Ramp Protocol Research Articles

MOTRPAC CPET CORE LAB - QUALITY CONTROL AND THRESHOLD DETERMINATIONS

https://youtu.be/KAfCLUuf1XY INTRODUCTION The Molecular Transducers of Physical Activity Consortium (MoTrPAC) protocol includes collection of cardiopulmonary exercise testing (CPET) data as a key clinical outcome. Due to the large volume of data and institutions involved in MoTrPAC, a CPET Core Lab was created to manage a CPET data repository, evaluate data quality, and analyze metabolic events in the continuous data like ventilatory thresholds (VT). METHODS All clinical centers involved in MoTrPAC conducted CPETs on cycle ergometers following individualized ramp protocols. The CPET Core Lab determines the VTs in all past and current CPETS: VT1 (ventilatory threshold 1) and VT2 (ventilatory threshold 2 or Respiratory Compensation Point) as data permits. VT1 is the point where VE and VCO2 increase at a greater rate than VO2. VT2 occurs when VE increases curvilinearly compensating for excess CO2 production. Two independent adjudicators will review each test and independently determine VT1 and VT2. To ensure quality control between adjudicators, repeated VT readings were performed 2 times on 20 blinded tests by 3 adjudicators. This quality control (QC) evaluation process was performed to establish between- and within-adjudicator concordance and agreement by concordance coefficient correlation (ρc) and Bland and Altman analysis, respectively. Adjudicators analyzed all CPETs without doing any additional confirmatory QC. RESULTS The metrics calculated on these data showed a high within-adjudicator concordance (ρc range 0.965 to 0.744) and agreement without significant proportional or systematic bias. Within-adjudicator coefficient of variation was below 8% (range 4.12% to 7.88%) for all adjudicators for both VT1 and VT2. The overall coefficient of variation for all adjudicators was 9.9% for VT1 and 10.7% for VT2 between adjudicators, and below 150 ml/min as empirically suggested. CONCLUSIONS VT1 and VT2 reading between-adjudicator had a good concordance and agreement. Additional QC procedures between adjudicators are planned to achieve higher levels of reliability and agreement.

Assessment of cardiac structure and function 1.5 years after COVID-19: results from the EPILOC study

Abstract Background Impaired left and right ventricular function have been observed mainly in hospitalized patients with acute SARS-CoV-2 infection. The long-term cardiac sequelae have not yet been conclusively clarified in large, well-defined cohorts. In addition, it is not yet certain whether cardiac function is related to persistent cardiopulmonary symptoms or reduced exercise capacity after COVID-19. Purpose Differences in cardiac structure and function in patients with suspected post-COVID syndrome (PCS) and in recovered control patients (CON) were analysed with regard to the association with cardiopulmonary symptoms and physical performance. Methods In this multicentre study, transthoracic echocardiography was performed in 1154 individuals (49±12 years, 760 women) 1.5 years after SARS-CoV-2 infection (October 2020 till April 2021) in southwest Germany. Left and right ventricular global longitudinal strain (LV/RV GLS) and RV free wall strain (FWS) were determined with post-processing software in 679 PCS and 475 CON. Cardiopulmonary exercise testing (CPET) was performed with a ramp protocol on a bicycle ergometer. Results PCS showed lower LV GLS (-20.25% vs. -20.73%, p=0.003), diastolic function (E/A 1.16 vs. 1.21, p=0.022) and TAPSE (24.45 vs. 25.05, p=0.022) compared to CON, while RV strain values did not differ. Echocardiographic parameters were within the normal clinical reference range. LV GLS was negatively associated with VO2max (p=0.004) and positively associated with rapid physical exhaustion (p=0.050), but not with cardiopulmonary symptoms. Conclusions Significantly reduced cardiac function in PCS compared to CON 1.5 years after SARS-CoV-2 infection could indicate long-term left myocardium involvement, while signs of RV involvement were inconsistent. The differences between the groups appear to be small and could be explained by deconditioning due to PCS or the more frequent presence of cardiovascular disease in PCS. Nevertheless, it cannot be ruled out that a slight reduction in cardiac function and physical performance could be a long-term consequence of COVID-19 in patients with persistent symptoms. Further (long-term) studies are therefore necessary to investigate the connection between persistent exercise intolerance and cardiac involvement. This could lead to further diagnostic steps and therapy recommendations.

