Post-COVID exercise intolerance is associated with capillary alterations and immune dysregulations in skeletal muscles

Towards an understanding of physical activity-induced post-exertional malaise: Insights into microvascular alterations and immunometabolic interactions in post-COVID condition and myalgic encephalomyelitis/chronic fatigue syndrome

BACKGROUND

A considerable number of patients who contracted SARS-CoV-2 are affected by persistent multi-systemic symptoms, referred to as Post-COVID Condition (PCC). Post-exertional malaise (PEM) has been recognized as one of the most frequent manifestations of PCC and is a diagnostic criterion of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Yet, its underlying pathomechanisms remain poorly elucidated.

PURPOSE AND METHODS

In this review, we describe current evidence indicating that key pathophysiological features of PCC and ME/CFS are involved in physical activity-induced PEM.

RESULTS

Upon physical activity, affected patients exhibit a reduced systemic oxygen extraction and oxidative phosphorylation capacity. Accumulating evidence suggests that these are mediated by dysfunctions in mitochondrial capacities and microcirculation that are maintained by latent immune activation, conjointly impairing peripheral bioenergetics. Aggravating deficits in tissue perfusion and oxygen utilization during activities cause exertional intolerance that are frequently accompanied by tachycardia, dyspnea, early cessation of activity and elicit downstream metabolic effects. The accumulation of molecules such as lactate, reactive oxygen species or prostaglandins might trigger local and systemic immune activation. Subsequent intensification of bioenergetic inflexibilities, muscular ionic disturbances and modulation of central nervous system functions can lead to an exacerbation of existing pathologies and symptoms.

Association of physical symptoms with accelerometer-measured movement behaviors and functional capacity in individuals with Long COVID

Long COVID has been linked to a decline in physical activity and functional capacity. However, it remains unclear which physical symptoms are associated with specific aspects of movement behaviors and functional capacity. We aimed to investigate the associations of fatigue, dyspnea, post-exertional malaise, myalgia, and the co-occurrence of symptoms with movement behaviors and functional capacity in individuals with Long COVID. A cross-sectional multicenter study was conducted. Questionnaires were used to assess fatigue, dyspnea, post-exertional malaise, and myalgia. Accelerometry was employed to assess sedentary time, steps per day, light physical activity, and moderate-to-vigorous physical activity. The six-minute walk test, 30-s chair stand test, and timed up and go were used to assess functional capacity. One hundred and two community-dwelling individuals who had been living with Long COVID for 15 ± 10 months participated in the study. Fatigue, post-exertional malaise, and the co-occurrence of physical symptoms showed a negative association with step count, while post-exertional malaise was also negatively associated with moderate-to-vigorous physical activity. Dyspnea showed a negative association with the functional score, including all tests. Our findings suggest that fatigue, post-exertional malaise, and the co-occurrence of physical symptoms are negatively associated with physical activity, while dyspnea is negatively associated with functional capacity in individuals with Long COVID.

Physical Health in Patients with Post-COVID-19 6 and 12 Months after an Inpatient Rehabilitation: An Observational Study

Background: Rehabilitation is an effective and feasible approach for post-COVID patients to improve physical health. However, knowledge regarding the long-term impact of rehabilitation on the physical health of these patients is lacking. Methods: Changes in physical health of 127 patients with COVID-19 as an occupational disease or work accident were assessed in a longitudinal observational study. Post-COVID symptoms, functional status, functional exercise capacity, endurance capacity, physical performance, quadricep strength, handgrip strength, motor balance ability, and self-reported physical performance were examined at the beginning as well as 6 and 12 months after the rehabilitation. Group differences concerning sex, age, acute COVID status, comorbidities prior to COVID-19, and aftercare interventions were also analysed. Results: Even 12 months after rehabilitation, the prevalence of post-COVID symptoms (28.6-94.7%) remained remarkably high in the study population. Significant improvements in various aspects of physical health were observed 6 (r = 0.288-0.755) and 12 months (r = 0.189-0.681) after the rehabilitation. Participants demonstrated enhanced endurance, strength, and balance function, as well as improvement in subjective physical ability. Significant group differences were observed between younger and older patients, those with mild-moderate and severe-critical COVID-19, and patients with and without pre-existing cardiovascular disease, metabolic disease, psychological disease, neuro-sensory disease, musculoskeletal disease, and exercising in an outpatient group. Conclusions: The study identifies persistent challenges in COVID-19 recovery, despite significant improvements in physical health 6 and 12 months after rehabilitation. Further research and the implementation of standardised approaches are required to enhance the outcomes of post-COVID rehabilitation, with a focus on developing personalised care strategies for long-term recovery.

