VO2 Recovery Research Articles

Exercise stress testing recovery kinetics: the forgotten phase

Abstract Background Impaired exercise capacity is a cardinal feature of heart failure (HF). Peak oxygen uptake (pVO2) and ventilatory efficiency (VE/VCO2 slope) during exercise are well-consolidated prognostic markers in patients with HF. A previous study suggested that abnormally prolonged VO2 recovery, specifically the failure to decrease VO2 from peak exercise by 10.5 mL/kg/min at 180 seconds of the recovery phase, predicts adverse outcomes in HF. However, it is unknown to what extent the recovery of VEqCO2, a marker of ventilation/perfusion mismatch, adds prognostic value to the already existing parameters. Purpose The aim of this study was to characterize the functional and prognostic significance of VEqCO2 kinetics following peak exercise in individuals with HF. Methods This retrospective single-center study included consecutive adult patients with chronic (>3 months) and stable HF with left ventricular ejection fraction (LVEF) <50% who underwent cardiopulmonary exercise testing (CPET) between 2015 and 2020. Following maximal exercise, patients recovered over a 3-minute period (walking 2km/h for 1 minute and sittng passively for 2 minutes). VO2 and VEqCO2 kinetics during recovery, described as the absolute difference to peak VO2 (difVO2) and VEqCO2 (difVEqCO2), were measured at 30, 60, 120, and 180 seconds. Outcomes were assessed as a composite of cardiovascular (CV) death, urgent cardiac transplant, or left ventricular assist device (LVAD) implantation at 1 year. Results A total of 238 patients were included (mean age 58 ± 12 years; 82% males; mean LVEF 34 ± 10%; 68% with ischemic HF; 75% in NYHA class II-III; mean pVO2 18 ± 6 mL/kg/min; mean VE/VCO2 slope 41 ± 12). During the 1-year follow-up, 19 patients met the endpoint (8 CV deaths, 8 urgent heart transplants, and 3 LVAD). ROC curve analysis showed that the best correlation between difVEqCO2 and outcomes was apparent at difVEqCO2 of 180 seconds (AUC 0.83) with a cut-off value of 1 (sensitivity 93%, specificity 58%). These patients, who had a decrease in VEqCO2 (difVEqCO2 >1) at 180 seconds, were significantly older (p=0.02), had a lower LVEF (p<0.001), and higher NYHA (p<0.001). They were at an increased risk of cardiovascular events compared to those with an increase in VEqCO2 (difVEqCO2 <1) at 180 seconds (event-free survival at 1 year 86% vs. 98%, log-rank p<0.001). In multivariate analysis, the statistical association between difVEqCO2 and outcomes remained significant, even after adjusting for difVO2 at 180 seconds (HR 4.315, CI95% (1.349-13.804), p=0.014). Conclusion Abnormal VEqCO2 kinetics in the recovery period of CPET is an easily recognizable non-invasively derived measurement that predicts outcomes in HF. VEqCO2 may complement the evaluation of VO2 and other parameters during recovery to further improve prognostic risk stratification in HF.

Mask vs. tent: effect of hypoxia method on repeated sprint ability and physiological parameters in cyclists

This study aimed to evaluate the effect of repeated sprint in hypoxia (RSH) training in mask vs. tent system on the physiological parameters associated with the cyclist’s performance. Sixteen well-trained cyclists (VO2max 66 ± 5.9 mL/kg/min) participated in a randomised and two parallel groups design. Participants were assigned to different hypoxia methods [RSHMask (n = 8) vs RSHTent (n = 8)]. The sprint number and power output were measured during a repeated sprint test to failure before and after the effect of eight sessions of RSH. In addition, the following physiological parameters were evaluated: oxygen consumption (VO2), heart rate (HR), arterial oxygen saturation (SpO2), muscle oxygen saturation (SmO2), lactate and core temperature (CoreT°). Linear mixed models were used for repeated measures (p value < 0.05), and the effect size (ES) between groups was reported. An inter-individual analysis of participants was also reported. There was an increase in sprint numbers in both groups (ES = 0.167, p = 0.023) and an increase in power output (∑w) in the RSHMask group (ES = 0.095, p = 0.038). The RSHMask group showed improvement in VO2 recovery (ES = 0.096, p = 0.031) and SmO2 desaturation % (ES = 0.112, p = 0.042) compared to the RSHTent group. Likewise, 50% of the participants in RSHTent showed adaptations to withstand higher T°Core (+ 0.45°), and eight participants showed lactate decreases between 2.9 and 3.1 mmol/L (−24%) after RSH in both groups. Generally, RSH improves the cyclist’s performance, whether the mask or tent method is used. However, RSHTent has the advantage of causing adaptations in T°Core, whilst RSHMask improves anaerobic performance in the oxygenation of peripheral muscles.

