Recovery kinetics of oxygen uptake and heart rate in patients with coronary artery disease and heart failure

Respiratory gas kinetics in patients with congestive heart failure during recovery from peak exercise

BACKGROUND

Cardiopulmonary Exercise Testing (CPX) is essential for the assessment of exercise capacity for patients with Chronic Heart Failure (CHF). Respiratory gas and hemodynamic parameters such as Ventilatory Efficiency (VE/VCO2 slope), peak oxygen uptake (peak VO2), and heart rate recovery are established diagnostic and prognostic markers for clinical populations. Previous studies have suggested the clinical value of metrics related to respiratory gas collected during recovery from peak exercise, particularly recovery time to 50% (T1/2) of peak VO2. The current study explores these metrics in detail during recovery from peak exercise in CHF.

METHODS

Patients with CHF who were referred for CPX and healthy individuals without formal diagnoses were assessed for inclusion. All subjects performed CPX on cycle ergometers to volitional exhaustion and were monitored for at least five minutes of recovery. CPX data were analyzed for overshoot of respiratory exchange ratio (RER=VCO2/VO2), ventilatory equivalent for oxygen (VE/VO2), end-tidal partial pressure of oxygen (PETO2), and T1/2 of peak VO2 and VCO2.

RESULTS

Thirty-two patients with CHF and 30 controls were included. Peak VO2 differed significantly between patients and controls (13.5 ± 3.8 vs. 32.5 ± 9.8 mL/Kg*min-1, p < 0.001). Mean Left Ventricular Ejection Fraction (LVEF) was 35.9 ± 9.8% for patients with CHF compared to 61.1 ± 8.2% in the control group. The T1/2 of VO2, VCO2 and VE was significantly higher in patients (111.3 ± 51.0, 132.0 ± 38.8 and 155.6 ± 45.5s) than in controls (58.08 ± 13.2, 74.3 ± 21.1, 96.7 ± 36.8s; p < 0.001) while the overshoot of PETO2, VE/VO2 and RER was significantly lower in patients (7.2 ± 3.3, 41.9 ± 29.1 and 25.0 ± 13.6%) than in controls (10.1 ± 4.6, 62.1 ± 17.7 and 38.7 ± 15.1%; all p < 0.01). Most of the recovery metrics were significantly correlated with peak VO2 in CHF patients, but not with LVEF.

CONCLUSIONS

Patients with CHF have a significantly blunted recovery from peak exercise. This is reflected in delays of VO2, VCO2, VE, PETO2, RER and VE/VO2, reflecting a greater energy required to return to baseline. Abnormal respiratory gas kinetics in CHF was negatively correlated with peak VO2 but not baseline LVEF.

The potential benefits of assessing post-cardiopulmonary exercise testing (CPET) in aging: a narrative review

Cardiopulmonary exercise testing (CPET) is an important tool to measure the cardiopulmonary fitness of an individual and has been widely used in athletic, clinical and research settings. Most CPET focus on analyzing physiological responses during exercise. We contend that the post-CPET recovery physiological responses offer further diagnostic and prognostic information about the health of the cardiopulmonary and metabolic systems, especially when testing apparently healthy middle-aged and older adults. However, there are limited studies that investigate physiological responses during the post-CPET recovery, and even less so in middle-aged and older adults. Therefore, this current review is aimed at discussing the contribution of post-CPET recovery parameters to cardiopulmonary health and their potential applications in aging populations. In addition to the existing methods, we propose to examine the aerobic and anaerobic recovery threshold post-CPET as novel potential diagnostic and/or prognostic tools.

Comparison of V̇O2-Kinetic Parameters for the Management of Heart Failure

Objective: The aim of this study was to analyze whether V̇O₂-kinetics during cardiopulmonary exercise testing (CPET) is a useful marker for the diagnosis of heart failure (HF) and to determine which V̇O₂-kinetic parameter distinguishes healthy participants and patients with HF.

Methods: A total of 526 healthy participants and 79 patients with HF between 20 and 90 years of age performed a CPET. The CPET was preceded by a 3-min low-intensity warm-up and followed by a 3-min recovery bout. V̇O₂-kinetics was calculated from the rest to exercise transition of the warm-up bout (on-kinetics), from the exercise to recovery transition following ramp test termination (off-kinetics) and from the initial delay of V̇O₂ during the warm-up to ramp test transition (ramp-kinetics).

