Chronic pain is an ever-present issue and some estimate its cost to society at $635 billion per year. Not only does chronic pain cause increased visits to medical personnel, it also complicates other medical conditions and lowers productivity in the workplace. One area of study includes Chronic Post Surgical Pain (CPSP) in children that have undergone spinal fusion surgery for Adolescent Idiopathic Scoliosis (AIS). Some of the major factors that may lead to CPSP include preoperative pain, psychosocial factors, age, intraoperative nerve injury, acute postoperative pain, and genetics. In order to explore the psychological factors, our lab has employed an Unpredictable Chronic Mild Stress (UCMS) paradigm, which models unforeseen life stressors and depression. Some sensory testing was conducted included Hot Plate and von Frey fiber testing. Previous studies from this lab have shown that adult male mice have hyperalgesia to thermal stimuli following a UCMS paradigm. To further explore this finding, a younger mice cohort of both sexes and a cohort that underwent Maternal Deprivation (MD) were added. Maternal Deprivation is a model of early-childhood stress and older female mice have been shown to have changes in thermal sensitivities as a result of early childhood stressors. Our lab found that stressed young females also exhibit a heightened sensitivity to thermal stimuli at 49°C compared to their male and control counter parts. These results indicate that the thermal sensitivity of young females can be affected by early childhood stress and depression.

To understand pain processing requires the assessment of an individual’s perception of pain with temporal stimulation over different periods. Offset analgesia (OA), a phenomenon widely studied, refers to a disproportionate decrease in pain experience following a small reduction in temperature during noxious thermal stimulation. OA leads to skin desensitization, causing brief pain inhibition at the stimulation site and leading to adaptation and a decrease in pain scores. To avoid sensitization and habituation during thermal pain procedures, previous studies have utilized protocols in which the thermal stimulation is applied to different areas of the skin (e.g., upper forearm versus lower forearm). The reliability of this thermal pain calibration procedure in producing a nonadaptive effect has been previously tested using pain rating scales. The utilization of neuroimaging to further elucidate these relationships has not been widely studied, but it is likely an important tool to investigate these constructs. Functional near-infrared spectroscopy (fNIRS) is a noninvasive optical imaging technique that measures changes in hemoglobin (Hb) concentrations within the brain using the characteristic absorption spectra of Hb in the near-infrared range. This thesis investigated whether adaptation exists across four conditions of the OA paradigm using fNIRS. Introducing fNIRS to define significant differences in brain metrics (e.g., activated regions of interest) in participants who have undergone surgery and are experiencing chronic pain as well as healthy, pain-free controls could have implications for more accurate measures of OA and more reliable pain treatment options. In this study, noxious thermal stimulation was given to 19 participants on the forearm of the nondominant hand through a commonly used three-temperature OA paradigm with offset, constant, and control trials. Each OA paradigm consisted of four conditions (A, B, C, and D) with a pseudorandom sequence design of three trials. OA was implemented with the participant while real-time fNIRS data were obtained on the subject’s prefrontal and somatosensory cortices, regions known to be involved in pain processing. Hemoglobin responses during the four OA trials were evaluated and compared within experimental conditions. Repeated measures ANOVA was used to analyze the significant differences among conditions. Results showed no significant differences among the four OA trials. The findings of this thesis study indicated that brain response from the prefrontal and somatosensory cortices is not affected within the four OA trials. The consistent brain activation across multiple trials of stimulation suggests an absence of adaptive responses. In line with previous findings, these results imply the reliability of such thermal pain calibration procedures by fNIRS brain imaging. Further investigation with a larger sample size is likely for the verification of the findings from this study. / 2026-02-14T00:00:00Z