Relationship between VO2peak, VO2 Recovery Kinetics, and Muscle Function in Older Adults

Introduction: The efficiency of the cardiovascular system to recover following an exercise bout is measured by oxygen (VO2) recovery kinetics. In older adults with a chronic disease, a higher aerobic capacity (VO2peak) and faster VO2 recovery kinetics are associated with higher muscle strength and physical capacity. Yet, this relationship in healthy older adults remains unclear. The aim of this cross-sectional study was to determine whether a higher VO2peak and faster VO2 recovery kinetics are associated with higher muscle strength and physical performance in healthy community-dwelling older adults. Methods: Thirty-five healthy older adults (female 25/male 10, mean age 73 ± 6 years) performed a graded exercise test on a cycle ergometer. VO2peak and VO2 recovery kinetics were assessed through gas exchange analysis. Muscle strength was determined by maximal leg (one-repetition maximum on leg press; 1RM) and grip strength, and physical performance was determined by the physical performance test (PPT) which assessed gait speed, stair ascent and descent, and timed up-and-go. Results: Higher VO2peak was associated with stronger leg (r = 0.59, p < 0.001) and grip strength (r = 0.39, p < 0.03), but no relationship to PPT (p > 0.05). There was also no relationship between VO2 recovery kinetics and leg and grip strength or PPT (p > 0.05). Conclusion: In healthy community-dwelling older adults, VO2peak, but not VO2 recovery kinetics, is associated with muscle strength. This suggests that muscle strength may be an important factor related to aerobic capacity that could assist in identifying older adults who should be prioritized for resistance training.

Long-Term Results of Serial Exercise Testing and Echocardiography Examinations in Patients with Pulmonary Stenosis.

Pulmonary stenosis (PS) affects cardiopulmonary function and exercise performance. Cardiopulmonary exercise testing (CPET) together with transthoracic echocardiography (TTE) can measure exercise performance, PS progression, and treatment effects. We assessed exercise capacity in PS patients using these methods. We enrolled 28 PS patients aged 6-35 years who received surgery, balloon pulmonary valvuloplasty, and follow-up care. The control population was selected by a 1:1 matching on age, sex, and body mass index. Baseline and follow-up peak pulmonary artery pulse wave velocity (PAV) were compared using TTE. Initial CPET revealed no significant differences in anaerobic metabolic equivalent (MET), peak oxygen consumption (VO2), and heart rate recovery between the two groups, nor were significant differences in pulmonary function identified. Within the PS group, there were no significant differences in MET, peak VO2, and heart rate recovery between the baseline and final CPET. Similarly, no significant differences were observed between the baseline and final PAV. The exercise capacity of patients with properly managed PS was comparable to that of healthy individuals. However, during the follow-up, declining trends in pulmonary function, aerobic metabolism, and peak exercise load capacity were observed among adolescents with PS. This study provides long-term data suggesting that PS patients should be encouraged to perform physical activity. Regular reevaluation should also be encouraged to limit performance deterioration.

Postexercise Oxygen Uptake Recovery Delay Among Patients with Heart Failure: A Systematic Review

Background: Peak oxygen uptake (VO2) is often the focal point of cardiopulmonary exercise testing among patients with heart failure (HF). Breath-by-breath VO2 kinetic patterns at exercise onset, during low-level and submaximal exercise, and during recovery may provide incremental insight into HF severity and etiologies of exercise limitation. Objective: The aim of this systematic review was to explore VO2 recovery delay (VO2RD) across the spectrum of left ventricular function. Methods: A systematic review was conducted using several online databases (EMBASE, Cumulative Index to Nursing and Allied Health Literature, PubMed and Web of Science). Steps outlined by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses were followed. Search terms included VO2RD OR VO2 off kinetics AND HF, peak VO2 AND recovery. All articles were uploaded to Covidence. Results: Four studies met the inclusion criteria. The definition of VO2RD varied across studies. Recovery delay was consistently observed in HF patients compared to controls indicating VO2RD discriminates between those with and without HF. Control groups showed VO2 decline almost immediately after exercise. VO2RD had a significant positive linear relationship to N-terminal prohormone of brain natriuretic and Doppler echo E/e' while demonstrating an inverse relationship with peak cardiac output and survival duration. Conclusions: VO2RD, unlike peak VO2, is relatively cardiospecific. Oxygen recovery kinetics offer insight into disease severity and discrimination of healthy participants from those with HF.