Results: V̇O₂ off-kinetics showed the highest z-score differences between healthy participants and patients with HF. Furthermore, off-kinetics was strongly associated with V̇O_2peak. In contrast, ramp-kinetics and on-kinetics showed only minimal z-score differences between healthy participants and patients with HF. The best on- and off-kinetic parameters significantly improved a model to predict the disease severity. However, there was no relevant additional value of V̇O₂-kinetics when V̇O_2peak was part of the model.

Conclusion: V̇O₂ off-kinetics appears to be superior for distinguishing patients with HF and healthy participants compared with V̇O₂ on-kinetics and ramp-kinetics. If V̇O_2peak cannot be determined, V̇O₂ off-kinetics provides an acceptable substitute. However, the additional value beyond that of V̇O_2peak cannot be provided by V̇O₂-kinetics.

Prognostic Value of NT-Pro Brain Natriuretic Peptide During Exercise Recovery in Ischemic Heart Failure of Reduced, Midrange, and Preserved Ejection Fraction

BACKGROUND

Ischemic heart disease is a leading cause of heart failure (HF), which continues to carry a high mortality despite considerable improvements in diagnosis and treatment. N-terminal-pro-B-type natriuretic peptide (NT-pro-BNP) measured at rest is a recognized diagnostic and prognostic marker of HF of reduced ejection fraction (HFrEF); however, its value in patients with HF of midranged/preserved ejection fraction (HFmrEF/HFpEF) is not well established. We examined the prognostic value of NT-pro-BNP during recovery from exercise in patients with ischemic HF (IHF) of any ejection fraction.

METHODS

Patients (n = 213) with HF (123 HFrEF, 90 HFmrEF/HFpEF) underwent cardiopulmonary exercise testing. Doppler echocardiography was used to estimate resting pulmonary artery systolic pressure (PASP) and tricuspid annular plane systolic excursion (TAPSE). NT-pro-BNP was determined at rest, peak exercise, and after 1 min of exercise recovery.

RESULTS

Patients with HFrEF had higher plasma levels of NT-pro-BNP at rest, peak exercise, and recovery than those with HFmrEF/HFpEF (984 ± 865 vs 780 ± 805; 1012 ± 956 vs 845 ± 895; 990 ± 1013 vs 808 ± 884 pg/mL; P < .01, respectively), whereas ΔNT-pro-BNP peak/rest and ΔNT-pro-BNP recovery/peak were similar (60 ± 100 vs 50 ± 96; -25 ± 38 vs -20 ± 41 pg/mL, P > .05). During the tracking period (22.4 ± 20.3 mo), 34 patients died, 2 underwent cardiac transplantation, and 3 had left ventricular assist device implantation. In a multivariate regression model, only NT-pro-BNP during exercise recovery and TAPSE/PASP were retained in the regression for the prediction of adverse events (χ2 = 11.4, P <.001).

CONCLUSIONS

NT-pro-BNP value during exercise recovery may be a robust predictor of adverse events in patients with IHF across a wide range of ejection fraction.

Stress hormones at rest and following exercise testing predict coronary artery disease severity and outcome

OBJECTIVES

Despite considerable knowledge regarding the importance of stress in coronary artery disease (CAD) pathogenesis, its underestimation persists in routine clinical practice, in part attributable to lack of a standardized, objective assessment. The current study examined the ability of stress hormones to predict CAD severity and prognosis at basal conditions as well as during and following an exertional stimulus.

MATERIALS AND METHODS

Forty Caucasian subjects with significant coronary artery lesions (≥50%) were included. Within 2 months of coronary angiography, cardiopulmonary exercise testing (CPET) on a recumbent ergometer was performed in conjunction with stress echocardiography (SE). At rest, peak and after 3 min of recovery following CPET, plasma levels of cortisol, adrenocorticotropic hormone (ACTH) and NT-pro-brain natriuretic peptide (NT-pro-BNP) were measured by immunoassay sandwich technique, radioimmunoassay, and radioimmunometric technique, respectively. Subjects were subsequently followed a mean of 32 ± 10 months.

