Cardiac output and arteriovenous oxygen difference contribute to lower peak oxygen uptake in patients with fibromyalgia

Abstract

Background: Patients with fibromyalgia (FM) exhibit low peak oxygen uptake ([Formula: see text]O_2peak). We aimed to detect the contribution of cardiac output to ([Formula: see text]) and arteriovenous oxygen difference [Formula: see text] to [Formula: see text] from rest to peak exercise in patients with FM.

Methods: Thirty-five women with FM, aged 23 to 65 years, and 23 healthy controls performed a step incremental cycle ergometer test until volitional fatigue. Alveolar gas exchange and pulmonary ventilation were measured breath-by-breath and adjusted for fat-free body mass (FFM) where appropriate. [Formula: see text] (impedance cardiography) was monitored. [Formula: see text] was calculated using Fick's equation. Linear regression slopes for oxygen cost (∆[Formula: see text]O₂/∆work rate) and [Formula: see text] to [Formula: see text]O₂ (∆[Formula: see text]/∆[Formula: see text]O₂) were calculated. Normally distributed data were reported as mean ± SD and non-normal data as median [interquartile range].

Results: [Formula: see text]O_2peak was lower in FM patients than in controls (22.2 ± 5.1 vs. 31.1 ± 7.9 mL∙min^-1∙kg^-1, P < 0.001; 35.7 ± 7.1 vs. 44.0 ± 8.6 mL∙min^-1∙kg FFM^-1, P < 0.001). [Formula: see text] and C(a-v)O₂ were similar between groups at submaximal work rates, but peak [Formula: see text] (14.17 [13.34-16.03] vs. 16.06 [15.24-16.99] L∙min^-1, P = 0.005) and C(a-v)O₂ (11.6 ± 2.7 vs. 13.3 ± 3.1 mL O₂∙100 mL blood^-1, P = 0.031) were lower in the FM group. No significant group differences emerged in ∆[Formula: see text]O₂/∆work rate (11.1 vs. 10.8 mL∙min^-1∙W^-1, P = 0.248) or ∆[Formula: see text]/∆[Formula: see text]O₂ (6.58 vs. 5.75, P = 0.122) slopes.

Conclusions: Both [Formula: see text] and C(a-v)O₂ contribute to lower [Formula: see text]O_2peak in FM. The exercise responses were normal and not suggestive of a muscle metabolism pathology.

Trial registration: ClinicalTrials.gov, NCT03300635. Registered 3 October 2017-Retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT03300635 .

Keywords: Cardiopulmonary exercise test; Impedance cardiography; Leisure-time physical activity; Oxygen cost; Ventilatory threshold.

Fig. 1

Flowchart of participant recruitment

Fig. 2

Self-reported leisure-time physical activity. White boxes, fibromyalgia (n = 31); shaded boxes, controls (n = 23). *, between-group difference significant (P < 0.05). Dashed line represents the lower bound of the WHO recommendations for moderate physical activity (see reference 53)

Fig. 3

Oxygen uptake (A-B), cardiac output (C-D), arteriovenous oxygen difference (E), and arterial oxygen saturation (F) as a function of work rate. White circles (○), fibromyalgia (n = 35); black circles (●), controls (n = 23). Values are group means, vertical error bars ± SD. Horizontal error bars represent ± SD of mean peak work rate. P values refer to repeated measures ANOVA. *, between-group difference significant (P < 0.05) at given work rate

Fig. 4

Heart rate (A), mean arterial pressure (B), systemic vascular resistance (C-D), and stroke volume (E–F) as a function of work rate. White circles (○), fibromyalgia (n = 35); black circles (●), controls (n = 23). Values are group means, vertical error bars ± SD. Horizontal error bars represent ± SD of mean peak work rate. P values refer to repeated measures ANOVA. *, between-group difference significant (P < 0.05) at given work rate

Fig. 5

Linear regression slopes for oxygen uptake as a function of work rate (A), heart rate (B) and cardiac output (C) as a function of oxygen uptake, and ventilation as a function of carbon dioxide production (ventilatory efficacy) (D). White circles (○), fibromyalgia (n = 35, except for panel D, n = 34); black circles (●), controls (n = 23). P values refer to the group*independent variable term in the regression model (see text for more information)