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

Abstract

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