PROSPECTIVE STUDY ON TACTILE SENSITIVITY IN THE HANDS OF A BRAZILIAN POPULATION USING THE PRESSURE-SPECIFIED SENSORY DEVICE

Thin slices of the finger pads of six individuals were fixed in buffered 1 per cent osmic acid, embedded in deaerated, nitrogenated methacrylate, and cut into thin sections for electron microscopic study. Before embedding, the slices were trimmed so as to include several digital tactile corpuscles. Some thin sections were stained in 10 per cent aqueous phosphotungstic acid solution. The principal part of Meissner's corpuscle is made up of flattened laminar cells stretching across the corpuscle in irregular layers. The perinuclear cytoplasm of these cells contains numerous small mitochondria, a sparse granular endoplasmic reticulum, and a large number of small vesicles. Nerve fibers enter the side or base of the corpuscle, lose their myelin sheaths, and follow a meandering course between the laminar cell plates. The nerve endings enter into a close appositional relationship with the flattened portions of the laminar cells. In some areas the apposed axolemma and cell membranes are slightly thickened with small vesicles located along the cell membrane or on both surfaces. These regions are interpreted as synapses. The most prominent feature of the nerve endings is an extraordinary accumulation of small mitochondria which vary in size and internal density. The nerve endings also contain vacuoles, groups of dense concentric membranes, and small dense vesicles of irregular distribution. The laminar cells are separated from one another by a dense intercellular substance of uniform thickness which also envelops the entire corpuscle. This material contains randomly oriented collagen fibers and fine fibrils bound together by a dense material at nodal points recurring at regular intervals of approximately 120 mµ. These findings are discussed in relation to the problems of the function of Meissner's corpuscle, neural material loss and replacement, and the presence of synapses.

To compare vibrotactile thresholds between five international test centres, to determine causes of variability, and to provide normative data for use by health professionals. Vibrotactile thresholds were measured on various fingers in 1,008 subjects at 31.5 Hz (2,531 measurements) and at 125 Hz (2,807 measurements). Three centres used the up-and-down method of limits, rate of change of stimulus 3dB/s, to obtain vibrotactile thresholds. The push force on the surround was 2 N, the probe contact force was 1 N and the probe diameter was 6 mm concentric to a 10-mm diameter hole in the surround. One centre used an up-and-down method of limits with a 5-dB step and a 1.26-mm diameter probe with no surround. Another centre used a stepping algorithm, no surround, and the force on the 6-mm-diameter probe was unspecified. The 31.5-Hz thresholds and 125-Hz thresholds, expressed in dB, were similar between centres using similar methods. There were small (<5 dB) differences in vibrotactile thresholds between male and female subjects, between white-collar and blue-collar workers and between fingers. Both 31.5-Hz and 125-Hz thresholds increased with age; the mean effect of age on 31.5-Hz thresholds was approximately 2 dB over 25 years, while the effect of age on 125 Hz-thresholds was as high as 10 dB over 25 years. Vibrotactile thresholds are influenced by measurement method but can be similar at different centres if similar methods are used. Effects of measurement location and gender are often negligible. Thresholds depend on age, but over the range of ages considered, only the effect on 125-Hz thresholds is sufficient for correction; methods of correcting for age are given. These normative data may be used to assist the diagnosis of peripheral neuropathy involving vibrotactile sensation.