Age-associated differences in responses to noxious stimuli.

Abstract

Although population-based studies typically report age-associated increases in clinical pain, laboratory-based pain assessment procedures generally indicate diminished pain sensitivity with age. The majority of these studies have utilized noxious thermal stimuli as the method of pain induction. However, other pain assessment methodologies, including ischemic pain induction, may have a more meaningful relationship to clinical pain. The present study examined the effects of age on responses to a variety of experimental noxious stimuli. In addition, relationships between cardiovascular measures and pain responses were investigated in both older and younger subjects. Responses to thermal, mechanical, and ischemic pain were assessed in 34 younger (mean age, 22.4 years) and 34 older adults (mean age, 62.2 years). In addition, relationships between resting blood pressure and pain responses were assessed separately for older and younger participants. Although group differences in thermal and mechanical pain responses did not achieve statistical significance, older individuals demonstrated substantially lower ischemic pain thresholds and tolerances assessed via the modified submaximal effort tourniquet procedure (ps < .01). Overall, higher resting arterial blood pressures were associated with increased pain thresholds and tolerances, although relationships between blood pressure and ischemic pain variables were evident only for the younger group. These findings indicate that age-related differences in responses to experimental noxious stimuli vary as a function of the pain induction task, with older individuals showing greater sensitivity to clinically relevant stimuli. In addition, the absence of a relationship between blood pressure and ischemic pain responses in older adults may suggest potential functional decrements in at least one endogenous pain-modulatory system.