Body Versus Machine: Deep Breathing Versus Vagus Stimulation for the Treatment of Fibromyalgia

The root mean square of successive differences (RMSSD) will be derived from photoplethysmography (PPG) recordings and serve as the primary HRV outcome of interest. RMSSD corresponds to the parasympathetic regulation of heart beats (i.e. vagal activity) which is associated with self-report average pain intensity in CWP patients. Three readings on the right index finger are taken in a sitting position, separated by a one minute intervals, and after a five minute acclimatization (resting) period. The average of the last two measurements will be used in the final analyses.

The NRS for pain is a unidimensional measure of pain intensity in adults. It is a segmented numeric version of the visual analog scale (VAS) in which a respondent selects a whole number (0-10 integers) that best reflects the intensity of their pain where 0 represents ''no pain'' and 10 represents ''the worst pain imaginable''.

FS is a self-report measure of a participant´s overall CWP/fibromyalgia severity composed of their widespread pain index (WPI) and symptom severity scale (SSS). The WPI (0-19) is the number of areas in which the patient has had pain over the last week (0-19). The SSS (0-12) is the sum of the severity scores of 3 symptoms (fatigue, waking unrefreshed, and cognitive symptoms) (0-9) plus the sum (0-3) of the number of the following symptoms the patient has been bothered by that occurred during the previous 6 months: (1) Headaches (0-1) (2) Pain or cramps in lower abdomen (0-1) (3) And depression (0-1). The fibromyalgia severity (FS) scale is the sum of the WPI and SSS.

Computerized cuff pressure algometry (CPA) will be used in order to safely and efficiently assess pain sensitivity mechanisms in CWP patients. The cuff will be placed on the mid-portion of the dominant lower leg and will use ramp inflation of 1 kPa/s until subjects indicate PDT, PTT, and PPL which is based upon an electronic 10cm visual analogue scale (VAS). PDT is the pressure value at the moment of transition between strong and painful pressure (the first time the VAS exceeds 0) whereas PTT is defined as the pressure value at the termination of pressure inflation (the corresponding VAS score is the PPL). The zero and 10 cm extremes on the VAS are defined accordingly as ''no pain'' and as ''the worst pain imaginable''.The subject is instructed to rate the pain intensity continuously on the VAS from the first sensation of pain and to press the hand-held pressure release button when the pain becomes unbearable. An average of three recordings will be used in the final analyses.

The HSCL-25 assesses emotional distress, anxiety, and depressive symptoms. The HSCL-25 scale consists of 25 questions about the presence and intensity of the most common psychiatric symptoms of anxiety and depression. Participants are asked: "To what extent have you been bothered by the following symptoms in the last 14 days including today?" Responses include: 1 (not at all), 2 (a little), 3 (quite a bit) and 4 (extremely).

Resting systolic and diastolic BP will be measured using an automated oscillometric device. The correct size cuff is chosen after the circumference of the upper arm is measured. Following a two minute rest, three readings on the upper right arm are taken in a sitting position separated by one minute intervals. The average of the last two readings will be used in the final analyses.

The EQ-5D-5L is a standardized instrument to measure health-related quality of life. The descriptive system comprises five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each of these dimensions has 5 levels: "no problems," "slight problems," "moderate problems," "severe problems" and "extreme problems". The digits for the five dimensions are then combined into a 5-digit number that describes the patient's health state. The EQ VAS uses a vertical visual analogue scale from 0 - 100 to record the patient's current state of health. The endpoints on the EQ VAS are labelled 'The best health you can imagine', indicated by 100, and 'The worst health you can imagine', indicated by 0.

The MAIA assesses participants' interoceptive body awareness and provides pertinent information in regards to how emotions and the perception of pain are related to interoception. The MAIA is a 32-item multidimensional instrument comprising of eight scales (e.g. noticing, non-distracting, not-worrying, attention regulation, emotional awareness, self-regulation, body listening, and trusting) ranging from 3 to 7 items each. Each of the 32-items are scored from a 0 to a 5 which indicates how often each statement applies in daily life (where 0 represents "never" and a 5 represents "always"). The average of all eight scales is then computed as a final score.

The SpREUK-15 investigates whether or not participants rely on spirituality as a resource to cope with pain. It investigates three factors: 1) having trust/faith; 2) search for a transcendent source to rely on; and 3) reflection of life and subsequent change of life and behavior. Items are scored on a 5-point scale from disagreement to agreement (0 - does not apply at all; 1 - does not truly apply; 2 - don't know (neither yes nor no); 3 - applies quite a bit; 4 - applies very much). The scores can be referred to a 100% level (transformed scale score). Scores > 50% indicate higher agreement (positive attitude), while scores < 50 indicate disagreement (negative attitude).

The PGIC is a self-report measure of participant belief about the efficacy of a treatment and their overall improvement. Participants rate their change on a 7 point scale: "very much improved," "much improved," "minimally improved," "no change," "minimally worse," "much worse," or "very much worse".

The CEQ is a a self-report measure of a participant´s expectations about the efficacy of a particular treatment and whether they think that the treatment is credible or not. In particular, it investigates two factors-- what one feels and what one thinks in regards to the treatment. The CEQ is composed of six items which are scored on a 9 point scale ranging from: "not at all logical", "somewhat logical", and "very logical". Items 4 and 6 ask the participant how they feel and how they think the administered treatment will improve their overall health state in regards to their pain on a 0 - 100% scale, where 0% represents "no improvement" whereas 100% represents "total improvement".