Ballistocardiography
Principle
Ballistocardiography is a noninvasive technique
for the assessment of cardiac function by detecting and
measure the recoil (the reaction) of the human body due to the blood that the heart
is currently pumping (the action). It is the derivative of the momentum (mass x
velocity) and consequently has the dimension mass x length/time.
To be more precise a ballistocardiogram (BCG) measures
the impact of blood colliding with the aortic arch, which causes the body to
have an upward thrust (reaction force) and then the downward thrust of the
blood descending. The ballistocardiogram is in the 1-20 Hz frequency range.
One example of the use of a BCG is a
ballistocardiographic scale, which measures the recoil of the person’s body that
is on the scale. A BCG scale is able to show a persons heart rate as well as
his weight.
Sensors are often hidden in the upholstery of
the chair and the electronics is also hidden. In this way the subject is not
aware of recording.
Fig. 1 A BCG
signal with spikes and wave complexes (from ref. 1).
Fig. 2 ECG
and BCG records of a normal subject using 1-45 Hz band pass filter for ECG and
1-10 HZ for BCG. (Motion artifacts in BCG signal are not removed).
Application
The charm of the method is that no electrodes are needed to be attached to the body during
measurements. This provides a potential application to assess a patient's heart
condition at home. Recordings can be transmitted real time to the clinic.
The BCG can show main heart malfunctions by observing and
analyzing the BCG signal.
BCG is used in heamodynamic modeling for calculating pulsatile fluid flows with large Womersley number in large arteries around the heart and valves.
A 3D version of BCG has been used in spaceflight
during free-floating microgravity.
More
info
A BCG can be recorded from the surface of body with
accelerometers, specific piezoelectric foil
sensors or charge-capacitive sensors (e.g. EMFi sensor). The measured signal is amplified by a charge amplifier.
Often the BCG is recorded together with the ECG (one
lead by strips of copper on the arm rests to measure R-peaks for heart rate), respiratory rate, respiratory amplitude, and body
movements, all wireless. This integrated technique is also called the static
charge-sensitive-bed (SCSB) method. It is for instance used for recording body
movements after exercise and during sleep.
As holds for many biological signals (EEG,
ECG etc.) analysis is nowadays often performed by wavelet analysis or an or
another component analysis. The analysis may be proceeded by applying an
artificial neural networks (ANNs).
References
1. www.arehna.di.uoa.gr/Eusipco2005/defevent/papers/cr1069.pdf
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2. Akhbardeh A., Junnila
S., Koivistoinen T., Värri A. Applying
Novel Supervised Fuzzy Adaptive Resonance Theory (SFART) Neural Network and
Biorthogonal Wavelets for Ballistocardiogram Diagnosis. Proceedings of the 2006
IEEE, International Symposium on Intelligent Control,
3. Xinsheng Yu; Dent, D.; Osborn, C. Classification of ballistocardiography using wavelet transform and neural
networks. Engineering in Medicine and Biology Society, 1996.
Bridging Disciplines for Biomedicine. Proceedings of the 18th Annual
International Conference of the IEEE. 1996, 3,:937 - 938