Impaired Hand Grip Strength Correlates with Greater Disability and Symptom Severity in Post-COVID Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background: Post-COVID syndrome (PCS) encompasses a diverse array of symptoms persisting beyond 3 months after acute SARS-CoV-2 infection, with mental as well as physical fatigue being the most frequent manifestations. Methods: In 144 female patients with PCS, hand grip strength (HGS) parameters were assessed as an objective measure of muscle fatigue, with 78 meeting the Canadian Consensus Criteria for postinfectious myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The severity of disability and key symptoms was evaluated using self-reported questionnaires. Results: Patients with ME/CFS exhibited heightened overall symptom severity, including lower physical function (p < 0.001), a greater degree of disability (p < 0.001), more severe fatigue (p < 0.001), postexertional malaise (p < 0.001), and autonomic dysfunction (p = 0.004) compared to other patients with PCS. While HGS was impaired similarly in all patients with PCS and exhibited a significant correlation with physical function across the entire patient group, HGS of patients with ME/CFS uniquely demonstrated associations with key symptoms. Conclusions: Thus, impaired HGS serves as an objective marker of physical function in patients with PCS. Only in patients meeting ME/CFS criteria is impaired HGS also associated with the severity of hallmark symptoms. This suggests a common mechanism for muscle fatigue and other symptoms in the ME/CFS subtype, distinct from that in other types of PCS.

Long COVID outcomes following omicron wave in non-hospital population

Background

The persistence of symptoms or the development of new symptoms following a diagnosis of SARS-CoV-2 has given rise to a multifaceted clinical condition referred to as "long COVID" (LC). The understanding of LC among China's non-hospitalized population continues to be insufficient. This investigation was designed to evaluate the protracted consequences amongst this demographic, as well as to identify the associated risk factors.

Methods

This research constitutes a prospective cohort study focusing on non-hospitalized individuals, aged between 18 and 59, who have been positively diagnosed with COVID-19. Each participant was subjected to a sequence of questionnaire-based surveys, designed to evaluate symptoms as well as the status of depression and anxiety. A logistic regression model, adjusted for multiple variables, was employed to scrutinize the correlation between demographic elements, lifestyle attributes, and health-related risk factors in relation to conditions and symptoms post COVID-19 infection.

Results

A total of 706 individuals participated in the 3 months follow-up, with 620 continuing on to the 6 months follow-up. The median age was 35 (28, 43) years, and 597 (85%) are female. Upon follow-up, Compared with patients without LC, patients with LC have a higher proportion of females (420 (87%) vs. 177 (79%); p = 0.010), were older (35 (29, 44) years vs. 33 (27, 41) years; p = 0.010) and have more comorbidities. Out of all participants, 483 (68.4%) reported experiencing at least one symptom at the 3 months mark, while 49.7% reported symptoms persisting at the 6 months mark. At the 3 months follow-up, the most prevalent persistent symptoms were cough (46%), fatigue (38%), and shortness of breath (34%). By the 6 months follow-up, fatigue (25%), shortness of breath (22%), and sleep disorders (16%) were the most commonly reported symptoms. Anxiety and depression were consistently reported as prevalent symptoms throughout the follow-up period. Most patient symptoms fade over time, with the quickest decreases observed in cough (from 46 to 9%), expectoration (from 26 to 6.3%), smell disorder (from 16 to 3.9%), and taste disorder (from 18 to 3.5%). Male and those possessing advanced educational qualifications exhibit a decreased susceptibility to the sustained incidence of coughing. Conversely, older age and the presence of comorbidities were identified as risk factors for persistent fatigue and shortness of breath.

Conclusion

In the after of COVID-19, it has been observed that the majority of patient symptoms tend to decrease over time. The primary residual symptoms noticed after a 6 month follow-up were fatigue, dyspnea, and sleep disturbances. However, it's noteworthy that the risk factors associated with these symptoms exhibit subtle variations. Furthermore, psychological sequelae, namely depression and anxiety, are frequently reported among COVID-19 survivors.

