Development, validation, and transportability of several machine-learned, non-exercise-based VO2max prediction models for older adults

BACKGROUND

There exist few maximal oxygen uptake (VO2max) non-exercise-based prediction equations, fewer using machine learning (ML), and none specifically for older adults. Since direct measurement of VO2max is infeasible in large epidemiologic cohort studies, we sought to develop, validate, compare, and assess the transportability of several ML VO2max prediction algorithms.

METHODS

The Baltimore Longitudinal Study of Aging (BLSA) participants with valid VO2max tests were included (n = 1080). Least absolute shrinkage and selection operator, linear- and tree-boosted extreme gradient boosting, random forest, and support vector machine (SVM) algorithms were trained to predict VO2max values. We developed these algorithms for: (a) the overall BLSA, (b) by sex, (c) using all BLSA variables, and (d) variables common in aging cohorts. Finally, we quantified the associations between measured and predicted VO2max and mortality.

RESULTS

The age was 69.0 ± 10.4 years (mean ± SD) and the measured VO2max was 21.6 ± 5.9 mL/kg/min. Least absolute shrinkage and selection operator, linear- and tree-boosted extreme gradient boosting, random forest, and support vector machine yielded root mean squared errors of 3.4 mL/kg/min, 3.6 mL/kg/min, 3.4 mL/kg/min, 3.6 mL/kg/min, and 3.5 mL/kg/min, respectively. Incremental quartiles of measured VO2max showed an inverse gradient in mortality risk. Predicted VO2max variables yielded similar effect estimates but were not robust to adjustment.

CONCLUSION

Measured VO2max is a strong predictor of mortality. Using ML can improve the accuracy of prediction as compared to simpler approaches but estimates of association with mortality remain sensitive to adjustment. Future studies should seek to reproduce these results so that VO2max, an important vital sign, can be more broadly studied as a modifiable target for promoting functional resiliency and healthy aging.

Quantifying assumptions underlying peak oxygen consumption equations across the body mass spectrum

The goal of this study is to quantify the assumptions associated with the Wasserman-Hansen (WH) and Fitness Registry and the Importance of Exercise: A National Database (FRIEND) predictive peak oxygen consumption (pVO2) equations across body mass index (BMI). Assumptions in pVO2 for both equations were first determined using a simulation and then evaluated using exercise data from the Stanford Exercise Testing registry. We calculated percent-predicted VO2 (ppVO2) values for both equations and compared them using the Bland-Altman method. Assumptions associated with pVO2 across BMI categories were quantified by comparing the slopes of age-adjusted VO2 ratios (pVO2/pre-exercise VO2) and ppVO2 values for different BMI categories. The simulation revealed lower predicted fitness among adults with obesity using the FRIEND equation compared to the WH equations. In the clinical cohort, we evaluated 2471 patients (56.9% male, 22% with BMI >30 kg/m2, pVO2 26.8 mlO2/kg/min). The Bland-Altman plot revealed an average relative difference of -1.7% (95% CI: -2.1 to -1.2%) between WH and FRIEND ppVO2 values with greater differences among those with obesity. Analysis of the VO2 ratio to ppVO2 slopes across the BMI spectrum confirmed the assumption of lower fitness in those with obesity, and this trend was more pronounced using the FRIEND equation. Peak VO2 estimations between the WH and FRIEND equations differed significantly among individuals with obesity. The FRIEND equation resulted in a greater attributable reduction in pVO2 associated with obesity relative to the WH equations. The outlined relationships between BMI and predicted VO2 may better inform the clinical interpretation of ppVO2 values during cardiopulmonary exercise test evaluations.

Accuracy of a non-exercise method using seismocardiography for the estimation of V̇O2peak in sub-elite football players

A non-exercise method equation using seismocardiography for estimating V̇O2peak (SCG V̇O2peak) has previously been validated in healthy subjects. However, the performance of the SCG V̇O2peak within a trained population is unknown, and the ability of the model to detect changes over time is not well elucidated. Forty-seven sub-elite football players were tested at the start of pre-season (SPS) and 36 players completed a test after eight weeks at the end of the pre-season (EPS). Testing included an SCG V̇O2peak estimation at rest and a graded cardiopulmonary exercise test (CPET) on a treadmill for determination of V̇O2peak. Agreement between SCG V̇O2peak and CPET V̇O2peak showed a large underestimation at SPS (bias ± 95% CI: -9.9 ± 1.8, 95% Limits of Agreement: 2.2 to -22.0 mL·min-1 kg-1). At EPS no interaction (p = 0.3590) but a main effect of time (p < 0.0001) and methods (p < 0.0001) was observed between SCG and CPET V̇O2peak. No correlation in V̇O2peak changes was observed between SCG and CPET (r = -20.0, p = 0.2484) but a fair agreement in classifying the correct directional change in V̇O2peak with the SCG method was found (Cohen's κ coefficient = 0.28 ± 0.25). Overall, the SCG V̇O2peak method lacks accuracy and despite being able to estimate group changes, it was incapable of detecting individual changes in V̇O2peak following a pre-season period in sub-elite football players. The SCG algorithm needs to be further adjusted and the accuracy and precision improved for the method to be applicable for use within a trained population.

Evaluating current assessment techniques of cardiorespiratory fitness

INTRODUCTION

Considerable and convincing global data from cohorts across the health spectrum (i.e. apparently healthy to known disease) indicate that cardiorespiratory fitness (CRF) is a major predictor of overall and cardiovascular disease (CVD)-survival, seemingly with greater prognostic resolution compared to other traditional CVD risk factors. Therefore, the assessment of CRF in research and clinical settings is of major importance.

AREAS COVERED

In this manuscript, we review the technology of measuring CRF assessed by the 'gold standard,' cardiopulmonary exercise testing (CPET), as well as with various other methods (e.g. estimated metabolic equivalents, 6-minute walk tests, shuttle tests, and non-exercise equations that estimate CRF), all of which provide significant prognostic information for CVD- and all-cause survival. The literature through May 2024 has been cited.

EXPERT OPINION

The promotion of physical activity in efforts to improve levels of CRF is needed throughout the world to improve lifespan and, more importantly, healthspan. The routine assessment of CRF should be considered a vital sign that is routinely assessed in clinical practice.

Characterizing the influence of cardiorespiratory fitness on left atrial size and function in the general population

Increased left atrial (LA) size and reduced LA function have been associated with heart failure and atrial fibrillation (AF) in at-risk populations. However, atrial remodeling has also been associated with exercise training and the relationship between fitness, LA size, and function has not been defined across the fitness spectrum. In a cross-sectional study of 559 ostensibly healthy participants, comprising 304 males (mean age, 46 ± 20 yr) and 255 females (mean age, 47 ± 15 yr), we sought to define the relationship between cardiorespiratory fitness (CRF), LA size, and function. We also aimed to interrogate sex differences in atrial factors influencing CRF. Echocardiographic measures included biplane measures of LA volumes indexed to body surface area (LAVi) and atrial deformation using two-dimensional speckle tracking. CRF was measured as peak oxygen consumption (V̇o2peak) during cardiopulmonary exercise testing (CPET). Using multivariable regression, age, sex, weight, and LAVi (P < 0.001 for all) predicted V̇o2peak (P < 0.001, R2 = 0.66 for combined model). After accounting for these variables, heart rate reserve added strength to the model (P < 0.001, R2 = 0.74) but LA strain parameters did not predict V̇o2peak. These findings add important nuance to the perception that LA size is a marker of cardiac pathology. LA size should be considered in the context of fitness, and it is likely that the adverse prognostic associations of increased LA size may be confined to those with LA enlargement and low fitness.NEW & NOTEWORTHY Left atrial (LA) structure better predicts cardiorespiratory fitness (CRF) than LA function. LA function adds little statistical value to predictive models of peak oxygen uptake (V̇o2peak) in healthy individuals, suggesting limited discriminatory for CRF once LA size is factored. In the wider population of ostensibly healthy individuals, the association between increased LA volume and higher CRF provides an important counter to the association between atrial enlargement and heart failure symptoms in those with cardiac pathology.

Reference Standards of Cardiorespiratory Fitness Measured With the Cardiopulmonary Exercise Test Using the Treadmill in Chinese Adults Younger Than 60 Years

PURPOSE

Cardiorespiratory fitness (CRF) is a strong predictor of cardiorespiratory diseases and varies by race. The purpose of this study was to provide CRF reference standards and a prediction equation for peak oxygen uptake (V˙O 2peak ) from treadmill-based cardiopulmonary exercise testing (CPX) in Chinese individuals.

METHODS

Healthy participants (n = 4199) who completed a CPX using a treadmill were studied. The percentiles of V˙O 2peak were determined for four age groups (decades). A regression prediction model was developed from the derivation cohort (n = 3361), validated in the independent validation cohort (n = 838), and compared with the widely used Wasserman equation and the Fitness Registry and the Importance of Exercise National Database (FRIEND) equation.

RESULTS

The mean V˙O 2peak values of four age groups (20-29, 30-39, 40-49, and 50-59 yr) were 42.6, 41.2, 38.7, and 35.9 mL/kg/min, respectively, for men, and 37.1, 34.7, 32.0, and 30.3 mL/kg/min, respectively, for women. The 50th percentiles of relative V˙O 2peak decreased with age for both sexes. The prediction equation was: Absolute V˙O 2peak (mL/min) = 236.68 - (504.64 × sex [male = 0; female = 1]) + (21.23× weight [kg]) - (14.31 × age [yr]) + (9.46 × height [cm]) (standard error of the estimate = 379.59 mL/min, R2 = 0.66, P < .001).Percentage predicted V˙O 2peak for the validation sample was 100.2%. The novel equation performed better than the other two equations.