RESULTS AND DISCUSSION

Mean ejection fraction was 56.7 ± 9.6%. Subjects with 1-2 stenotic coronary arteries (SCA) demonstrated a significantly lower plasma cortisol levels during CPET compared to those with 3-SCA (p < .05), whereas ACTH and NT-pro-BNP were not significantly different (p > .05). Among CPET, SE, and hormonal parameters, cortisol at rest and during CPET recovery demonstrated the best predictive value in distinguishing between 1-, 2-, and 3-SCA [area under ROC curve 0.75 and 0.77 (SE = 0.11, 0.10; p = .043, .04) for rest and recovery, respectively]. ΔCortisol peak/rest predicted cumulative cardiac events (area under ROC curve 0.75, SE = 0.10, p = .049).

CONCLUSIONS

Cortisol at rest and following an exercise test holds predictive value for CAD severity and prognosis, further demonstrating a link between stress and unwanted cardiac events.

Differential Responses of Post-Exercise Recovery of Leg Blood Flow and Oxygen Uptake Kinetics in HFpEF versus HFrEF

The goals of the current study were to compare leg blood flow, oxygen extraction and oxygen uptake (VO₂) after constant load sub-maximal unilateral knee extension (ULKE) exercise in patients with heart failure with reduced ejection fraction (HFrEF) compared to those with preserved ejection fraction (HFpEF). Previously, it has been shown that prolonged whole body VO₂ recovery kinetics are directly related to disease severity and all-cause mortality in HFrEF patients. To date, no study has simultaneously measured muscle-specific blood flow and oxygen extraction post exercise recovery kinetics in HFrEF or HFpEF patients; therefore it is unknown if muscle VO₂ recovery kinetics, and more specifically, the recovery kinetics of blood flow and oxygen extraction at the level of the muscle, differ between HF phenotypes. Ten older (68±10yrs) HFrEF (n = 5) and HFpEF (n = 5) patients performed sub-maximal (85% of maximal weight lifted during an incremental test) ULKE exercise for 4 minutes. Femoral venous blood flow and venous O₂ saturation were measured continuously from the onset of end-exercise, using a novel MRI method, to determine off-kinetics (mean response times, MRT) for leg VO₂ and its determinants. HFpEF and HFrEF patients had similar end-exercise leg blood flow (1.1±0.6 vs. 1.2±0.6 L/min, p>0.05), venous saturation (42±12 vs. 41±11%, p>0.05) and VO₂ (0.13±0.08 vs. 0.11±0.05 L/min, p>0.05); however HFrEF had significantly delayed recovery MRT for flow (292±135sec. vs 105±63sec., p = 0.004) and VO₂ (95±37sec. vs. 47±15sec., p = 0.005) compared to HFpEF. Impaired muscle VO₂ recovery kinetics following ULKE exercise differentiated HFrEF from HFpEF patients and suggests distinct underlying pathology and potential therapeutic approaches in these populations.

Impact of percutaneous pulmonary valve implantation for right ventricular outflow tract dysfunction on exercise recovery kinetics

The recovery of cardiopulmonary variables from peak exercise in patients with pulmonary stenosis (PS) or regurgitation (PR) is delayed, but the impact of treating PS or PR on exercise recovery kinetics is unknown. 43 patients (median age 14 years) with PS (n = 23) or PR (n = 20) after repair of congenital heart disease underwent successful percutaneous pulmonary valve implantation (PPVI). Cardiopulmonary exercise tests (CPET) were performed both before and within 1 month after PPVI. Apart from peak oxygen uptake (VO2), the constant decay of VO2, CO2 output (VCO2), minute ventilation (VE), and heart rate (HR) and oxygen pulse were calculated for the first minute of recovery as the first-degree slope of a single linear relation. PPVI led to a significant improvement in NYHA functional class in the PS and PR groups (p<0.001 and p=0.0015, respectively). On CPET, peak VO2 improved post-PPVI only in the PS (25.6 ± 6.2 vs. 27.8 ± 7.9 ml/kg/min; p = 0.01) but not PR group (29.0 ± 9.8 vs. 28.6 ± 8.9 ml/kg/min; p = 0.6). However, VO2 slope improved in the PS (0.40 ± 0.23 vs. 0.65 ± 0.27, p < 0.001) as well as in the PR group (0.56 ± 0.37 vs. 0.67 ± 0.37, p = 0.003) as did VCO2 slope (0.39 ± 0.2 vs. 0.55 ± 0.24, p = 0.002 and 0.42 ± 0.33 vs. 0.53 ± 0.35, p = 0.02: for the PS and PR groups, respectively). The VE and HR slopes did not change after PPVI. Despite the lack of improvement in exercise capacity in the PR group, treatment of PS and PR by PPVI induces significant and similar improvements in the ability of recovering from maximal exercise in the 2 groups.