Functional and Morphological Differences of Muscle Mitochondria in Chronic Fatigue Syndrome and Post-COVID Syndrome

Patients suffering from chronic fatigue syndrome (CFS) or post-COVID syndrome (PCS) exhibit a reduced physiological performance capability. Impaired mitochondrial function and morphology may play a pivotal role. Thus, we aimed to measure the muscle mitochondrial oxidative phosphorylation (OXPHOS) capacity and assess mitochondrial morphology in CFS and PCS patients in comparison to healthy controls (HCs). Mitochondrial OXPHOS capacity was measured in permeabilized muscle fibers using high-resolution respirometry. Mitochondrial morphology (subsarcolemmal/intermyofibrillar mitochondrial form/cristae/diameter/circumference/area) and content (number and proportion/cell) were assessed via electron microscopy. Analyses included differences in OXPHOS between HC, CFS, and PCS, whereas comparisons in morphology/content were made for CFS vs. PCS. OXPHOS capacity of complex I, which was reduced in PCS compared to HC. While the subsarcolemmal area, volume/cell, diameter, and perimeter were higher in PCS vs. CFS, no difference was observed for these variables in intermyofibrillar mitochondria. Both the intermyofibrillar and subsarcolemmal cristae integrity was higher in PCS compared to CFS. Both CFS and PCS exhibit increased fatigue and impaired mitochondrial function, but the progressed pathological morphological changes in CFS suggest structural changes due to prolonged inactivity or unknown molecular causes. Instead, the significantly lower complex I activity in PCS suggests probably direct virus-induced alterations.

Microvascular Capillary and Precapillary Cardiovascular Disturbances Strongly Interact to Severely Affect Tissue Perfusion and Mitochondrial Function in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Evolving from the Post COVID-19 Syndrome

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a frequent, debilitating and still enigmatic disease. There is a broad overlap in the symptomatology of ME/CFS and the Post-COVID-19 Syndrome (PCS). A fraction of the PCS patients develop the full clinical picture of ME/CFS. New observations in microvessels and blood from patients suffering from PCS have appeared and include microclots and malformed pathological blood cells. Capillary blood flow is impaired not only by pathological blood components but also by prothrombotic changes in the vascular wall, endothelial dysfunction, and the expression of adhesion molecules in the capillaries. These disturbances can finally cause a low capillary flow and even capillary stasis. A low cardiac stroke volume due to hypovolemia and the inability of the capacitance vessels to adequately constrict to deliver the necessary cardiac preload generate an unfavorable low precapillary perfusion pressure. Furthermore, a predominance of vasoconstrictor over vasodilator influences exists, in which sympathetic hyperactivity and endothelial dysfunction play a strong role, causing the constriction of resistance vessels and of precapillary sphincters, which leads to a fall in capillary pressure behind the sphincters. The interaction of these two precapillary cardiovascular mechanisms causing a low capillary perfusion pressure is hemodynamically highly unfavorable in the presence of a primary capillary stasis, which is already caused by the pathological blood components and their interaction with the capillary wall, to severely impair organ perfusion. The detrimental coincidence of microcirculatory and precapillary cardiovascular disturbances may constitute the key disturbance of the Post-COVID-19 syndrome and finally lead to ME/CFS in predisposed patients because the interaction causes a particular kind of perfusion disturbance-capillary ischemia/reperfusion-which has a high potential of causing mitochondrial dysfunction by inducing sodium- and calcium-overload in skeletal muscles. The latter, in turn, worsens the vascular situation through the generation of reactive oxygen species to close a vicious cycle from which the patient can hardly escape.

Muscle abnormalities worsen after post-exertional malaise in long COVID

A subgroup of patients infected with SARS-CoV-2 remain symptomatic over three months after infection. A distinctive symptom of patients with long COVID is post-exertional malaise, which is associated with a worsening of fatigue- and pain-related symptoms after acute mental or physical exercise, but its underlying pathophysiology is unclear. With this longitudinal case-control study (NCT05225688), we provide new insights into the pathophysiology of post-exertional malaise in patients with long COVID. We show that skeletal muscle structure is associated with a lower exercise capacity in patients, and local and systemic metabolic disturbances, severe exercise-induced myopathy and tissue infiltration of amyloid-containing deposits in skeletal muscles of patients with long COVID worsen after induction of post-exertional malaise. This study highlights novel pathways that help to understand the pathophysiology of post-exertional malaise in patients suffering from long COVID and other post-infectious diseases.