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.

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Theory and Developments in an Unobtrusive Cardiovascular System Representation: Ballistocardiography

The mechanism of cardiovascular action of nitroglycerine. An example of integrated response during the unsteady state.

Physical basis of ballistocardiography. III.

The ballistocardiograms of young normal subjects as recorded with a wide frequency range technic are described. These records contain high frequency forces not previously described. An analysis of these components in terms of known cardiovascular events strongly suggests that they have definite dynamic significance. In addition, these correlations offer evidence as to the genesis of some forces in the ballistocardiogram.

Wide frequency range force ballistocardiogram; its correlation with cardiovascular dynamics.

1. (1) The general characteristics of normal human displacement (D), velocity (V), and acceleration (A) ballistocardiograms from an ultra-low frequency (ULF) system have been described. 2. (2) Detailed time and amplitude measurements were made on the records (D, V, and A) obtained from 100 normal subjects from 20 to 39 years of age and some of the results reported. 3. (3) The possible role of certain general physical properties of the circulatory system in the origin of the ULF ballistocardiogram was briefly considered. 4. (4) The temporal relationship of human ULF ballistocardiograms (D, V, and A) to various mechanical events in the cardiac cycle was discussed. Tentative views were expressed concerning the origin of some of the waves of normal ballistocardiograms. 5. (5) The design, construction and performance of a practical and convenient ULF ballistocardiographic system, based on the differential-pendulum principle, is described in an appendix.

The nature of records from ultra-low frequency ballistocardiographic systems and their relation to circulatory events

In part I was discussed the nature and magnitude of force artefacts in the ballistocardiogram (BCG) arising from coupling the body to ground. The effect of this grounding on the reading of cardiovascular motion, momentum and force was explained, using the simple one-mass dynamics. Part II dealt with the effects on the ballistocardiogram of a second mass, a platform supporting the body. The body itself is a cutoff filter (of the resonant type) by its springy supporting tissues which couple the body and platform masses. In the displacement ballistocardiogram this attenuates the upper frequencies recorded from stiffly sprung platforms, or from the direct-body whatever its coupling to earth. In the acceleration record, the body mass and spring cut off the lower ballistocardiographic frequencies, while platform mass and body-spring cut off the higher frequencies. The size of these errors and their bearing on multilateral recording were discussed.)

W. K. Harrison

Papers

Dynamic Comparison of Current Ballistocardiographic Methods