Noninvasive measurement of cardiac performance in recovery from exercise in heart failure patients

OBJECTIVE

To examine the association between cardiac performance during recovery and the severity of heart failure, as determined by clinical and cardiopulmonary exercise test responses.

METHODS

As part of a retrospective cohort study, 46 heart failure patients and 13 normal subjects underwent cardiopulmonary exercise testing while cardiac output was measured using a noninvasive device. Cardiac output in recovery was expressed as the slope of a single exponential relationship between cardiac output and time; the recovery-time constant was assessed in relation to indices of cardiac function, along with clinical, functional, and cardiopulmonary exercise responses.

RESULTS

The recovery time constant was delayed in patients with heart failure compared with normal subjects (296.7 ± 238 vs. 110.1 ±27 seconds, p <0.01), and the slope of the decline of cardiac output in recovery was steeper in normal subjects compared with heart failure patients (p<0.001). The slope of the decline in cardiac output recovery was inversely related to peak VO(2) (r = -0.72, p<0.001) and directly related to the VE/VCO(2) slope (r = 0.57, p,0.001). Heart failure patients with abnormal recovery time constants had lower peak VO(2), lower VO(2) at the ventilatory threshold, lower peak cardiac output, and a heightened VE/VCO(2) slope during exercise.

CONCLUSIONS

Impaired cardiac output recovery kinetics can identify heart failure patients with more severe disease, lower exercise capacity, and inefficient ventilation. Estimating cardiac output in recovery from exercise may provide added insight into the cardiovascular status of patients with heart failure.

Oxygen uptake kinetics during exercise in adults with Down syndrome

Persons with Down syndrome (DS) have diminished submaximal and peak work capacity. This study evaluated the dynamic response of oxygen uptake at onset and recovery (VO(2) kinetics) of constant-load exercise (moderate intensity 45% VO(2peak)) in adults with DS. A total of 27 healthy participants aged 18-50 years performed graded treadmill exercise to assess peak VO(2): 14 with DS (9 males and 5 females) and 13 controls without disabilities (9 males and 4 females). Subjects also performed constant-load exercise tests at 45% VO(2peak) to determine VO(2) on-transient and VO(2) off-transient responses. Peak VO(2) was lower in participants with DS as compared to controls (DS 30.2 ± 7.1; controls 46.1 ± 9.6 mL kg(-1) min(-1), P < 0.05). In contrast, at 45% VO(2peak), the time constants for the VO(2) on-transients (DS 34.6 ± 9.1; controls 37.6 ± 9.0 s) and VO(2) off-transients (DS 36.5 ± 12.3; controls 37.7 ± 7.0 s) were not significantly different between the groups. Additionally, there were no differences between on-transient and off-transient time constants in participants with DS or controls. These data demonstrate that the VO(2) kinetics at onset and recovery of moderate intensity exercise is similar between adults with DS and controls. Therefore, the submaximal exercise performance of these individuals is not affected by slowed VO(2) kinetics.

Recovery kinetics of heart rate and oxygen uptake in long-term survivors of acute leukemia in childhood

Analysis of the recovery period following physical exercise has gained importance in evaluating cardiopulmonary capacity, not only in athletes but also in patients with proven or suspected heart failure. The purpose of this study was to apply these methods to long-term survivors of acute lymphoblastic leukemia (ALL) in childhood, who are at risk of developing anthracycline-induced cardiomyopathy. Nine children (mean age 12 years) and 10 adults (mean age 24 years) were included in the study after treatment for childhood ALL. Recovery of oxygen uptake and heart rate following maximal spiroergometric exercise was compared to that in 29 trained and untrained age-matched controls. The change in oxygen uptake (DeltaVO2) and heart rate (DeltaHR) between maximal effort and 60 s of recovery did not differ significantly, either between children after oncological therapy (DeltaVO2: 14.95 ml/kg, DeltaHR: 35 bpm) and healthy children (DeltaVO2: 15.85 ml/kg, DeltaHR: 37 bpm), or between adult former oncological patients (DeltaVO2: 13.1 ml/kg, DeltaHR: 27 bpm) and untrained adults (DeltaVO2: 15.7 ml/kg, DeltaHR: 31 bpm). There was, however, a significant difference in DeltaVO2 between trained adults (DeltaVO2: 24.5 ml/kg) and both untrained adult controls (DeltaVO2: 15.7 ml/kg, p=0.004) and adult patients (DeltaVO2: 13.1 ml/kg, p=0.0002). This difference was not detected for heart rate. In conclusion, the recovery period did not reveal a discernible difference in cardiopulmonary capacity between former ALL patients and untrained age-matched controls. We did confirm that heart rate and oxygen uptake recovery serve as indicators of physical fitness.

