Spatial and temporal aspects of deep tissue pain assessed by cuff algometry

This study assessed spatial and temporal aspects of pressure pain during increasing and constant compressions using a cuff algometer and during adaptive compressions using a closed-loop feedback system for maintaining stable pain. Experimental setup consisted of a pneumatic tourniquet cuff, a computer-controlled air compressor, and a 10-cm electronic visual analogue scale (VAS). The first experiment assessed spatial summation for cuff pain by recording the pressure-pain stimulus-response (SR) function during increasing compressions with single and double cuffs. The second experiment assessed temporal profile of cuff pain during constant compression for 10 min beginning at pain intensities of 2, 4, and 6 cm on the VAS. The third experiment assessed temporal pressure profile when pain was maintained for 10 min by a close-loop system within target zones of +/-0.5 cm VAS at pain intensities of 2, 4, and 6 cm on the VAS.Doubling the tissue volume under the cuff shifted the SR function to the left, demonstrating spatial summation. The constant cuff pressure evoked typical biphasic response consisting of an overshoot in pain intensity, followed by decreasing pain, or adaptation. The pain intensity was significantly correlated to the time of constant stimulation, showing time-dependency of pain encoding. Both overshoot magnitude and adaptation rate were dependent on the starting pain intensity. The pain decrease rate was lowest for a pain intensity of 2 cm on the VAS. The overshoot magnitude was lowest for a pain intensity of 6 cm on the VAS. Both the overshoot and the adaptation were maximal for a pain intensity of 4 cm on the VAS. The oscillating pressure generated by closed-loop system led to constant rather than adapting pain at intensities of 2, 4, and 6 cm on the VAS. The cuff algometer is highly configurable tool for assessment of pain sensitivity by pressure-pain and time-pain functions. The presented models are useful additions to a researcher's armamentarium for further pharmacological and clinical studies on deep tissue pain and related mechanisms.