Indexes of Fat Oxidation from Ramp vs. Graded Incremental Protocols in Postmenopausal Women

The maximal rate of fat oxidation (MFO, in g∙min−1) and the relative exercise intensity at which it occurs (FATmax, as %V̇O2max) are indexes of metabolic flexibility. The time-consuming, graded exercise protocol required for MFO/FATmax determination hinders the extensive use of these indexes for individualized exercise prescription and monitoring. Purpose: validate ramp testing for MFO and FATmax measures in postmenopausal women. Methods: Seventeen healthy women (age: 54 ± 4 years, BMI 22 ± 3 kg·m−2, and V̇O2max 36.4 ± 5.3 mL·min−1), who were 4 ± 3 years from menopause, performed on a cycle-ergometer, a ramp, and a graded incremental test. Based on V̇O2 and respiratory exchange ratio from the ramp and graded protocol (i.e., the 5th minute of each step), MFO and FATmax were determined. Data from the two protocols were compared using paired t-tests, linear regression, and Bland–Altman analysis. Results: The MFO measured with a ramp protocol was not different from (0.24 ± 0.09 vs. 0.20 ± 0.08 g·min−1, p = 0.10), and moderately associated with, that of the graded protocol (r2 = 0.46). FATmax occurred at similar exercise intensity for both protocols (47.8 ± 5.1 vs. 47.5 ± 4.3 %V̇O2max, p = 0.91, r2 = 0.52). The comparison of MFO and FATmax across the protocols yields a non-significant bias but a relatively large limit of agreement (respectively, 0.05 g·min−1, LOA = −0.08, and 0.19 g·min−1; 0.3 %V̇O2max, LOA = −7.8, and 10.6 %V̇O2max). Conclusions: In postmenopausal women, ramp testing offers a valid alternative to the graded protocol for identifying MFO and FATmax. The availability of a time- and cost-efficient approach, which can be incorporated into standard ramp incremental testing, can facilitate using these indexes of metabolic flexibility in research and medicine.

Ramp Protocol for Non-linear Cerebrovascular Reactivity with Transcranial Doppler Ultrasound.

Cerebrovascular reactivity (CVR) reflects the ability of cerebral blood vessels to adjust their diameter in response to vasoactive stimuli, which is crucial for maintaining brain health. Traditional CVR assessments commonly use a two-point measurement, assuming a linear relationship between cerebral blood flow (CBF) and arterial CO2. However, this approach fails to capture non-linear characteristics, particularly the plateaus at extreme CO2 levels. This study introduces a cost-effective, ramp-based end-tidal CO2 (PETCO2) protocol to assess non-linear aspects of CVR. Using transcranial Doppler ultrasound, we monitored blood velocity responses to progressive increases in arterial CO2 levels in eleven healthy adults, covering a spectrum from hypocapnia to hypercapnia. All eleven participants successfully completed the protocol, with an average PETCO2 range of 26 ± 4mmHg and blood velocity changes from -29% to +50% relative to baseline. Non-linear CVR characteristics were observed in all subjects. Sigmoid models provided significantly better fits to the CVR data than linear models, while Bayesian approaches followed expected physiological ranges more accurately than least squares regression methods. Unlike traditional CVR methods, this ramp protocol captures the full, non-linear CVR profile. The sigmoid modeling approach offers a more accurate representation of cerebrovascular dynamics, particularly at CO2 extremes. The PETCO2 ramp protocol with non-linear CVR modeling shows promise as an accessible and reliable tool for assessing CBF dynamics. With high completion rates, straightforward implementation, and low equipment cost, this approach holds significant potential for clinical applications in cerebrovascular health evaluation.

Abstract 4131424: Exercise Stress Perfusion Cardiac MRI in Pediatric Patients with Coronary Anomalies

Introduction: Anomalous aortic origin of a coronary artery (AAOCA) can result in sudden cardiac death in the young and risk stratification is challenging. Though dobutamine stress cardiac MRI (DS-CMR) is feasible in pediatric patients, exercise stress CMR (ES-CMR) has lower rates of adverse events, higher diagnostic accuracy, and the ability to better reflect the physiologic changes occurring with exercise. No studies have evaluated ES-CMR in the pediatric population. We aim to describe our institution’s experience with ES-CMR using supine bicycle ergometry in patients with AAOCA. Methods: We retrospectively reviewed the medical records of AAOCA patients who underwent ES-CMR at our institution between 2011 and 2024 for demographic, clinical presentation, cardiopulmonary exercise test (CPET) and ES-CMR data. The exercise-based portion of the CMR consisted of supine cycle ergometry utilizing a ramp protocol, immediately after which perfusion imaging was performed. We used descriptive statistics for data analysis. Results: Of 38 patients who underwent ES-CMR, the median age was 16 years (range 13-24) and 68% were male. Diagnoses included anomalous right coronary artery (N=28), anomalous left coronary artery (N=8), and single coronary artery (N=1 single right, N=1 single left). Median maximal heart rate (HR) during ES-CMR was 160 bpm (range 130-190, median 80% predicted) with a median maximal HR during patients’ most recent CPET of 187 bpm (range 160-203, median 97% predicted). No patients had perfusion defects at rest or with exercise stress, or evidence of myocardial scarring. There were no adverse events. Discussion: We demonstrate for the first time the use of ES-CMR in a cohort of pediatric and young adult patients with AAOCA. ES-CMR can provide a unique modality to assess for ischemia at rest and stress as a means of risk stratification and simulate physiologic changes occurring with exercise stress in a single study. Although maximum heart rates during supine cycle ergometry are lower than those reached during CPET, they are similar to those reached during DS-CMR. ES-CMR can be a helpful and safe diagnostic tool in patients with AAOCA.

