The Influence of Autonomic Function on Pain Modulation Before and After Exercise and Cognitive Task in Fibromyalgia
Fibromyalgia (FM) is a chronic pain condition characterized by widespread pain. People with FM have alterations in autonomic function compared to healthy individuals. Exercise can decrease pain in people with FM, however some people with FM experience pain exacerbation when initiating exercise. Whether variability in pain at rest and following exercise is related to altered autonomic function, including the potential implications with other stressful events such as mental math, is not known. This dissertation aimed at investigating: 1) the relation between cardiovascular autonomic function and central pain facilitation and inhibition, measured by temporal summation of pain (TS) and conditioned pain modulation (CPM) and 2) the relation between cardiovascular autonomic function and pain modulation following submaximal isometric exercise and mental math in people with and without FM.For aim 1, sympathetic and parasympathetic function, measured by Valsalva maneuver and deep breathing test, were measured along with CPM (assessed at the forearm and quadriceps) and TS (assessed at the forearm). Only control participants had CPM at the quadriceps while both groups had similar CPM at the forearm. Sympathetic function was associated with CPM at the forearm in people with FM only. Both groups had similar TS which was not associated with baseline autonomic function. Parasympathetic function was not related to CPM or TS. For aim 2, autonomic function was assessed at baseline and during exercise and mental math. Pressure pain thresholds were assessed before and after exercise and mental math to assess the change of pain. Following exercise, only control participants reported pain relief while people with FM had variable pain responses, whereas both groups had variable pain responses following mental math. People that reported greater pain relief following exercise also reported greater pain relief following mental math and had greater baseline sympathetic function. Our results show that sympathetic function is related to central pain inhibition but not central pain facilitation. Additionally, sympathetic function may help explain the variability in pain following exercise and mental math. Thus, future studies should investigate whether interventions that improve sympathetic function can improve central pain inhibition and pain sensitivity to physical and cognitive stress.