Actigraphy is graphical representation of motor activity as well as method of human motor activities monitoring. Aсtigraphy can be used both independently and as part of the combined methods of monitoring. Actigraphs, instruments for this technique, are widely used in sleep medicine, but may be integrated into devices for ABP and/or AECG monitoring.
The basic principles of aсtigraphy
The actigraph unit itself is an electronic device which generally consists of an accelerometer, a filter, an interface. You can understand the principle of a simple single-axis accelerometer, looking at the figure.
Imagine a box (1) inside which the mass (2) is suspended on the springs (3). When the box experiences acceleration (4), the mass is displaced to the point that the spring is able to accelerate the mass at the same rate as the box. The displacement (5) is then measured to give the acceleration value.
Of course, the accelerometers which are used for actigraphy are not so simple, but the principle is the same. Mechanical motions of mass which have inertia are converted into an electrical signal by piezoelectric, piezoresistive and capacitive components, or micro electro-mechanical systems. During the monitoring period these signals are filtered and recorded into the memory of device. If aсtigraphy is used in the monitoring of the cardiovascular system, aсtigram is analyzed synchronously with blood pressure and/or ECG.
The purpose of actigraphy using with ABPM and/or AECG
Diurnal variation in blood pressure (dipping/non-dipping status) can differ depending on the technique used to define awake and asleep periods. If you are using aсtigraphy for this, you will more accurately define the dipping/non-dipping status, than if you are using the patient diary. Similarly, actigraphy allows more accurate estimating the results of power spectral analysis of heart rate variability using 24-hour ambulatory ECG monitoring.