Abstract 4126333: TRPC6 A404V is a gain-of-function variant associated with doxorubicin-induced cardiotoxicity in patients

Background: Gain-of-function mutations in the canonical transient receptor potential 6 (TRPC6) channel contribute to heart failure (HF) and focal segmental glomerulosclerosis in humans. Our GWAS results indicated that the TRPC6 A404V variant, having a minor allele frequency of 12% in the population, is associated with doxorubicin-induced cardiotoxicity. However, the underlying ionic mechanisms of this variant have not been fully examined. Methods: Combining patch clamp recording, site-directed mutagenesis, and in-silico analysis, we evaluated the TRPC6 A404V variant function. Results: Whole-cell TRPC6 currents were elicited in HEK293 cells using a voltage ramp protocol from -100 mV to +100 mV with a holding potential of -60 mV, 48 hours after transfection with TRPC6 WT or A404V cDNAs. The inward-current densities at -100 mV and the outward-current densities at +100 mV for TRPC6 WT and A404V variant were similar at baseline. However, after exposure to 50 μM 1-oleoyl acetyl-sn-glycerol (OAG, a TRPC6 activator), these current densities were significantly increased by 2.6-fold and 4.5-fold respectively in the WT (n=20 cells), and by 8.4-fold and 8.9-fold respectively in the A404V variant (n=12 cells, p<0.05 vs. WT). The OAG effects were abolished by superfusion with 1 μM BI-749327 (a specific TRPC6 inhibitor). Moreover, a 24-hour treatment with 0.5 μM doxorubicin (DOX) further amplified the effects of OAG, increasing the total inward- and outward-current densities by 7.2-fold and 9.5-fold respectively in TRPC6 WT (n=11 cells), and by 13.9-fold and 14.7-fold respectively in the A404V variant (n=13 cells, p<0.05 vs. WT). In comparison, the OAG effects on TRPC6 WT and A404V channels were not potentiated by treatment with 0.5 μM doxorubicinol (DOXol, a metabolite of DOX) for 24 h (n=10-12 cells, p=N.S.). Molecular docking studies showed that OAG had a lower binding energy (-5.60 kcal/mol) and a smaller apparent equilibrium constant (Kd) of 0.079 mM with the A404V variant, compared to those of -4.49 kcal/mol and 0.511 mM respectively with TTRPC6 WT. Conclusion: TRPC6 A404V is a gain-of-function variant with a higher binding affinity to OAG. Treatment with DOX but not DOXol greatly enhances TRPC6 WT and A404V channel activation by OAG. Thus, cancer patients carrying the TRPC6 A404V variant may be more vulnerable to develop HF upon treatment with anthracycline.

Evidence that mitral and/or tricuspid regurgitation diminishes stroke volume increase during exercise

Abstract Background and Purpose The severity of heart failure can be evaluated by peak oxygen consumption (VO2). Cardiac output is one of the major essential factors to determine the VO2. Therefore, cardiac output increases linearly as the exercise intensity increases. However, in mitral regurgitation, effective stroke volume decreases due to some blood flowing back into the left atrium from the left ventricle. This reduction may compromise oxygen delivery to working muscles and diminish oxygen uptake. Peak VO2/HR is known to indicate the stroke volume at the peak exercise, but since c(A-V)O2 difference shows almost a similar change pattern during a ramp protocol, VO2/HR during the load is also reported to be an indicator of stroke volume (SV) at that work rate. However, there are no investigations that have examined the extent to which the increase in cardiac output during stress is affected by the severity of mitral regurgitation. Therefore, we investigated the influence of the degree of regurgitant volume in mitral regurgitation (MR) and tricuspid regurgitation (TR) affects the SV increasing response to exercise load. Additionally, we examined whether blunted SV increase influences on the peak VO2. Methods Among 525 patients who underwent cardiopulmonary exercise test (CPX) at our institution from January 2023 to October 2023, 518 patients (143 females, 375 males, mean age 65.2±15.0 years old) where precise analyses of CPX was possible. CPX was performed using breath-by-breath gas analysis, and an incremental load test (10watts/min) was administered until exhaustion. The rate of increase in VO2/HR per watt during an incremental loading (Δ(VO2/HR)/ΔWR) was used as an indicator of the degree of increase in SV. Typically, SV increases up to 60% of maximum load, around AT, after which it stops increasing and plateaus. Therefore, the slope of Δ(VO2/HR)/ΔWR was examined from the initiation of ramp loading to AT. The degree of reflux was evaluated by echocardiography and classified as none/trivial, mild and moderate/severe. The number of people in each group of None/trivial, mild, moderate/severe was, 392, 83, 30 for MR, and 416, 64, 24 for TR. Δ(VO2/HR)/ΔWR was evaluated for each degree of reflux, using ANOVA to determine whether there was a difference between groups. Results As shown in the Figure1, Δ(VO2/HR)/ΔWR decreased as the reflux flow rate increased for both MR and TR. Concurrently, peak VO2 also decreased in the moderate/severe group compared to the non/trivial-reflux group for both MR and TR (MR: 17.5±5.4 mL/min/kg vs. 14.9±3.5 mL/min/kg, TR: 17.2±5.3 mL/min/kg vs. 13.6±3.8 mL/min/kg). Conclusion The Δ(VO2/HR)/ΔWR obtained through CPX has been shown to be an index that can evaluate the severity of reflux. Additionally, it was also demonstrated that as regurgitation flow increased, true stroke volume decreases, which is correlated with a reduction in peak VO2.

