Temporal Dynamics of Heat Pain Sensations

The moment-to-moment fluctuations in pain-evoked sensory and emotional qualities, and how the pain experience differs between sexes are not well understood. Therefore, this thesis sought to 1) characterise the temporal profiles of the most prominent noxious heat-evoked sensations, 2) characterise sex differences in these sensations, 3) evaluate the magnitude of sharp pain quality evoked in hairy and glabrous skin, and 4) determine the role of absolute stimulus temperatures on sex differences in pain adaptation and habituation. A broad-based heat pain model was developed for this study that incorporates a temporally-continuous assessment of multiple sensory and affective pain dimensions, including pain, burning, sharp, stinging, cutting, and annoyance evoked by two types (static, dynamic) of repeated prolonged noxious heat stimuli. The salient hypotheses were: 1) Burning sensations have a different temporal profile compared with sharp and other related qualities, 2) The temporal dynamics of heat pain intensity and annoyance differ between males and females, 3) Sex differences in heat pain are associated with specific pain qualities and specific types of skin, and 4) Moderate-high temperatures induce pain adaptation and habituation in females but not in males. The most prominent findings were 1) sharp, stinging and cutting sensations adapted when stimulus intensity was static, but burning sensations were evoked during static and dynamic stimulus phases, 2) pain and annoyance in women were greater than men during the dynamic phases of the first stimulus but less than men during static stimulus phases and on stimulus repetition, 3) the sex difference in pain adaptation occurred with percept-fixed stimulus intensities and with absolute stimulus temperatures, 4) the sex effects associated with dynamic stimuli occurred in hairy but not glabrous skin. These findings give new insights into the relationships between pain intensity, quality and affect and have strong implications for views on sex differences in pain sensitivity.Ph