Longitudinal Analysis of Quadriceps Muscle Strength in Patients with Previous COVID-19 Hospitalization and in Patients with Post-Acute Sequelae following Mild COVID-19.

Muscle weakness is a prominent symptom in post-acute sequelae of COVID-19 (PASC). However, few studies have objectively and longitudinally assessed muscle strength after varying COVID-19 severity grades. This observational study aimed to explore the prevalence, determinants, and 1.5 years change of quadriceps muscle weakness in 98 patients discharged from COVID-19 hospitalization and in 50 patients with PASC following mild COVID-19. Isometric quadriceps maximal voluntary contraction (MVC) was assessed on a computerized dynamometer at three visits. Also, in a subgroup of 14 post-COVID-19 patients with quadriceps muscle weakness, muscle thickness and echo intensity were determined by muscle ultrasound of nine upper and lower extremity muscles. Muscle weakness was found in 59% of post-hospitalized patients and in 65% of those with PASC following mild COVID-19 at ~14 weeks after acute COVID-19. Whereas during ~1.5 years follow-up MVC modestly improved, muscle weakness prevalence remained unchanged. Hospital length of stay and diabetes mellitus were identified as possible predictors of muscle weakness following COVID-19 hospitalization. No predictors could be identified in those with PASC following mild COVID-19. Ultrasound outcomes revealed no large structural abnormalities. In conclusion, clinically relevant muscle weakness is common after COVID-19 and its long-term improvement is poor. Future studies with relevant control groups are warranted to confirm our data.

Persistent Exertional Dyspnea and Perceived Exercise Intolerance After Mild COVID-19: A Critical Role for Breathing Dysregulation?

OBJECTIVE: After mild COVID-19, a subgroup of patients reported post-acute-phase sequelae of COVID-19 (PASC) in which exertional dyspnea and perceived exercise intolerance were common. Underlying pathophysiological mechanisms remain incompletely understood. The purpose of this study was to examine outcomes from cardiopulmonary exercise testing (CPET) in these patients. METHODS: In this observational study, participants were patients who were referred for the analysis of PASC after mild COVID-19 and in whom CPET was performed after standard clinical workup turned out unremarkable. Cardiocirculatory, ventilatory, and metabolic responses to and breathing patterns during exercise at physiological limits were analyzed. RESULTS: Twenty-one patients (76% women; mean age = 40 years) who reported severe disability in physical functioning underwent CPET at 32 weeks (interquartile range = 22-52) after COVID-19. Mean peak O2 uptake was 99% of predicted with normal anaerobic thresholds. No cardiovascular or gas exchange abnormalities were detected. Twenty of the 21 patients (95%) demonstrated breathing dysregulation (ventilatory inefficiency [29%], abnormal course of breathing frequency and tidal volume [57%], absent increase of end-tidal Pco2 [57%], and abnormal resting blood gases [67%]). CONCLUSION: Breathing dysregulation may explain exertional dyspnea and perceived exercise intolerance in patients with PASC after mild COVID-19 and can be present in the absence of deconditioning. This finding warrants further study on the levels of neural control of breathing and muscle function, and simultaneously provides a potential treatment opportunity. IMPACT: This study contributes to the understanding of persistent exertional dyspnea and perceived exercise intolerance following mild COVID-19, which is vital for the development of effective rehabilitation strategies.