This expert opinion paper focuses on the clinical implementation, execution and interpretation of Cardiopulmonary Exercise Testing (CPET), providing comprehensive insights into its recognised prognostic, diagnostic and prescriptive value in everyday clinical practice. A practical guide offers step-by-step instructions on conducting and interpreting CPET, emphasising the importance of high-quality testing for the benefit of patients, healthy individuals and athletes. The approach considers test objectives, how to adapt procedures for different medical inquiries and reporting. A systematic method for interpreting CPET data is outlined, covering aerobic/exercise capacity evaluations with subsequent analyses of ventilatory, cardiovascular, cardiorespiratory gas-exchange and muscular-metabolic responses to exercise. Special attention is given to post-exercise recovery and other novel parameters for informed clinical decision-making. The outcomes emphasise the need for better implementation of CPET for prognostic evaluations and in diagnostic pathways. Barriers to its adoption are discussed, including logistical challenges or resource constraints, and strategies for integrating CPET into routine care pathways are proposed. The statement provides further details on how to utilise CPET outcomes to tailor exercise prescription based on identified functional limitations and adjust exercise intensity using different physiological and pathological thresholds for both patients and athletes. Finally, the latest advancements in CPET are explored, including novel portable systems and integration with transcutaneous blood-gas monitoring, imaging, and (non-)invasive haemodynamic measures, also addressing the potential for smaller clinics, improving accessibility in clinical practice. This expert opinion statement aims to offer a roadmap for making CPET a more standardised and accessible tool in clinical care.

BACKGROUND:Post-acute sequelae of SARS-CoV-2 infection, more commonly known as long COVID, has emerged as a major health problem. The pathogenesis of long COVID is unknown, but among the leading hypotheses is viral persistence. We aimed to investigate whether the use of the SARS-CoV-2 antiviral nirmatrelvir-ritonavir improved long COVID symptoms. METHODS:We conducted a double-blind, placebo-controlled, randomised trial involving adults who had developed persistent symptoms (≥12 weeks) associated with three major symptom phenotypes (cognitive, autonomic, or exercise) after acute SARS-CoV-2 infection at 69 US sites. Participants were eligible if they were 18 years or older and had a previous suspected, probable, or confirmed SARS-CoV-2 infection, as defined by the Pan American Health Organization. Eligible participants were also required to have either at least two moderate symptoms from the same phenotype or one severe phenotype-associated symptom, as identified with the Cluster Targeted COVID-19 Symptom Questions. Participants were randomly allocated in a double-blind manner in a 1:1:1 ratio using permuted blocks of size 30 to receive either 15 days of active intervention followed by 10 days of placebo (300 mg nirmatrelvir-100 mg ritonavir twice daily, then 100 mg ritonavir-placebo); 25 days of active intervention (300 mg nirmatrelvir-100 mg ritonavir twice daily); or 25 days of placebo-ritonavir (100 mg ritonavir-placebo). A clinically significant change in patient-reported outcomes at day 90 comprised the primary endpoint: Patient-Reported Outcomes Measurement Information System Cognitive Function Short Form 8a, Orthostatic Hypotension Questionnaire question 1, and a modified version of the DePaul Symptom Questionnaire Post-Exertional Malaise short form. Secondary outcomes were phenotype-specific performance measures. The study was registered at ClinicalTrials.gov (NCT05595369) and is complete. FINDINGS:Between July 27, 2023, and Sept 6, 2024, 1207 individuals were screened. Of these, 964 were randomly allocated and 959 participants, excluding four participants who were later found ineligible and one who did not initiate treatment, were enrolled in the three phenotypes: 332 to cognitive, 334 to autonomic, and 332 to exercise. In the 959 participants in the mITT population, 643 (67%) self-reported as female, 314 (33%) were male, and two participants had a sex of unknown or undifferentiated; 750 (78%) were White; and 108 (11%) were Hispanic, Latino, or Spanish. The median age was 49 years (IQR 38-59). No statistically significant benefits were observed for any phenotype for primary endpoints. For the cognitive phenotype, adjusted differences compared to placebo were 3·2% (95% CI -10·4 to 16·8, p=0·65) for the 25-day regimen and -2·2% (-15·5 to 11·1, p=0·74) for the 15-day regimen. For the autonomic phenotype, adjusted differences were -6·4% (-18·5 to 5·7, p=0·30) for the 25-day regimen compared to placebo and -0·1% (-12·5 to 12·3, p=0·99) for the 15-day regimen compared to placebo. For exercise, adjusted differences were -7·8% (-19·5 to 3·8, p=0·19) for the 25-day regimen compared to placebo and 0·9% (-11·4 to 13·2, p=0·88) for the 15-day regimen compared to placebo. There were no differences in secondary endpoints, and no safety signals were observed; there were no deaths, and 52 serious adverse events occurred in 42 (4%) of 963 participants over the course of the study. INTERPRETATION:Nirmatrelvir-ritonavir for 15 days or 25 days showed no evidence of benefit in long COVID in any of the three phenotypes studied. These findings suggest additional approaches to measuring the symptom burden and treating Long COVID are needed. FUNDING:National Institutes of Health.