CONCLUSION

This study reports the first CRF reference standards and prediction equation generated from treadmill CPX in China. These reference standards provide a framework for interpreting the CRF of the Chinese population and could be useful information for a global CRF database.

How to interpret a cardiorespiratory fitness assessment - Key measures that provide the best picture of health, disease status and prognosis

Graded exercise testing is a widely accepted tool for revealing cardiac ischemia and/or arrhythmias in clinical settings. Cardiopulmonary exercise testing (CPET) measures expired gases during a graded exercise test making it a versatile tool that helps reveal underlying physiologic abnormalities that are in many cases only present with exertion. It also characterizes one's health status and clinical trajectory, informs the therapeutic plan, evaluates the efficacy of therapy, and provides submaximal and maximal information that can be used to tailor an exercise intervention. Practitioners can also modify the mode and protocol to allow individuals of all ages, fitness levels, and most disease states to perform a CPET. When used to its full potential, CPET can be a key tool used to optimize care in primary and secondary prevention settings.

2023 update: The importance of cardiorespiratory fitness in the United States

The American Heart Association issued a Policy Statement in 2013 that characterized the importance of cardiorespiratory fitness (CRF) as an essential marker of health outcomes and specifically the need for increased assessment of CRF. This statement summarized the evidence demonstrating that CRF is "one of the most important correlates of overall health status and a potent predictor of an individual's future risk of cardiovascular disease." Subsequently, this Policy Statement led to the development of a National Registry for CRF (Fitness Registry and the Importance of Exercise: A National Data Base [FRIEND]) which established normative reference values for CRF for adults in the United States (US). This review provides an overview of the progress made in the past decade to further our understanding of the importance of CRF, specifically related to prevention and for clinical populations. Additionally, this review overviews the evolvement and additional uses of FRIEND and summarizes a hierarchy of assessment methods for CRF. In summary, continued efforts are needed to expand the representation of data from across the US, and to include data from pediatric populations, to further develop the CRF Reference Standards for the US as well as further develop Global CRF Reference Standards.

Breathing a low-density gas reduces respiratory muscle force development and marginally improves exercise performance in master athletes

INTRODUCTION

We tested the hypothesis that breathing heliox, to attenuate the mechanical constraints accompanying the decline in pulmonary function with aging, improves exercise performance.

METHODS

Fourteen endurance-trained older men (67.9 ± 5.9 year, [Formula: see text]O2max: 50.8 ± 5.8 ml/kg/min; 151% predicted) completed two cycling 5-km time trials while breathing room air (i.e., 21% O2-79% N2) or heliox (i.e., 21% O2-79% He). Maximal flow-volume curves (MFVC) were determined pre-exercise to characterize expiratory flow limitation (EFL, % tidal volume intersecting the MFVC). Respiratory muscle force development was indirectly determined as the product of the time integral of inspiratory and expiratory mouth pressure (∫Pmouth) and breathing frequency. Maximal inspiratory and expiratory pressure maneuvers were performed pre-exercise and post-exercise to estimate respiratory muscle fatigue.

RESULTS

Exercise performance time improved (527.6 ± 38 vs. 531.3 ± 36.9 s; P = 0.017), and respiratory muscle force development decreased during inspiration (- 22.8 ± 11.6%, P < 0.001) and expiration (- 10.8 ± 11.4%, P = 0.003) with heliox compared with room air. EFL tended to be lower with heliox (22 ± 23 vs. 30 ± 23% tidal volume; P = 0.054). Minute ventilation normalized to CO2 production ([Formula: see text]E/[Formula: see text]CO2) increased with heliox (28.6 ± 2.7 vs. 25.1 ± 1.8; P < 0.001). A reduction in MIP and MEP was observed post-exercise vs. pre-exercise but was not different between conditions.

CONCLUSIONS

Breathing heliox has a limited effect on performance during a 5-km time trial in master athletes despite a reduction in respiratory muscle force development.

Deep learned representations of the resting 12-lead electrocardiogram to predict at peak exercise

AIMS

To leverage deep learning on the resting 12-lead electrocardiogram (ECG) to estimate peak oxygen consumption (V˙O2peak) without cardiopulmonary exercise testing (CPET).

METHODS AND RESULTS

V ˙ O 2 peak estimation models were developed in 1891 individuals undergoing CPET at Massachusetts General Hospital (age 45 ± 19 years, 38% female) and validated in a separate test set (MGH Test, n = 448) and external sample (BWH Test, n = 1076). Three penalized linear models were compared: (i) age, sex, and body mass index ('Basic'), (ii) Basic plus standard ECG measurements ('Basic + ECG Parameters'), and (iii) basic plus 320 deep learning-derived ECG variables instead of ECG measurements ('Deep ECG-V˙O2'). Associations between estimated V˙O2peak and incident disease were assessed using proportional hazards models within 84 718 primary care patients without CPET. Inference ECGs preceded CPET by 7 days (median, interquartile range 27-0 days). Among models, Deep ECG-V˙O2 was most accurate in MGH Test [r = 0.845, 95% confidence interval (CI) 0.817-0.870; mean absolute error (MAE) 5.84, 95% CI 5.39-6.29] and BWH Test (r = 0.552, 95% CI 0.509-0.592, MAE 6.49, 95% CI 6.21-6.67). Deep ECG-V˙O2 also outperformed the Wasserman, Jones, and FRIEND reference equations (P < 0.01 for comparisons of correlation). Performance was higher in BWH Test when individuals with heart failure (HF) were excluded (r = 0.628, 95% CI 0.567-0.682; MAE 5.97, 95% CI 5.57-6.37). Deep ECG-V˙O2 estimated V˙O2peak <14 mL/kg/min was associated with increased risks of incident atrial fibrillation [hazard ratio 1.36 (95% CI 1.21-1.54)], myocardial infarction [1.21 (1.02-1.45)], HF [1.67 (1.49-1.88)], and death [1.84 (1.68-2.03)].

CONCLUSION

Deep learning-enabled analysis of the resting 12-lead ECG can estimate exercise capacity (V˙O2peak) at scale to enable efficient cardiovascular risk stratification.

Is cardiorespiratory fitness associated with cognitive outcomes in mid-adulthood? Findings from the 1958 British birth cohort

Identifying causal factors to intervene on to delay age-related declines in cognitive function is urgently needed. We examined associations between non-exercise testing cardiorespiratory fitness (NETCRF; estimated using sex, age, body mass index, resting heart rate, and physical activity) at 45 years and cognitive function outcomes (immediate and delayed verbal memory; verbal fluency; visual processing speed) at 50 years in 8130 participants from the 1958 British birth cohort. In unadjusted models, higher NETCRF was associated with better cognitive function across all outcomes. When adjusted for confounding factors, associations disappeared. In this cohort, associations between 45 years NETCRF and 50 years cognitive function likely result from confounding factors.

Effect of High-Intensity Interval Training and Moderate-Intensity Continuous Training in People With Poststroke Gait Dysfunction: A Randomized Clinical Trial

Background The exercise strategy that yields the greatest improvement in both cardiorespiratory fitness (V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ ) and walking capacity poststroke has not been determined. This study aimed to determine whether conventional moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) have different effects on V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ and 6-minute walk distance (6MWD). Methods and Results In this 24-week superiority trial, people with poststroke gait dysfunction were randomized to MICT (5 days/week) or HIIT (3 days/week with 2 days/week of MICT). MICT trained to target intensity at the ventilatory anaerobic threshold. HIIT trained at the maximal tolerable treadmill speed/grade using a novel program of 2 work-to-recovery protocols: 30:60 and 120:180 seconds. V̇O2 and heart rate was measured during performance of the exercise that was prescribed at 8 and 24 weeks for treatment fidelity. Main outcomes were change in V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ and 6MWD. Assessors were blinded to the treatment group for V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ but not 6MWD. Secondary outcomes were change in ventilatory anaerobic threshold, cognition, gait-economy, 10-meter gait-velocity, balance, stair-climb performance, strength, and quality-of-life. Among 47 participants randomized to either MICT (n=23) or HIIT (n=24) (mean age, 62±11 years; 81% men), 96% completed training. In intention-to-treat analysis, change in V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ for MICT versus HIIT was 2.4±2.7 versus 5.7±3.1 mL·kg-1·min-1 (mean difference, 3.2 [95% CI, 1.5-4.8]; P<0.001), and change in 6MWD was 70.9±44.3 versus 83.4±53.6 m (mean difference, 12.5 [95% CI, -17 to 42]; P=0.401). HIIT had greater improvement in ventilatory anaerobic threshold (mean difference, 2.07 mL·kg-1·min-1 [95% CI, 0.59-3.6]; P=0.008). No other between-group differences were observed. During V̇O2 monitoring at 8 and 24 weeks, MICT reached 84±14% to 87±18% of V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ while HIIT reached 101±22% to 112±14% of V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ (during peak bouts). Conclusions HIIT resulted in more than a 2-fold greater and clinically important change in V ̇ O 2 peak $$ \dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}} $$ than MICT. Training to target (ventilatory anaerobic threshold) during MICT resulted in ~3 times the minimal clinically important difference in 6MWD, which was similar to HIIT. These findings show proof of concept that HIIT yields greater improvements in cardiorespiratory fitness than conventional MICT in appropriately screened individuals. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03006731.

Muscle oxygenation of the paretic and nonparetic legs during and after exercise in chronic stroke: Implications for mobility

BACKGROUND

Oxygen delivery and demand are reduced in the paretic leg of individuals after stroke. However, it is unknown how muscle oxygenation, the balance between delivery and utilization of oxygen at the muscle, is altered post-stroke during aerobic exercise and how it relates to mobility.

