key: cord-0768955-ep4gkshr
authors: Frazao, M.; Santos, A. d. C.; Cacau, L. d. A. P.; Silva, P. E.; Petrucci, T. R.; Assis, M. C.; Leal, R. d. A.; Forjaz, C. L. d. M.; Brasileiro-Santos, M. d. S.
title: Cardiorespiratory Fitness and Neuromuscular Performance in Patients Recovered from COVID-19
date: 2021-01-13
journal: nan
DOI: 10.1101/2021.01.11.20248930
sha: 7c435fff2274e2afd418466e2fd455ed2823b18f
doc_id: 768955
cord_uid: ep4gkshr

Objective: COVID-19 affects cardiorespiratory and muscular systems, causing dysfunctions that may persist after recovery from the acute infection and treatment. The aim of this study was to evaluate cardiorespiratory fitness and neuromuscular performance in these patients. Methods: Patients recovered from mild (n=31) and severe (n=17) COVID-19 were evaluated and compared to healthy subjects (n=15). All volunteers underwent a maximal cardiopulmonary exercise test with simultaneous acquisition of electromyography (EMG). Power output, oxygen uptake (VO2), pulse oxygen (O2Pulse), cardiovascular efficiency ({Delta}HR/{Delta}VO2), ventilation (VE), breathing reserve (BR) and ventilatory efficiency (VE/VCO2 slope) were analyzed. From EMG, power output for type Ia and IIa activation as well as total neuromuscular efficiency ({Delta}watts/{Delta}%RMS) were determined. Results: Patients with severe COVID-19 presented lower VO2, O2Pulse and VE than mild COVID-19 patients and healthy subjects (p < 0.05 for all comparisons). No differences in {Delta}HR/{Delta}VO2, BR or VE/VCO2 slope were observed among the groups (p > 0.05 for all comparisons). Type IIa and IIb fibers were activated at lower power output in severe than in mild COVID-19 patients and healthy subjects (p < 0.05). {Delta}watts/{Delta}%RMS was lower in severe than in mild COVID-19 patients and healthy subjects (p < 0.05). Conclusion: Patients recovered from severe COVID-19 present low cardiorespiratory fitness, activate glycolytic fibers at low power outputs, and show low neuromuscular efficiency; while patients recovered from mild COVID-19 do not present these sequels.

In late December 2019, a previously unidentified coronavirus, currently named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged from Wuhan, China, and resulted in a formidable outbreak in many cities (1) . Coronaviruses are found in a variety of birds and mammals throughout the world and have a proclivity for emergence. In the past 20 years, three novel SARS-CoV-2 is a beta coronavirus that is genetically related to but distinct from SARS-CoV. To gain entry into the host cell, the SARS-CoV-2 glycoprotein binds to the cellular receptor angiotensin-converting enzyme 2 (2) . The viral response phase starts during the first days of infection, and flu-like symptoms are common (mild phase). Some patients progress to an inflammatory response phase. During this stage, patients develop viral pneumonia, and dyspnea/hypoxia might appear. A minority of COVID-19 patients transit into the third and most severe stage of the illness that manifests as systemic hyperinflammation syndrome and multiorgan dysfunction (3) . In the respiratory system, the virus targets cells lining the respiratory epithelium, causing from an asymptomatic infection to severe end-stage lung disease requiring mechanical ventilation. Disease severity is likely to be a combination of direct virus-induced pathology and the host inflammatory response to the infection (2) . In the cardiovascular system, there is evidence of myocardial injury with some patients presenting abnormalities similar to myocarditis(4). In the skeletal muscle, some patients showed malaise, muscle soreness, and elevated levels of blood creatine kinase, which is considered an indicator of muscle damage and inflammatory response (5) .

As a result of this multisystemic effect, it is reasonable to suggest that COVID-19 can decrease cardiorespiratory fitness and muscular performance, affecting these functions in a direct association with the disease severity.

Additionally, these compromises may persist after the patients have recovered from the COVID-19. However, to date, very few data exist about COVID-19 impact on these capacities after recovery and thus the performance sequels of this illness are still poorly understood. Therefore, the aim of this study was to evaluate cardiorespiratory fitness and neuromuscular performance in patients recovered from mild to severe COVID-19. These data could provide physiological guidance for rehabilitation training programs after COVID-19. We hypothesized that recovery patients present impaired cardiorespiratory and neuromuscular performances in accordance to the disease severity.

An observational study was carried out. In a single-day evaluation, the patients underwent a cardiopulmonary exercise test (CPET) with simultaneous assessment of muscle electromyography (EMG is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint COVID-19 diagnosis was established by clinical symptoms (fever, fatigue, muscle soreness, cough, dyspnea, etc.) associated with a positive laboratory test (nasal swab or serology) and/or chest tomography (ground-glass opacity).