Pros and Cons of Two Methods of Anaerobic Alactic Energy Assessment in a High-Intensity CrossFit® Workout

The current study aimed to evidence the strengths and weaknesses of two indirect methods for assessing the anaerobic alactic contribution to a specific CrossFit® workout. Thirty experienced crossfitters performed the Fran workout at maximal intensity, and ventilatory data were collected during the recovery period using a telemetric portable gas analyser to assess the oxygen uptake (VO2) of the off-kinetics fast component (Anarecovery). The kinetics of maximal phosphocreatine splitting (AnaPCr) were determined based on the literature. No differences between the two methods were observed (31.4 ± 4.0 vs. 30.4 ± 4.1 kJ for Anarecovery and AnaPCr, respectively). Despite the existence of some caveats (e.g., errors derived from a delay at the onset of VO2 recovery and the assumption of given values in the concentration of phosphocreatine per kilogram of wet muscle, respectively) in both methods, the data indicate that they yield similar results and allow for estimations of alactic energy contribution from a short-duration and high intensity CrossFit® routine. The current data contributes to CrossFit® workout evaluations and training strategies, helping researchers to evaluate crossfitters more accurately. The advantage of the two methods used in the current study is that they are non-invasive, which differs greatly from muscle biopsies.

Physiologic responses to exercise in survivors of critical illness: an exploratory pilot study

BackgroundICU survivors suffer from impaired physical function and reduced exercise capacity, yet the underlying mechanisms are poorly understood. The goal of this exploratory pilot study was to investigate potential mechanisms of exercise limitation using cardiopulmonary exercise testing (CPET) and 6-min walk testing (6MWT).MethodsWe enrolled adults aged 18 years or older who were treated for respiratory failure or shock in medical, surgical, or trauma ICUs at Vanderbilt University Medical Center (Nashville, TN, United States). We excluded patients with pre-existing cardiac dysfunction, a contraindication to CPET, or the need for supplemental oxygen at rest. We performed CPET and 6MWT 6 months after ICU discharge. We measured standard CPET parameters in addition to two measures of oxygen utilization during exercise (VO2-work rate slope and VO2 recovery half-time).ResultsWe recruited 14 participants. Low exercise capacity (i.e., VO2Peak < 80% predicted) was present in 11 out of 14 (79%) with a median VO2Peak of 12.6 ml/kg/min [9.6–15.1] and 6MWT distance of 294 m [240–433]. In addition to low VO2Peak, CPET findings in survivors included low oxygen uptake efficiency slope, low oxygen pulse, elevated chronotropic index, low VO2-work rate slope, and prolonged VO2 recovery half-time, indicating impaired oxygen utilization with a hyperdynamic heart rate and ventilatory response, a pattern seen in non-critically ill patients with mitochondrial myopathies. Worse VO2-work rate slope and VO2 recovery half-time were strongly correlated with worse VO2Peak and 6MWT distance, suggesting that exercise capacity was potentially limited by impaired muscle oxygen utilization.ConclusionsThese exploratory data suggest ICU survivors may suffer from impaired muscular oxygen metabolism due to mitochondrial dysfunction that impairs exercise capacity long-term. These findings should be further characterized in future studies that include direct assessments of muscle mitochondrial function in ICU survivors.

Telerehabilitation in patients with recent hospitalization due to acute decompensated heart failure: protocol for the Tele-ADHF randomised controlled trial

Abstract Funding Acknowledgements Type of funding sources: None. Background/introduction Cardiac rehabilitation (CR) has favourable effects in chronic heart failure (CHF) patients on exercise capacity, the risk at hospital (re-)admission and quality of life. Although CR is generally recommended, it is still under-utilized in the daily clinical practice partly due to logistics reasons, limited availability, and patient-related barriers. Cardiac telerehabilitation (CTR) could solve some of these barriers, and have the same favourable outcomes. Purpose The aim of this study is to investigate if CTR in recently hospitalized CHF patients improves their physical functional capacity when compared to no rehabilitation. Methods This randomised controlled trial compares CTR with no rehabilitation after hospitalization for acute decompensated heart failure (ADHF). 64 patients will be included during hospitalization, and start with Remote Patient Management (RPM). After a short period of stable CHF, the patients will be randomised for RPM combined with CTR (intervention group), or RPM alone (control group). The intervention group will start with an 18-weeks program with exercise training, supported by a (remote) technology-assisted dietary intervention and mental health guiding. The training program starts with three centre-based and two home-based video training sessions followed by video coaching sessions. The primary endpoint is physical functional capacity, evaluated using the Short Physical Performance Battery (SPPB) score. Secondary endpoints are recovery after submaximal exercise by evaluating VO2 recovery kinetics (τ-rec), subjective health status, health related quality of life, compliance and acceptance, and readmission rate. Future implications This will be the first study to use an CTR program with integrated RPM after hospitalization for ADHF.

