Theory and developments in an unobtrusive cardiovascular system representation: ballistocardiography

Abstract

Due to recent technological improvements, namely in the field of piezoelectric sensors, ballistocardiography - an almost forgotten physiological measurement - is now being object of a renewed scientific interest.Transcending the initial purposes of its development, ballistocardiography has revealed itself to be a useful informative signal about the cardiovascular system status, since it is a non-intrusive technique which is able to assess the body's vibrations due to its cardiac, and respiratory physiological signatures.Apart from representing the outcome of the electrical stimulus to the myocardium - which may be obtained by electrocardiography - the ballistocardiograph has additional advantages, as it can be embedded in objects of common use, such as a bed or a chair. Moreover, it enables measurements without the presence of medical staff, factor which avoids the stress caused by medical examinations and reduces the patient's involuntary psychophysiological responses.Given these attributes, and the crescent number of systems developed in recent years, it is therefore pertinent to revise all the information available on the ballistocardiogram's physiological interpretation, its typical waveform information, its features and distortions, as well as the state of the art in device implementations.

Keywords: Ballistocardiography; biomedical measurements; cardiac signal analysis; cardiovascular system monitoring; unobtrusive instrumentation..

Fig. (1)

Depiction of typical displacement records from different ballistocardiographic systems shown to illustrate differences in timing of waves and relationship between them and the electrocardiogram and phonocardiogram. In descending order: electrocardiogram, phonocardiogram, ultra-low frequency ballistocardiograph [4, 5, 10-14], Starr’s ballistocardiograph [8], Nickerson’s ballistocardiograph [9], and Dock’s ballistocardiograph [15-19].

Fig. (2)

Depiction of the typical waveforms obtained from a direct body system showing the relationship to the carotid pulse, and electrocardiogram. In descending order: electrocardiogram, carotid pulse, acceleration ballistocardiogram, velocity ballistocardiogram, and displacement ballistocardiogram (adapted from [48]).

Fig. (3)

Depiction of the typical waveforms obtained from an ultra-low frequency system showing the relationship to the electrocardiogram. In descending order: electrocardiogram, acceleration ballistocardiogram, velocity ballistocardiogram, and displacement ballistocardiogram.

Fig. (4)

Composition showing ballistocardiogram, apex cardiogram, and phonocardiogram (in descending order).

Fig. (5)

MB-1 Ballistocardiograph, image courtesy of Nihon Kohden.

Fig. (6)

Ballistocardiograms obtained from a chair’s seat and backrest with the device of [126], with some fluctuations due to motion being noticeable. These two measurements spots give emphasis to different waves of the BCG. The backrest sensor highlights the ejection waves. The seat sensor outputs pre-ejection and ejection waves with similar amplitude..

Fig. (7)

Prototype described in [58], implementing skin conductivity and ballistocardiogram acquisition and processing.

Fig. (8)

Radar BCG system implemented in [162]. Block diagram and signal obtained for a healthy subject.