Patients were classified as mild (major clinical symptoms without dyspnea or respiratory failure) or severe (major clinical symptoms with dyspnea or respiratory failure), as postulated by Tian et al (6) . Patients who met the following inclusion criteria were enrolled: recovered (less than 30 days) from mild to severe COVID- 19 . Exclusion criteria were based on comorbidity confounding factors. Thus, patients with critical COVID-19 (i.e. who had required intubation and mechanical ventilation) and those with previous cardiac, pulmonary, neurological, hematological or muscular diseases were excluded.

The technical procedures for CPET followed the American Thoracic Society/American College of Chest Physicians guidelines for cycle ergometer testing(7). The CPET was performed on a CG-04 cycle ergometer (INBRAMED, Porto Alegre, Brazil). Each subject performed a ramp-up protocol, starting with warm-up unloaded pedaling for 2 minutes followed by a workload increment individually selected to achieve maximum effort within 8 to 12 min. Subjects were strongly encouraged by verbal stimuli to achieve maximum effort. The VO2000 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ;

During CPET, neuromuscular activity was analyzed by EMG using a signal acquisition module with a 12-bit resolution A/D converter (EMG800C, EMG System, São José dos Campos, Brazil). Sampling frequency was adjusted to 1000 Hz, frequency band to 20-500 Hz and gain to 1000 times. Bipolar Ag/AgCl self-adhesive surface electrodes were used and placed 20 mm apart (center to center) at the right vastus lateralis (2/3 of the way from the anterior superior iliac spine to the lateral side of the patella), according to Surface Electromyography for the Non-Invasive Assessment of Muscles recommendations (9) .

Root mean square (RMS) values were used for analysis. EMG breakpoints were analyzed during the ramp-up protocol, as previously described by Lucía et al (10) . The increased EMG amplitude reflects the recruitment of additional motor units (11) . Based on this, the first EMG breakpoint was assumed to be type IIa fiber activation, and the second EMG breakpoint was assumed to be type IIb fiber activation (Henneman's principle) (12) . The power outputs at the first and second EMG breakpoints were analyzed (figure 1A). For neuromuscular efficiency analysis, EMG data were normalized by the RMS obtained at the maximum effort (%RMS). Neuromuscular efficiency was determined by the relationship between the power output and EMG (watts/%RMS) at each exercise intensity (25%, 50%, 75% and 100% of maximum power output) (figure 1B), while total neuromuscular efficiency (Δwatts/Δ%RMS) was determined by the relationship between the variation in power output and EMG from unloaded pedaling to maximum exercise intensity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint Neuromuscular efficiency determined by relationship between power output and electromyography (EMG). RMS: root mean square.

Data normality was verified using the Shapiro-Wilk test. Ordinary one-way ANOVA with Tukey's multiple comparison test were used to evaluate intergroup differences for data with a Gaussian distribution. The Kruskal-Wallis test with Dunn's multiple comparisons test were used to evaluate intergroup differences for data without a Gaussian distribution. The categorical variables were analyzed by Fisher's exact test. The effect size was calculated by the F test family (ANOVA: fixed effects, omnibus, one-way) and post hoc type of analysis. The input parameters were as follows: the effect size, f; total sample size; number of groups = 3 and error probability α = 0.05. The effect size, f, was directly calculated from the partial η 2 . The effect size convention was f ≥ 0.1 (small), f ≥ 0.25 (medium) and f ≥ 0.40 (large) (13) . A statistical significance value of p ≤ 0.05 was set for all analyses. GraphPad Prism 7.0 and GPower 3.1.9.7 software were used.

According to data normality distribution, data are presented as means ± standard deviations or as medians and interquartile ranges and percentages.

A total of 66 patients were enrolled in the study, but 18 were excluded due to comorbidities (asthma = 9, heart failure = 3, critical COVID-19 = 3, COPD = 2 and fibromyalgia = 1). From the remained 48 patients, 31 had mild and 17 severe disease. The healthy group was composed by 15 subjects. Characteristics of each group are presented in table 1. Anthropometric characteristics are similar among the groups, while COVID symptoms were more frequent in the severe group that also used zinc more frequently as therapy. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint compared to healthy subjects), without a difference between mild COVID-19 patients and healthy subjects (p > 0.9999) (tables 2 and 3). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint

The main finding of this study was that 1) patients recovered from severe COVID-19 had lower cardiorespiratory fitness, activate muscle fibers Ia and Ib at lower power outputs and present lower neuromuscular efficiency than patients with mild COVID-19 and healthy subjects; while 2) patients recovered from mild COVID-19 had cardiorespiratory fitness and neuromuscular performance similar to healthy subjects.

Peak oxygen uptake reflects functional capacity and has high prognostic value in clinical populations (14) (15) . The expected behavior of this variable in patients recovered from COVID-19 is unknown. The present study showed that COVID-19 can have a significant impact on this variable in those patients who had the severe disease but have no effect on those who had only mild symptoms.

The hazardous impact observed on VO2 may derived from COVID-19's effects as this disease produces pulmonary function landings (16) , myocardial injury (17), and neuromuscular dysfunction (5), but it may also derived from functional impairment imposed by inactivity and hospitalization (18) . In a clinical perspective, the reduced VO2 observed after severe COVID-19 suggest a worst prognosis for these patients, which should be investigated.