The Persistence of SARS-CoV-2 in tissues has been proposed as a driver of prolonged symptoms in long COVID. Pulmonary rehabilitation with exercise training is a well-established intervention for improving symptoms, functional capacity, and inflammation in chronic cardiorespiratory diseases. To investigate whether long COVID is associated with persistent viral or immune-related signals, we analyzed the long RNA profile of circulating extracellular vesicles (EVs) to determine the presence of virus-related transcripts and assess changes in response to exercise training. Fourteen adults with long COVID participated in this single-center pilot clinical trial and completed a 10-week aerobic exercise training program (twenty 1.5 h sessions). Serum-derived EV RNA profiles were analyzed via sequencing at rest (T0) and peak cardiopulmonary exercise testing (T1), before (V2) and after (V24) exercise training. Differentially expressed genes (DEGs) were identified (q < 0.05), and pathway activation analysis was performed. Serum EVs carried diverse RNA species, including protein-coding RNAs, long non-coding RNAs, short non-coding RNAs, and pseudogenes, with no virus-related RNAs detected. No significant DEGs were identified at rest between pre- and post-training, nor in response to acute exercise at pre-training. However, following training, 53 DEGs were found at peak exercise (V24T1) compared to rest (V24T0), including three upregulated genes (ANK3, FTO, FCN1) and 50 downregulated genes (TOP 5: MYL9, NRGN, H2AC6, MAP3K7CL, B2M). These genes were primarily involved in inflammation and metabolism. Pathway analysis revealed significant regulation of 100 pathways at post-training compared to pre training, predominantly inactivated, including pathways involved in inflammation (STAT3 signaling) and metabolism (O-linked glycosylation). Acute exercise and exercise training modulated EV-associated gene expression in long COVID, primarily through transcriptional downregulation. Suppression of inflammation- and immune-related genes post-training highlights potential molecular mechanisms underlying symptom improvement and identifies candidate biomarkers of recovery biology in long COVID. Importantly, while exercise training did not substantially alter EV RNA content at rest, it enhanced the body’s ability to mount a dynamic EV-mediated molecular response during exertion, reflecting improved physiological adaptability. Clinical trial registration number: NCT05398692.

What effect does elevated resting hyperlactatemia have on the response to a moderate level of exercise and on the determination of the gas-exchange threshold (GET)? We first identified 163 diabetic patients treated with metformin, a medication that has been shown to produce, in a significant proportion of patients, an innocuous high resting hyperlactatemia and who underwent cardio-pulmonary exercise testing at the Cleveland Clinic. We found that 102 patients had resting [La] < 2 mM (Group 0); 37 had [La] between 2 and 3 mM (Group 1); 12 had [La] between 3 and 3.5 mM (Group 2); and 12 had [La] > 3.5 mM (Group 3). We examined relationships between resting [La], minute ventilation, pulmonary gas exchange, pH, and arterial blood gases at rest and during exercise (Welch’s test, and Cohen’s d to estimate effect size). None of the baseline data exhibited an effect size consistent with a clinically meaningful confounder. Group 3 had significantly lower HCO₃⁻ (22.5 ± 2.3 mM) than Group 0 (24.2 ± 2.4 mM, p < 0.01). V̇ E was also significantly higher in Group 3. Despite elevated lactate in Group 3 at rest, the respiratory exchange ratio (RER) averaged 0.85 ± 0.12 and did not differ from the other groups. GET could be identified based on the V̇ O₂/ V̇ CO₂ relationship in all groups. Finally, the ventilatory and gas exchange responses to exercise showed no differences between groups. An elevated blood lactate concentration is insufficient, by itself, to reproduce the gas-exchange signature of supra-threshold exercise or to disrupt GET determination.

