A novel technique for the evaluation of mechanical pain and hyperalgesia

We describe a new technique which is useful for the evaluation of mechanically induced pain and hyperalgesia. Light metal cylinders are guided and accelerated in a barrel. On impact against the skin they elicit a brief sensation of pain. This method allows the application of a wide range of controllable innocuous and noxious impact velocities of the cylinder at variable stimulus repetition rates. The system is sufficiently flexible to stimulate perpendicularly any skin area and to move rapidly to adjacent target regions if desired. Psychophysical testing using magnitude estimation techniques revealed that pain thresholds were normally distributed. Over a wide range of stimulation intensities monotonically increasing stimulus response functions were obtained. Repeated testing showed a good intra-individual reproducibility of both threshold and supramaximal pain ratings. The method was also useful in determining the time course of pain and mechanical hyperalgesia following a brief painful stimulus. We conclude that the new technique is useful for evaluating psychophysical stimulus response functions of mechanically induced pain and its changes following tissue injury. This technique may also hold some promise in quantifying altered pain sensitivity in patients.