OBJECTIVE

To monitor muscle oxygenation changes between the paretic and nonparetic legs of individuals after stroke during treadmill exercise and the 6-minute walk test and analyze the association with mobility.

DESIGN

Cross-sectional study.

SETTING

Cardiac rehabilitation program.

PATIENTS

Eleven male participants were enrolled in the study. Ten men (30.8 ± 4.1 months post-stroke; age 63.9 ± 13.9 years) with hemiparetic gait pattern finished the study.

METHODS OR INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Muscle oxygenation was measured with near-infrared spectroscopy placed on the vastus lateralis of each leg during treadmill exercise at the first ventilatory threshold and during a 6-minute walk test.

RESULTS

The desaturation slope during treadmill exercise was significantly steeper (p = .047) in the paretic (-0.7 ± 0.6%/s) compared to the nonparetic leg (-0.3 ± 0.2%/s). There was no other significant difference between legs. The 6-minute walk test distance was not correlated with 6-minute walk test muscle oxygenation in either leg (paretic: r = 0.20, p = 0.590; nonparetic: r = 0.42, p = .232).

CONCLUSIONS

At the onset of treadmill exercise, the paretic leg was unable to effectively match the oxygen demand and extraction of the nonparetic leg, suggesting the need for an immediate cardiovascular warmup prior to initiating moderate intensity exercise in this population. Because the exercise desaturation rate is thought to indicate increased anaerobic metabolism and lactate production, efforts to delay rapid desaturation could improve the sustainability of activities of daily living and exercise.

A Machine Learning Approach to Developing an Accurate Prediction of Maximal Heart Rate During Exercise Testing in Apparently Healthy Adults

PURPOSE

Maximal heart rate (HR max ) continues to be an important measure of adequate effort during an exercise test. The aim of this study was to improve the accuracy of HR max prediction using a machine learning (ML) approach.

METHODS

We used a sample from the Fitness Registry of the Importance of Exercise National Database, which included 17 325 apparently healthy individuals (81% males) who performed a maximal cardiopulmonary exercise test. Two standard formulas for HR max prediction were tested: Formula1 = 220 - age (yr), root-mean-squared error (RMSE) 21.9, relative root-mean-squared error (RRMSE) 1.1; and Formula2 = 209.3 - 0.72 × age (yr), RMSE 22.7 and RRMSE 1.1. For ML model prediction, we used age, weight, height, resting HR, and systolic and diastolic blood pressure. The following ML algorithms to predict HR max were applied: lasso regression (LR), neural networks (NN), support vector machine (SVM) and random forests (RF). An evaluation was performed using cross-validation and by computing the RMSE and RRMSE, Pearson correlation, and Bland-Altman plots. The best predictive model was explained with Shapley Additive Explanations (SHAP).

RESULTS

The HR max for the cohort was 162 ± 20 bpm. All ML models improved HR max prediction and reduced RMSE and RRMSE compared with Formula1 (LR: 20.2%, NN: 20.4%, SVM: 22.2%, and RF: 24.7%). The predictions of all algorithms significantly correlated with HR max ( r = 0.49, 0.51, 0.54, 0.57, respectively; P < .001). Bland-Altman analysis demonstrated lower bias and 95% CI for all ML models in comparison with standard equations. The SHAP explanation showed a high impact of all selected variables.

CONCLUSIONS

Machine learning, particularly the RF model, improved prediction of HR max using readily available measures. This approach should be considered for clinical application to refine HR max prediction.

The effects of age on dyspnea and respiratory mechanical and neural responses to exercise in healthy men

The respiratory muscle pressure generation and inspiratory and expiratory neuromuscular recruitment patterns in younger and older men were compared during exercise, alongside descriptors of dyspnea. Healthy younger (n = 8, 28 ± 5 years) and older (n = 8, 68 ± 4 years) men completed a maximal incremental cycling test. Esophageal, gastric (Pga ) and transdiaphragmatic pressures, and electromyography (EMG) of the crural diaphragm were measured using a micro-transducer and EMG catheter. EMG of the parasternal intercostals, sternocleidomastoids, and rectus abdominis were measured using skin surface electrodes. After the exercise test, participants completed a questionnaire to evaluate descriptors of dyspnea. Pga at end-expiration, Pga expiratory tidal swings, and the gastric pressure-time product (PTPga ) at absolute and relative minute ventilation were higher (p < 0.05) for older compared to younger men. There were no differences in EMG responses between older and younger men. Younger men were more likely to report shallow breathing (p = 0.005) than older men. Our findings showed younger and older men had similar respiratory neuromuscular activation patterns and reported different dyspnea descriptors, and that older men had greater expiratory muscle pressure generation during exercise. Greater expiratory muscle pressures in older men may be due to compensatory mechanisms designed to offset increasing airway resistance due to aging. These results may have implications for exercise-induced expiratory muscle fatigue in older men.

Sex differences and predictors of completion of a 6-month exercise-based cardiac rehabilitation program in 1,536 people following stroke

OBJECTIVE

To retrospectively examine sex-differences and predictors of completion in consecutively-referred patients to a 6-month exercise-based cardiac rehabilitation program (CRP) from 2006 to 2017.

MATERIALS/METHODS

People with hemiplegic gait participated in stroke-adapted-CRP; otherwise, traditional-CRP. Reasons for non-completion were ascertained by interview. Regression-analyses were conducted to determine non-completion in all patients and women and men separately.

RESULTS

There were 1536 patients (30.3% women), mean age 64.5 ± 12.5 with 23% initiating the stroke-adapted-CRP. Overall, 75.1% completed the CRP (87.3% stroke-adapted-CRP vs 71.5% traditional-CRP; p < .001). There was no difference in completion between women and men (74.5% vs 75.4%; p=0.7), or in attendance to pre-scheduled sessions (p=0.6) or reasons for non-completion (p > .05, all). The only sex difference in completion by age (decade) occurred in those <41 years (59% women vs 85% men; p=.02). Baseline predictors of non-completion among all patients included not being enrolled in the stroke-adapted-CRP, lower V̇O_2peak, smoking, diabetes (prescribed insulin) and depression but not sex (p=.5) or age (p=.15). Unique predictors in women vs men were younger age, lower V̇O_2peak, smoking, diabetes (prescribed insulin), depression, and cancer diagnoses. Unique to men was having >1 stroke and diabetes (any anti-diabetes medication). The strongest predictor of non-completion among all models was not being enrolled in stroke-adapted-CRP.

CONCLUSIONS

While there were no sex-differences in adherence to the CRP, women and men have mostly unique predictors of non-completion. Younger women are at greatest risk for non-completion. Practitioners should provide sex-specific, tailored strategies for enhancing completion with a focus on younger women and offering a stroke-adapted-CRP with close attention to those with diabetes.

A Nonexercise Prediction of Peak Oxygen Uptake for Patients With Cardiovascular Disease: DATA FROM THE FITNESS REGISTRY AND THE IMPORTANCE OF EXERCISE INTERNATIONAL DATABASE (FRIEND)

PURPOSE

Nonexercise predictions of peak oxygen uptake (V˙ o2peak ) are used clinically, yet current equations were developed from cohorts of apparently healthy individuals and may not be applicable to individuals with cardiovascular disease (CVD). Our purpose was to develop a CVD-specific nonexercise prediction equation for V˙ o2peak .

METHODS

Participants were from the Fitness Registry and Importance of Exercise International Database (FRIEND) with a diagnosis of coronary artery bypass surgery (CABG), myocardial infarction (MI), percutaneous coronary intervention (PCI), or heart failure (HF) who met maximal effort criteria during a cardiopulmonary exercise test (n = 15 997; 83% male; age 63.1 ± 10.4 yr). The cohort was split into development (n = 12 798) and validation groups (n = 3199). The prediction equation was developed using regression analysis and compared with a previous equation developed on a healthy cohort.

RESULTS

Age, sex, height, weight, exercise mode, and CVD diagnosis were all significant predictors of V˙ o2peak . The regression equation was:V˙ o2peak (mL · kg -1 · min -1 ) = 16.18 - (0.22 × age [yr]) + (3.63 × sex [male = 1; female = 0]) + (0.14 × height [cm]) - (0.12 × weight [kg]) + (3.62 × mode [treadmill = 1; cycle = 0]) - (2.70 × CABG [yes = 1, no = 0]) - (0.31 × MI [yes = 1, no = 0]) + (0.37 × PCI [yes = 1, no = 0]) - (4.47 × HF [yes = 1, no = 0]). Adjusted R 2 = 0.43; SEE = 4.75 mL · kg -1 · min -1 .Compared with measured V˙ o2peak in the validation group, percent predicted V˙ o2peak was 141% for the healthy cohort equation and 100% for the CVD-specific equation.

CONCLUSIONS

The new equation for individuals with CVD had lower error between measured and predicted V˙ o2peak than the healthy cohort equation, suggesting population-specific equations are needed for predicting V˙ o2peak ; however, errors associated with nonexercise prediction equations suggest V˙ o2peak should be directly measured whenever feasible.

Characteristics of individuals with moderate to severe asthma who better respond to aerobic training: a cluster analysis

OBJECTIVE

To determine the characteristics of individuals with asthma who are responsive to aerobic training.

METHODS

This post hoc analysis of pooled data from previous randomized controlled trials involved 101 individuals with moderate to severe asthma who underwent aerobic training. Participants underwent a maximal cardiopulmonary exercise test and completed the Asthma Control Questionnaire and the Asthma Quality of Life Questionnaire before and after a 24-session aerobic training program. Better and worse responders to aerobic training were identified by cluster analysis.

