Pacinian channel mediated vasoconstriction in the fingers during vibration exposure

Abstract

A review of the literature showed that acute vascular responses to hand-transmitted vibration depend on the magnitude, the frequency, and the duration of the vibration but the mechanisms involved in the immediate vasoconstriction on exposure to vibration are not clear. This research was designed to advance understanding of the relation between the characteristics of vibration and changes in vascular circulation on exposed hands, and to develop a model of the mechanoreceptor channel involved in mediating vascular changes during vibration.

Study 1 was designed to determine an appropriate temperature for investigating changes in finger circulation induced by hand-transmitted vibration. Subjects were exposed to vibration with two room temperatures (20°C and 28°C). The reduction in absolute finger blood flow was greater with the higher room temperature, but the percentage reduction in finger blood flow relative to FBF during pre-exposure to vibration was similar. The room temperature was then setting up at 25°C to maintain suitable absolute finger blood flow value and obtain clear reduction pattern for digits circulation during vibration exposure.

Three experiments were designed to investigate the role of the Pacinian channel in mediating vasoconstriction in the fingers during exposure to 125-Hz vibration. In study 2, the association between vibration-induced reductions in finger blood flow and vibrotactile perception thresholds was investigated. Thresholds for the perception of 125-Hz vibration were measured on the thenar eminence of the right hand and then changes in finger blood flow were measured when exposed to vibration (125-Hz at 0.5 and 1.5 ms-2 r.m.s.). When the vibration magnitude was greater than individual vibration thresholds, vasoconstriction was correlated with thresholds at both vibration magnitudes. In study 3, the relation between thresholds and vasoconstriction was investigated with 125-Hz vibration and two contactors: 3-mm and 6-mm diameter probes. Subjects provided thresholds for perceiving vibration with both contact areas. With the magnitude of vibration 15 dB above each individual’s threshold with the 3-mm probe, the reduction in FBF with the 6-mm probe was greater than with the 3-mm probe. There were similar reductions in finger circulation when vibration was presented by the two sizes of contactor at the same sensation level. In study 4, the relationship between 125-Hz perception thresholds and vascular changes was investigated by applying vibration to different body locations. Vibration (125-Hz 15 dB above the individual threshold at the right thenar eminence) was applied to three body locations: right index finger, right thenar eminence, and left thenar eminence. Differences in reductions in finger blood flow caused by vibration at each location were correlated with differences in thresholds: subjects with a greater difference in threshold between fingertip and thenar eminence showed a greater difference in the vascular changes when vibration was applied to the fingertip and the thenar eminence.

Study 5 investigated the role of the Pacinian channel in mediating vascular responses to vibration at different frequencies of vibration. Subjects were exposed to 10 magnitudes of vibration (from -10 dB to 40 dB sensation level) at 8, 16, 31.5, 63, 125, and 250 Hz . Finger blood flow was reduced by 63-, 125-, and 250-Hz vibration when the vibration magnitude reached a sensation level of 10 dB. With 8-, 16- and 31.5-Hzvibration, 25 dB sensation level was required to cause vasoconstriction .

It is concluded that acute reductions in finger blood flow during vibration are mediated by the Pacinian channel through the sympathetic nervous reflex. The differences in the reductions in finger blood flow induced by vibration when exposed to different contact areas, body locations, and frequencies reflect the variation of the sensitivity of the Pacinian channel due to its characteristics (i.e., spatial summation, receptor density, frequency-dependent sensitivity).

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ORCID for M.J. Griffin: orcid.org/0000-0003-0743-9502

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