Impact of exercise based cardiac rehabilitation program in patients with transcatheter aortic valve replacement

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Due to the increase in global prevalence of degenerative valve disease, aortic stenosis (AS) has played a preponderant role in the cardiovascular scenario, especially in patients undergoing transcatheter aortic valve replacement (TAVR). An alternative management for this patients are the cardiac rehabilitation programs (CRP); however, their effect has not been completely understood, both in exercise capacity and quality of life, but neither in the improvement of cardiopulmonary performance and other cardiovascular outcomes. Purpose: To evaluate the effect of the CRP on exercise tolerance and cardiopulmonary performance in patients with AS undergoing TAVR. Methods: A cohort study was conducted including 26 patients with AS undergoing TAVR and divided into an intervention group who performed a 4-week supervised training program in the Cardiac Rehabilitation Service and a control group to whom instructions and recommendations to performed unsupervised exercise at home were given. Demographic and clinical data (VO2Max, METS12, oxygen pulse, heart rate, double product, left ventricular ejection fraction, body mass index) were collected at baseline and after a 4-week follow-up. Results: 15 patients were included in the intervention group and 11 patients in the control group. There were no baseline significant differences between groups. After the intervention, significant differences were observed in the METS 12 final gain variable between the control and intervention group (4.55 vs 3.1 p = 0.01). Intergroup analysis showed significant differences (percentage changes) in the intervention group with an increase of METS12 (67.4%, p = 0.001), oxygen pulse (18.21%, p = 0.01), final METS (39.47% p = 0.001) and a decrease in VO2 recovery time (-12.5%, p = 0.05), in the ergometric performance index by heart rate (-38.17%, p = 0.001) and by double product (-38.1%, p = 0.001). Conclusions A 4-week cardiac rehabilitation program is effective to improve exercise tolerance and cardiopulmonary response in patients with AS undergoing TAVR; improvement was statistically significant in METS12, oxygen pulse, VO2 recovery time, METS-load and ergometric performance index for heart rate and double product. METS12 final gain was statistically significant in intervention group in comparison with the control group. Abstract Figure. Control vs Intervention Group (METS12)

Cardiorespiratory responses to acute bouts of high-intensity functional training and traditional exercise in physically active adults.

High-intensity functional training is a popular form of exercise, but little is known about how it compares to more traditional exercise patterns. Thirty healthy, physically active adults (15 males, 15 females) performed a high-intensity functional training workout (HIFT) and a traditional workout (TRAD). Cardiorespiratory responses were measured during and for 15 min after each workout. Peak heart rate (males: 187±7 vs. 171±10 bpm, P<0.001; females: 191±9 vs. 175±6 bpm, P<0.001), peak VO<inf>2</inf> (males: 3.80±0.58 vs. 3.26±0.60 L/min, P<0.001; females: 2.65±0.26 vs. 2.36±0.21, P<0.001), and average 15 min recovery VO<inf>2</inf> (males: 1.15±0.20 vs. 0.99±0.17 L/min, P<0.001; females: 0.77±0.10 vs. 0.71±0.07 L/min, P=0.019) were significantly higher in HIFT vs. TRAD. Aerobic energy expenditure was significantly higher in HIFT compared to TRAD in males (9.01±1.43 vs. 8.53±1.38 kcal/min, P=0.002) but was not significantly different between the two workouts in females (6.04±0.53 vs. 5.97±0.50 kcal/min, P=0.395). Postexercise systolic blood pressure (SBP) was significantly higher than pre-exercise SBP following both HIFT (males: 124±13 mmHg pre to 154±28 mmHg post, P<0.001; females: 110±7 mmHg pre to 140±15 mmHg post, P<0.001) and TRAD (males: 124±13 mmHg pre to 142±16 mmHg post, P=0.002; females: 112±8 mmHg pre to 123±10 mmHg post, P=0.002), however, HIFT led to a greater increase compared to TRAD in females (P=0.001). Postexercise diastolic blood pressure (DBP) was significantly lower than pre-exercise DBP following both HIFT (males: 77±9 mmHg pre to 64±6 mmHg post, P<0.001; females: 71±8 mmHg pre to 64±7 mmHg post, P=0.011) and TRAD (males: 82±7 mmHg pre to 72±7 mmHg post, P<0.001; females: 73±8 mmHg pre to 65±8 mmHg post, P<0.001). Mean arterial blood pressure was unchanged following both workouts. High-intensity functional training may be an effective form of exercise for caloric expenditure and may elicit greater cardiorespiratory stress than traditional exercise.