RESULTS

Two clusters were identified according to the improvement in peak VO2 after aerobic training (better and worse responders). Characteristics of the better responder group were being older, being female, having higher BMI, and having higher cardiac reserve at baseline when compared with the worse responder group. Also, better responders had worse clinical control, worse quality of life, and lower physical capacity at baseline. After training, worse responders, in comparison with better responders, showed half the improvement in Δpeak VO2 (7.4% vs. 13.6%; 95% CI, -12.1 to -0.92%; p < 0.05) and worse asthma control. A weak, negative, but significant association (r = -0.35; p < 0.05) was observed between clinical control and aerobic fitness only in the better responder group. Both groups showed significant improvement in quality of life.

CONCLUSIONS

Obese individuals with worse exercise capacity, clinical control, and quality of life showed improvement with aerobic training. Moreover, worse responders also improved with training, but to a lesser extent.

Reduced cardiovascular reserve capacity in long-term allogeneic stem cell transplant survivors

Premature cardiovascular mortality is increased in long-term allogeneic stem cell transplant (allo-SCT) survivors, but little information exists regarding subclinical cardiovascular dysfunction in this population. We compared peak oxygen uptake ([Formula: see text]O_2peak), a prognostic cardiovascular marker, and its determinants between long-term allo-SCT survivors and non-cancer controls. Fourteen allo-SCT survivors (mean ± SD, 44 ± 15 years, 50% male, median time since allo-SCT: 6.5 years [range 2-20]) and 14 age- and sex-matched controls (46 ± 13 years, 50% male) underwent cardiopulmonary exercise testing to quantify [Formula: see text]O_2peak. Resting echocardiography (left-ventricular ejection fraction and strain), exercise cardiac MRI (peak cardiac and stroke volume index [CI_peak, SVI_peak]), biochemistry (hemoglobin, troponin-I, B-natriuretic peptide), dual-energy x-ray absorptiometry (lean [LM] and fat [FM] mass, percent body fat [%BF]) and Fick-principal calculation (arteriovenous oxygen difference) were also performed. Survivors exhibited impaired [Formula: see text]O_2peak as compared with controls (25.9 ± 5.1 vs. 33.7 ± 6.5 ml kg^-1 min^-1, p = 0.002), which coincided with reduced CI_peak (6.6 ± 0.8 vs. 8.6 ± 1.9 L min^-1 m^-2; p = 0.001) secondary to reduced SVI_peak (48 ± 4 vs. 61 ± 8 ml m^-2; p < 0.001) rather than chronotropic impairment, and higher %BF (difference, 7.9%, p = 0.007) due to greater FM (5.8 kg; p = 0.069) and lower LM (4.3 kg, p = 0.25). All other measures were similar between groups. Despite comparable resting cardiac function and biomarker profiles, survivors exhibited reduced [Formula: see text]O_2peak and exercise cardiac function and increased %BF relative to controls. These results highlight potential therapeutic avenues and the utility of exercise-based cardiovascular assessment in unmasking cardiovascular dysfunction in allo-SCT survivors.

Validation, Recalibration, and Predictive Accuracy of Published V̇O 2max Prediction Equations for Adults Ages 50-96 Yr

PURPOSE

Maximal oxygen uptake ( ) is the criterion measure of cardiorespiratory fitness. Lower cardiorespiratory fitness is a strong predictor of poor health outcomes, including all-cause mortality. Because testing is resource intensive, several non-exercise-based V˙O 2max prediction equations have been published. We assess these equations' ability to predict measured V˙O 2max , recalibrate these equations, and quantify the association of measured and predicted V˙O 2max with all-cause mortality.

METHODS

Baltimore Longitudinal Study of Aging participants with valid V˙O 2max tests were included ( n = 1080). Using published V˙O 2max prediction equations, we calculated predicted V˙O 2max and present performance metrics before and after recalibration (deriving new regression estimates by regressing measured V˙O 2max on Baltimore Longitudinal Study of Aging covariates). Cox proportional hazards models were fit to quantify associations of measured, predicted, and recalibration-predicted values of V˙O 2max with mortality.

RESULTS

Mean age and V˙O 2max were 69.0 ± 10.4 yr and 21.6 ± 5.9 mL·kg -1 ·min -1 , respectively. The prediction equations yielded root mean square error values ranging from 4.2 to 20.4 mL·kg -1 ·min -1 . After recalibration, these values decreased to 3.9-4.2 mL·kg -1 ·min -1 . Adjusting for all covariates, all-cause mortality risk was 66% lower for the highest quartile of measured V˙O 2max relative to the lowest. Predicted V˙O 2max variables yielded similar estimates in unadjusted models but were not robust to adjustment.

CONCLUSIONS

Measured V˙O 2max is an extremely strong predictor of all-cause mortality. Several published V˙O 2max prediction equations yielded the following: 1) reasonable performance metrics relative to measured V˙O 2max especially when recalibrated, and 2) all-cause mortality hazard ratios similar to those of measured V˙O 2max , especially when recalibrated, yet 3) were not robust to adjustment for basic demographic covariates likely because these were used in the equation for predicted V˙O 2max .

Percentage of Age-Predicted Cardiorespiratory Fitness May Be a Stronger Risk Indicator for Incident Type 2 Diabetes Than Absolute Levels of Cardiorespiratory Fitness

PURPOSE

There are inverse and independent associations between cardiorespiratory fitness (CRF) and several adverse cardiometabolic outcomes. The percentage of age-predicted CRF (%age-predicted CRF) is comparable to absolute CRF as a risk indicator for some of these outcomes, but the association between %age-predicted CRF and risk of type 2 diabetes (T2D) has not been previously investigated. We aimed to assess the association between %age-predicted CRF and T2D in a prospective cohort study.

METHODS

Cardiorespiratory fitness, as measured directly by peak oxygen uptake, was assessed in 1901 men aged 42-60 yr who underwent cardiopulmonary exercise testing. The age-predicted CRF estimated from a regression equation for age was converted to %age-predicted CRF using (achieved CRF/age-predicted CRF) × 100. Hazard ratios (95% CI) were estimated for T2D.

RESULTS

During a median follow-up of 26.8 yr, 227 T2D cases were recorded. The risk of T2D decreased continuously with increasing %age-predicted CRF ( P value for nonlinearity = .30). A 1-SD increase in %age-predicted CRF was associated with a decreased risk of T2D in analysis adjusted for established risk factors (HR = 0.68: 95% CI, 0.59-0.79). The corresponding adjusted risk was (HR = 0.51: 95% CI, 0.35-0.75) comparing extreme tertiles of %age-predicted CRF. The respective estimates for the association between absolute CRF and T2D were-HR (95% CI)-0.71 (0.60-0.83) and 0.64 (0.44-0.95).

CONCLUSIONS

Percentage of age-predicted CRF is linearly, inversely, and independently associated with the risk of incident T2D and may be a stronger risk indicator for T2D compared to absolute CRF in a general population of middle-aged and older men.

Estimated cardiorespiratory fitness in relation to overall, breast and prostate cancer incidence: the Norwegian HUNT study

PURPOSE

To investigate the relationships between the estimated cardiorespiratory fitness (eCRF) and the incidence of overall, breast, and prostate cancer in a large prospective cohort study.

METHODS

We included 46,968 cancer-free adults who participated in the second survey of the Trøndelag Health Study in Norway. Sex-specific non-exercise algorithms were used to estimate CRF. eCRF was classified into sex and age-specific tertiles, that is, into low, medium and high levels. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Over a median of 22.1 years' follow-up, there were 7752 overall, 858 breast and 1376 prostate cancer cases. Medium and high levels of eCRF were associated with a reduced incidence of overall cancer in a dose-response manner in all participants (HR 0.96; 95% CI, 0.90-1.01 and HR 0.85; 95% CI, 0.79-0.91, respectively, and P-value for trend <.001). No association was observed between eCRF and breast cancer incidence in women. Only the high level of eCRF seemed to be associated with a reduced incidence of prostate cancer in men (HR 0.85; 95% CI, 0.72-1.02).

CONCLUSIONS

eCRF may be a practical and cost-effective means of investigating the association between the CRF and cancer incidence.

External validation of VO2max prediction models based on recreational and elite endurance athletes

In recent years, numerous prognostic models have been developed to predict VO2max. Nevertheless, their accuracy in endurance athletes (EA) stays mostly unvalidated. This study aimed to compare predicted VO2max (pVO2max) with directly measured VO2max by assessing the transferability of the currently available prediction models based on their R2, calibration-in-the-large, and calibration slope. 5,260 healthy adult EA underwent a maximal exertion cardiopulmonary exercise test (CPET) (84.76% male; age 34.6±9.5 yrs.; VO2max 52.97±7.39 mL·min-1·kg-1, BMI 23.59±2.73 kg·m-2). 13 models have been selected to establish pVO2max. Participants were classified into four endurance subgroups (high-, recreational-, low- trained, and "transition") and four age subgroups (18-30, 31-45, 46-60, and ≥61 yrs.). Validation was performed according to TRIPOD guidelines. pVO2max was low-to-moderately associated with direct CPET measurements (p>0.05). Models with the highest accuracy were for males on a cycle ergometer (CE) (Kokkinos R2 = 0.64), females on CE (Kokkinos R2 = 0.65), males on a treadmill (TE) (Wasserman R2 = 0.26), females on TE (Wasserman R2 = 0.30). However, selected models underestimated pVO2max for younger and higher trained EA and overestimated for older and lower trained EA. All equations demonstrated merely moderate accuracy and should only be used as a supplemental method for physicians to estimate CRF in EA. It is necessary to derive new models on EA populations to include routinely in clinical practice and sports diagnostic.