Background: Long COVID patients present with a myriad of symptoms that can include fatigue, exercise intolerance and post exertional malaise (PEM). Long COVID has been compared to other post viral syndromes, including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), where a reduction in day 2 cardiopulmonary exercise test (CPET) performance of a two-day CPET protocol is suggested to be a result of PEM. We investigated cardiopulmonary and perceptual responses to a two-day CPET protocol in Long COVID patients. Methods: 15 Long COVID patients [n=7 females; mean (SD) age: 53(11) yr; BMI = 32.2(8.5) kg/m(2)] performed a pulmonary function test and two ramp-incremental CPETs separated by 24 hr. CPET variables included gas exchange threshold (GET), peak oxygen uptake (VO2peak) and peak work rate (WRpeak). Ratings of perceived dyspnoea and leg effort were recorded at peak exercise using the modified 0-10 Borg Scale. PEM (past six months) was assessed using the modified DePaul Symptom Questionnaire (mDSQ). One-sample t-tests were used to test significance of mean difference between days (p<0.05). Results: mDSQ revealed PEM in 80 % of patients. Lung function was normal. Responses to day 1 CPET were consistent with the presence of aerobic deconditioning in 40 % of patients (VO2peak <80 % predicted, in the absence of evidence of cardiovascular and pulmonary limitations). There were no differences between day-1 and day-2 CPET responses (all p>0.05). Conclusion: PEM symptoms in Long COVID patients, in the absence of differences in two-day CPET responses separated by 24 hours, suggests that PEM is not due to impaired recovery of exercise capacity between days.

Exercise intolerance is a cardinal symptom in patients with heart failure (HF), and cardiopulmonary exercise testing (CPET) is the gold standard method for its assessment. The treadmill and cycle ergometers (upright and recumbent) are used in clinical practice for tracking disease progression and risk stratification, therefore, understanding the physiological differences related to ergometer is important. The aim of this study was to compare the physiological responses to exercise on treadmill and recumbent cycle ergometer in patients with HF with reduced ejection fraction (HFrEF) using a linear ramp protocol matched with controlled work rate (WR) profiles. Thirteen patients with HFrEF (left ventricular ejection fraction: 34.5 V̇_E / V̇ CO2 slope) (30.8 ± 4.7 vs 30.9 ± 7.3, P = 0.981). However, exercising on recumbent cycle resulted in lower peak oxygen uptake ( V̇ O2) (13.4 [11.3–15.9] vs 15.8 [14.7–18.4] mL/kg/min, p = 0.002) and higher Weber HF severity classification (p = 0.034). Considering the higher V̇ O2 peak reached and its role in clinical decision-making—despite similar V̇_E / V̇ CO2 slope between ergometers—treadmill should be considered the optimal ergometer for exercise intolerance and risk stratification assessment in patients with HFrEF, since it reflects a more accurate exercise capacity and disease severity.

We previously hypothesized that the inflection point of the oxygen dissociation curve (ODC) is linked to the gas exchange threshold (GET) during cardiopulmonary exercise testing. This hypothesis was supported by femoral venous blood gas data sampled during constant exercise below and above the GET, which showed that the ODC shifts rightward at the GET. What had gone unnoticed since these original observations in 1994 was that this rightward shift begins slightly earlier, precisely when the oxygen saturation crosses the ODC inflection point. To investigate this phenomenon, we analyzed the 1994 femoral venous blood gas data obtained during cardiopulmonary exercise testing using a modern validated mechanistic biochemical model of oxygen (O2), carbon dioxide (CO2), and proton binding to hemoglobin (Hb). We constructed the ODC for each data point, as well as the in vivo ODC-a composite curve reflecting changes in dynamic blood chemistry during exercise-to assess its alignment with the GET. The model revealed that, at the in vitro ODC inflection point (36% O2Hb saturation), the amounts of CO2 bound to Hb equalized with HbNH3+ eventually predominating. This equilibrium apparently triggered the Bohr shift, steepening the in vivo ODC to improve O2 unloading to the tissues. Shortly afterwards, the in vivo ODC reached its inflection point, matching the measured GET. Our findings support that the GET is mechanistically linked to the in vivo ODC inflection point. These results highlight the physiological relevance of determining the ODC inflection point and its alignment with HbNH3+ and CO2 binding as critical factors in understanding ODC shifts during cardiopulmonary exercise testing.