Acute Cardiopulmonary And Hemodynamic Responses To Exercise With Blood-flow Restriction In Heart Failure Patients

Muscle training with blood flow restriction (BFR) can induce significant increases in muscle strength and mass, while BFR during low intensity aerobic training increases aerobic capacity more than the usual aerobic exercise at the same intensity. However, little is known about the safety and feasibility of BFR training in patients with chronic heart failure (CHF). PURPOSE: This study compared hemodynamic and cardiopulmonary responses during low intensity aerobic exercise with and without BFR in CHF patients. METHODS: Nine CHF patients, 7 males and 2 females (age: 55.6±12.2 years, height: 175.0±10.3 cm, body mass: 89.6±29.1 kg, VO2peak: 22.4±5.04 ml/kg/min, ejection fraction: 36±6%, NYHA: I-II) volunteered to participate in this crossover study. Each participant performed the same aerobic exercise protocol, i.e. a 20-minute cycling bout at 65% of VO2peak, with (BFR) and without BFR (control) in random order, using a cycle ergometer. In the BFR condition, an occlusion cuff was used to regulate the occlusion pressure applied to both limbs that was proportional to thigh circumference. Mean oxygen uptake (VO2) during the 20 minutes exercise, VO2 recovery during the first minute of recovery (VO2/t slope), heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure at 6 min, 12 min and 18 min of exercise, fatigue and dyspnea perception were assessed. ANOVA or paired t-test was used for statistics and data are presented as mean±SD. RESULTS: Mean VO2 during exercise was higher in BFR compared to control (70.6±9.8% vs 64.0±10.1%, p=0.003), while VO2/t slope was higher in control (0.79±0.23 vs 0.53±0.11, p= 0.008). HR was higher during the BFR exercise (94±15 vs 88±15, 97±20 vs 90±19, 96±10 vs 84±9 at 6, 12 and 18 min, respectively; p<0.05), whereas SBP and DBP did not differ between the two conditions at any time point (p>0.05). Fatigue (12.4±2.7 vs 8.8±1.7, p=0.002) and dyspnea (11.5±2.5 vs 9.2±1.9, p=0.03) perception were significantly higher in BFR compared to control. CONCLUSIONS: To our knowledge, this is the first study examined BFR exercise in CHF patients, revealing specific cardiopulmonary and hemodynamic responses and suggesting that this exercise strategy is safe and feasible in those patients. More studies are needed to verify and further characterize the acute and chronic effects of BFR training in CHF patients.

Impaired glucose control is associated with multiple cardiovascular impairments.

Impairments in several markers of the cardiovascular system have been described in impaired glucose tolerance (IGT) and diabetes, but the relative importance of those is not known. We aimed to investigate which cardiovascular markers were most closely linked to an impaired glucose control. In a population-based study of individuals all aged 50years, the Prospective study of Obesity, Energy and Metabolism (POEM), 502 subjects were thoroughly investigated regarding endothelial function, arterial compliance, heart rate variability, arterial blood flow and atherosclerosis, performance at an exercise test with gas exchange (VO2 and VCO2 ), left ventricular structure and function, lung function and multiple measurements of blood pressure. Based on an oral glucose tolerance test (OGTT), the participants were grouped into normal, IGT and diabetes. Of all haemodynamic and structural variables analysed, an impaired glucose control was most closely related to resting heart rate (based on chi-square value at ANOVA). Heart rate was followed by maximal workload, VO2 recovery 5min following exercise, reflectance index at pulse wave analysis, manual systolic blood pressure, ambulatory pulse and pulse pressure, echogenicity of carotid intima-media complex at ultrasound, and pulse wave velocity (p<.0005 for all variables). All of these variables still showed p<.05 versus an impaired glucose control following adjustment for BMI. Of multiple measured cardiovascular markers, resting heart rate was most closely related to an impaired glucose control. Also exercise capacity and the recovery in VO2 following exercise were amongst the top-ranked cardiovascular impairments linked to an impaired glucose control.