The Ramp protocol: Uncovering individual differences in walking to an auditory beat using TeensyStep

Intentionally walking to the beat of an auditory stimulus seems effortless for most humans. However, studies have revealed significant individual differences in the spontaneous tendency to synchronize. Some individuals tend to adapt their walking pace to the beat, while others show little or no adjustment. To fill this gap we introduce the Ramp protocol, which measures spontaneous adaptation to a change in an auditory rhythmic stimulus in a gait task. First, participants walk at their preferred cadence without stimulation. After several steps, a metronome is presented, timed to match the participant’s heel-strike. Then, the metronome tempo progressively departs from the participant’s cadence by either accelerating or decelerating. The implementation of the Ramp protocol required real-time detection of heel-strike and auditory stimuli aligned with participants’ preferred cadence. To achieve this, we developed the TeensyStep device, which we validated compared to a gold standard for step detection. We also demonstrated the sensitivity of the Ramp protocol to individual differences in the spontaneous response to a tempo-changing rhythmic stimulus by introducing a new measure: the Response Score. This new method and quantification of spontaneous response to rhythmic stimuli holds promise for highlighting and distinguishing different profiles of adaptation in a gait task.

Aerobic capacity and respiratory indices of junior cross-country skiers and biathletes during incremental exercise testing.

The present study compared the isocapnic buffering phase (ICB), hypocapnic hyperventilation phase, ventilatory threshold (VT), respiratory compensation point (RCP), and maximum oxygen uptake (VO2max) among biathlon and cross-country ski athletes during an incremental exercise test. 37 male and 33 female Turkish National Team athletes volunteered to participate in the research. Body fat percentage, lean mass, and fat mass values of athletes were measured using the bioelectrical impedance analysis method, and oxygen consumption (VO2) was measured with a portable cardiopulmonary exercise test system with a ramp protocol on the treadmill. In VT, RCP, and VO2max phases, male athletes had higher VO2 and speed values than female athletes (p < 0.05). In contrast, they had similar values across different categories of sports (biathlon and cross-country skiing) (p > 0.05). Additionally, XC skiers and males had higher absolute (Abs) VO2 and mass-normalized (Rel) VO2 values than biathletes and females in exhaustion times and ICBs (p < 0.05). In contrast, they had similar Abs VO2 and Rel VO2 values in hypocapnic hyperventilation phases (p > 0.05). In addition, XC skiers and males had higher absolute (Abs) VO2 and relative (Rel) VO2 values than biathletes and females in exhaustion times and ICBs (p < 0.05). In contrast, they had similar Abs VO2 and Rel VO2 values in hypocapnic hyperventilation phases (p > 0.05). These results indicate significant differences in physiological profiles between male and female athletes and between XC skiers and biathletes.

Risk factors of hematoma after SWL for renal calculi: analysis from RCTs and a literature review.

To identify risk factors of perinephric hematoma following extracorporeal shockwave lithotripsy (SWL) for renal calculi through combined analysis of two randomized controlled trials. This post-hoc analysis included adult patients with solitary renal calculi ranging from 5 to 15mm, treated with SWL between 2016 and 2022. All patients received cross-sectional imaging (either non-contrast computer tomography scan or magnetic resonance imaging) two days post-SWL to assess the presence and severity of perinephric hematoma. Among 573 patients analyzed, 173 (30.9%) developed perinephric hematoma by Day 2 post-SWL. Multivariate logistic regression identified higher total energy delivered (odds ratio [OR] = 1.533, p = 0.003), higher mean stone density (OR = 2.603, p = 0.01), higher maximal stone density (OR = 3.578, p = 0.03), and lower pole stone location (OR = 1.545, p = 0.029) were risk factors for the development of hematoma. Conversely, the stepwise ramping protocol was a protective factor for hematoma formation. (OR = 0.572, p = 0.042). This study elucidates key factors influencing the risk of perinephric hematoma post-SWL, highlighting the importance of procedural adjustments such as the stepwise ramping protocol to reduce complications. These insights call for targeted patient and treatment strategy optimization to enhance SWL safety and efficacy.

