Apparatus to deliver pressure-induced sensations

#This invention relates to the measurement of tactile sensation, and more particularly to measurement of both a minimum force to elicit touch sensation and a minimum force to elicit pain sensation in humans, and thus is useful for the measurement of skin irritation in humans.

#The present invention is applicable to measuring irritation on various human tissues for example, the oral mucosa, and the like. Journal of the Society of Cosmetic Chemists, Volume 39, pages 315-320 describes the effect irritation has on the relationship of the touch and pain thresholds to one another. Other prior art, Semmes, J., Weinstein, S., Ghent, L. and Teuber H. L. (1960) Somatosensory Changes after Penetrating Brain Wounds in Man, particularly at page 61, Table B-1, describes the Semmes-Weinstein Pressure Aesthesiometer (trade name used by NCRL (NeuroCommunication Research Laboratories, Inc.), Danbury, Conn.) also generally referred to in the art as Semmes-Weinstein Monofilaments (as sold by North Coast Medical, Inc. of Campbell Calif.). This esthesiometer is a well known device to measure tactile thresholds. It comprises a set of several plastic filaments of constant length with various diameters that result in differing applied maximal forces across the different filaments. An alternative conventional device, e.g., such as the Cochet-Bonet esthesiometer, which is now out of favor, employs a single constant diameter filament which varies in length to control force.

#For the purposes of measuring skin irritation according to the model of Weinstein, Drozdenko, and Weinstein (1988), Journal of the Society of Cosmetic Chemists, 39, 315-320., for example, it is necessary to measure the thresholds of touch and pain as precisely as possible. In addition, it is necessary to measure the thresholds as rapidly as possible both: (1) to prevent subject fatigue from influencing results, and (2) to obtain a measure of the potentially time-varying level of irritation. Each monofilament is applied to produce a touch or pain sensation depending on the force applied, the subject's threshold and the peculiar characteristics (i.e., whether the tip is flat, sharp or rounded) of each monofilament. The conventional esthesiometer, however, was not reliable, and hence not valid, for producing constant pressure stimulation. That is, the conventional esthesiometer caused pain beyond what would be expected for the applied pressure; this point will be expanded upon below. Moreover, this property of unexpected pain in the prior art is not consistent, but rather is probabilistic, which means that the prior art stimulus characteristics can not reliably form the basis of an evaluative model, such as the aforementioned irritation model.

#FIG. 1A illustrates the conventional esthesiometer having a conventional stimulation tip.

#FIG. 1B illustrates the conventional stimulation tip under conventional conditions applying pressure to a subject surface.

#FIG. 1C illustrates the conventional stimulation tip applying pressure to a subject surface with a twisting-error.

#The apparatus of the present invention for use in measuring, e.g., skin irritation, will now be described with reference to the figures.

#FIG. 1A shows a monofilament 20 having a stimulating tip 10 at one end and being connected at its other end substantially perpendicularly to a handle 30, of the conventional Semmes-Weinstein Pressure Aesthesiometer. A set of such objects is conventionally known, each of length about 38 mm and having a different diameter, ranging from 0.0635 mm to 1.143 mm, that conveys a different stimulation force, ranging from 0.0045 gm to 447 gm (see Appendix B, Table B-1, Semmes, Weinstein, et al.). FIG. 1B shows the expected, flat face presentation of the conventional tip 10 to a subject skin surface 50, and FIG. 1C shows the conventional tip 10 during a twisting-error presentation. As shown in FIG. 1C, the face of the conventional tip 10 presented to the subject skin surface 50 is sharp and unpredictably different from the expected-use conditions.

#FIG. 2A shows the present invention, which comprises a unitarily formed monofilament 200 having a textured, rounded tip 100 at one end and being connected substantially perpendicularly to a handle 300 at its other end. FIG. 2B presents the invention under expected-use conditions, and FIG. 2C presents the invention under a twisting condition wherein the textured, rounded tip 100 nevertheless presents a face to a subject skin surface 500 that is similar to the expected-use condition.