Conceptualization and quantification of oriented membrane processes for recovering vanadium ions from acidic industrial discharges

In the present research, polymer inclusion membranes with polyvinyl alcohol (as polymeric support), Tris 2-aminoethyl amine and nitrilotriacetic acid (as extractive agents), were developed according to heat vulcanization method and characterized by Fourier-transform infrared spectrometry and scanning electron microscopy techniques. The as-synthesized membranes can be used for the extraction and recovery of VO2+ ions from highly acidic discharges of phosphate industries. Macroscopic parameters,viz., permeability (P) and initial flux (J0), were experimentally measured in order to evaluate the performances of the developed membranes. Similarly, microscopic parameters, viz., association constant (Kass) related to the interaction of the substrate (VO+2 ions) with extractive agents and apparent diffusion coefficient (D*) related to the migration of VO2+ ions through the membrane phase, were also determined. Further, the influences of temperature on the extraction process were examined, and the activation parameters, viz., energy (Ea), enthalpy (ΔH≠), and entropy (ΔS≠), were determined.The obtained results elucidated that the proposed oriented processes occurred due to successive jumps of VO2+ ions from one interaction site to another of each extractive agent in the membrane phase. Finally, the parameter values of thermodynamic enthalpy (ΔHth) and activation dissociation enthalpy (ΔH≠dis) indicated an energetic control for the studied oriented processes through adopted membranes.

Post‐Exercise Oxygen Uptake and Muscle Oxygenation in Pediatric Heart Transplant Recipients

Pediatric heart transplant recipients (HTR) have reduced exercise tolerance and peak oxygen uptake (VO2) values are 57–73% of age‐predicted norms. Slow post‐exercise VO2 and muscle oxygenation recovery are related to exercise intolerance. However, despite clear exercise tolerance limitations and post‐exercise fatigue, VO2 and muscle oxygenation during recovery responses are unknown in this population.PurposeWe tested the hypothesis that both post‐exercise VO2 recovery and muscle oxygenation recovery would be slower after peak exercise in pediatric HTR compared to controls.MethodsFive pediatric HTR (mean ± SD age = 10.6 ± 3.0 years) and six healthy controls (age = 11.7 ± 2.7 years) performed cycle ergometry to peak exercise followed by 5 minutes of 20‐W cycle recovery. Pulmonary VO2 and muscle oxygenation (vastus lateralis tissue oxygenation index, TOI using near infrared spectroscopy) were sampled continuously during exercise and recovery. Data were linearly interpolated to 1‐s intervals, and both VO2 and TOI data were averaged into 5‐s and 10‐s time bins, respectively. VO2 recovery data were mono‐exponentially curve‐fitted to yield a recovery time constant (tau). TOI recovery was normalized from 0% (end exercise) to 100% (5 min post‐exercise) and data analyzed at set time points to characterize TOI time course changes (0s, 15s, 30s, 60s, 90s, 120s, 180S, 240s, and 300s). Statistical analyses included independent t‐tests for VO2 data and a between‐within (2 × 9, group × time) factorial ANOVA for TOI time course changes. Significance was accepted at p&lt; 0.05.ResultsRecovery VO2 tau was significantly slower in pediatric HTR compared to healthy controls (68 ± 17 vs. 47 ± 12 s, respectively; p=0.044). There was a significant group × time interaction for TOI recovery (p=0.003) where TOI in HTR was significantly lower compared to controls at 15s (8 ± 8 vs. 46 ± 19%; p=0.003), 30s (22 ± 13 vs. 91 ± 31%; p=0.001), and 60s (47 ± 23 vs. 117 ± 36%; p=0.005). TOI was not statistically different between groups by 90s onwards (all p&gt;0.05).ConclusionsPost‐exercise VO2 and TOI recovery are prolonged in pediatric HTR compared to healthy controls. These findings suggest that non‐cardiac factors may contribute to the excessive recovery time following peak exercise in pediatric HTR.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Peak Exercise and Post‐Exercise Recovery Oxygen Uptake and Muscle Oxygenation in Patients with Heart Failure and Preserved Ejection Fraction and Healthy Matched Adults

