Background Long-term health sequelae of COVID-19 may be multiple but have thus far not been systematically studied. Methods All patients discharged after COVID-19 from the Radboud university medical centre, Nijmegen, The Netherlands, were consecutively invited to a multidisciplinary outpatient facility. Also, non-admitted patients with mild disease but with symptoms persisting >6 weeks could be referred by general practitioners. Patients underwent a standardized assessment including measurements of lung function, chest CT/X-ray, 6-minute walking test, body composition, and questionnaires on mental, cognitive, health status and quality of life (QoL). Results 124 patients (age 59±14 years, 60% male) were included; 27 with mild, 51 with moderate, 26 with severe and 20 with critical disease. Lung diffusion capacity was below lower limit of normal in 42% of discharged patients. Ninety-nine percent of discharged patients had reduced ground-glass opacification on repeat CT imaging, and normal chest X-rays were found in 93% of patients with mild diseases. Residual pulmonary parenchymal abnormalities were present in 91% of discharged patients, and correlated with reduced lung diffusion capacity. Twenty-two percent had low exercise capacity, 19% low fat-free mass index, and problems in mental and/or cognitive function were found in 36% of the patients. Health status was generally poor, particularly in the domains functional impairment (64%), fatigue (69%) and QoL (72%). Conclusions This comprehensive health assessment revealed severe problems in several health domains in a substantial number of ex-COVID-19 patients. Longer follow-up studies are warranted to elucidate natural trajectories and to find predictors of complicated long-term trajectories of recovery.

Rationale: The clinical significance of diaphragm weakness in critically ill patients is evident: it prolongs ventilator dependency, and increases morbidity and duration of hospital stay. To date, the nature of diaphragm weakness and its underlying pathophysiologic mechanisms are poorly understood.Objectives: We hypothesized that diaphragm muscle fibers of mechanically ventilated critically ill patients display atrophy and contractile weakness, and that the ubiquitin-proteasome pathway is activated in the diaphragm.Methods: We obtained diaphragm muscle biopsies from 22 critically ill patients who received mechanical ventilation before surgery and compared these with biopsies obtained from patients during thoracic surgery for resection of a suspected early lung malignancy (control subjects). In a proof-of-concept study in a muscle-specific ring finger protein-1 (MuRF-1) knockout mouse model, we evaluated the role of the ubiquitin-proteasome pathway in the development of contractile weakness during mechanical ventilation.Measurements and Main Results: Both slow-and fast-twitch diaphragm muscle fibers of critically ill patients had approximately 25% smaller cross-sectional area, and had contractile force reduced by half or more. Markers of the ubiquitin-proteasome pathway were significantly up-regulated in the diaphragm of critically ill patients. Finally, MuRF-1 knockout mice were protected against the development of diaphragm contractile weakness during mechanical ventilation.Conclusions: These findings show that diaphragm muscle fibers of critically ill patients display atrophy and severe contractile weakness, and in the diaphragm of critically ill patients the ubiquitin-proteasome pathway is activated. This study provides rationale for the development of treatment strategies that target the contractility of diaphragm fibers to facilitate weaning.

Smoking is the most important risk factor for the development of chronic obstructive pulmonary disease (COPD). Patients with COPD commonly suffer from skeletal muscle dysfunction, and it has been suggested that cigarette smoke exposure contributes to the development of skeletal muscle dysfunction even before overt pulmonary pathology. This review summarizes the evidence that muscles of nonsymptomatic smokers are weaker and less fatigue resistant than those of nonsmokers. Although physical inactivity of many smokers contributes to some alterations observed in skeletal muscle, exposure to cigarette smoke per se can also induce skeletal muscle dysfunction. Cigarette smoke constituents and systemic inflammatory mediators enhance proteolysis and inhibit protein synthesis, leading to loss of muscle mass. Reduced skeletal muscle contractile endurance in smokers may result from impaired oxygen delivery to the mitochondria and ability of the mitochondria to generate ATP due to interaction of carbon monoxide with hemoglobin, myoglobin, and components of the respiratory chain. Besides hampering contractile function, smoking may have immediate beneficial effects on motor skills, which are attributable to nicotine. In contrast to pulmonary pathology, many of the effects of smoking on skeletal muscle are most likely reversible by smoking cessation.

Evidence has accumulated that respiratory muscle dysfunction develops in critically ill patients and contributes to prolonged weaning from mechanical ventilation. Accordingly, it seems highly appropriate to monitor the respiratory muscles in these patients. Today, we are only at the beginning of routinely monitoring respiratory muscle function. Indeed, most clinicians do not evaluate respiratory muscle function in critically ill patients at all. In our opinion, however, practical issues and the absence of sound scientific data for clinical benefit should not discourage clinicians from having a closer look at respiratory muscle function in critically ill patients. This perspective discusses the latest developments in the field of respiratory muscle monitoring and possible implications of monitoring respiratory muscle function in critically ill patients.

Rationale: Studies show that the myosin content of the diaphragm in patients with mild to moderate chronic obstructive pulmonary disease (COPD) is reduced, compromising diaphragm contractile performance. The mechanisms for reduced contractile protein content are unknown. In the present study we hypothesized that the loss of contractile protein content is associated with activation of the ubiquitin-proteasome pathway in the diaphragm of patients with mild to moderate COPD. Methods: Proteolytic activity of isolated 20S proteasomes was determined in diaphragm biopsies from patients with and without COPD (predicted mean FEV 1 , 66 and 93%, respectively). In addition, we determined 20S proteasome subunit C8 protein levels by means of Western blotting, ubiquitin-ligase mRNA levels by means of realtime polymerase chain reaction, and caspase-3 activity by determining the hydrolysis of fluorogenic substrates. Results: The 20S proteasome activity was about threefold increased in the diaphragm of patients with COPD. C8 protein levels were not significantly different between COPD and non-COPD diaphragm, indicating increased specific activity of individual proteasomes, rather than an increased number of proteasomes. mRNA levels of the muscle-specific ubiquitin-ligase MAFbx were significantly higher in diaphragm from patients with COPD compared with patients without COPD. Caspase-3-mediated cleavage of actomyosin complexes is considered an initial step in muscle wasting, yielding fragments that can be degraded by the ubiquitin-proteasome pathway. In line with the increased ubiquitin-proteasome activity, caspase-3 activity was higher in diaphragm homogenates from patients with COPD. Conclusions: The present study is the first to demonstrate increased activity of the ubiquitin-proteasome pathway in COPD diaphragm. Importantly, these changes occur in patients with only mild to moderate COPD (Global Initiative for Chronic Obstructive Lung Disease stage I/II).