Retrograde Flow to Aortic Root Predicts Inferior Cardiopulmonary Performance and Restrictive Lung Physiology in Fontan Circulation

BackgroundCardiac output in Fontan circulation depends on systemic venous pressure, pulmonary vascular resistance, and ventricular function. Because myocardial function is dependent on coronary perfusion, we studied whether retrograde flow to aortic root in the mitral/aortic atresia subgroup of hypoplastic left heart syndrome (HLHS) affects cardiopulmonary performance. MethodsWe studied 26 stable Fontan patients (14.4 ± 2.4 years) with right (RV, n = 17) and left (LV, n = 9) systemic ventricle morphology. All RV patients had HLHS and were subdivided according to postnatal flow to the hypoplastic ascending aorta being antegrade (HLHS-A) or retrograde (HLHS-R) due to valve atresia. Physical activity was assessed by questionnaire (LASERI, a questionnaire for Finnish children regarding physical activity), cardiopulmonary exercise test (1-minute ramp protocol), body composition (Biacorpus RX 4000), and muscle fitness (EUROFIT). These data were correlated with the postnatal aorta size and current branch pulmonary artery size index (McGoon index). ResultsPatients with HLHS-R seldom self-reported engagement in vigorous physical activity and had significantly lower cardiopulmonary performance (peak oxygen uptake [VO2peak]) than patients with LV morphology (P = 0.037), but not compared with patients with HLHS-A. Branch pulmonary artery size did not correlate with VO2peak. Patients with HLHS-R had most severe lung restrictions (forced vital capacity z-score –3 ± 0.9, P = 0.0073; forced expiratory volume in 1 second z-score –3.3 ± 1.1, P = 0.001). ConclusionsYoung Fontan patients with LV had better cardiopulmonary performance than patients with HLHS. Patients with HLHS-R were the least active and had the lowest VO2peak and most restrictive lungs. It is important to recognize postnatally single ventricle patients at high risk for inactivity to promote an active and healthy lifestyle.

Abstract We147: The Utility of Cardiopulmonary Exercise Testing (CPET) Amongst Male and Female athletes to Differentiate Between Physiological Left Ventricular Enlargement and Mildly Depressed Resting Systolic Function and Athletic Individuals with Dilated Cardiomyopathy.

Background: Athletes frequently reveal a dilated left ventricle (LV),some also demonstrate a co-existent mildly depressed LV ejection fraction, raising the possibility of mild dilated cardiomyopathy (DCM). The maximal oxygen consumption(VO2max) is a valuable tool for assessing fitness, largely determined by cardiac output. References ranges derived from the general population, may have limitations when assessing athletes with primary myocardial disease. This study investigated the role of VO2max and VO2max predicted (V02pred) to differentiate between physiological LV dilatation and athletic individuals with DCM in male and female athletes. Methods: 147 male and 35 female athletes with dilated LV(mean age 35.4years, 34.5 years respectively) underwent a 25watt cycle ergometer continuous ramp protocol. 75% males and 67% females participated in endurance sports, remaining participating in mixed sports. 52 had mild DCM, 62 defined as healthy control athletes(dilated LV) and 68 were Grey zone (dilated LV and mildly depressed LVEF) Results: DCM males (N=39) revealed a lower mean VO2max than male control (N=46), 34.9ml/kg/min and 48ml/kg/min respectively (p value &lt;0.001). DCM females(N=13) showed lower VO2max of 29.9ml/min/kg than female control (N=16) who revealed similar values to male controls (48 ml/kg/min)(p value &lt;0.001). 62 male Grey zones and 6 female Grey zone revealed lower VO2max than controls 43.1ml/min/kg and 34.1ml/min/kg respectively. DCM females had lower VO2pred than control females 119% and 161% respectively but significantly higher than their male counterparts, means of 106% and 123% respectively (p value &lt;0.001). Male and female grey zones had lower mean VO2pred than controls, 121% and 106% respectively. Higher VO2max of ≥38ml/kg/min and VO2pred of ≥120% gave a sensitivity, specificity of 84.7% and 77%respectively to differentiate healthy athletes and athletic DCMs in males and females. Only41.1% Grey zone athletes were able to achieve above these thresholds. Conclusion: Female athletes with dilated LV may reveal supranormal VO2max which can equal their male counterparts. Furthermore, athletic females with physiological or pathological LV dilatation can reveal higher VO2pred than male athletes. Most athletic DCM individuals show lower CPET parameters than controls athletes but can still achieve greater than normal measurements seen in healthy general population. VO2 may have a role in assisting in differentiating healthy athletes from athletic DCM.