Rapid cardiovascular aging following allogeneic hematopoietic cell transplantation for hematological malignancy

Introduction

Allogeneic hematopoietic cell transplantation (allo-HCT) offers a potential cure for high-risk hematological malignancy; however, long-term survivors experience increased cardiovascular morbidity and mortality. It is unclear how allo-HCT impacts cardiovascular function in the short-term. Thus, this 3-month prospective study sought to evaluate the short-term cardiovascular impact of allo-HCT in hematological cancer patients, compared to an age-matched non-cancer control group.

Methods

Before and ~3-months following allo-HCT, 17 hematological cancer patients (45 ± 18 years) underwent cardiopulmonary exercise testing to quantify peak oxygen uptake (VO₂peak)-a measure of integrative cardiovascular function. Then, to determine the degree to which changes in VO₂peak are mediated by cardiac vs. non-cardiac factors, participants underwent exercise cardiac MRI (cardiac reserve), resting echocardiography (left-ventricular ejection fraction [LVEF], global longitudinal strain [GLS]), dual-energy x-ray absorptiometry (lean [LM] and fat mass [FM]), blood pressure (BP) assessment, hemoglobin sampling, and arteriovenous oxygen difference (a-vO₂diff) estimation via the Fick equation. Twelve controls (43 ± 13 years) underwent identical testing at equivalent baseline and 3-month time intervals.

Results

Significant group-by-time interactions were observed for absolute VO₂peak (p = 0.006), bodyweight-indexed VO₂peak (p = 0.015), LM (p = 0.001) and cardiac reserve (p = 0.019), which were driven by 26, 24, 6, and 26% reductions in the allo-HCT group (all p ≤ 0.001), respectively, as no significant changes were observed in the age-matched control group. No significant group-by-time interactions were observed for LVEF, GLS, FM, hemoglobin, BP or a-vO₂diff, though a-vO₂diff declined 12% in allo-HCT (p = 0.028).

Conclusion

In summary, allo-HCT severely impairs VO₂peak, reflecting central and peripheral dysfunction. These results indicate allo-HCT rapidly accelerates cardiovascular aging and reinforces the need for early preventive cardiovascular intervention in this high-risk group.

An Equation With Clinical Applicability and Adequate Validity to Predict the Maximum Oxygen Consumption of Individuals Post-stroke

OBJECTIVE

To develop an equation with clinical applicability and adequate validity to predict the maximum oxygen consumption (V̇o_2max) of individuals post-stroke.

DESIGN

A cross-sectional study.

SETTING

A university laboratory.

PARTICIPANTS

Individuals post-stroke in the chronic phase (at least 6 months post-stroke). Step-1 (equation development): n=50, aged 55±12 years; Step-2 (validity investigation): n=20, aged 58±8 years (N=50 [step 1], N=20 [step 2]).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE(S)

Step-1 (equation development): multiple linear regression analysis was performed.

DEPENDENT VARIABLE

V̇o_2max (mL/kg^/min) in the cardiopulmonary exercise test.

INDEPENDENT VARIABLES

age (years), sex (1-women, 2-men), body mass index (BMI) (kg/m²), and distance (meters) in the Six-Minute Walk Test (6MWT) (6MWT-Equation) or in the Incremental Shuttle Walk Test (ISWT) (ISWT-Equation). Step-2 (validity investigation): agreement between the V̇o_2max measured and predicted was evaluated with the intraclass correlation coefficient (ICC) with 95% confidence interval (CI) and the Bland-Altman method (α=5%).

RESULTS

In step-1 (equation development), the 4 independent variables for each equation were retained (6MWT-Equation: R²=0.68, P<.001; ISWT-Equation: R²=0.58, P<.001). In step-2 (validity investigation), the 6MWT-Equation showed an ICC of 0.73 (95% CI=0.30, 0.89; P=.004) and a mean bias of 0.003 mL/kg/min; and the ISWT-Equation showed an imprecise ICC of 0.55 (95% CI=-0.12, 0.82; P=.045) and a mean bias of 0.971 mL/kg/min. 6MWT-Equation (V̇o_2max=22.239+0.02 × distance in the 6MWT+4.039 × sex-0.157 × age-0.265 × BMI) showed adequate validity.

CONCLUSIONS

An equation with clinical applicability and adequate validity in the investigated sample was developed to predict the V̇o_2max of individuals post-stroke in the chronic phase (6MWT-Equation). Future studies with larger sample should investigate its external validity.

Reference Standards for Cardiorespiratory Fitness in Brazil: A POOLED ANALYSIS AND OVERVIEW OF HETEROGENEITY IN NATIONAL AND INTERNATIONAL STUDIES

PURPOSE

This study aimed to propose reference standards for cardiorespiratory fitness (CRF) for Brazil from a pooled analysis and to compare peak oxygen uptake (V˙ o2peak ) in Brazilian, United States (US), and Norwegian samples, exploring possible national and international differences.

METHODS

Reference values for treadmill V˙ o2peak in three different Brazilian regions were assessed from previous publications. We analyzed available samples to assess possible differences, generate weighted average data for Brazil, and compared them with US and Norwegian data.

RESULTS

Brazilian reference values had a lower V˙ o2peak value for the Northeast region and a higher V˙ o2peak value for the Southeast region for all sex and age groups. International comparisons with the Brazilian pooled data (n = 26661) revealed higher values for the Norwegian sample (n = 3810) and lower values for the US sample (n = 16278). The observed heterogeneity in CRF is possibly related to differences in anthropometric (weight, height) and socioeconomic factors, which differed among the samples. Also, Brazilian data showed a curvilinear V˙ o2peak age reduction trend rather than the linear characteristic commonly utilized, and the regression curves were different from those for US and Norwegian data.

CONCLUSION

This study provides new CRF reference standards for Brazil. After pooling data from three Brazilian regions, a comparison revealed notable differences between regions, evidencing a negative gradient from Southern to Northern regions. Similarly, the international comparisons between Brazil, US, and Norway data revealed CRF heterogeneity, with differences in the V˙ o2peak values and in the age relationship patterns. These findings reinforce the importance of using national- or regional-specific V˙ o2peak reference values, ensuring proper CRF evaluation.

Estimated Oxygen Consumption with the Abbreviated Method and Its Association with Vaccination and PCR Tests for COVID-19 from Socio-Demographic, Anthropometric, Lifestyle, and Morbidity Outcomes in Chilean Adults

COVID-19 causes cardiovascular and lung problems that can be aggravated by confinement, but the practice of physical activity (PA) could lessen these effects. The objective of this study was to evaluate the association of maximum oxygen consumption (V˙O2max) with vaccination and PCR tests in apparently healthy Chilean adults. An observational and cross-sectional study was performed, in which 557 people from south-central Chile participated, who answered an online questionnaire on the control of COVID-19, demographic data, lifestyles, and diagnosis of non-communicable diseases. V˙O2max was estimated with an abbreviated method. With respect to the unvaccinated, those who received the first (OR:0.52 [CI:0.29;0.95], p = 0.019) and second vaccine (OR:0.33 [CI:0.18;0.59], p = 0.0001) were less likely to have an increased V˙O2max. The first vaccine was inversely associated with V˙O2max (mL/kg/min) (β:−1.68 [CI:−3.06; −0.3], p = 0.017), adjusted for BMI (β:−1.37 [CI:−2.71; −0.03], p = 0.044) and by demographic variables (β:−1.82 [CI:−3.18; −0.46], p = 0.009); similarly occur for the second vaccine (β: between −2.54 and −3.44, p < 0.001) on models with and without adjustment. Having taken a PCR test was not significantly associated with V˙O2max (mL/kg/min). It is concluded that vaccination significantly decreased V˙O2max, although it did not indicate cause and effect. There is little evidence of this interaction, although the results suggest an association, since V˙ O2max could prevent and attenuate the contagion symptoms and effects.

Age-Related Differences for Cardiorespiratory Fitness Improvement in Patients Undergoing Cardiac Rehabilitation

Objective

We investigated age-related differences for peak oxygen uptake (peak VO₂) improvement with exercise training during cardiac rehabilitation (CR).

Patients and Methods

This was a retrospective cohort study of the Mayo Clinic Rochester CR program including adult patients who attended CR (≥1 session) for any eligible indication between 1999 and 2017 and who had a cardiopulmonary exercise test pre and post CR with VO₂ data (peak respiratory exchange ratio ≥1.0). Younger (20–49 yrs), midlife (50–64 yrs), and older adults (≥65 yrs) were compared using ANOVA for delta and percent change in peak VO₂; and percentage of peak VO₂ responders (>0% change).

Results

708 patients (age: 60.8 ± 12.1 years; 24% female) met inclusion criteria. Delta and percent change in peak VO₂ was lower for older adults (1.6 ± 3.2 mL.kg.min⁻¹; 12 ± 27%) compared with younger (3.7 ± 4.0 mL.kg.min⁻¹, p < 0.001; 23 ± 28%, p = 0.002) and midlife adults (2.8 ± 3.8 mL.kg.min⁻¹, p < 0.001; 17 ± 28%, p = 0.04). For midlife, delta change, but not percent change in peak VO₂ was significantly lower (p = 0.02) compared with younger. Percentage of responders was only different between older and younger (72 vs. 86%; p = 0.008). Sensitivity analyses in non-surgical patients showed similar differences for delta change, and differences in percent change remained significant between older and younger adults (10 ± 20% vs. 16 ± 18%; p = 0.04).

