A comparison between ultralow-frequency ballistocardiograms and those secured by an improved high-frequency technique, with studies to explain remaining differences.
TL;DR: The advance in ballistocardiographic instrumentation which has been so rapid and so encouraging in recent years has been due primarily to the use of certain physical principles, but on the assumption that well-known physical formulae could be properly applied to the vibration problems of the human body, a new viewpoint emerged.
Abstract: The advance in ballistocardiographic instrumentation which has been so rapid and so encouraging in recent years has been due primarily to the use of certain physical principles. On the assumption that well-known physical formulae could be properly applied to the vibration problems of the human body, a new viewpoint emerged. This included a well-based criticism of the high-frequency (HF) ballistocardiograph, ¹⁻² i.e., that the movement which took place between body and table was introducing an error, and that the vibration properties of this movement between body and table led to an undue magnification of certain components of the recorded forces, those delivered in resonance with the body's own vibration properties, and undue attenuation of others, those above the body's resonance frequency. It was proposed to avoid or minimize such errors by using another type of instrument, the ultralow-frequency (ULF) ballistocardiograph.³⁻⁶
Summary (2 min read)
- Because their room had a low ceiling, their bed---like Rappaport's instrument, and like Henderson's table of 50 years agois displaced laterally by a pair of pins (AC, Pig. 3), sharp at each end and 13.7 cm. long.
- This system renders their records almost altogether free of building vibration.
- Of great value has been a secondary electrical circuit, with dry cells and a milliammeter, which indicates when one of the magnets touches the inside of its coil, an error of technique very likely to pass unnoticed without this warning device, and capable of causing marked distortion of the ballistocardiogram.
- On the assumption that the body moves methods of tightening the subject the as a unit, the physical characteristics of restoring force and damping are about the coupling between body and table can doubled.
- Comparison of the ULF and HF force records ift healthy persons.
- The measurements secured in the 30 men were used to construct a grand average normal male ballistocardiogram of the HF type, and another of the ULF type.
- The tips of the H and I waves of the HF records follow those of the ULF records by an average of 0.012 and 0.022 second, respectively, and these are significant differences.
- In the first group are the differences in size and shape of the waves.
- If this were true, the authors should be able to start with the record secured by one instrument and, through the use of physical principles, compute the record of the other.
It became possible only recently
- With the development of the digital computer.
- The authors took as a starting point a typical complex secured by the low-frequency instrument, a complex midway between the largest and smallest ones of the respiratory cycle.
- The results (Figs. 12,D and 13,D) show clearly that the curves thus constructed from measurements made on low-frequency ballistocardiograms bear a close resemblance in shape and amplitude to the HF ballistocardiograms (Figs. 10 and 11 ) secured experimentally on the same subjects.
- Obviously, therefore, the authors have a clear understanding of the reason for the major points of difference between the two types of records,9 the average differences of wave height and timing shown in Fig. 7,A and B .
- Theoretical studies on the effect of loose masses within the body.
- (a) The HF force tracing is distorted by movement of the body on the table, although it should be noted that because of recent improvements this movement is much smaller and the distortion caused is much less than that sometimes seen on records secured by older instruments with high natural frequency.
- It is far from certain that all the slurs and notches so commonly seen in ULF ballistocardiograms have their origin in the circulation, and, if not, a better estimate of circulatory abnormalities might be made if they were not recorded.
- The chief argument in favor of a circulatory origin for the notches so often seen in ULF record lies in their apparent movement with respiration.
- Chiefly because of the difference in J-wave amplitude, the over-all amplitudethe vertical distance between the tips of the I and J waves-is larger in HF than in ULF records.
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Cites background from "A comparison between ultralow-frequ..."
...The issue of comparing BCG displacements, velocities, and accelerations has also been raised: Starr and Noordergraaf remarked on the similarity of the HF BCG (displacement) to the second derivative (acceleration) of the ULF BCG ....
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Q1. What are the contributions in this paper?
With this experience before us the instrument used in this study was constructed by Mr. George Peirce. The authors expected that a study of the differences between the two force records would provide important information, because each instrument approached the problem from a different direction, and neither method seemed altogether free of error.