Examining Racial and SocioEconomic Disparities (ERASED) in Chronic Low Back Pain Study

Pain threshold refers to the intensity at which a stimulus is first perceived as painful. Heat stimuli will be delivered using a computer-controlled thermal stimulation system with a 30 millimeter X 30 millimeter probe. From a baseline of 32 degrees Celsius, the probe temperature will increase at a rate of .5 degrees Celsius/second until the participant responds by pressing a button on a handheld device. For heat pain threshold, participants will be instructed to press the button when the sensation "first becomes painful". Heat pain threshold was assessed at the lumbar spine. On a scale of 32 degrees Celsius to 51 degrees Celsius, with 51 being the hottest temperature.

Pain tolerance refers to the maximum amount of pain produced by a stimulus that a person is able/willing to tolerate. Heat stimuli will again be delivered using the computer-controlled thermal stimulation system. From a baseline of 32 degrees Celsius, the probe temperature will increase at a rate of .5 degrees Celsius/second until the participant responds by pressing a button on a handheld device. For heat pain tolerance, participants will be instructed to press the button when they are "no longer willing to tolerate" the painful sensation. Heat pain tolerance was assessed at the lumbar spine. Scale range from 32 degrees Celsius to 51 degrees Celsius with 51 being the hottest.

Temporal summation of pain refers to a form of endogenous pain facilitation characterized by the perception of increased pain despite constant or even reduced peripheral afferent input. Temporal summation is presumed to be the psychophysical manifestation of wind-up. Wind-up is a phenomenon where repetitive stimulation of C primary afferents at rates greater than 0.3 Hertz produces a slowly increasing response of second-order neurons in the spinal cord. Temporal summation was assessed at the lumbar spine using a 512 milliNewton punctate probe. Participants are stimulated once with the punctate probe and asked to provide a pain rating from 0-100 whereby 0 = no pain and 100 = most intense pain imaginable. They are then stimulated 10 consecutive times with the punctate probe and asked to provide another pain rating from 0-100. Temporal summation is the difference between these two ratings, such that positive scores indicate pain facilitation and negative scores indicate pain inhibition.

Pressure was manually applied and increased at a rate of 30 kPa/s. Participants indicated when the pressure was first perceived to be painful (pressure pain threshold) via button-push. Three applications of a handheld algometer were used to determine baseline pressure pain thresholds (PPTs). Following this, participants underwent two trials of cold pressor immersion. Participants placed their entire hand, up to the wrist, into 12 °C water for 60 s. Immediately following withdrawal of the hand from the cold pressor, the algometer was re-applied at the lumbar region. Participants again indicated when they first perceived the pressure as painful (conditioned PPT). The trial was repeated following a two-minute rest period. The baseline PPTs were averaged, as were the two conditioned PPTs. Conditioned pain modulation was calculated as the difference between Conditioned PPT - Baseline PPT. Positive difference scores indicate pain inhibition and negative scores indicate facilitation.

A single blood draw was collected from each participant during their one week follow up visit. The blood was processed and serum was used to quantify C-reactive protein, which is a marker of systemic pro-inflammation. Increasing levels of C-reactive protein are suggestive of greater inflammation.

Fibrinogen is a protein that plays a crucial role in blood clotting. It is produced by the liver and is present in the blood plasma. Fibrinogen is considered a key player in inflammation, acting as a pro-inflammatory molecule by directly interacting with immune cells and promoting their migration to the site of injury, essentially serving as a "scaffold" for the inflammatory response, and its levels significantly increase during inflammatory conditions, making it a marker for inflammation in the body; high fibrinogen levels often indicate an ongoing inflammatory process.

Serum amyloid A (SAA) is considered a key marker of inflammation, as its levels significantly increase in the blood during an inflammatory response, acting as an "acute phase reactant" produced by the liver when stimulated by pro-inflammatory cytokines like interleukin-6 (IL-6); essentially, high SAA levels indicate the presence of active inflammation in the body.

Vitamin D (also referred to as calciferol) is a fat-soluble vitamin that is naturally present in a few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet (UV) rays from sunlight strike the skin and trigger vitamin D synthesis. We quantified Vitamin D from blood serum. Lower levels of Vitamin D have been associated with greater musculoskeletal pain severity and worse bone and muscle health.

Oxytocin is a hormone that plays a crucial role in various physiological and behavioral processes, particularly in reproduction, social bonding, and emotional well-being.

Insomnia Severity Index (ISI) was used to measure sleep quality. The ISI is a seven-item questionnaire used to evaluate the severity and impact of insomnia. Participants used a 5-point Likert scale to rate severity of difficulties with sleep onset and sleep maintenance as well as problems with early morning awakenings, sleep dissatisfaction, and interference of sleep difficulties with daytime functioning within the last month. Items are summed to calculate a total score ranging from 0 to 28, thus, indicating absence of insomnia (0-7), subthreshold insomnia (8-14), moderate insomnia (15-21) and severe insomnia (22-28).

Self-reported disability was assessed using the Graded Chronic Pain Scale (GCPS) - interference scale. A higher score on the interference section indicates a greater level of disruption to daily life due to pain. The GCPS scale ranges from 0-100 and higher scores are indicative of greater self-reported disability.

The Short Physical Performance Battery was used to assess movement-evoked pain. Participants completed three movements (balance, chair stands, and walking). After completion of each movement task, participants were asked to provide a pain intensity rating for any movement-evoked pain experienced during completion of the balance, chair stands, and walking tests. The 0-100 numeric rating scale was utilized for this purpose, whereby: (0 = no pain and 100 = most intense pain imaginable). Average pain intensity was calculated across the three movements.

The Short Physical Performance Battery (SPPB) is an objective measurement instrument of balance, lower extremity strength, and functional capacity in adults. The test includes three different domains (walking, sit-to-stand and balance) to assess functional mobility. Scores range from 0 to 12 with higher scores suggest of better functional performance.