Conclusions

In CR patients, older adults had lower improvement in cardiorespiratory fitness than younger and midlife adults. While excluding surgical patients reduced age-related differences, older adults still had lower cardiorespiratory fitness improvement during CR. These findings may have implications for individualizing CR programming in aging populations to reduce future cardiovascular risk.

Phenotyping Cardiopulmonary Exercise Limitations in Chronic Obstructive Pulmonary Disease

Background

Exercise limitation in chronic obstructive pulmonary disease (COPD) is commonly attributed to abnormal ventilatory mechanics and/or skeletal muscle function, while cardiovascular contributions remain relatively understudied. To date, the integrative exercise responses associated with different cardiopulmonary exercise limitation phenotypes in COPD have not been explored but may provide novel therapeutic utility. This study determined the ventilatory, cardiovascular, and metabolic responses to incremental exercise in patients with COPD with different exercise limitation phenotypes.

Methods

Patients with COPD (n = 95, FEV₁:23–113%pred) performed a pulmonary function test and incremental cardiopulmonary exercise test. Exercise limitation phenotypes were classified as: ventilatory [peak ventilation (V_Epeak)/maximal ventilatory capacity (MVC) ≥ 85% or MVC-V_Epeak ≤ 11 L/min, and peak heart rate (HR_peak) < 90%pred], cardiovascular (V_Epeak/MVC < 85% or MVC-V_Epeak > 11 L/min, and HR_peak ≥ 90%pred), or combined (V_Epeak/MVC ≥ 85% or MVC-V_Epeak ≤ 11 L/min, and HR_peak ≥ 90%pred).

Results

FEV₁ varied within phenotype: ventilatory (23–75%pred), combined (28–90%pred), and cardiovascular (68–113%pred). The cardiovascular phenotype had less static hyperinflation, a lower end-expiratory lung volume and larger tidal volume at peak exercise compared to both other phenotypes (p < 0.01 for all). The cardiovascular phenotype reached a higher V_Epeak (60.8 ± 11.5 L/min vs. 45.3 ± 15.5 L/min, p = 0.002), cardiopulmonary fitness (VO_2peak: 20.6 ± 4.0 ml/kg/min vs. 15.2 ± 3.3 ml/kg/min, p < 0.001), and maximum workload (103 ± 34 W vs. 72 ± 27 W, p < 0.01) vs. the ventilatory phenotype, but was similar to the combined phenotype.

Conclusion

Distinct exercise limitation phenotypes were identified in COPD that were not solely dependent upon airflow limitation severity. Approximately 50% of patients reached maximal heart rate, indicating that peak cardiac output and convective O₂ delivery contributed to exercise limitation. Categorizing patients with COPD phenotypically may aid in optimizing exercise prescription for rehabilitative purposes.

Updated Reference Standards for Cardiorespiratory Fitness Measured with Cardiopulmonary Exercise Testing: Data from the Fitness Registry and the Importance of Exercise National Database (FRIEND)

OBJECTIVE

To provide updated reference standards for cardiorespiratory fitness (CRF) for the United States derived from cardiopulmonary exercise (CPX) testing when using a treadmill or cycle ergometer.

PATIENTS AND METHODS

Thirty-four laboratories in the United States contributed data to the Fitness Registry and the Importance of Exercise National Database. Analysis included 22,379 tests (16,278 treadmill and 6101 cycle ergometer) conducted between January 1, 1968, through March 31, 2021, from apparently healthy adults (aged 20 to 89 years). Percentiles of peak oxygen consumption for men and women were determined for each decade from 20 through 89 years of age for treadmill and cycle exercise modes, as well as when defining maximal effort as respiratory exchange ratio (RER) greater than or equal to 1.0 or RER greater than or equal to 1.1.

RESULTS

For both men and women, the 50^th percentile scores for each exercise mode decreased with age and were higher in men across all age groups and higher for treadmill compared with cycle CPX. The average rate of decline per decade over a 6-decade period was 13.5%, 4.0 mLO₂·kg^-1·min^-1 for treadmill CPX and 16.4%, 4.3 mLO₂·kg^-1·min^-1 for cycle CPX. Observationally, the mean peak oxygen consumption was similar whether using an RER criterion of greater than or equal to 1.0 or greater than or equal to 1.1 across the different test modes, ages, and for both sexes. The updated reference standards for treadmill CPX were 1.5 - 4.6 mLO₂·kg^-1·min^-1 lower compared with the previous 2015 standards whereas the updated cycling standards were generally comparable to the original 2017 standards.

CONCLUSION

These updated cardiorespiratory fitness reference standards improve the representativeness of the US population compared with the original standards.

Muscle Oxygenation of the Paretic and Nonparetic Legs During and After Arterial Occlusion in Chronic Stroke

Oxygen delivery and demand are reduced in the paretic leg post-stroke, reflecting decreased vascular function and reduced muscle quantity and quality. However, it is unknown how muscle oxygenation, the balance between muscle oxygen delivery and utilization, is altered in chronic stroke during and after occlusion-induced ischemia.

OBJECTIVES

The objective was to determine muscle oxygen consumption rate, microvascular responsiveness and reactive hyperemia in the paretic and nonparetic legs during and after arterial occlusion post-stroke.

MATERIALS AND METHODS

Muscle oxygen saturation was measured with near-infrared spectroscopy on the vastus lateralis of each leg during 3-minute arterial occlusion and recovery (3 min). Muscle oxygen consumption was derived from the desaturation slope during ischemia, microvascular responsiveness was derived from the resaturation slope after ischemia and reactive hyperemia was derived from the area under the curve above baseline after ischemia.

RESULTS

Eleven subjects (91% male; 32.2±6.1 months post-stroke; age 62.9±13.6 years) with a hemiparetic gait pattern participated. There was no significant between-leg muscle oxygenation difference at rest (paretic: 64.9±16.6%; nonparetic: 70.6±15.6%, p = 0.13). Muscle oxygen consumption in the paretic leg (-0.53±0.24%/s) was significantly reduced compared to the nonparetic leg (-0.70±0.36%/s; p = 0.03). Microvascular responsiveness was significantly reduced in the paretic leg compared to the nonparetic leg (paretic: 4.6±1.8%/s; nonparetic: 5.7±1.6%/s, p = 0.04). Reactive hyperemia was not significantly different between legs (paretic:4384±2341%·s; nonparetic: 3040±2216%·s, p = 0.07).

CONCLUSION

Muscle oxygen consumption and microvascular responsiveness are impaired in the paretic compared to the nonparetic leg, suggesting both reduced skeletal muscle aerobic function and reduced ability to maximally perfuse muscle tissue.

Performance of Heart Failure Patients with Severely Reduced Ejection Fraction during Cardiopulmonary Exercise Testing on Treadmill and Cycle Ergometer; Similarities and Differences

BACKGROUND

Peak oxygen consumption (VO₂) measured by cardiopulmonary exercise testing (CPET) is a significant predictor of mortality and future transplantation in heart failure patients with severely reduced ejection fraction (HFrEF). The present study evaluated the differences in peak VO₂ and other prognostic variables between treadmill and cycle CPETs in these patients.

METHODS

In this cross-over study design, thirty males with severe HFrEF underwent CPET on both a treadmill and a cycle ergometer within 2-5 days apart, and important CPET parameters between two exercise test modalities were compared.

RESULTS

Peak VO₂ was 23.12% higher on the treadmill than on cycle (20.55 ± 3.3 vs. 16.69 ± 3.01, p < 0.001, respectively). Minute ventilation to carbon dioxide production (VE/VCO₂) slope was not different between the two CPET modes (p = 0.32). There was a strong positive correlation between the VE/VCO₂ slopes during treadmill and cycle testing (r = 0.79; p < 0.001). VE/VCO₂ slope was not related to peak respiratory exchange ratio (RER) in either modality (treadmill, r = 0.13, p = 0.48; cycle, r = 0.25, p = 0.17). The RER level was significantly higher on the cycle ergometer (p < 0.001).

CONCLUSION

Peak VO₂ is higher on treadmill than on cycle ergometer in severe HFrEF patients. In addition, VE/VCO₂ slope is not a modality dependent parameter and is not related to the patients' effort during CPET.

Comparison of the FRIEND and Wasserman-Hansen Equations in Predicting Outcomes in Heart Failure

Background

Percentage of age‐predicted peak oxygen uptake (VO₂) achieved (ppVO₂) has been widely used to stratify risk in patients with heart failure. However, there are limitations to traditional normal standards. We compared the recently derived FRIEND (Fitness Registry and the Importance of Exercise: A National Data Base) equation to the widely used Wasserman‐Hansen (WH) ppVO₂ equation to predict outcomes in patients with heart failure.

Methods and Results

A subgroup of 4055 heart failure patients from the FRIEND registry (mean age 53±15 years) was followed for a mean of 28±16 months. The FRIEND and WH equations along with measured peak VO₂ expressed in mL/kg⁻¹ per min⁻¹ were compared for mortality and composite cardiovascular events. ppVO₂ was higher for the FRIEND versus the WH equation (66±30% versus 58±25%; P<0.001). The areas under the receiver operating characteristic curves were slightly but significantly higher for the FRIEND equation for mortality (0.74 versus 0.72; P=0.03) and cardiac events (0.70 versus 0.68; P=0.008). Area under the receiver operating characteristic curve for measured peak VO₂ was 0.70 (P<0.001) for mortality and 0.73 (P<0.001) for cardiovascular events. For each 1‐SD higher ppVO₂ for the FRIEND equation, mortality was reduced by 18% (hazard ratio, 0.82; 95% CI, 0.69–0.97; P<0.02); for each 1‐SD higher ppVO₂ for the WH equation, the mortality was reduced by 17% (hazard ratio, 0.83; 95% CI, 0.71–0.97; P=0.02). The corresponding reductions in risk per 1 SD for cardiovascular events for the FRIEND and WH equations were 23 and 21%, respectively (both P<0.001).