Letter to the EditorReply to Francescato and CettoloMichele Girardi, Chiara Gattoni, William W. Stringer, Harry B. Rossiter, Richard Casaburi, Carrie Ferguson, and Carlo CapelliMichele GirardiThe Lundquist Institute for Biomedical Innovation, Harbor-University of California Los Angeles Medical Center, Torrance, California, United States, Chiara GattoniThe Lundquist Institute for Biomedical Innovation, Harbor-University of California Los Angeles Medical Center, Torrance, California, United States, William W. StringerThe Lundquist Institute for Biomedical Innovation, Harbor-University of California Los Angeles Medical Center, Torrance, California, United States, Harry B. RossiterThe Lundquist Institute for Biomedical Innovation, Harbor-University of California Los Angeles Medical Center, Torrance, California, United States, Richard CasaburiThe Lundquist Institute for Biomedical Innovation, Harbor-University of California Los Angeles Medical Center, Torrance, California, United States, Carrie FergusonThe Lundquist Institute for Biomedical Innovation, Harbor-University of California Los Angeles Medical Center, Torrance, California, United States, andCarlo CapelliDepartment of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, ItalyPublished Online:22 Mar 2024https://doi.org/10.1152/ajpregu.00028.2024MoreSectionsPDF (324 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat reply: We appreciate the interest of Drs. Francescato and Cettolo (1) in our recent work (2). Their letter presents an excellent opportunity to reinforce and extend some of the arguments detailed in our review.Our review does not advocate for relating volumes computed using one definition of the breathing cycle to gas tensions measured using a different definition. Relating pulmonary ventilation (V̇e) calculated using a classical definition of the breathing cycle (i.e., between onset of two consecutive inspirations) to alveolar CO2 output derived from an alternative definition (e.g., between two equal FCO2/FN2 values) would clearly be inappropriate. This mismatch would likely lead to misinterpretation of key cardiopulmonary exercise testing (CPET) variables, e.g., ventilatory equivalents for O2 and CO2 (V̇e/V̇o2 and V̇e/V̇co2), as the gas and volume responses would not be paired appropriately, as previously discussed in the literature (3, 4).Instead, our review emphasized the physiological implications of ventilatory-based variables in CPET when applying different definitions of the breathing cycle. For instance, when using an alternative definition of the breathing cycle to measure alveolar O2 uptake and CO2 output, we suggested investigating an approach to identify the equivalent value for pulmonary ventilation that allows V̇e/V̇o2 and V̇e/V̇co2 measurements comparable with those obtained using the classical definition of a breath (see Limitations, Methodological Considerations, and Future Directions in Ref. 2). As acknowledged in our review, further studies are required to validate this approach.The implications of using different definitions of the breathing cycle extend beyond specific information obtained from CPET and may involve other broad areas in physiology and medicine. Uniformity in defining tidal volume, breathing rate, and V̇e is crucial across these fields. Variations in these definitions can lead to practical challenges in the clinical setting, such as ventilator management in intensive care units. They may influence the diagnosis and treatment of conditions that rely on accurate ventilatory pattern analysis, such as dysfunctional breathing (5, 6) and periodic breathing (7, 8).The effect of accepting different definitions of the breathing cycle becomes even more complex when considering disease states that alter the physiological dead space to tidal volume ratio (VD/VT). VD/VT is determined by arterial and mixed expired CO2 partial pressures of a conventional expiratory phase. When measured on a breath-by-breath basis, however, its determination requires ventilatory-based variables (9, 10). The physiological meaning of VD/VT when calculated using different breath definitions (if, indeed, this is possible) currently is unknown.As singular constructs, these measures can be significantly altered by how a breath is defined, potentially influencing CPET interpretation. The effect of using different definitions of a breath may be less influential when considering V̇e/V̇co2 and V̇e/V̇o2, because both numerator and denominator of the ratio are altered. However, further research is needed to establish this suggestion, and this also does not negate the broader implications of different definitions on other crucial respiratory measurements.Although alternative breathing cycle definitions are appealing in that they may enrich the information provided by measurement of gas exchange and its kinetics, the applications of these alternatives remain limited. This is partially due to the lack of