Correlating Heart Rate Variability and Chronic Pain

Objective The Canadian Armed Forces (CAF) has limited data on baseline quality of life measures and objective measures of function, for active serving members with chronic pain. This study aims to collect this data using patient reported outcomes and 2 minute walk test (2MWT) while validating the newly created Elevation Movement Lift Off Test (EMLi) and correlating the data with heart rate variability (HRV) while comparing performance to healthy controls.

Procedure Patients will complete pre-defined questionnaires on their pain condition, potential risk factors, and function. This data includes information on demographics, occupation, pain conditions and its impact on life, exercise levels, mood, childhood experiences, views on your condition and requests for care support. For patients and controls investigators will collect performance and heart rate measures while at rest, walking and lifting tests.

Risks and Mitigation Strategies Participation in this study is voluntary and volunteers can withdraw consent at any time without having any effect on access to future medical care.

Due to the nature of this study there are no significant associated risks. Any patients developing issues consistent with cardiopulmonary compromise will be treated according to the standard of care, stabilized and referred on for further evaluation.

The data collected will be stored in a locked Protected-B cabinet at the Canadian Forces Health Services Centre only and access will be restricted to the research team. The spreadsheet generated from this data will be password protected and anonymized. Only the research team will have access to this data.

The data intake protocol included completing a questionnaire with:

1. Demographics - age, gender, rank, working status, medical category
2. Height and weight, waist to hip ratio
3. Medications in the following groups
4. Antipsychotics
5. Antihypertensives
6. Antidepressants
7. Oral Contraceptive Pill
8. Stimulants
9. Cannabinoids
10. Activity and Food Intake
11. Alcohol, caffeine, energy drinks, food, intense exercise, tobacco, cannabis
12. Patient Reported Outcomes at baseline (Appendix B)
13. Body Pain Diagram
14. Pain, Enjoyment and General Activity Scale (PEG)
15. Pain Disability Index
16. Hospital Anxiety and Depressions Scale (HADS)
17. Adapted Deployment Risk \& Resilience Inventory 2 Section J: Unit Support Exercise Questionnaire
18. Brief Trauma Questionnaire (BTS)
19. Litigation Status

The physical activity measures to be taken are:

1. 2 minute walk test (2MWT)
2. Elevation \& Movement Lift test (EMLi)
3. Heart rate variability and Vagal Tone (VT) indices (12 minutes total) - Firstbeat Bodyguard 2 (Firstbeat Finland)
4. Supine (3 minutes)
5. Sit (3 minutes)
6. Stand (3 minutes)
7. 2MWT (2 minutes)
8. EMLI (1 min)
9. Borg Perceived Exertion Scale

Sample Size Calculation Current studies on chronic pain and HRV ranged from samples sizes of 12-731 patients and 11-1633 controls showing a standard mean difference of 0.15 to 73.6 depending on the variable and condition being studied. Quintana described an analysis of 297 HRV effect sizes from between-group/case-control studies and concluded that for HRV studies a sample size of 233, 61, and 21 participants are required, respectively, to detect small, medium and large effect sizes, respectively. The Laborde et al. guidelines for HRV and VT research rely on this estimation and therefore investigators have selected a sample of 100 patients with chronic pain and 50 controls .

Statistical analysis The difference in performance during the upper and lower repetition tests will be evaluated between the groups. This includes vagal tone measures/ heart rate variability, number of repetitions and perceived exertion. This will be evaluated using multiple ANOVA tests, corrected for multiple comparisons using the Games-Howell post-hoc test.

Correlation analysis between selected variables will be done using multiple Pearson correlations, and adjusted for multiple comparisons using the Benjamini-Hochberg false discovery rate equation.

Acquisition of electrocardiogram data (ECG) data will be via a HRV capture device with data sampled at 1000 Hz. Disposable electrodes will be placed on the participant chest (Bodyguard) or ear (EM Wave Pro Plus). Only one device will be used for all patients in the study as each device is currently being vetted by the research team. The electrodes will be positioned in accordance to the device use guidelines. When needed, the skin will be prepared, in order to improve signal quality (cleaning or hair removal). The ECG sampling rate of 1000 Hz, which is consistent with the more conservative guidelines.The participant may be asked to sit quietly for 5 minutes prior to data collection and then deep breath in and out for 1 minute.

VT Analysis HRV data will be visually inspected and edited off-line with CardioEdit software (Brain-Body Center, the University of Illinois at Chicago). HRV and VT indices will be calculated using CardioBatch Plus software (Brain-Body Center for Psychophysiology and Bioengineering, the University of North Carolina at Chapel Hill, 2016) consistent with procedures developed by Prof. Porges. The edited heart period sequences were analyzed with specific algorithms developed to quantify three metrics of respiratory sinus arrhythmia (RSA): Porges-Bohrer time domain method (RSAP-B), peak-to-trough (P2T), and the accumulated variances across a high frequency band (HF) from the spectral analyses.

Vagal efficiency will be calculated by the slope between the dynamic and synchronous shifts in RSA and heart period, which provides a measure of regulation of heart rate by vagal pathways.