Conclusions

Peak VO₂ expressed as percentage of an age‐predicted standard strongly predicts mortality and major cardiovascular events in patients with heart failure. The FRIEND registry equation exhibited test characteristics slightly superior to the commonly used WH equation.

Cardiopulmonary Exercise Test Parameters in Athletic Population: A Review

Although still underutilized, cardiopulmonary exercise testing (CPET) allows the most accurate and reproducible measurement of cardiorespiratory fitness and performance in athletes. It provides functional physiologic indices which are key variables in the assessment of athletes in different disciplines. CPET is valuable in clinical and physiological investigation of individuals with loss of performance or minor symptoms that might indicate subclinical cardiovascular, pulmonary or musculoskeletal disorders. Highly trained athletes have improved CPET values, so having just normal values may hide a medical disorder. In the present review, applications of CPET in athletes with special attention on physiological parameters such as VO₂max, ventilatory thresholds, oxygen pulse, and ventilatory equivalent for oxygen and exercise economy in the assessment of athletic performance are discussed. The role of CPET in the evaluation of possible latent diseases and overtraining syndrome, as well as CPET-based exercise prescription, are outlined.

Traditional markers of cardiac toxicity fail to detect marked reductions in cardiorespiratory fitness among cancer patients undergoing anti-cancer treatment

AIMS

Left ventricular ejection fraction (LVEF) is standard of care for evaluating chemotherapy-associated cardiotoxicity, although global longitudinal strain (GLS) offers advantages. However, neither change in LVEF or GLS has been associated with short-term symptoms, functional capacity, or long-term heart failure (HF) risk. We sought to determine whether an integrative measure of cardiovascular function (VO2peak) that is strongly associated with HF risk would be more sensitive to cardiac damage induced by cancer treatment than LVEF, GLS, or cardiac biomarkers.

METHODS AND RESULTS

Patients (n = 206, 53 ± 13 years, 35% male) scheduled to commence anti-cancer treatment completed assessment prior to, and within 6 months after therapy. Changes in echocardiographic measures of LV function (LVEF, GLS), cardiac biomarkers (troponin and BNP), and cardiorespiratory fitness (VO2peak) were measured. LV function was normal prior to treatment (LVEF 61 ± 5%; GLS -19.4 ± 2.1), but VO2peak was only 88 ± 26% of age-predicted. After treatment, VO2peak was reduced by 7 ± 15% (equivalent of 7 years normal ageing, P < 0.0001) and the rates of functional disability (defined as VO2peak ≤ 18 mL/min/kg) almost doubled (15% vs. 26%, P = 0.016). In contrast, small, reductions in LVEF (59 ± 5% vs. 58 ± 5%, P = 0.03) and GLS (-19.4 ± 2.1 vs. -18.9 ± 2.2, P = 0.002) and an increase in troponin levels (4.0 ± 6.9 vs. 26.4 ± 26.2 ng/mL, P < 0.0001) were observed.

CONCLUSION

Anti-cancer treatment is associated with marked reductions in functional capacity that occur independent of reductions in LVEF and GLS. The assessment of VO2peak prior to, and following treatment may be a more sensitive means of identifying patients at increased risk of HF.

Prediction Equations for Maximal Aerobic Capacity on Cycle Ergometer for the Spanish Adult Population

BACKGROUND

Frequently used reference values for clinical exercise testing have been derived from non-random samples and some with poorly defined maximal criteria. Our objective was to obtain population based reference values for peak oxygen uptake (V?O₂) and work rate (WR) for cardiopulmonary exercise testing in a representative sample of Caucasian Spanish men and women.

METHODS

182 men and women, 20-85 years old, were included and exercised on cycle-ergometer to exhaustion. (V?O₂) and WR were measured. The equations obtained from this sample were validated in an independent cohort of 69 individuals, randomly sampled form the same population. Then a final equation merging the two cohorts (=251) was produced.

RESULTS

Height, sex and age resulted predictive of both V?O₂ peak and WR. Weight and physical activity added very little to the accuracy to the equations. The formulas V?O₂peak=0.017·height?(cm)-0.023·age?(years)+0.864·sex?(female=0/male=1)±179?l?min^-1, and peak WR=1.345 · height (cm) - 2.074 · age (years)+76.54 · sex (female=0/male=1)±21.2W were the best compromise between accuracy and parsimony.

CONCLUSIONS

This study provides new and accurate V?O₂ peak and WR rate reference values for individuals of European Spanish descent.

Effect of a Home-Based Exercise Program on Indices of Physical Function and Quality of Life in Elderly Maintenance Hemodialysis Patients

BACKGROUND

Patients on maintenance hemodialysis (MHD) exhibit muscle wasting and impaired physical function which can be reversed with regular exercise, but accessibility to exercise programs for this unique population is lacking. We assessed the efficacy of a home-based exercise program on a broad range of indices of physical function, quality of life (QoL), and cognitive decline in patients with MHD.

DESIGN AND METHODS

Twenty-eight MHD patients, mean age 66 ± 7 years, were randomized to a 12-week home-based, case-managed aerobic and resistance exercise program or to usual care (13 exercise and 15 usual care). Comparisons were made for peak VO2, ventilatory inefficiency, 6-min walk test (6MWT), 1-min sit-to-stand (1STS), muscle strength, body composition, QoL, and cognitive measures.

RESULTS

Peak VO2 improved significantly in the exercise group (p = 0.01 between groups); exercise time improved by 41 and 36% at the ventilatory threshold and peak exercise, respectively (p < 0.01 between groups), but there were no differences in ventilatory efficiency. Trends for improvements in 6MWT and 1STS in the exercise group were observed, but no differences were observed in strength or body composition. Among measures of QoL, general health determined by the SF-36 improved in the exercise group, but there were no differences between groups in cognitive function.

CONCLUSIONS

MHD patients improved exercise capacity and some indices of QoL following a 12-week home-based exercise program. Home-based exercise is feasible for patients undergoing MHD and may help to obviate accessibility barriers to regular exercise.

Cardiorespiratory Fitness: Reference on the Six-Minute Walk Test and Oxygen Consumption in Adolescents from South-Central Chile

Cardiorespiratory fitness (CRF) provides oxygen to the exercising muscles and is related to body adiposity, with cardiometabolic variables. The aim was to develop reference values and a predictive model of CRF in Chilean adolescents. A total of 741 adolescents of both genders (15.7 years old) participated in a basic anthropometry, performance in the six-minute walk test (SMWT), and in Course Navette was measured. Percentiles were determined for the SMWT, for the V̇O₂max, and an equation was developed to estimate it. The validity of the equation was checked using distribution assumptions and the Bland–Altman diagram. The STATA v.14 program was used (p < 0.05). The 50th percentile values for males and females in the SMWT and in the V̇O₂max of Course Navette were, respectively, from 607 to 690 and from 630 to 641 m, and from 43.9 to 45 and from 37.5 to 31.5 mlO₂·kg·min⁻¹, for the range of 13 to 17 years. For its part, the model to predict V̇O₂max incorporated gender, heart rate, height, waist-to-height ratio (WHR), and distance in the SMWT (R² = 0.62; estimation error = 0.38 LO₂·min⁻¹; p <0.001). Reference values can guide physical fitness in Chilean adolescents, and V̇O₂max was possible to predict from morphofunctional variables.

Prediction Equations for Maximal Aerobic Capacity on Cycle Ergometer for the Spanish Adult Population

BACKGROUND

Frequently used reference values for clinical exercise testing have been derived from non-random samples and some with poorly defined maximal criteria. Our objective was to obtain population based reference values for peak oxygen uptake (V˙O2) and work rate (WR) for cardiopulmonary exercise testing in a representative sample of Caucasian Spanish men and women.

METHODS

182 men and women, 20-85 years old, were included and exercised on cycle-ergometer to exhaustion. (V˙O2) and WR were measured. The equations obtained from this sample were validated in an independent cohort of 69 individuals, randomly sampled form the same population. Then a final equation merging the two cohorts (=251) was produced.

RESULTS

Height, sex and age resulted predictive of both V˙O2 peak and WR. Weight and physical activity added very little to the accuracy to the equations. The formulas V˙O2peak=0.017⋅height(cm)-0.023⋅age(years)+0.864⋅sex(female=0/male=1)±179lmin-1, and peak WR=1.345 · height (cm) - 2.074 · age (years)+76.54 · sex (female=0/male=1)±21.2W were the best compromise between accuracy and parsimony.

CONCLUSIONS

This study provides new and accurate V˙O2 peak and WR rate reference values for individuals of European Spanish descent.

Exercise cardiovascular magnetic resonance reveals reduced cardiac reserve in pediatric cancer survivors with impaired cardiopulmonary fitness

BACKGROUND

Pediatric cancer survivors are at increased risk of cardiac dysfunction and heart failure. Reduced peak oxygen consumption (peak VO2) is associated with impaired cardiac reserve (defined as the increase in cardiac function from rest to peak exercise) and heart failure risk, but it is unclear whether this relationship exists in pediatric cancer survivors. This study sought to investigate the presence of reduced peak VO2 in pediatric cancer survivors with increased risk of heart failure, and to assess its relationship with resting cardiac function and cardiac haemodynamics and systolic function during exercise.

