Present studies evaluated the functions of thick and thin nerve fibers in carpal tunnel syndrome (CTS) to determine whether data of thin nerve fibers can add further information to the diagnosis of CTS. Measurements were performed in 22 patients and 16 age-matched control subjects. Motor and sensory nerve conduction, vibratory testing, thresholds of warmth and cold sensations, suprathreshold magnitude of pain and flare response, as well as sympathetic reflexes induced by noxious mechanostimulation were examined before and 1, 3, 6, 12, and 18 months after decompression of the median nerve. Nerve dysfunction in CTS was mainly indicated by the electrophysiological parameters of thick myelinated nerve fibers. Impairment of thin nerve functions in CTS and postoperative recovery was demonstrated by quantitative somatosensory thermotesting. In contrast, assessment of flare response and sympathetic reflexes using infrared thermography and photoplethysmography did not add further information for the diagnosis of CTS.

A commercial capacitive hygrometer device manufactured for use in technical or chemical laboratory environments has been used for quantitative and dynamic assessment of sweat gland activity in selected skin areas. For this purpose the hygrometer device was supplemented by a chamber attached to the skin for collecting evaporated water and a supply of dry nitrogen gas providing a gas flow through the chamber and through the hygrometer capsule. The accuracy of the technique was proven in pilot experiments in which fixed amounts of water were evaporated. A positive correlation was found between the weight of the water and the water evaporation computed from the hygrometer readings (r = 0.997). The time constant of the device was in the range of 10 s. This time constant appears to be fast enough for recording physiological changes in the sweating rate of human subjects. In experiments on healthy subjects sudomotor reflexes were assessed and compared to vasoconstrictor responses and to thermographically measured temperature changes of the skin during the Valsalva manoeuvre and a painful mechanical stimulus. Direct measurement of water evaporation such as by this technique may provide information on sympathetic reactions which could be utilized in both physiological and pathophysiological states.