BackgroundExercise intolerance and muscle dysfunction characterize heart failure with preserved ejection fraction (HFpEF). Exercise intolerance, as measured by low peak oxygen uptake (VO2), and slow post‐exercise VO2 recovery are predictors of mortality. The relationship between peak exercise and recovery VO2 and muscle oxygenation is unknown in this population.PurposeWe tested the hypothesis that post‐exercise VO2 recovery would be slower in patients with HFpEF compared to controls, and that slower post‐exercise VO2 recovery would be related to slower muscle oxygenation recovery in patients with HFpEF.MethodsEight patients with HFpEF and 8 healthy age‐and sex‐matched controls completed a stationary cycling peak exercise test to volition fatigue followed by 5‐min of passive recovery. Pulmonary VO2 (gas exchange via metabolic cart) and muscle oxygenation (tissue muscle oxygenation index, TOI) and deoxygenated hemoglobin (HHb via near infrared spectroscopy) were sampled continuously during the exercise test and recovery. Breath‐by‐breath VO2 data were linearly interpolated to 1‐s intervals, and both VO2 and NIRS data were averaged into 5‐s time bins. VO2 recovery data were mono‐exponentially curve‐fitted (OriginPro, 2017) to yield a recovery time constant (tau) and amplitude change. TOI and HHb at end‐exercise, end‐recovery, and the amplitude change were calculated as 10‐s averages. Statistical analyses included independent t‐tests and stepwise multiple regression. Significance was accepted at P&lt;0.05.ResultsPeak VO2 (15.8 ± 5.9 vs. 24.6 ± 6.6 mL/kg/min, P = 0.011) and VO2 recovery amplitude (−10.0 ± 4.9 vs. −15.1 ± 4.2 mL/kg/min, P = 0.041) were significantly lower in patients with HFpEF compared to matched controls. However, there were no differences between groups in VO2 recovery tau (98 ± 43 vs. 71 ± 16 s, P = 0.122) nor in any TOI or HHb parameter (all P&gt;0.05). Stepwise regression by group to predict peak VO2 yielded a positive regression using both peak‐exercise HHb and VO2 recovery amplitude in HFpEF (R2 = 0.957, P&lt;0.001) but only VO2 recovery amplitude in controls (R2 = 0.947, P&lt;0.001). The same parameters predicted VO2 recovery tau in HFpEF (R2 = 0.940, P = 0.001) with no significant finding in controls (P&gt;0.05).ConclusionsSlower post‐exercise VO2 recovery in patients with HFpEF compared to their healthy counterparts was not confirmed with these data, although this may be largely influenced by the elevated variance in the HFpEF group, or the mild‐moderate HFpEF severity. Regression analyses suggest that the level of muscle deoxygenation, i.e., the level of O2 extraction, during peak exercise may be a more important contributor to peak VO2 in patients with HFpEF compared to their healthy counterparts. The latter may suggest a muscle‐based limitation in HFpEF not observed in healthy controls.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Phase transition performance recovery of W-doped VO2 by annealing treatment

W-doped monoclinic VO2 nanoparticles were synthesized using a hydrothermal method. The phase transition temperature of these nanoparticles was lowered to approximately 26 °C when doped with 2 at% W. The temperature reduction efficiency was found to be −22 °C/at% W. An annealing process was used to improve phase transition performance of doped VO2 samples. The latent heat of the phase transition for the doped VO2 sample increased at higher annealing temperatures, and it was comparable to that of undoped VO2 when annealed at 950 °C. This work showed that the phase transition performance of doped VO2 was improved following annealing and the phase transition temperature could remain relatively low. Additionally, annealing was found to eliminate the amorphous VO2 coating that surrounded the VO2 particles and enhance the crystallinity of doped VO2, which led to the recovery of the transition performance of W-doped VO2.

Post-Exercise Oxygen Uptake Recovery Delay: A Novel Index of Impaired Cardiac Reserve Capacity in Heart Failure

ObjectivesThis study sought to characterize the functional and prognostic significance of oxygen uptake (VO2) kinetics following peak exercise in individuals with heart failure (HF). BackgroundIt is unknown to what extent patterns of VO2 recovery following exercise reflect circulatory response during exercise in HF with preserved ejection fraction (HFpEF) and HF with reduced ejection fraction (HFrEF). MethodsWe investigated patients (30 HFpEF, 20 HFrEF, and 22 control subjects) who underwent cardiopulmonary exercise testing with invasive hemodynamic monitoring and a second distinct HF cohort (n = 106) who underwent noninvasive cardiopulmonary exercise testing with assessment of long-term outcomes. Fick cardiac output (CO) and cardiac filling pressures were measured at rest and throughout exercise in the initial cohort. A novel metric, VO2 recovery delay (VO2RD), defined as time until post-exercise VO2 falls permanently below peak VO2, was measured to characterize VO2 recovery kinetics. ResultsVO2RD in patients with HFpEF (median 25 s [interquartile range (IQR): 9 to 39 s]) and HFrEF (28 s [IQR: 2 to 52 s]) was in excess of control subjects (5 s [IQR: 0 to 7 s]; p < 0.0001 and p = 0.003, respectively). VO2RD was inversely related to cardiac output augmentation during exercise in HFpEF (ρ = −0.70) and HFrEF (ρ = −0.73, both p < 0.001). In the second cohort, VO2RD predicted transplant-free survival in univariate and multivariable Cox regression analysis (Cox hazard ratios: 1.49 and 1.37 per 10-s increase in VO2RD, respectively; both p < 0.005). ConclusionsPost-exercise VO2RD is an easily recognizable, noninvasively derived pattern that signals impaired cardiac output augmentation during exercise and predicts outcomes in HF. The presence and duration of VO2RD may complement established exercise measurements for assessment of cardiac reserve capacity.

