable from a recording to another.

	Mean	SDD	r
24h average (mmHg) Daytime Night-time Lying Sitting Standing Lying asleep Lying awake Sitting Standing immobile Walking	105.7 109.8 99.1 100.2 110.5 111.8 98.6 104.4 110.5 109.1 116.9	4.9 5.3 5.2 61. 4.3 9.5 4.4 9.3 4.3 11.3 9.7	0.84 0.85 0.85 0.72 0.93 0.55 0.87 0.67 0.93 0.4 0.66

Conclusion
This new device allows a reliable and efficient analysis of the patient's positions and activities during BP and HR monitoring. Analysis of BP and HR according to these information allow to limit the influence of changes in activity on the interpretation of the results.

Abstract: 4C.1
Journal of Hypertension Volume 23, Supplement 2, June 2005, page S135

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Validation of a two-axis accelerometer for monitoring patient activity during blood pressure or ECG holter monitoring.
 
Wetzler ML et al.

OBJECTIVES
The aim of the study was to evaluate the efficiency of a position/activity monitoring system based on a dual-axis accelerometer strapped to the subject's thigh and a position sensor located within a monitor placed on the subject's belt

METHODS
Twenty-six subjects wearing two monitors (one accelerometer on each thigh) were submitted to various activities and positions under the control of an observer. An analysis of each tracing was performed both manually by a technician and automatically by dedicated software before being compared with the information gathered during the study.

RESULTS
The accelerometer allowed accurate discrimination between the standing versus the sitting and lying positions. The sitting and lying positions were correctly detected by the built-in position sensor provided the unit was firmly attached. Walking was adequately detected by the accelerometer. The activity score was well correlated with treadmill speed. Changes in position and activity were detected with a mean error of less than 3 s.

CONCLUSIONS
The combination of an accelerometer placed on the subject's thigh and a position sensor located at the subject's waist appeared to be a suitable system for position/activity monitoring during ambulatory ECG and blood pressure monitoring.

Wetzler ML et al.: Validation of a two-axis accelerometer for monitoring patient activity during blood pressure or ECG holter monitoring.

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2003, Blood Press Monit., 8:229-35.