Effects of underwater environmental conditions on vibrotactile thresholds

Abstract

The effects of low-frequency, water-borne vibration upon the cutaneous surface of swimmers and divers are virtually unknown. It has been reported that divers can ‘‘feel’’ underwater sounds on various parts of their bodies. The current experiments were conducted in two parts as initial investigations of these reports. The first experiments were to determine if changes in barometric pressure and breathing mixture have an effect on vibrotactile thresholds measured in air. Vibrotactile thresholds at the thenar eminence were measured on eight divers during two saturation dives in a dry hyperbaric chamber. Measurements were made on four subjects before and after a 6-day saturation dive that simulated an excursion to 300 feet of seawater (fsw). Measurements on another four subjects were made at 1 atmosphere absolute (ATA) before and after an 8-day simulated 300-fsw dive, and at 5, 7, and 10.1 ATA (300 fsw). The gas mixture in which the divers lived was varied according to standard procedures to prevent adverse body reactions during compression and decompression. Vibrotactile thresholds were measured by standard psychophysical methods at 1, 10, 100, and 250 Hz. Results suggest that neither increased atmospheric pressure nor breathing gas had any effect on vibrotactile thresholds within any of the four mechanoreceptor channels that innervate normal skin. The second set of experiments was performed to assess the effect of complete seawater hydration of the skin upon vibrotactile threshold sensitivity measured at the thenar eminence and the volar surface of the forearm. In-air thresholds of three subjects were measured by standard psychophysical methods at 1, 10, 100, and 250 Hz. The measurements were repeated underwater after the forearm and hand were submerged for 20 min in a seawater solution. With the exception of 1 Hz, no statistically significant changes were found at either site when compared to threshold measured in air. At 1 Hz there appears to be an increase in sensitivity of approximately 3 dB when the skin is hydrated with seawater.