Cardiopulmonary, metabolic, and perceptual responses during exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): A Multi-site Clinical Assessment of ME/CFS (MCAM) sub-study

Exercise does not cause post-exertional malaise in Veterans with Gulf War Illness: A randomized, controlled, dose-response, crossover study

Chronic multisymptom illnesses (CMI) such as Myalgic Encephalomyelitis/Chronic Fatigue Syndrome, Long-COVID, and Gulf War Illness (GWI) are associated with an elevated risk of post-exertional malaise (PEM), an acute exacerbation of symptoms and other related outcomes following exercise. These individuals may benefit from personalized exercise prescriptions which prioritize risk minimization, necessitating a better understanding of dose-response effects of exercise intensity on PEM.

METHODS

Veterans with GWI (n = 40) completed a randomized controlled crossover experiment comparing 20 min of seated rest to light-, moderate-, and vigorous-intensity cycling conditions over four separate study visits. Symptoms, pain sensitivity, cognitive performance, inflammatory markers (C-reactive protein and plasma cytokines) were measured before and within 1 h after exercise and seated rest. Physical activity behavior was measured ≥ 7 days following each study visit via actigraphy. Linear mixed effects regression models tested the central hypothesis that higher intensity exercise would elicit greater exacerbation of negative outcomes, as indicated by a significant condition-by-time interaction for symptom, pain sensitivity, cognitive performance, and inflammatory marker models and a significant main effect of condition for physical activity models.

RESULTS

Significant condition-by-time interactions were not observed for primary or secondary measures of symptoms, pain sensitivity, cognitive performance, and a majority of inflammatory markers. Similarly, a significant effect of condition was not observed for primary or secondary measures of physical activity.

CONCLUSIONS

Undesirable effects such as symptom exacerbation were observed for some participants, but the group-level risk of PEM following light-, moderate-, or vigorous-intensity exercise was no greater than seated rest. These findings challenge several prior views about PEM and lend support to a broader body of literature showing that the benefits of exercise outweigh the risks.

Post-exertional malaise in daily life and experimental exercise models in patients with myalgic encephalomyelitis/chronic fatigue syndrome

Post-exertional malaise (PEM) is commonly recognized as a hallmark of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and is often used as one of several criteria for diagnosing ME/CFS. In this perspective paper we want to reflect on how PEM is understood, assessed, and evaluated in scientific literature, and to identify topics to be addressed in future research. Studies show that patients use a wide variety of words and concepts to label their experience of PEM in everyday life, and they report physical or mental exertions as triggers of PEM. They also report that PEM may have an immediate or delayed onset and may last from a few days to several months. When standardized exercise tests are used to trigger PEM experimentally, the exacerbation of symptoms has a more immediate onset but still shows a wide variability in duration. There are indications of altered muscular metabolism and autonomic nervous responses if exercise is repeated on successive days in patients with ME/CFS. The decreased muscular capacity appears to be maintained over several days following such controlled exercise bouts. These responses may correspond to patients' experiences of increased exertion. Based on this background we argue that there is a need to look more closely into the processes occurring in the restitution period following exercise, as PEM reaches the peak in this phase.

Orthostatic chronotropic incompetence in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Background

Orthostatic intolerance (OI) is a core diagnostic criterion in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The majority of ME/CFS patients have no evidence of hypotension or postural orthostatic tachycardia syndrome (POTS) during head-up tilt, but do show a significantly larger reduction in stroke volume index (SVI) when upright compared to controls. Theoretically a reduction in SVI should be accompanied by a compensatory increase in heart rate (HR). When there is an incomplete compensatory increase in HR, this is considered chronotropic incompetence. This study explored the relationship between HR and SVI to determine whether chronotropic incompetence was present during tilt testing in ME/CFS patients.

Methods

From a database of individuals who had undergone tilt testing with Doppler measurements for SVI both supine and end-tilt, we selected ME/CFS patients and healthy controls (HC) who had no evidence of POTS or hypotension during the test. To determine the relation between the HR increase and SVI decrease during the tilt test in patients, we calculated the 95% prediction intervals of this relation in HC. Chronotropic incompetence in patients was defined as a HR increase below the lower limit of the 95th % prediction interval of the HR increase in HC.

Results

We compared 362 ME/CFS patients with 52 HC. At end-tilt, tilt lasting for 15 (4) min, ME/CFS patients had a significantly lower SVI (22 (4) vs. 27 (4) ml/m²; p < 0.0001) and a higher HR (87 (11) vs. 78 (15) bpm; p < 0.0001) compared to HC. There was a similar relationship between HR and SVI between ME/CFS patients and HC in the supine position. During tilt ME/CFS patients had a lower HR for a given SVI; 37% had an inadequate HR increase. Chronotropic incompetence was more common in more severely affected ME/CFS patients.

Conclusion

These novel findings represent the first description of orthostatic chronotropic incompetence during tilt testing in ME/CFS patients.