Background: Thousands of Canadians undergo cardiac surgery each year with the aim of relieving symptoms (e.g., angina) and improving health-related-quality-of-life (HRQoL). Despite the demonstrated symptom-related benefits of these surgeries, evidence suggests that the development of chronic post-surgical pain (CPSP) is a major clinical problem. To date, several perioperative factors have been examined for their potential to confer risk for CPSP. Purpose: The purpose of the study was to explore the association between preoperative moderate to severe anxiety and depressive symptoms; moderate to severe acute postoperative pain; and cumulative opioid dose consumption with the development of CPSP at six months and 12 months after cardiac surgery. Method: Design. This thesis was a prospective observational cohort sub-study of adults undergoing cardiac surgery in a tertiary care hospital setting (n=735), recruited from Hamilton Health Sciences, Canada over a five year period. Measures. The independent variables included state anxiety, depressive symptoms, acute postoperative pain intensity, and opioid dose consumption. At baseline, the Spielberger State-Trait Anxiety Inventory (STAI) assessed state anxiety and the Hospital Anxiety and Depression Scale (HADS) assessed depressive symptoms. The Brief Pain Inventory-Short Form (BPI-SF) assessed acute postoperative pain intensity on postoperative days three (in-hospital) and 30 (at home via telephone). All instruments have established reliability and validity in cardiac surgery patients (e.g., STAI Cronbach’s alpha (α) =0.82; HADS α=0.81; BPI-SF α=0.87). Medical records were reviewed and total dose of opioids consumed up to three days postoperatively, were collected via analgesic chart audit and converted into milligrams of parenteral morphine equivalent dose using standard dosage tables. Dependent variable. The primary outcome of CPSP was assessed dichotomously (i.e., yes/no) at six months and 12 months after cardiac surgery. If present, CPSP was assessed via the BPI-SF. At baseline, data was collected on pre-specified model covariates (e.g., age, sex). Data Analyses. Logistic regression was used to model the primary outcome with the presence of CPSP at six months and 12 months, while adjusting for model covariates. Secondary linear regression models were constructed to examine the effect of the independent variables on the severity of CPSP with statistical significance set at p-values <0.05. Results: The incidence of CPSP was 8.7% at six months and 4.1% at 12 months after cardiac surgery. Baseline demographics (i.e., age, sex) and medical status (i.e., diabetes mellitus) were significantly associated with the presence of CPSP. Moderate to severe preoperative anxiety was not significantly associated with CPSP at six months (adjusted OR 0.629, 95% CI [0.300, 1.322], p=0.222) or 12 months (adjusted OR 0.743, 95% CI [0.242, 2.285], p=0.604). Moderate to severe preoperative depressive symptom was not significantly associated with CPSP at six months (adjusted OR 0.676, 95% CI [0.152, 3.005], p=0.607) or 12 months (adjusted OR 3.216, 95% CI [0.835, 12.382], p=0.089). Acute postoperative pain rated as pain ‘right now’ on day three was significantly associated with CPSP at six months (adjusted OR 2.263, 95% CI [1.255, 4.081], p=0.007) and 12 months (adjusted OR 2.749, 95% CI [1.174, 6.441], p=0.020). Acute postoperative pain ‘right now’ on day 30 was significantly associated with CPSP at six months (adjusted OR 2.913, 95% CI [1.304, 6.505], p=0.009). Cumulative opioid dose consumed was significantly associated with the development of CPSP at six months (adjusted OR 1.001, 95% CI [1.000, 1.002], p=0.003) and 12 months (adjusted OR 1.001, 95% CI [1.000, 1.001], p=0.033) after cardiac surgery. Significance: The findings demonstrate that acute postoperative pain ‘right now’ and cumulative opioid dose consumed are risk factors for CPSP after cardiac surgery. These findings offer targets for nursing staff to identify potentially at-risk patients, implement evidence-based pain management strategies, as well as contribute to nursing-led research designed to target CPSP after cardiac surgery. / Dissertation / Doctor of Philosophy (PhD)

With chronic post surgical pain affecting up to one third of patients undergoing surgeries and the price of treatment being astoundingly high there has been a transition in research to investigate and identify risk factors. Through identification of risk factors new preventative measures can be taken to ensure better surgical outcomes. The role that psychosocial factors can play in the development of chronic post surgical pain has long been recognized yet its mechanisms are still unknown. We aim to investigate how environment can play a direct role in pain perception and sensitivity. We used a Chronic Mild Stress (CMS) paradigm to induce depression in 10 adult male mice, we used 10 control mice who were left in standard opti cages, and 10 enriched mice who were placed in large enrichment cages. CMS mice were exposed to a series of stressors and all mice underwent spared nerve injury surgery. During spared nerve injury the common peroneal and tibial branches of the sciatic nerve were severed while the sural branch was left intact. Overall well-being and pain threshold of mice were tested via Von Frey, Hot Plate, Heat Place Preference, Dynamic Weight Bearing, Hole Board, and Social Interaction. It was found that CMS mice experienced thermal hyperalgesia yet normal thermal threshold sensation. CMS mice also spent less time interacting with novel mice in social interaction, and less amount of time exploring the center of the hole board arena than control or enriched mice. While Von Frey results did not change over the course of the experiment, dynamic weight bearing results indicated spared nerve injury surgery was successful and produced chronic pain. Results indicate that environment plays a role in thermal pain perception and CMS affected overall well being of mice as CMS mice exhibited more timid and anxious behavior.