Machine learning predicts peak oxygen uptake and peak power output for customizing cardiopulmonary exercise testing using non-exercise features

PurposeCardiopulmonary exercise testing (CPET) is considered the gold standard for assessing cardiorespiratory fitness. To ensure consistent performance of each test, it is necessary to adapt the power increase of the test protocol to the physical characteristics of each individual. This study aimed to use machine learning models to determine individualized ramp protocols based on non-exercise features. We hypothesized that machine learning models will predict peak oxygen uptake (V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{V}$$\\end{document}O2peak) and peak power output (PPO) more accurately than conventional multiple linear regression (MLR).MethodsThe cross-sectional study was conducted with 274 (♀168, ♂106) participants who performed CPET on a cycle ergometer. Machine learning models and multiple linear regression were used to predict V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{V}$$\\end{document}O2peak and PPO using non-exercise features. The accuracy of the models was compared using criteria such as root mean square error (RMSE). Shapley additive explanation (SHAP) was applied to determine the feature importance.ResultsThe most accurate machine learning model was the random forest (RMSE: 6.52 ml/kg/min [95% CI 5.21–8.17]) for V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{V}$$\\end{document}O2peak prediction and the gradient boosting regression (RMSE: 43watts [95% CI 35–52]) for PPO prediction. Compared to the MLR, the machine learning models reduced the RMSE by up to 28% and 22% for prediction of V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{V}$$\\end{document}O2peak and PPO, respectively. Furthermore, SHAP ranked body composition data such as skeletal muscle mass and extracellular water as the most impactful features.ConclusionMachine learning models predict V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{V}$$\\end{document}O2peak and PPO more accurately than MLR and can be used to individualize CPET protocols. Features that provide information about the participant's body composition contribute most to the improvement of these predictions.Trial registration numberDRKS00031401 (6 March 2023, retrospectively registered).

Effects of Daily Physical Activity on Exercise Capacity in Chronic Obstructive Pulmonary Disease.

Background and Objectives: In adults, 150 to 300 min a week of moderate-intensity physical activity is the recommended daily level to maintain or improve fitness. In subjects with chronic obstructive pulmonary disease (COPD), reductions in daily physical activity (DPA) amounts are related to clinically significant outcomes. In this study, we ascertain whether or not COPD patients, when clustered into active (DPA ≥ 30 min a day, 5 days a week) and inactive (DPA < 30 min a day, 5 days a week), may differ in exercise capacity, as assessed by a cardiopulmonary exercise test (CPET). Materials and Methods: A large sample of clinically stable COPD patients was retrospectively recruited and then underwent spirometry and an incremental ramp protocol 5-15 watts/min CPET. DPA was assessed by a questionnaire. Results: A total of 83 (female 25%, age range 41-85 y) active and 131 (female 31%, age range 49-83 y) inactive participants were enrolled. They were similar in age, sex distribution, body mass index (BMI) and in spirometry. The two groups were significantly different in dyspnea on exertion, as assessed by the modified Medical Research Council (mMRC), and in cardio-metabolic parameters, but not in ventilatory ones, as confirmed by the CPET. Conclusions: COPD patients experiencing physical activity of at least 30 min a day, 5 days a week, showed a greater exercise capacity and an improved cardiovascular response to exercise, when compared to inactive ones. Active and inactive participants did not differ in terms of airflow obstruction severity as well as in dynamic hyperinflation and ventilatory inefficiency during exercise. This study further suggests the benefits of regular physical activity in COPD.

Heart Rate, Oxygen Uptake and Anaerobic Thresholds During a Maximal Treadmill Test with World Class Mixed Martial Arts Fighters

Measuring heart rate responses during a competitive mixed martial arts (MMA) fight is not feasible; therefore, a method is needed to assess physiological responses in MMA fighters outside of competition. Quantifying and evaluating heart rate, oxygen uptake, and anaerobic threshold during a maximal treadmill test can provide interpretation for in-competition physiological responses of MMA fighters The retrospective analysis was conducted on 20 world-class MMA fighters predating the beginning of their fight camps (ages 29.0 ± 4.8 years old). A maximal treadmill test utilizing a ramp protocol was conducted eight weeks prior to a professional competition. Fighters’ data were divided in two groups based on weight status: lighter, &lt; 185 pounds (n = 12) and heavier, ≥ 185 pounds (n = 8) weight groups. Heart rate (HR), anaerobic thresholds from respiratory exchange rate (RER-AT), and oxygen uptake (VO2max) were recorded and compared between weight groups. VO2max was the only physiological variable measured that differed between lighter (53.4 ± 4.5 ml . kg−1 . min−1) and heavier (48.1 ± 5.7 ml . kg−1 . min−1) fighters (p = 0.033). Previous literature has commonly used 1.0 RER to determine the breaking point in anaerobic thresholds. All other variables were not different (p ≥ 0.204) between groups. Differences in VO2max between lighter and heavier fighters is likely due to differences in body mass. While there were no differences in heart rates at RER-AT or time to exhaustion between weight status groups, using RER-AT at 0.95 or 1.0 RER may be a valuable way to ensure an MMA athlete achieve anaerobic training in fight preparation. Performance coaches may utilize physiological variables such as RER-AT acquired from maximal treadmill testing to guide the training demands of MMA competition.