Reproducibility of onset and recovery oxygen uptake kinetics in moderately impaired patients with chronic heart failure

Oxygen (O₂) kinetics reflect the ability to adapt to or recover from exercise that is indicative of daily life. In patients with chronic heart failure (CHF), parameters of O₂ kinetics have shown to be useful for clinical purposes like grading of functional impairment and assessment of prognosis. This study compared the goodness of fit and reproducibility of previously described methods to assess O₂ kinetics in these patients. Nineteen CHF patients, New York Heart Association class II–III, performed two constant-load tests on a cycle ergometer at 50% of the maximum workload. Time constants of O₂ onset- and recovery kinetics (τ) were calculated by mono-exponential modeling with four different sampling intervals (5 and 10 s, 5 and 8 breaths). The goodness of fit was expressed as the coefficient of determination (R²). Onset kinetics were also evaluated by the mean response time (MRT). Considering O₂ onset kinetics, τ showed a significant inverse correlation with peak- \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{2} $$\end{document} (R = −0.88, using 10 s sampling intervals). The limits of agreement of both τ and MRT, however, were not clinically acceptable. O₂ recovery kinetics yielded better reproducibility and goodness of fit. Using the most optimal sampling interval (5 breaths), a change of at least 13 s in τ is needed to exceed normal test-to-test variations. In conclusion, O₂ recovery kinetics are more reproducible for clinical purposes than O₂ onset kinetics in moderately impaired patients with CHF. It should be recognized that this observation cannot be assumed to be generalizable to more severely impaired CHF patients.

Impact of pulmonary regurgitation and right ventricular dysfunction on oxygen uptake recovery kinetics in repaired tetralogy of Fallot

BACKGROUND

Patients with repaired tetralogy of Fallot (ToF) featuring severe pulmonary regurgitation (PR) and/or right ventricular (RV) dysfunction have reduced exercise tolerance.

AIMS

To assess the impact of PR and of RV function on the ability to recover from exercise in ToF patients.

METHODS

61 consecutive patients aged 23.1+/-12.1 years underwent maximal cardiopulmonary exercise test (CPX), transthoracic echocardiography and magnetic resonance imaging. This data was compared to those of 153 matched healthy subjects.

RESULTS

19 patients (31%) had severe PR. RV dysfunction was noted in 19 patients (31%). Nine patients (15%) had both severe PR and RV dysfunction. Patients had lower peak oxygen uptake (VO2), VO2 slope, carbon dioxide production (VCO2) slope and O2 pulse slope (p < 0.0001), especially those with severe PR and RV dysfunction (p < 0.0001). Heart rate slope was similar between groups. No patient with severe PR and RV dysfunction had a predicted peak VO2 > 40%. CPX had a high sensitivity and specificity to identify patients with severe PR and RV dysfunction.

CONCLUSIONS

In ToF patients, severe PR and RV dysfunction lead to delayed recovery from exercise. CPX can identify patients with severe PR and RV dysfunction and may be useful to guide the pulmonary valve replacement decision-making process.

Postexercise VO2 “Hump” phenomenon as an indicator for inducible myocardial ischemia in patients with acute anterior myocardial infarction

OBJECTIVES

At exercise testing with respiratory gas analysis in patients with inducible myocardial ischemia, we have occasionally observed abnormal transient oxygen uptake (VO2) components with a characteristic "Hump"-shaped morphology early after exercise, which may serve as an index for inducible ischemia. We examined this hypothesis in patients with anterior q-wave myocardial infarction in whom the accuracy to identify ischemia by exercise ECG is limited.