Exercise Pathophysiology in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Postacute Sequelae of SARS-CoV-2: More in Common Than Not?

TOPIC IMPORTANCE

Postacute sequelae of SARS-CoV-2 (PASC) is a long-term consequence of acute infection from COVID-19. Clinical overlap between PASC and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) has been observed, with shared symptoms including intractable fatigue, postexertional malaise, and orthostatic intolerance. The mechanistic underpinnings of such symptoms are poorly understood.

REVIEW FINDINGS

Early studies suggest deconditioning as the primary explanation for exertional intolerance in PASC. Cardiopulmonary exercise testing reveals perturbations related to systemic blood flow and ventilatory control associated with acute exercise intolerance in PASC, which are not typical of simple detraining. Hemodynamic and gas exchange derangements in PASC have substantial overlap with those observed with ME/CFS, suggestive of shared mechanisms.

SUMMARY

This review illustrates exercise pathophysiologic commonalities between PASC and ME/CFS that will help guide future diagnostics and treatment.

ME/CFS and Long COVID share similar symptoms and biological abnormalities: road map to the literature

Some patients remain unwell for months after "recovering" from acute COVID-19. They develop persistent fatigue, cognitive problems, headaches, disrupted sleep, myalgias and arthralgias, post-exertional malaise, orthostatic intolerance and other symptoms that greatly interfere with their ability to function and that can leave some people housebound and disabled. The illness (Long COVID) is similar to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) as well as to persisting illnesses that can follow a wide variety of other infectious agents and following major traumatic injury. Together, these illnesses are projected to cost the U.S. trillions of dollars. In this review, we first compare the symptoms of ME/CFS and Long COVID, noting the considerable similarities and the few differences. We then compare in extensive detail the underlying pathophysiology of these two conditions, focusing on abnormalities of the central and autonomic nervous system, lungs, heart, vasculature, immune system, gut microbiome, energy metabolism and redox balance. This comparison highlights how strong the evidence is for each abnormality, in each illness, and helps to set priorities for future investigation. The review provides a current road map to the extensive literature on the underlying biology of both illnesses.

Use of Cardiopulmonary Exercise Testing to Evaluate Long COVID-19 Symptoms in Adults: A Systematic Review and Meta-analysis

IMPORTANCE

Reduced exercise capacity is commonly reported among individuals with COVID-19 symptoms more than 3 months after SARS-CoV-2 infection (long COVID-19 [LC]). Cardiopulmonary exercise testing (CPET) is the criterion standard to measure exercise capacity and identify patterns of exertional intolerance.

OBJECTIVES

To estimate the difference in exercise capacity among individuals with and without LC symptoms and characterize physiological patterns of limitations to elucidate possible mechanisms of LC.

DATA SOURCES

A search of PubMed, EMBASE, Web of Science, preprint servers, conference abstracts, and cited references was performed on December 20, 2021, and again on May 24, 2022. A preprint search of medrxiv.org, biorxiv.org, and researchsquare.com was performed on June 9, 2022.

STUDY SELECTION

Studies of adults with SARS-CoV-2 infection more than 3 months earlier that included CPET-measured peak oxygen consumption (V̇o2) were screened independently by 2 blinded reviewers; 72 (2%) were selected for full-text review, and 35 (1%) met the inclusion criteria. An additional 3 studies were identified from preprint servers.

DATA EXTRACTION AND SYNTHESIS

Data extraction was performed by 2 independent reviewers according to the PRISMA reporting guideline. Data were pooled using random-effects models.

MAIN OUTCOMES AND MEASURES

Difference in peak V̇o2 (in mL/kg/min) among individuals with and without persistent COVID-19 symptoms more than 3 months after SARS-CoV-2 infection.

RESULTS

A total of 38 studies were identified that performed CPET on 2160 individuals 3 to 18 months after SARS-CoV-2 infection, including 1228 with symptoms consistent with LC. Most studies were case series of individuals with LC or cross-sectional assessments within posthospitalization cohorts. Based on a meta-analysis of 9 studies including 464 individuals with LC symptoms and 359 without symptoms, the mean peak V̇o2 was -4.9 (95% CI, -6.4 to -3.4) mL/kg/min among those with symptoms with a low degree of certainty. Deconditioning and peripheral limitations (abnormal oxygen extraction) were common, but dysfunctional breathing and chronotropic incompetence were also described. The existing literature was limited by small sample sizes, selection bias, confounding, and varying symptom definitions and CPET interpretations, resulting in high risk of bias and heterogeneity.

CONCLUSIONS AND RELEVANCE

The findings of this systematic review and meta-analysis study suggest that exercise capacity was reduced more than 3 months after SARS-CoV-2 infection among individuals with symptoms consistent with LC compared with individuals without LC symptoms, with low confidence. Potential mechanisms for exertional intolerance other than deconditioning include altered autonomic function (eg, chronotropic incompetence, dysfunctional breathing), endothelial dysfunction, and muscular or mitochondrial pathology.