Effects of preparticipating hypohydration oncardiac burden in recreational athletes.

The global temperature rise will have extensive consequences on our organ systems, but hypohydration caused by reduced water intake or increased water loss through sweating plays the most relevant role. Many studies have already demonstrated the association between hypohydration and impaired exercise performance, but data related to the cardiac burden of hypohydration are scarce. This study is a sub-investigation of our large, prospective, self-controlled trial on the effects of hypohydration on cardiopulmonary exercise capacity with previously published results. In the current sub-study, we analyzed the impact of hypohydration on cardiac burden in this cohort of fifty healthy, recreational athletes during cardiopulmonary exercise test.Therefore, each participant underwent cardiopulmonary exercise test with a standardized ramp protocol twice, once in hypohydrated state and once in euhydrated state as control, and the cardiac markers Troponin T, NT-pro-BNP and Chromogranin A were measured before and after the exercise test at each state. Mean age was 29.7 years and 34% of probands were female. Hypohydration led to a reduced body water, a significant decrease in oxygen uptake and lower levels of power output. Yet, Troponin T, NT-proBNP, Chromogranin A and lactate levels did not significantly differ between the two conditions.In this study cohort, decreased exercise capacity during hypohydration was more likely due to impaired cardiac output with diminished plasma volume rather than measurable cardiac stress from fluid deprivation. However, whether these data are generalizable to a diseased cohort is left unanswered and should be addressed in future randomized controlled trials.

Is breathing frequency a potential means for monitoring exercise intensity in people with atrial fibrillation and coronary heart disease when heart rate is mitigated?

PurposeModerate-intensity aerobic exercise is safe and beneficial in atrial fibrillation (AF) and coronary heart disease (CHD). Irregular or rapid heart rates (HR) in AF and other heart conditions create a challenge to using HR to monitor exercise intensity. The purpose of this study was to assess the potential of breathing frequency (BF) to monitor exercise intensity in people with AF and CHD without AF.MethodsThis observational study included 30 AF participants (19 Male, 70.7 ± 8.7 yrs) and 67 non-AF CHD participants (38 Male, 56.9 ± 11.4 yrs). All performed an incremental maximal exercise test with pulmonary gas exchange.ResultsPeak aerobic power in AF (V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\dot{\ ext{V}}}$$\\end{document}O2peak; 17.8 ± 5.0 ml.kg−1.min−1) was lower than in CHD (26.7 ml.kg−1.min−1) (p < .001). BF responses in AF and CHD were similar (BF peak: AF 34.6 ± 5.4 and CHD 36.5 ± 5.0 breaths.min−1; p = .106); at the 1st ventilatory threshold (BF@VT-1: AF 23.2 ± 4.6; CHD 22.4 ± 4.6 breaths.min−1; p = .240). %V˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\dot{\ ext{V}}}$$\\end{document}O2peak at VT-1 were similar in AF and CHD (AF: 59%; CHD: 57%; p = .656).ConclusionWith the use of wearable technologies on the rise, that now include BF, this first study provides an encouraging potential for BF to be used in AF and CHD. As the supporting data are based on incremental ramp protocol results, further research is required to assess BF validity to manage exercise intensity during longer bouts of exercise.

Mitochondrial-targeted Antioxidant Enhancing Effects on Vascular Endothelial Function in Middle-aged and Older Adults Is Influenced by Cardiorespiratory Fitness