DESIGN

From patients with acute anterior q-wave infarction but without clinically overt heart failure who underwent pre-discharge exercise testing, we examined patients with (Group-I, n = 30) and without (Group-N, n = 29) inducible ischemia. To identify "Hump", postexercise VO2 (up to 4 min) standardized for peak VO2 was exponentially fitted with use of peak VO2 and VO2 of 90-240 s, yielding "expected VO2". "D-curve" was obtained by subtracting "expected VO2" from measured VO2.

RESULTS

Although exercise-induced ST depressions more frequently appeared in Group-I (27%) than in Group-N (3%, p < 0.05), the prevalence was low. D-curve peaked later (p < 0.01) and its value was greater (p < 0.05) in Group-I than in Group-N. When "Hump" was defined to be present if D-curve peaked > or =40 s and its peak value > or =15%, it was far more frequently found in Group-I (n = 17/30) than in Group-N (n = 1/29, p < 0.01). Thus, "Hump" could diagnose inducible ischemia with a sensitivity of 57% and a specificity of 97%.

CONCLUSIONS

Although not highly sensitive, postexercise VO2 "Hump" with its peak occurring around 60 s after exercise is a specific marker for inducible ischemia. The identification may be useful, particularly in patients with limited accuracy of exercise ECG such as those with q-wave anterior infarction.

Autonomic nervous system interaction with the cardiovascular system during exercise

There is considerable recent evidence that parameters thought to reflect the complex interaction between the autonomic nervous system and the cardiovascular system during exercise testing can provide significant prognostic information. Specific variables of great importance include heart rate (HR) response to exercise (reserve), HR recovery after exercise, and multiple components of HR variability both at rest and with exercise. Poor HR response to exercise has been strongly associated with sudden cardiac death and HR recovery from a standard exercise test has been shown to be predictive of mortality. In addition, there are limited studies evaluating the components of HR variability at rest and during exercise and their prognostic significance. Research continues seeking to refine these exercise measurements and further define their prognostic value. Future findings should augment the power of the exercise test in risk-stratifying cardiovascular patients.

Recovery kinetics of oxygen uptake is abnormally prolonged in patients with Mustard/Senning repair for transposition of the great arteries

The aim of this study was to evaluate the ability to recover from exercise in patients with a Mustard/Senning (M/S) repair for transposition of the great arteries and to identify the major determinants. A total of 40 consecutive patients with a M/S repair at a mean age of 10.0 +/- 9.8 months underwent maximal cardiopulmonary exercise testing at 19.5 +/- 11.3 years of age. Results were compared to those of a cohort of 153 healthy individuals. Decay of oxygen uptake (VO2), CO2 (VCO2), minute ventilation (VE), heart rate (HR) was calculated for the first minute of recovery. M/S patients had reduced peak VO2(22.9 +/- 7.2 vs 34.2 +/- 9.5 ml O2/kg/min, p < 0.0001) and VO2 slope (0.27 +/- 0.10 vs 0.47 +/- 0.2 L O2/min, p < 0.0001), Peak O2 pulse (p < 0.0001) and peak HR (p = 0.001) were reduced. VCO2 and VE slopes were reduced (p < 0.0001 for both), whereas HR slope was similar (p = 0.38). In M/S patients, the only independent determinants of VO2 slope during recovery were pulse O2 slope (p < 0.0001) and VCO2 slope (p < 0.0001). In M/S patients, a limited cardiopulmonary reserve affects not only maximal exercise responses but also the recovery phase. A prolonged recovery of O2 pulse and a prolonged CO2 retention with subsequent prolonged hyperpnea are the main determinants of the delayed recovery.

Recovery kinetics of oxygen uptake is prolonged in adults with an atrial septal defect and improves after transcatheter closure

BACKGROUND

In adults with an atrial septal defect (ASD) transcatheter closure leads to an improvement of peak oxygen uptake (VO2), but the kinetics of recovery of VO2 after maximal exercise in this patient population and the impact of transcatheter ASD closure have never been investigated.

METHODS

Twenty consecutive patients underwent a maximal cardiopulmonary exercise test both the day before and 6 months after transcatheter ASD closure. For comparison, an age- and sex-matched group consisting of 53 healthy adults was built. The constant decay of VO2, CO2 production (VCO2), minute ventilation (VE), and heart rate (HR), expressed as the first-degree slope of a single linear relation, were calculated for the first minute of recovery.

