Rydel and Seiffer vibrating fork
The Rydel-Seiffer tuning fork (named after Adam Rydel and Friedrich Wilhelm Seiffer ) is a medical instrument that can be used to examine people's sensation of vibration ( pallesthesia ).
Physical and physiological basics
The legs of a tuning fork vibrate horizontally, creating vertical vibrations / shock movements of the tuning fork handle. If the tuning fork handle is placed on an object (capable of vibrating), the impact movements are transferred to it and make it vibrate (through energy transfer). This dampens the oscillation amplitude and shortens the period of oscillation. Receptors for vibration stimuli in humans are the Pacini bodies at the endings of myelinated Aβ nerve fibers; through their stimulation, the sensory modality “vibration sensation” (pallesthesia) arises.
Description of the instrument
It is a common 128 Hz tuning fork that is approx. 23 cm long and specially prepared. Its legs are weighted at the ends with removable metal weights of 25 g each (which reduces their natural frequency to 64 Hz). A geometric figure (Gradenigo triangle, after Giuseppe Gradenigo (1859–1926)) and an eight-part scale ascending from proximal to distal are printed on the weights. A modern Rydel-Seiffer tuning fork, as shown, weighs approx. 128 g.
Gradenigo triangle
When looking at the Gradenigo triangle, which oscillates back and forth 64 times per second, the human eye sees the triangle, which is deflected to the right and left, at the same time and quasi stationary, and in between, due to the partial superposition of both triangle phenomena, the impression of a likewise non-oscillating third triangle . This becomes larger and larger with the weakening oscillation, its tip tends towards the end of the scale (from 0 to 8), while the lateral triangles move closer and closer together and their overlap increases. If the vibrations have come to a standstill, the three triangular phenomena are completely superimposed in a resting Gradenigo triangle.
This optical phenomenon is based on the property of the human eye to no longer distinguish images that act more than 30 times per second in succession as individual images, but to merge them - this makes it possible to project more than 30 Images per second to create the impression of “moving images” in the viewer (film). See also flicker fusion frequency .
Use of the instrument
The examiner holds the tuning fork on the handle with one hand between thumb and forefinger and sets it in maximum vibrations with the other hand (by squeezing and abruptly letting go of the legs). He places the end of the stalk on the structure to be examined (e.g. a palpable protrusion of bone such as the metatarsophalangeal joint of the big toe) and observes the swinging of the thighs based on the visual appearance of a Gradenigo triangle.
These phenomena and their meaning are reproduced here in the words of the first person to describe them:
The weights (clamps) placed on the tuning fork carry a strip of paper with a geometric figure, preferably a high, black triangle (see Fig. 2 and 3). The height of the triangle is divided into several equal parts by vertical lines. If you now set the tuning fork provided with it vibrating, the contours of the triangle are blurred, in that two blurred triangles located next to each other are created. With the decrease in amplitude, i.e. at the same time as the intensity of the vibration sensation decreases, the two triangles gradually dissolve into one, which lies in the middle between the blurred ones and becomes higher and higher during the further decrease in the oscillation amplitude, i.e. with its apex ever higher horizontal lines reached. Only when the fork has stopped swinging completely do we see the original triangle completely and sharply contoured again. According to Gradenigo, the time values in which the triangle passes from one horizontal line to the other behave as n²: n³: n4: n5. If we now name the individual tick marks with numbers, we can designate the duration of the sensation according to these numbers; It is then also possible to briefly state that with a certain individual and with a certain tuning fork the vibration is felt at this and that point up to the division 3, 4 or 5, etc. [...] The period of time during which the optical figure still shows vibrations is indicated by the numbers 1 to 8, depending on the horizontal line; If the feeling of vibration lasted a little longer in the examined person than the visible vibration of the optical figure, we designated this degree with the number 9, but a very long persistence of the feeling of vibration with the number 10. (A. Rydel, W Seiffer, Archiv für Psychiatrie and Nervous Diseases 1903; 37 (2): 488-536)
The maximum period of oscillation from the beginning of the oscillation (on scale 0) to the end of the oscillation is approx. 30 seconds. The division 8 on the scale - and thus the vibration standstill - is reached for the human eye after approx. 20 seconds. By placing the tuning fork base on an object that can vibrate, vibration energy is transferred from the tuning fork to the object, which dampens the vibrations and shortens the maximum period of oscillation to approx. 25 seconds (and accordingly the time intervals between the graduation marks).
The time intervals calculated according to Gradenigo until reaching the next scale division are listed in the table, based on an interval of 8 seconds between division 7 and 8:
| Time intervals between the tick marks calculated according to Gradenigo | ||
| Scaling, tick marks | Time interval, rounded | |
| 0-1 | 1.02 seconds | |
| 1-2 | 1.03 seconds | |
| 2-3 | 1.07 seconds | |
| 3-4 | 1.14 seconds | |
| 4-5 | 1.29 seconds | |
| 5-6 | 1.68 seconds | |
| 6-7 | 2.8 seconds | |
| 7-8 | 8 seconds | |
The table shows that vibrations with a large oscillation amplitude (up to division 3) only take place for a total of 3 seconds, and up to division 5 there is only about 1 second per division interval for reading. This fact strongly affects the accuracy of the reading in this scale range and means that values> 4 can be read more reliably (and therefore probably more frequently diagnosed) than values <4.