METHODS

Twenty pediatric cancer survivors (8-24 years; 10 male) treated with anthracycline chemotherapy ± radiation underwent cardiopulmonary exercise testing to quantify peak VO2, with a value < 85% of predicted defined as impaired peak VO2. Resting cardiac function was assessed using 2- and 3-dimensional echocardiography, with cardiac reserve quantified from resting and peak exercise heart rate, stroke volume index (SVI) and cardiac index (CI) using exercise cardiovascular magnetic resonance (CMR).

RESULTS

Twelve of 20 survivors (60%) had reduced peak VO2 (70 ± 16% vs. 97 ± 14% of age and gender predicted). There were no differences in echocardiographic or CMR measurements of resting cardiac function between survivors with normal or impaired peak VO2. However, those with reduced peak VO2 had diminished cardiac reserve, with a lesser increase in CI and SVI during exercise (Interaction P < 0.01 for both), whilst the heart rate response was similar (P = 0.71).

CONCLUSIONS

Whilst exercise intolerance is common among pediatric cancer survivors, it is poorly explained by resting measures of cardiac function. In contrast, impaired exercise capacity is associated with impaired haemodynamics and systolic functional reserve measured during exercise. Consequently, measures of cardiopulmonary fitness and cardiac reserve may aid in early identification of survivors with heightened risk of long-term heart failure.

Normative Peak Cardiopulmonary Exercise Test Responses in Canadian Adults Aged ≥40 Years

BACKGROUND

Up-to-date normative reference sets for cardiopulmonary exercise testing (CPET) are important to aid in the accurate interpretation of CPET in clinical or research settings.

RESEARCH QUESTION

This study aimed to (1) develop and externally validate a contemporary reference set for peak CPET responses in Canadian adults identified with population-based sampling; and (2) evaluate previously recommended reference equations for predicting peak CPET responses.

STUDY DESIGN AND METHODS

Participants were healthy adults who were ≥40 years old from the Canadian Cohort Obstructive Lung Disease who completed an incremental cycle CPET. Prediction models for peak CPET responses were estimated from readily available participant characteristics (age, sex, height, body mass) with the use of quantile regression. External validation was performed with a second convenience sample of healthy adults. Peak CPET parameters that were measured and predicted in the validation cohort were assessed for equivalence (two one-sided tests of equivalence for paired-samples and level of agreement (Bland-Altman analyses). Two one-sided tests of equivalence for paired samples assessed differences between responses in the derivation cohort using previously recommended reference equations.

RESULTS

Normative reference ranges (5th-95th percentiles) for 28 peak CPET parameters and prediction models for 8 peak CPET parameters were based on 173 participants (47% male) who were 64 ± 10 years old. In the validation cohort (n = 84), peak CPET responses that were predicted with the newly generated models were equivalent to the measured values. Peak cardiac parameters predicted by the previously recommended reference equations by Jones and colleagues and Hansen and colleagues were significantly higher.

INTERPRETATION

This study provides reference ranges and prediction models for peak cardiac, ventilatory, operating lung volume, gas exchange, and symptom responses to incremental CPET and presents the most comprehensive reference set to date in Canadian adults who were ≥40 years old to be identified with population-based sampling.

Accuracy of Nonexercise Prediction Equations for Assessing Longitudinal Changes to Cardiorespiratory Fitness in Apparently Healthy Adults: BALL ST Cohort

Background

Repeated assessment of cardiorespiratory fitness (CRF) improves mortality risk predictions in apparently healthy adults. Accordingly, the American Heart Association suggests routine clinical assessment of CRF using, at a minimum, nonexercise prediction equations. However, the accuracy of nonexercise prediction equations over time is unknown. Therefore, we compared the ability of nonexercise prediction equations to detect changes in directly measured CRF.

Methods and Results

The sample included 987 apparently healthy adults from the BALL ST (Ball State Adult Fitness Longitudinal Lifestyle Study) cohort (33% women; average age, 43.1±10.4 years) who completed 2 cardiopulmonary exercise tests ≥3 months apart (3.2±5.4 years of follow‐up). The change in estimated CRF (eCRF) from 27 distinct nonexercise prediction equations was compared with the change in directly measured CRF. Analysis included Pearson product moment correlations, SEE values, intraclass correlation coefficient values, Cohen's κ coefficients, γ coefficients, and the Benjamini‐Hochberg procedure to compare eCRF with directly measured CRF. The change in eCRF from 26 of 27 equations was significantly associated to the change in directly measured CRF (P<0.001), with intraclass correlation coefficient values ranging from 0.06 to 0.63. For 16 of the 27 equations, the change in eCRF was significantly different from the change in directly measured CRF. The median percentage of participants correctly classified as having increased, decreased, or no change in CRF was 56% (range, 39%–61%).

Conclusions

Variability was observed in the accuracy between nonexercise prediction equations and the ability of equations to detect changes in CRF. Considering the appreciable error that prediction equations had with detecting even directional changes in CRF, these results suggest eCRF may have limited clinical utility.

Serial Analysis of Cardiopulmonary Fitness and Echocardiography in Patients with Fabry Disease Undergoing Enzyme Replacement Therapy

Objective

Fabry disease, a rare X-linked disorder, can lead to exercise intolerance. In Taiwan, the cardiac variant of Fabry disease has a significantly higher prevalence than the classic variant. The cardiac variant of Fabry disease primarily involves the heart. Enzyme replacement therapy has been used to treat both variants. We aimed to study the impact of enzyme replacement therapy on exercise and cardiac structures between the classic (CL-FD) and cardiac variant (CV-FD) Fabry disease.

Design and methods

Retrospective analysis of 2 groups of patients with Fabry disease (5 patients with the classic variant and 5 with the cardiac variant), who were undergoing enzyme replacement therapy. Patients were assessed annually for 3 years using symptom-limited cycle ergometry and echocardiography.

Results

Subjects were 5 women, mean age 53 (standard deviation (SD) 14.05) years with CL-FD Fabry disease, and 5 men, mean age 65 (SD 2.35) years with CV-FD. The percentage of peak oxygen consumption to predicted value for all included patients was significantly lower (78.78% (SD 12.72)) than 100%. Annual serial measurement showed that peak metabolic equivalent and percentage of peak oxygen consumptiondecreased significantly over a period of 3 years in patients with CV-FD (p = 0.002, and p =0.004, respectively), but not in those with CL-FD. There were no significant changes in annual serial measurements of left ventricular mass or interventricular septal thickness in patients with either variant of Fabry disease over a period of 3 years.

Conclusion

Peak exercise capacity of the patients with Fabry disease was lower than that of normal peers. Peak exercise capacity decreased over time

Development of Global Reference Standards for Directly Measured Cardiorespiratory Fitness: A Report From the Fitness Registry and Importance of Exercise National Database (FRIEND)

OBJECTIVE

To begin the process of developing global reference standards for adults from directly measured cardiorespiratory fitness (CRF).

METHODS

Percentiles of maximal oxygen consumption (VO₂max) for men and women were determined for each decade from 20 through 79 years of age using International data from the Fitness Registry and Importance of Exercise: A National Database (FRIEND-I) along with previously published data from seven studies. FRIEND-I data from January 1, 2014, through January 1, 2019, included 11,678 maximal treadmill tests from three countries, whereas the previously published reports included 32,329 maximal treadmill tests from six countries.

RESULTS

FRIEND-I data revealed significant differences between sex and age groups for VO₂max (P<0.01). For the 20- to 29-years of age group, the 50^th percentile VO₂max in men and women were 49.5 mLO₂⋅kg^-1⋅min^-1 and 40.6 mLO₂⋅kg^-1⋅min^-1, respectively. VO₂max declined an average of 9% per decade with the 50^th percentile for the 70- to 79-years of age group having a VO₂max of 30.8 mLO₂⋅kg^-1⋅min^-1 in men and 25.0 mLO₂⋅kg^-1⋅min^-1 in women. These results were similar in magnitude and direction to the previously published literature. Within both the FRIEND-I and previously published data there were CRF differences between countries.

CONCLUSION

This report begins to establish global reference standards for CRF. Continued development of FRIEND-I will increase global representation providing an improved ability to identify and stratify CRF risk categories.

Reference values for aerobic capacity estimated by cardiopulmonary exercise test on a cycle ergometer in a healthy Greek population

OBJECTIVE

Aerobic capacity (AC) is inversely associated with a high risk of cardiovascular morbidity and mortality as well as all-cause mortality. Cardiopulmonary exercise testing (CPET) represents the gold standard for assessing exercise capacity based on maximum oxygen uptake (VO₂max). The purpose of our study was to provide for the first time CPET-derived normative reference values in a Greek cohort of apparently healthy men and women on a cycle ergometer to evaluate their AC, and to compare our results with similar studies from other countries.

METHODS

A cohort of 194 apparently healthy subjects (118 males and 76 females, age range, 15-69 years) was submitted to CPET using a cycle ergometer. Mean ± SD values for several exercise parameters, VO₂max included, were determined. We compared our results with existing data derived from USA and North Europe cohorts.

RESULTS

Male subjects achieved significantly higher levels of relative and absolute VO₂max (p < 0.001) across all ages compared to female subjects. A decline in relative and absolute VO₂max among older participants was observed in both sexes. Greek subjects had lower AC than the North Europe cohort and almost similar to the USA cohort.

CONCLUSION

We provide the first reference data for AC in apparently healthy Greek subjects based on CPET using cycle ergometer. Our findings will allow for more accurate interpretation of CPET in several groups of healthy subjects or patients with CV diseases. The differences found between our reference values and those reported from the USA and northern European countries, underscore the need for individual countries to develop their own AC reference values.