Regarding pulmonary function, it is interesting to note that despite the pulmonary compromise usually seen during COVID-19 evolution, patients with severe symptoms had preserved breath reserve and ventilatory efficiency although peak ventilation was reduced. Xiaoneng et al (19) is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint reported that spirometry values were not affected (forced vital capacity and VEF1 > 90% of predicted), while diffusion capacity (64.7% predicted) and total lung capacity (79.2% predicted) were compromised in severe patients. This finding suggests that pulmonary sequalae related to severe COVID may mainly related to lung total volume and gas diffusion, and not to functional volumes that were used during exercise.

Once spirometry values normalize in severe patients and present only a slight reduction in total lung capacity (19) , ventilatory performance may have been impaired by respiratory muscle dysfunction. In addition to peripheral muscle, respiratory muscle may present lower performance in severe COVID-19 patients.

As demonstrated in healthy (20) (21) and other disease models(22), there is a relationship between peripheral muscle performance and respiratory muscle performance.

Multiple mechanisms of deregulation in pulmonary perfusion exist in COVID-19: the abolition of hypoxic pulmonary vasoconstriction, causing an increase in venous admixture, and excessive pulmonary vasoconstriction and microthrombosis or macrothrombosis, leading to increased deadspace (23) .

Despite this, the VE/VCO2 slope was normal in our sample (even in severe patients). A significant reduction in O2pulse was also observed in the group of individuals with severe manifestations; however, the normal ascending behavior of the O2pulse curve and preserved ventilatory efficiency reduced the probability of central cardiovascular limitation. One possibility is that those deregulatory mechanisms do not persist after a time of recovery. Another possibility is that only critical patients present significant pulmonary perfusion deregulation.

Thus, individuals recovered from COVID-19 who had severe manifestations had lower functional capacity, without evidence of significant central cardiorespiratory changes, than those recovered from mild COVID-19 or healthy subjects. The reduction in neuromuscular efficiency demonstrated through electromyography suggests that the effort limitation of these individuals is related to a peripheral mechanism.

Severe COVID-19 patients presented lower neuromuscular efficiency, probably due to myositis and a higher inflammatory pattern. Myositis is characterized by the presence of prominent muscle membrane irritability. In myositis, there is invasion and destruction of muscle fibers by cytotoxic T . CC-BY-ND 4.0 International license It is made available under a perpetuity.

is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint cells (24) . SARS-CoV-2 activates inflammatory cytokines, causing inflammatory injury in muscle cells (25) . The degree of abnormal muscle membrane irritability is related to disease severity. Mao et al. (26) showed that 11% of the patients had evidence of skeletal muscle injury (creatinine kinase>200 U/L and skeletal muscle pain). Injury was significantly more common in patients with severe disease (19%) than in those with non severe disease (5%). Pizon et al. (5) demonstrated, in a meta-analysis of prevalence based on each neurological manifestation, that muscle injury or myalgia was the most common (19.2%) neurological symptom in individuals with COVID-19.

Type IIa and IIb fibers were activated at much lower power output in severe COVID-19 patients, suggesting worse performance in type I and IIa fibers.

Currently, there is insufficient knowledge about muscle histology and fiber-type composition in COVID-19. Independent of any specific pathological process, muscle inactivity causes significant atrophy of all muscle fiber types. Bed rest appears to most strongly induce type I fiber atrophy, accompanied by a fiber-type shift from type I and IIa fibers to type IIb fibers. Taken together, the type of injury, the muscle group affected and the time since injury or rest may all influence how specific muscle fiber types are affected (27) .

The pathological process in myopathies results in dysfunction and the dropout of individual muscle fibers located randomly within the motor unit. In myositis, motor neurons and motor axons are not affected. Motor unit action potentials become polyphasic, short in duration and low in amplitude (28) . Severe COVID-19 patients presented high EMG activity with low power output because each small motor unit was able to generate only a reduced amount of force, requiring the recruitment of many motor units.

The current study shows a consistent external validity once CPET and EMG are low cost and non-invasive methods, available in the majority of clinical exercise laboratories. However, it is important to point out that we assessed a small sample from a single city in Brazil.

Our study has some limitations. First, a priori sample size calculation was not conducted, however posteriori calculation considering VO2 variable resulted in a power of 0.99 and an effect size of 0.54. Sex distribution was different between severe and mild COVID-19 patients, however data presented the same pattern in both sex. Unfortunately, other variables, such as respiratory muscle is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted January 13, 2021. ; https://doi.org/10.1101/2021.01.11.20248930 doi: medRxiv preprint performance (power and strength) and lactate concentrations that might help to explain the lower capacity observed in severe COVID-19 patients were not assessed in the present study and future studies should evaluate them.

Patients recovered from severe COVID-19 present low cardiorespiratory fitness, activate glycolytic fibers at low power outputs, and show low neuromuscular efficiency; while patients recovered from mild COVID-19 do not present these sequels.

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