Pulmonary Function and Functional Capacity in COVID19 Survivors with and Without Persistent Dyspnea in a Mexican Population

Abstract

Rationale: Dyspnea is one of the most common symptoms associated with coronavirus disease 2019 (COVID-19). Over 40% of COVID-19 survivors experience persistent dyspnea approximately 60 days following hospital discharge (Carfi et al., JAMA, 2020). Understanding differences in pulmonary function and functional capacity between those that do and do not experience persistent dyspnea may provide insight into the underlying mechanisms of this symptom in survivors of COVID-19. Accordingly, the purpose of this study was to compare spirometry, diffusing capacity of the lungs for carbon monoxide (DLCO), and 6-minute walk test (6MWT) outcomes in COVID-19 patients with and without persistent dyspnea. We hypothesized that COVID-19 patients with persistent dyspnea would have lower forced vital capacity (FVC), DLCO, and 6-minute walk distance (6MWD) compared to patients without persistent dyspnea. Methods: Non-critical patients (n=186) with varying degrees of COVID-19 severity reported all persistent symptoms using a standardized questionnaire and underwent pulmonary function testing and a 6MWT between 30 and 90 days following the onset of acute COVID-19 symptoms. Patients were divided into those with (n=70) and those without (n=116) persistent dyspnea. Independent t-tests and Fisher's Exact test were used where appropriate to compare anthropometric, pulmonary function, symptoms, and 6MWT variables. Results: There was no difference in the time of experimental testing relative to the onset of acute COVID-19 symptoms between those with vs. those without dyspnea (59±13 vs. 60±14 days, respectively). Groups had similar age, height, mass, body mass index, sex, and frequency of comorbidities. Patients with persistent dyspnea had significantly lower FVC (p=0.03), forced expiratory volume in 1 second (p=0.04), and DLCO (p=0.01) compared to non-dyspnea patients. 47% of patients with persistent dyspnea had a restrictive pattern on spirometry compared to 33% in the non-dyspnea group. Patients with persistent dyspnea also had lower 6MWD (% predicted, p=0.03) and nadir oxygen saturation (p<0.001), and higher Borg 0-10 ratings of dyspnea and fatigue (both p<0.001) during the 6MWT compared to patients without persistent dyspnea. Conclusions: We have shown that dyspnea is a common persistent symptom across varying degrees of initial COVID-19 severity. Patients with persistent dyspnea had a number of abnormalities compared to well-matched patients without persistent dyspnea, including greater restriction on spirometry, lower DLCO, reduced functional capacity, and increased desaturation and exertional symptoms during a 6MWT. This suggests that there is a true physiological mechanism that may explain persistent dyspnea after COVID-19.