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 (V ˙ O2peak). We aimed to detect the contribution of cardiac output to (Q ˙) and arteriovenous oxygen difference [C (a-v) O 2] to V ˙ O 2 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. Q ˙ (impedance cardiography) was monitored. C (a-v) O 2 was calculated using Fick’s equation. Linear regression slopes for oxygen cost (∆ V ˙ O2/∆work rate) and Q ˙ to V O2 (∆ Q ˙ /∆ V ˙ O2) were calculated. Normally distributed data were reported as mean ± SD and non-normal data as median [interquartile range]. Results: V ˙ O2peak 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). Q ˙ and C(a-v)O2 were similar between groups at submaximal work rates, but peak Q ˙ (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 ∆ V ˙ O2/∆work rate (11.1 vs. 10.8 mL∙min−1∙W−1, P = 0.248) or ∆ Q ˙ /∆ V ˙ O2 (6.58 vs. 5.75, P = 0.122) slopes. Conclusions: Both Q ˙ and C(a-v)O2 contribute to lower V ˙ O2peak 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 .