Effects of nociceptive and mechanosensitive afferents sensitization on central and peripheral hemodynamics following exercise-induced muscle damage

This study aims to test the separated and combined effects of mechanoreflex activation and nociception through exercise-induced muscle damage (EIMD) on central and peripheral hemodynamics before and during single passive leg movement (sPLM). Eight healthy young males undertook four experimental sessions, in which a sPLM was performed on the dominant limb while in each specific session the contralateral was: 1) in a resting condition (CTRL), 2) stretched (ST), 3) resting after EIMD called delayed onset muscle soreness (DOMS) condition, or 4) stretched after EIMD (DOMS + ST). EIMD was used to induce DOMS in the following 24-48 h. Femoral blood flow (FBF) was assessed using Doppler ultrasound whereas central hemodynamics were assessed via finger photoplethysmography. Leg vascular conductance (LVC) was calculated as FBF/mean arterial pressure (MAP). RR-intervals were analyzed in the time (root mean squared of successive intervals; RMSSD) and frequency domain [low frequency (LF)/high frequency (HF)]. Blood samples were collected before each condition and gene expression analysis showed increased fold changes for P2X4 and IL1β in DOMS and DOMS + ST compared with baseline. Resting FBF and LVC were decreased only in the DOMS + ST condition (-26 mL/min and -50 mL/mmHg/min respectively) with decreased RMSSD and increased LF/HF ratio. MAP, HR, CO, and SV were increased in ST and DOMS + ST compared with CTRL. Marked decreases of Δpeaks and AUC were observed for FBF (Δ: -146 mL/min and -265 mL respectively) and LVC (Δ: -8.66 mL/mmHg/min and ±1.7 mL/mmHg/min respectively) all P < 0.05. These results suggest that the combination of mechanoreflex and nociception resulted in decreased vagal tone and concomitant rise in sympathetic drive that led to increases in resting central hemodynamics with reduced limb blood flow before and during sPLM.NEW & NOTEWORTHY Exercise-induced muscle damage (EIMD) is a well-known model to study mechanical hyperalgesia and muscle peripheral nerve sensitizations. The combination of static stretching protocol on the damaged limb extensively increases resting central hemodynamics with reduction in resting limb blood flow and passive leg movement-induced hyperemia. The mechanism underlining these results may be linked to reduction of vagal tone with concomitant increase in sympathetic activity following mechano- and nociceptive activation.

Cardiopulmonary exercise testing to evaluate post-acute sequelae of COVID-19 ("Long COVID"): a systematic review and meta-analysis

IMPORTANCE

Reduced exercise capacity is commonly reported among individuals with Long COVID (LC). Cardiopulmonary exercise testing (CPET) is the gold-standard to measure exercise capacity to identify causes of exertional intolerance.

OBJECTIVES

To estimate the effect of SARS-CoV-2 infection on exercise capacity including those with and without LC symptoms and to characterize physiologic patterns of limitations to elucidate possible mechanisms of LC.

DATA SOURCES

We searched PubMed, EMBASE, and Web of Science, preprint severs, conference abstracts, and cited references in December 2021 and again in May 2022.

STUDY SELECTION

We included studies of adults with SARS-CoV-2 infection at least three months prior that included CPET measured peak VO ₂ . 3,523 studies were screened independently by two blinded reviewers; 72 (2.2%) were selected for full-text review and 36 (1.2%) met the inclusion criteria; we identified 3 additional studies from preprint servers.

DATA EXTRACTION AND SYNTHESIS

Data extraction was done by two independent reviewers according to PRISMA guidelines. Data were pooled with random-effects models.

MAIN OUTCOMES AND MEASURES

A priori primary outcomes were differences in peak VO ₂ (in ml/kg/min) among those with and without SARS-CoV-2 infection and LC.

RESULTS

We identified 39 studies that performed CPET on 2,209 individuals 3-18 months after SARS-CoV-2 infection, including 944 individuals with LC symptoms and 246 SARS-CoV-2 uninfected controls. Most were case-series of individuals with LC or post-hospitalization cohorts. By meta-analysis of 9 studies including 404 infected individuals, peak VO ₂ was 7.4 ml/kg/min (95%CI 3.7 to 11.0) lower among infected versus uninfected individuals. A high degree of heterogeneity was attributable to patient and control selection, and these studies mostly included previously hospitalized, persistently symptomatic individuals. Based on meta-analysis of 9 studies with 464 individuals with LC, peak VO ₂ was 4.9 ml/kg/min (95%CI 3.4 to 6.4) lower compared to those without symptoms. Deconditioning was common, but dysfunctional breathing, chronotropic incompetence, and abnormal oxygen extraction were also described.

CONCLUSIONS AND RELEVANCE

These studies suggest that exercise capacity is reduced after SARS-CoV-2 infection especially among those hospitalized for acute COVID-19 and individuals with LC. Mechanisms for exertional intolerance besides deconditioning may be multifactorial or related to underlying autonomic dysfunction.