Vascular endothelial dysfunction in middle-aged and older (MA/O, ≥ 45 y) adults is partly attributable to excess mitochondrial reactive oxygen species (mtROS) production. Aerobic exercise preserves endothelial function in preclinical models via lower mtROS and mitigates the deleterious effects of aging on cardiorespiratory fitness (CRF). However, the acute effects of a mitochondrial-targeted antioxidant on age-related vascular endothelial function in the context of CRF are currently unknown. We hypothesized lower CRF resulting from a physically inactive lifestyle contributing to age-related endothelial dysfunction is mediated via greater mtROS in humans. In a double-blind, randomized, placebo-controlled crossover study design MA/O adults were divided into two groups: exercisers (EX, n=11, age 60.0 ± 4.0 y, BMI 25.0 ± 0.9 kg/m2) and non-exercisers (NEX, n=12, age 64.0 ± 2.8 y, BMI 28.2 ± 1.0 kg/m2). CRF, assessed via VO2max, was measured on a cycle ergometer from an incremental ramp protocol (10 or 20 watts/min). Vascular endothelial function from brachial artery flow mediated dilation (FMDBA) was acquired before (pre-ingestion) and ~1 h after MitoQ (single dose, 80 mg) or placebo supplementation. A two-way repeated measures ANOVA with a Bonferroni post-hoc analysis was used to determine the effects of MitoQ and placebo on FMDBA. Compared to placebo, MitoQ increased FMDBA in NEX (pre: 4.9 ± 0.4 vs post: 7.0 ± 0.4 %, p&lt;0.05) by +37% and brachial artery diameter (pre: 0.18 ± 0.02 vs post: 0.24 ± 0.02 mm, p&lt;0.05) by +34% whereas no changes were observed for FMDBA (pre: 6.8 ± 0.5 vs post: 7.0 ± 0.3 %, p&gt;0.05) or brachial artery diameter (pre: 0.25 ± 0.02 vs post: 0.26 ± 0.02 mm, p&gt;0.05) in EX. CRF was positively correlated with baseline FMDBA (n=17, r=0.56, p=0.01) whereas the change in FMDBA with MitoQ was inversely correlated with CRF (r=-0.54, p=0.02). These data demonstrate the acute MitoQ-enhancing effects on vascular endothelial function in MA/O adults is attributable, in part, to greater mtROS in physically inactive adults with lower CRF. Funding for this study was provided, in part, by Ball State University ASPiRE internal research grant (N.A. Carlini). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Critical Ambient Temperature Threshold for Safe Fan Use in Young Adults During Extreme Heat Exposure

Introduction: The electric fan may be an effective, low-cost heat resilience solution during extreme heat. Fans have been shown to attenuate the rise in cardiovascular and thermal strain relative to still air in young adults, particularly during exposure to more humid conditions. When ambient temperature exceeds skin temperature, a fan improves sweat evaporation from the skin surface, which counterbalances the increased rate of convective heat gain. However, at higher air temperatures, the increased convective heat gain may exceed the rate of evaporative heat loss resulting in net heat gain and increasing physiological strain. The purpose of the present study was to identify the critical ambient temperature limit, where increased physiological strain will be observed, with a fan in comparison to still air. Method: To date, 6 participants (4 females; 24±9 y; 72.8±17.8 kg; 1.8±0.2 m) have completed two 180-minute temperature ramp heat-exposures (37°C to 47°C at ~0.05°C/min, 25%RH) on separate days. Wearing standardized t-shirts and shorts, the participants remained seated while either i) facing an electric fan (5.3±0.9 m/s) or ii) in still air (0.1±0.0 m/s). Rectal and skin temperature, heart rate, blood pressure, whole-body sweat loss, thermal comfort, and thermal sensation were measured every 10 minutes. Results: Rectal temperature was similar between fan and still air up to 43°C (P&gt;0.92), however was greater with a fan from 44°C onwards (p&lt;0.05). Skin temperature was higher with a fan compared to still air throughout the exposure (p&lt;0.001). Heart rate was similar between fan and still air until 44°C (P&gt;0.61), after which heart rate was higher with a fan (p&lt;0.05). Mean arterial pressure was not different between fan and still air at any air temperature (P=0.53). The rate pressure product was higher with a fan compared to still air when the ambient temperature exceeded 44°C (p&lt;0.05). Whole-body sweat losses were greater with a fan (1215±250 g) compared to still air (675±103 g, P=0.006). No differences between fan and still air were observed for thermal comfort (P=0.22) or thermal sensation (P=0.73) throughout the temperature ramp protocol. Conclusion: When ambient temperature exceeds 43°C, electric fan use results in greater physiological strain at rest in young healthy adults relative to still air. This research was supported by Dr. Ravanelli’s Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effect of Backpack Loads on the Timing of Cardiopulmonary Response in Healthy Men

The backpack used commonly affects posture and physical performance, resulting in increased oxygen uptake and energy expenditure. The purpose of this study is to confirm the effect of the chest loads on the reaching time of the cardiopulmonary response. Seventeen healthy men participants were monitored for cardiopulmonary function continuously during walking exercise with the Ramp protocol and recorded the time taken to reach THR, VO2 peak, RR Difference, maximal METs, maximal FECO2, and minimum FEO2. During the exercise test, subjects were instructed to carry a backpack loaded at no load, 5%, 10%, and 15% body weight in random order. There was a significant difference in the time to reach the THR, the oxygen intake peak time, the maximum metabolic equivalent time, the respiratory rate increase, the minimum oxygen amount, and the maximum carbon dioxide amount at no load and more than 5% load. However, no significant difference was found between the loads. It is thought that even a 5% backpack load of one's body weight can impose on cardiopulmonary energy costs, and this is thought to help improve training programs with a gradual increase in mechanical chest load.