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

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] O(2)/∆work rate) and [Formula: see text] to [Formula: see text] O(2) (∆[Formula: see text] /∆[Formula: see text] O(2)) 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)O(2) 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)O(2) (11.6 ± 2.7 vs. 13.3 ± 3.1 mL O(2)∙100 mL blood(−1), P = 0.031) were lower in the FM group. No significant group differences emerged in ∆[Formula: see text] O(2)/∆work rate (11.1 vs. 10.8 mL∙min(−1)∙W(−1), P = 0.248) or ∆[Formula: see text] /∆[Formula: see text] O(2) (6.58 vs. 5.75, P = 0.122) slopes. CONCLUSIONS: Both [Formula: see text] and C(a-v)O(2) 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.