The subdivision of the oscillation duration can be viewed as a measure for the subdivision of the oscillation amplitude, because the oscillation amplitude is inversely related to the duration of the oscillation and decreases exponentially with time after the oscillation begins, as McKinley demonstrated in 1928 on a 128 Hz tuning fork. The oscillation amplitude and thus the vibration stimulus is greatest at 0 and smallest at 8.
Relationship between oscillation amplitude and oscillation duration
Carol Liniger et al. were able to use parallel measurements with an electromagnetic vibrameter and the Rydel-Seiffer tuning fork to assign the corresponding vibration amplitudes (in µm) to the eighth graduation marks on the scale from 0-8.
| Rydel-Seiffer tuning fork, oscillation duration and oscillation amplitude, after Liniger 1990, Fig. 2 | ||
|---|---|---|
| Period of oscillation, according to the scale | Vibrameter (vibration amplitude, median (range), µm) | |
| Section 1-2, corresponds | approx. 15 (4-170) µm | |
| Section 3-4, corresponds | approx. 7 (2-22) µm | |
| Section 5-6 | approx. 1 (0.5-7) µm | |
| Section 7-8 | approx. 0.4 (0.1-4) µm | |
Examination process and interpretation of the findings
The person to be examined is informed that the use of the tuning fork causes them to vibrate and that they should state the exact point in time at which their perception of these vibrations has completely ceased. The tuning fork, which is set in maximum vibrations, is placed on the structure to be examined, with the examiner keeping a close eye on the Gradenigo triangle on one tuning fork leg and having the person examined specify the exact point in time (now!) At which the feeling of vibration has ceased . At this point the position of the triangle tip on the eight-part scale is read by the examiner.
A low value on the scale means a high perception threshold (low sensitivity), a high value the opposite.
According to modern understanding, the read result should not represent the duration of vibration perception (oscillation duration), but the perception threshold for a certain stimulus strength (vibration strength, vibration amplitude), as Lehmacher and Berger put it in 1992: The tuning fork has a measuring device (scaling from 0-8) which the oscillation amplitude can be read off and thus a quantification of the vibration sensitivity is possible.
Carol Liniger et al. not only validated the Rydel-Seiffer tuning fork in 1990 with an electromagnetic vibrameter, they also created age-adjusted tuning fork standard values and made findings in the case of diabetic polyneuropathy .
Limitations of the Rydel-Seiffer investigation method
Since the oscillation amplitude of a tuning fork decreases exponentially after the beginning of the oscillation, coarse oscillation (large amplitude, rough vibration) only occurs very briefly after the beginning of the oscillation and can only be visually detected with difficulty by the examiner at the Gradenigo triangle; In contrast, moderate and weak vibrations can be safely observed by the examiner. The stimulus presentation of the different vibration strengths (vibration amplitudes) is of different length, which impairs the comparability of the perceptions of different vibration strengths: very brief, coarse vibrations can only be felt indistinctly by the person examined, long-lasting weak vibrations can be felt comparatively excessively. The variance of the measurement results is therefore considerable, a vibrameter ( pallesthesiometer ) measures more precisely.
Clinical dissemination
The Rydel-Seiffer tuning fork has been used around the world since 1990, is currently used in the context of quantitative sensory testing , and is required by the diabetes disease management programs (DMP) of the German health insurances and the national supply guidelines for diabetes mellitus.
Diagnostics for nerve damage
When examining suspected nerve damage, the Rydel-Seiffer tuning fork allows the detection of so-called polyneuropathy damage. One uses the fact that the vibration sensation can be impaired (pallhypesthesia).
Web links
A. Rydel, W.Seiffer: Investigations into the vibration sensation or the so-called bone sensitivity (pallesthesia) . Retrieved May 27, 2020 .
https://en.wikipedia.org/wiki/Tuning_fork
literature
- A. Rydel and FW Seiffer: Investigations into the feeling of vibration or the so-called "bone sensitivity" (pallesthesia) . In: Archiv für Psychiatrie und Nervenkrankheiten , 37 (1903), pp. 488-536.
Individual evidence
- ↑ JC. McKinley: A simple method for determining the threshold value of vibration sense . In: Proc Soc Exp Biol Med . tape 25 , 1928, pp. 827-831 .
- ↑ C. Liniger, A. Albeanu, D. Bloise, JP. Assal: The tuning fork revisited . In: Diabetic Medicine . tape 7 , 1990, pp. 859-864 , doi : 10.1111 / j.1464-5491.1990.tb01319.x .
- ^ J. Charnley McKinley: A Simple Method for Determination of Threshold Value of Vibration Sense. In: Proceedings of the Society for Experimental Biology and Medicine. 1928, pp. 827-831 , accessed July 20, 2020 .
- ↑ Emil Joseph Lehmacher, Michael Berger: The history of the Rydel-Seifferschen tuning fork . Kirchheim Verlag, Mainz 1992, ISBN 3-87409-059-0 .
- ↑ JM. Goldberg, U. Lindblom: Standardized method of determining vibratory perception thresholds for diagnosis and screening in neurological investigation . In: J Neurol Neurosurg Psychiatry . tape 42 , 1979, pp. 793-803 .