comprehensive data on how these alternative definitions impact the assessment and interpretation of key ventilatory-based variables routinely used in CPET.In conclusion, although we acknowledge Drs. Francescato and Cettolo's concerns, it is essential to understand the broader ramifications of altering the definitions of a breathing cycle. Our review aimed, among other objectives, to highlight these concerns.GRANTSThis article was supported by National Institutes of Health Grants P50HD098593, R01DK122767, R01HL166850, R01HL153460, and R01HL151452 (to H.B.R.) and R01HL166850 (to C.F.). H.B.R. was also supported by Tobacco-Related Disease Research Program Grant T31IP1666.DISCLOSURESM. Girardi is supported by the Johnny Carson Foundation. H. B. Rossiter reports consulting fees from Omniox Inc. and is involved in contracted clinical research with Boehringer Ingelheim, GlaxoSmithKline, Novartis, AstraZeneca, Astellas, United Therapeutics, Genentech, and Regeneron. He is a visiting professor at the University of Leeds, UK. R. Casaburi is involved in contracted research with United Therapeutics, Genentech, and Regeneron. He is an advisory board member for Inogen and Abbott and a speaker bureau member for GlaxoSmithKline. C. Ferguson is involved in contracted clinical research with United Therapeutics, Genentech, Regeneron, and Respira Therapeutics. She is a visiting associate professor at the University of Leeds, UK. None of the other authors has any conflicts of interest, financial or otherwise, to disclose.AUTHOR CONTRIBUTIONSM.G., C.G., W.W.S., H.B.R., R.C., C.F., and C.C. conceived and designed research; M.G., C.G., W.W.S., H.B.R., R.C., C.F., and C.C. drafted manuscript; M.G., C.G., W.W.S., H.B.R., R.C., C.F., and C.C. edited and revised manuscript; M.G., C.G., W.W.S., H.B.R., R.C., C.F., and C.C. approved final version of manuscript.REFERENCES1. Francescato MP, Cettolo V. Letter to the editor: is the current definition of ventilation congruent with the alveolar gas exchange? Am J Physiol Regul Integr Comp Physiol 326. doi:10.1152/ajpregu.00289.2023.Link | Google Scholar2. Girardi M, Gattoni C, Stringer WW, Rossiter HB, Casaburi R, Ferguson C, Capelli C. Current definitions of the breathing cycle in alveolar breath-by-breath gas exchange analysis. Am J Physiol Regul Integr Comp Physiol 325: R433–R445, 2023. doi:10.1152/ajpregu.00065.2023. Link | ISI | Google Scholar3. 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Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESCorrespondence: M. Girardi (michele.girardi@lundquist.org) Download PDF Previous Back to Top FiguresReferencesRelatedInformation Related ArticlesIs the current definition of ventilation congruent with the alveolar gas exchange? 22 Mar 2024American Journal of Physiology-Regulatory, Integrative and Comparative Physiology More from this issue > Volume 326Issue 4April 2024Pages R331-R332 Crossmark Copyright & PermissionsCopyright © 2024 the American Physiological Society.https://doi.org/10.1152/ajpregu.00028.2024PubMed38518073History Received 1 February 2024 Accepted 16 February 2024 Published online 22 March 2024 Published in print 1 April 2024 Keywordscardiopulmonary exercise testing;lung gas stores;respiratory cycle;breathing cycle; Metrics

AbstractChronic obstructive pulmonary disease (COPD) is a respiratory disease characterized by pulmonary and systemic inflammation. Inflammatory mediators show relationships with shortness of breath, exercise intolerance and health related quality of life. Pulmonary rehabilitation (PR), a comprehensive education and exercise training programme, is the most effective therapy for COPD and is associated with reduced exacerbation and hospitalization rates and increased survival. Exercise training, the primary physiological intervention within PR, is known to exert a beneficial anti‐inflammatory effect in health and chronic diseases. The question of this review article is whether exercise training can also make such a beneficial anti‐inflammatory effect in COPD. Experimental studies using smoke exposure mice models suggest that the response of the immune system to exercise training is favourably anti‐inflammatory. However, the evidence about the response of most known inflammatory mediators (C‐reactive protein, tumour necrosis factor α, interleukin 6, interleukin 10) to exercise training in COPD patients is inconsistent, making it difficult to conclude whether regular exercise training has an anti‐inflammatory effect in COPD. It is also unclear whether COPD patients with more persistent inflammation are a subgroup that would benefit more from hypothesized immunomodulatory effects of exercise training (i.e., personalized treatment). Nevertheless, it seems that PR combined with maintenance exercise training (i.e., lifestyle change) might be more beneficial in controlling inflammation and slowing disease progress in COPD patients, specifically in those with early stages of disease.