RESULTS

Patients with an ASD had a prolonged VO2 slope (P =.0012), VCO2 slope (P =.0003), and VE slope (0.013) when compared with control subjects. Six months after transcatheter ASD closure, significant improvements of VO2 slope (P =.0043) and of VCO2 slope (P =.0022) were recorded, so that no difference was found when compared with those of the control group (P =.1 and P =.06, respectively). The VE slope and HR slope did not change after closure. A significant association between VO2 slope and peak VO2 in the group of patients with ASD was shown by the Spearman correlation, both before (r = 0.67, P =.0012) and after ASD closure (r = 0.71, P =.0004).

CONCLUSIONS

A limited cardiopulmonary reserve in adults with no symptom who have an ASD appears to affect not only maximal exercise responses but also the recovery phase. Transcatheter ASD closure induces a significant improvement of the ability of recovering from maximal exercise and eliminates the difference with a healthy population.

Oxygen cost of exercise is increased in heart failure after accounting for recovery costs

STUDY OBJECTIVES

The oxygen cost during exercise has been reported to be decreased in patients with congestive heart failure (CHF), implying an increased efficiency (lower oxygen uptake [VO(2)] per Watt [VO(2)/W]); however, these studies ignored the oxygen debt that is increased in heart failure.

SUBJECTS

The primary aim of this research was to evaluate the total oxygen cost (work VO(2)/W) during exercise and recovery in patients with heart failure as compared with healthy adults.

DESIGN AND PATIENTS

We performed a retrospective analysis comparing the exercise VO(2)/W, the recovery VO(2)/W, the work VO(2)/W, and the VO(2)/W relationship above and below the ventilatory threshold (VT) in 11 healthy control subjects and 45 patients with CHF.

RESULTS

The exercise VO(2)/W was decreased by 29% (p < 0.0001) in patients with CHF; however, the recovery VO(2)/W was increased by 167% (p < 0.0001) and the work VO(2)/W was increased by 14% in patients with CHF (p = 0.014). The VO(2)/W slope increased above the VT (+ 27%, p = 0.0017) in both normal subjects and patients with CHF, suggesting a decrease in efficiency above the VT. There was an inverse correlation (r = 0.646, p < 0.0001) between exercise VO(2)/W and recovery VO(2)/W, implying that subjects with a low exercise VO(2)/W were not efficient but rather accumulated a large oxygen debt that was repaid following completion of exercise.

CONCLUSIONS

Heart failure is associated with lower exercise VO(2)/W; however, the patient with heart failure is not efficient, but rather accumulating a large oxygen debt (recovery VO(2)/W) that is repaid following exercise. In addition, the work VO(2)/W (including both exercise and recovery) is increased in patients with heart failure in comparison to control subjects, and correlates inversely with the percentage of predicted VO(2). The large recovery VO(2)/W is likely due to impaired oxygen delivery to exercising muscle during exercise. The increase in the work VO(2)/W is probably due to changes in skeletal muscle fiber type that occur in patients with heart failure (type I to type IIb).

Early recovery of oxygen kinetics after submaximal exercise test predicts functional capacity in patients with chronic heart failure

BACKGROUND

Oxygen (O2) uptake at peak exercise (VO2 peak) is an objective measurement of functional capacity in patients with chronic heart failure (CHF). The significance of recovery O2 kinetics parameters in predicting exercise capacity, and the parameters of submaximal exercise testing have not been thoroughly examined.

