The Rydel-Seiffer tuning fork is an (almost) normal tuning fork with fundamental frequencies of 64 and 128 Hz, the natural C and c vibrations, which differ slightly from the concert pitch vibration commonly used today, which is based on the concert pitch a at 440 Hz. The Rydel-Seiffer tuning fork is used to diagnose functional impairments of the peripheral nerves, as well as to diagnose whether a middle ear or sensorineural hearing loss is present when hearing impairment is present.
What is the Rydel-Seiffer tuning fork?
The name Rydel-Seiffer tuning fork can be traced back to Adam Rydel and Friedrich Wilhelm Seiffer. The name Rydel-Seiffer tuning fork goes back to Adam Rydel and Friedrich Wilhelm Seiffer, who both jointly proposed a method for measuring vibration sensation using a tuning fork in 1903. Today, the tuning fork and method still represent an important and initial diagnostic procedure for detecting neuropathy or other problems of the peripheral nervous system. In addition, the Rydel-Seiffer tuning fork is a simple and reliable way to determine whether a hearing loss is a middle ear or sensorineural hearing loss. In principle, it is a tuning fork in the fundamental frequency c with 128 Hz, whereby two weights (vibration dampers), which are attached to both ends of the tines, reduce the vibration by one octave to 64 Hz. Vibration sensitivity measurements are always performed with dampers attached, i.e. with a vibration frequency of 64 Hz. The dampers bear markings and a scale from 1 to 8, from which the vibration intensity can be read visually. After the tuning fork is tapped, the vibration corresponds to 1 and gradually reaches the value of 8 immediately before the vibration completely decays. The use of the Rydel-Seiffer tuning fork is based on the knowledge that vibration sensation can serve as the best early indicator in neuropathological impairments. At 64 Hz, the C vibration does not quite match the concert pitch, whose low C vibrates at 65.4 Hz.
Shapes, types and kinds
All Rydel-Seiffer tuning forks offered in specialized shops work on the same principle. They are always tuning forks that vibrate at 128 Hz when the dampers are not attached and one octave lower, at 64 Hz, when the dampers are screwed on. All Rydel-Seiffer tuning forks suitable for neuropathological examinations have two triangles each, which produce an optical effect from which the respective vibration intensity can be read. The standardized intensity scale ranges from 1 (strong vibration) to 8 (weakest vibration). The price range for Rydel-Seiffer tuning forks suitable for use in medical diagnostics is kept within narrow limits. Neuropathological measurements of peripheral nerves are always performed only at the frequency reduced to 64 Hz, while weights are removed for examination of hearing.
Structure and mode of operation
Rydel-Seiffer tuning forks are very similar in construction to the tuning forks used in music. However, they always have a hard rubber base which, after the tuning fork has been scribed, can be placed on specific parts of the body – preferably perpendicular to the surface of the skin – in order to measure the vibration sensitivity at the corresponding point or of a specific nerve. The two weights, which can be placed on the two ends of the tuning fork and screwed tight by means of knurled screws, not only serve the purpose of reducing the vibration from 128 Hz to 64 Hz, but also allow the respective vibration intensity to be read. To measure the vibration sensitivity, the tuning fork is scribed and the foot is placed on the terminal site of the nerve to be examined. If a systemic neuropathy is suspected, the foot of the torn tuning fork can be placed, for example, on one of the four tarsometatarsal joints that connect the metatarsal and tarsal bones. The so-called Weber and Rinne tests, both of which are performed with the dampers removed, i.e. at 128 Hz, are used to examine hearing deficiencies. With the attenuators removed, the vibration intensity can no longer be read, which is not a problem in the hearing tests, since they are mainly concerned with qualitative effects.
Medical and health benefits
Sensory vibrations are perceived by the so-called Vater-Pacini corpuscles.These are medullary ends of peripheral nerves surrounded by a medullary sheath. The nerve endings are surrounded by lamellae, encapsulated and found in varying density in the subcutis. The Vater-Pacini corpuscles have the highest sensitivity of all mechanoreceptors, so that they also react very sensitively to functional restrictions of the sensitive nerves, for example as a result of an incipient neuropathy. Neuropathies can be caused, for example, by metabolic disorders as a result of diabetes, by manifest deficiency of vitamin B-12, by neurotoxins, by bacterial nerve inflammation or also by chronic alcohol abuse. The detection and rough quantification of such nerve damage can be performed very inexpensively – and yet accurately – with little effort by testing with the Rydel-Seiffer tuning fork. The tests and subsequent diagnosis must take into account that vibration sensation diminishes with age. While younger people should still perceive the lowest level on the Rydel-Seiffer tuning fork (8/8), the decrease in sensitivity to 6/8 in people over 70 represents the normal case. Another possible application concerns the qualitative testing of hearing in the presence of hearing loss. Hearing loss can be caused by problems with the outer ear (ear canal and eardrum), the middle ear (ossicles), or the inner ear (cochlea). While damage in the outer ear, such as a blocked ear canal or a defective eardrum, is relatively easy to diagnose, it is difficult to distinguish whether there is a problem in the conversion of the received sound via the ossicles to the cochlea or whether the hearing loss is due to the conversion of the mechanical stimuli to nervous impulses and the transmission. The so-called Weber test and the subsequent Rinne test, both performed with the Rydel-Seiffer tuning fork without weights (i.e., at 128 Hz), provide certainty as to which ear has sensorineural or middle ear hearing loss.
