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.

About: This article is published in American Heart Journal.The article was published on 1962-07-01 and is currently open access. It has received 11 citations till now.

Summary

Instruments

• 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.

Results

• 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.

Discussion

• (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.

Figures

Table 1V. Average values and standard deviations for restoring jorce and damping as the 3 subjects were tightened on our HF table

Table V. Averages of the di’erences found between the four main systolic waves of ULF and HF ballistocardiograms in 30 healthy men and 20 healthy women

Fig. 2. Our ULF ballistocardiograph. A, The table. B, “Mine jacks,” columns of heavy pipe extending between floor and ceiling to support the frame from which the table is suspended. Only the base is shown in the figure. C, Support wires. D, Lateral support. F, Coils shown withdrawn from magnets E. G, Footboard.

Table VII. Comparison of the clinical interpretation given to HF and ULF records secured on the same persoq in 250 patients

Table III. Effect of tightening the subject on the HF table. The frequency and damping of movement between subject and table under various conditions

Fig. 19. Response of the ULF instruments to a triangular shaped internal acceleration of the center of gravity 2, (proportional to internal force) (boltom in B, D, F, and H). A, (kq5) The acceleration ib of the T’LF instrument for cases a and d of Fig. 18,A and B. D, (lop) The displacement xb of the HF instrument for the same cases. F, (top) The acceleration ?b of the ULF instrument for cases a and d of Fig. 18,D and E. H, (top) The displacement xb of the HF instrument for the same cases.

Fig. 4. Our newest HF ballistocardiograph, shown tilted, and in the horizontal position in which it is usually employed. A, The table. Neither the S-cm. suspension nor the strong restraining spring is shown. The table is made of 24 st aluminum, and with the footplate and bracing weighs 24 kilograms. B, The footplate. C. Movable crossoiece and DiDes L I which attack it to ‘footplate, used ‘to support the shoulder yoke. D, Main table frame of cold rolled steel, weighing 110 kilograms. E, Base frame of cold rolled steel, also weighing 110 kilograms. F, The lifting mechanism, which weighs about 90 kilograms. Between base frame and floor are 4 pads of corrugated rubber and 2 of cork, each about 7 by 7 cm. and 7 mm. thick.

Fig. 5. Diagram of the movement of the body on a HF table, or on any other immobile surface, when a force applied headward or footward is suddenlv released.

Fig. 17. Forces registered in ULF records after a transient force has been applied and withdrawn as rapidly as possible. Top row: Typical examples of records secured after the subject was tapped on the head. Bottom WW: Typical examples of records obtained when a thread attached around the chest, neck, or feet was pulled until it broke. Note the secondary vibrations set up and the slow return to the base line often seen. The record was attenuated until the ballistocardiogram was hardly detectable.

Frequently asked questions

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.