Lung Ventilation Efficiency and Quality of Life After Orthotopic Heart Transplantation

The study involved 40 patients with terminal chronic heart failure (CHF) included in the waiting list for heart transplantation. Before surgery and after OHT all patients underwent cardiopulmonary exercise testing, evaluation of clinical status and quality of life (QL) according to the 36-Item Short Form Survey (SF-36). During the follow-up period (5 years) after OHT there were a significant increase in physical capacity, two-fold increase of peak oxygen consumption (VO2), normalization of VE/VCO2 slope level, improvement of the efficiency of the VO2 recovery within first minute and reduction of the VO2 recovery time. OHT was associated with significant improvement of physical and mental health components of QL. Among exercise test parameters significantly associated with improved physical health component of QL were increments in exercise capacity, peak VO2, rate of VO2 recovery within first minute. There was no relationship between cardiopulmonary parameters of exercise test and mental health component of QL. In patients with terminal CHF OHR led to significant increase of the lung ventilation efficiency and QL. Factors contributing to QL improvement after OHT were augmentation of left ventricular ejection fraction and reduction of CHF NYHA class. Among cardiopulmonary exercise test parameters, a high predictive value relative to improvement of subjective assessment of physical health component of QL showed exercise capacity, peak VO2, and efficiency of VO2 recovery within first minute.

Recovery Responses to Maximal Exercise in Healthy-Weight Children and Children With Obesity

ABSTRACTPurpose: The purpose of this study was to examine differences in heart rate recovery (HRRec) and oxygen consumption recovery (VO2 recovery) between young healthy-weight children and children with obesity following a maximal volitional graded exercise test (GXTmax). Method: Twenty healthy-weight children and 13 children with obesity completed body composition testing and performed a GXTmax. Immediately after the GXTmax, HRRec and VO2 recovery were measured each minute for 5 consecutive minutes. Results: There were no statistically significant group differences in HRRec for the 5 min following maximal exercise, Wilks’s Lambda = .885, F(4, 28) = 0.911, p = .471, between the healthy-weight children and children with obesity despite statistically significant differences in body fat percentage (BF%; healthy-weight children, 18.5 ± 6.1%; children with obesity, 41.1 ± 6.9%, p < .001) and aerobic capacity relative to body mass (VO2 peak; healthy-weight children, 46.8 ± 8.2 mL/kg/min; children with obesity, 31.9 ± 4.7 mL/kg/min, p < .001). There were statistically significant differences in VO2 recovery for the 5 min following exercise, Wilks’s Lambda = .676, F(4, 26) = 3.117, p = .032. There were no statistically significant correlations between HRRec and body mass index (BMI), BF%, VO2peak, or physical activity. Conclusions: In a healthy pediatric population, obesity alone does not seem to significantly impact HRRec, and because HRRec was not related to obesity status, BMI, or BF%, it should not be used as the sole indicator of aerobic capacity or health status in children. Using more than one recovery variable (i.e., HRRec and VO2 recovery) may provide greater insight into cardiorespiratory fitness in this population.

Oxygen delivery is not a limiting factor during post-exercise recovery in healthy young adults

PurposeIt is still equivocal whether oxygen uptake recovery kinetics are limited by oxygen delivery and can be improved by supplementary oxygen. The present study aimed to investigate whether measurements of muscle and pulmonary oxygen uptake kinetics can be used to assess oxygen delivery limitations in healthy subjects. MethodsSixteen healthy young adults performed three sub-maximal exercise tests (6 min at 40% Wmax) under hypoxic (14%O2), normoxic (21%O2) and hyperoxic (35%O2) conditions on separate days in randomized order. Both Pulmonary VO2 and near infra red spectroscopy (NIRS) based Tissue Saturation Index (TSI) offset kinetics were calculated using mono-exponential curve fitting models. ResultsTime constant τ of VO2 offset kinetics under hypoxic (44.9 ± 7.3s) conditions were significantly larger than τ of the offset kinetics under normoxia (37.9 ± 8.2s, p = 0.02) and hyperoxia (37±6s, p = 0.04). TSI mean response time (MRT) of the offset kinetics under hypoxic conditions (25.5 ± 13s) was significantly slower than under normoxic (15 ± 7.7, p = 0.007) and hyperoxic (13 ± 7.3, p = 0.008) conditions. ConclusionThe present study shows that there was no improvement in the oxygen uptake and muscle oxygenation recovery kinetics in healthy subjects under hyperoxic conditions.Slower TSI and VO2 recovery kinetics under hypoxic conditions indicate that both NIRS and spiro-ergometry are appropriate non-invasive measurement tools to assess the physiological response of a healthy individual to hypoxic exercise.