Presence, Severity and Evolution of Long COVID Dyspnea Correlate with Functional Capacity Measured with the Six-Minutes Walking Test (6MWT): Data from a Multicenter Cohort from Italy

The present national observational cohort study investigated in patients followed for long COVID—mostly hospitalized during acute infection—the presence, severity and evolution of dyspnea and its functional correlates. Dyspnea was assessed with the modified Medical Research Council (mMRC) dyspnea scale and its functional correlates via six-minutes walking distance (6MWD). A total of 217 individuals were evaluated. The mean difference in 6MWD between patients with and without dyspnea (mMRC score ≥ 1) was 87 m (95%CI 56–117, p < 0.001). Significant declines were observed between four and eight months from COVID-19 in prevalence of dyspnea (from 56.7% to 36.4%, p < 0.001), mean mMRC score (from 0.95 to 0.63, p < 0.001), and proportion of patients with 6MWD ˂ 65% of predicted value (from 15.5% to 9.4%, p = 0.035). Each additional point in mMRC score corresponded to −56.3 m walked at first assessment and to −47.7 m walked at second assessment. In the longitudinal analysis, each unitary mMRC score increase between the two assessments corresponded to a concurrent 6MWD reduction of 22.5 m (95%CI −40.1 to −4.8 m, p = 0.013). Although the prevalence of dyspnea reduced significantly over time, roughly one-third of patients remained affected eight months after COVID-19. The 6MWD was a sensitive measure in capturing the functional correlates of presence, severity and evolution of dyspnea.