METHODS AND RESULTS

Thirty-six patients (mean age = 48+/-14 years) with CHF and New York Heart Association functional class I, II, or III, and eight healthy volunteers (mean age = 39+/-13 years) were studied with maximal and submaximal cardiopulmonary exercise testing (CPET). The first degree slope of O2 uptake decay during early recovery from maximal (VO2/t-slope), and submaximal exercise (VO2/t-slope)(sub), were calculated, along with VO2 half-time (T(1/2)VO2). Patients with CHF had a longer recovery of O2 uptake after exercise than healthy volunteers, expressed by a lower VO2/t-slope (0.616+/-0.317 vs. 0.956+/-0.347 l min(-1) min(-1), P=0.029) and greater T(1/2)VO2 (1.28+/-0.30 vs. 1.05+/-0.15 min, P = 0.005). VO2/t-slope correlated with the VO2 peak (r = 0.84, P<0.001), anaerobic threshold (r = 0.79, P<0.001), and T(1/2)VO2, a previously established estimate of recovery O2 kinetics (r = -0.59, P<0.001). (VO2/t-slope)(sub) was highly correlated with VO2/t-slope after maximal exercise (r=0.87, P<0.001), with the VO2 peak (r=0.87, P<0.001) and with T(1/2)VO2 after maximal exercise (r=-0.62, P<0.001). VO2/t-slope after maximal and submaximal exercise was reduced in patients with severe exercise intolerance (F=9.3, P<0.001 and F=12.8, P<0.001, respectively).

CONCLUSIONS

Early recovery O2 kinetics parameters after maximal and submaximal exercise correlate closely with established indices of exercise capacity in patients with CHF and in healthy volunteers. These findings support the use of early recovery O2 kinetics after submaximal exercise testing as an index of functional capacity in patients with CHF.

Effect of exercise training on postexercise oxygen uptake kinetics in patients with reduced ventricular function

BACKGROUND

The time required for oxygen uptake (O(2)) to return to baseline level (recovery kinetics) is prolonged in patients with reduced ventricular function, and the degree to which it is prolonged is related to the severity of heart failure, markers of abnormal ventilation, and prognosis. In the present study, we sought to determine the effect of exercise training on O(2) recovery kinetics in patients with reduced ventricular function.

METHODS

Twenty-four male patients with reduced ventricular function after a myocardial infarction were randomized to either a 2-month high-intensity residential exercise training program or to a control group. O(2) kinetics in recovery from maximal exercise were calculated before and after the study period and expressed as the slope of a single exponential relation between O(2) and time during the first 3 min of recovery.

RESULTS

Peak O(2) increased significantly in the exercise group (19.4 +/- 3.0 mL/kg/min vs 25.1 +/- 4.7 mL/kg/min, p < 0.05), whereas no change was observed in control subjects. The O(2) half-time in recovery was reduced slightly after the study period in both groups (108.7 +/- 33.1 to 102.1 +/- 50.5 s in the exercise group and 122.3 +/- 68.7 to 107.5 +/- 36.0 s in the control group); neither the change within or between groups was significant. The degree to which O(2) was prolonged in recovery was inversely related to measures of exercise capacity (peak O(2), watts achieved, and exercise time; r = - 0.48 to - 0.57; p < 0.01) and directly related to the peak ventilatory equivalents for oxygen (r = 0.59, p < 0.01) and carbon dioxide (r = 0.57, p < 0.01).

CONCLUSION

Two months of high-intensity training did not result in a faster recovery of O(2) in patients with reduced ventricular function. This suggests that adaptations to exercise training manifest themselves only during, but not in, recovery from exercise.

Exercise and autonomic function in health and cardiovascular disease

Autonomic nervous system activity contributes to the regulation of cardiac output during rest, exercise, and cardiovascular disease. Measurement of HRV has been particularly useful in assessing parasympathetic activity, while its utility for assessing sympathetic function and overall sympathovagal balance remains controversial. Studies have revealed that parasympathetic tone dominates the resting state, while exercise is associated with prompt withdrawal of vagal tone and subsequent sympathetic activation. Conversely, recovery is characterized by parasympathetic activation followed by sympathetic withdrawal, although clarification of the normal trajectory and autonomic basis of heart rate decay following exercise is needed. Abnormalities in autonomic physiology--especially increased sympathetic activity, attenuated vagal tone, and delayed heart rate recovery--have been associated with increased mortality. Exercise training is associated with a relative enhancement of vagal tone, improved heart rate recovery after exercise, and reduced morbidity in patients with cardiovascular disease. However, whether exercise training leads to reduced mortality in this population because of its ability to specifically modulate autonomic function is unknown at the present time. Although the results of a recent randomized study in patients with CHF and a meta-analysis in the setting of a recent myocardial infarction determined that exercise training leads to improved outcomes in these populations, neither study measured autonomic function. Improved autonomic function due to exercise training is a promising rationale for explaining improvements in outcome, although more research is needed to confirm this hypothesis.