Attenuation of hypercapnic carbon dioxide chemosensitivity after postinfarction exercise training: possible contribution to the improvement in exercise hyperventilation

Abnormal Sleep-Related Breathing Related to Heart Failure

Sleep-disordered breathing (SDB) is highly prevalent in patients with heart failure (HF). Untreated obstructive sleep apnea (OSA) and central sleep apnea (CSA) in patients with HF are associated with worse outcomes. Detailed sleep history along with polysomnography (PSG) should be conducted if SDB is suspected in patients with HF. First line of treatment is the optimization of medical therapy for HF and if symptoms persist despite optimization of the treatment, positive airway pressure (PAP) therapy will be started to treat SDB. At present, there is limited evidence to prescribe any drugs for treating CSA in patients with HF. There is limited evidence for the efficacy of continuous positive airway pressure (CPAP) or adaptive servo-ventilation (ASV) in improving mortality in patients with heart failure with reduced ejection fraction (HFrEF). There is a need to perform well-designed studies to identify different phenotypes of CSA/OSA in patients with HF and to determine which phenotype responds to which therapy. Results of ongoing trials, ADVENT-HF, and LOFT-HF are eagerly awaited to shed more light on the management of CSA in patients with HF. Until then the management of SDB in patients with HF is limited due to the lack of evidence and guidance for treating SDB in patients with HF.

Acute Cardiorespiratory Responses to Different Exercise Modalities in Chronic Heart Failure Patients-A Pilot Study

The purpose of this study was to compare the acute cardiorespiratory responses and time spent above different %VO_2peak intensities between three "iso-work" protocols: (a) a high intensity interval training protocol (HIIT), (b) a higher intensity continuous protocol (CON₇₀) and (c) a lower intensity continuous protocol (CON₅₀) in patients with chronic heart failure (CHF). Ten male CHF patients (aged 55.1 ± 16.2 years) performed in separate days a single session of a HIIT protocol consisted of 4 sets × 4 min cycling at 80% VO_2peak with 3 min of recovery at 50% VO_2peak, a CON₇₀ protocol corresponding to 70% VO_2peak and a CON₅₀ protocol corresponding to 50% VO_2peak. Cardiopulmonary data were collected by an online gas analysis system. The HIIT and CON₇₀ elicited higher cardiorespiratory responses compared to CON₅₀ with no differences between them (p > 0.05). In HIIT and CON₇₀, patients exercised longer at >80% and >90% VO_2peak. The completion rate was 100% for the three protocols. Not any adverse events were observed in either protocol. Both HIIT and CON₇₀ elicited a stronger physiological stimulus and required shorter time than CON₅₀. Both HIIT and CON₇₀ also induced comparable hemodynamic responses and ventilatory demand.

Participation in physical activity is associated with reduced nocturnal hypoxaemia in males

Moderate to vigorous physical activity (MVPA) interventions reduce the severity of obstructive sleep apnoea (OSA); however, little epidemiological research exists to confirm these findings.

789 participants from the population-based Men Androgen Inflammation Lifestyle Environment and Stress (MAILES) Study underwent polysomnography. MVPA was assessed using the Active Australia questionnaire, which was completed when participants were first recruited to the MAILES study (2002–2006), and again in 2010. Multinomial logistic regressions established odds ratio between OSA severity categories with MVPA, whilst adjusted linear models determined associations between OSA metrics with MVPA.

Cross-sectionally, each hour of MVPA was associated with reduced severity of mean oxygen desaturation (unstandardised β (B)=−0.002, p=0.043) and reduced time below 90% oxygen saturation (B=−0.03, p=0.034).

Longitudinally, each hour increase in MVPA was associated with a 4% reduction in the odds of severe OSA and less severe mean oxygen desaturation (B=−0.003, p=0.014), time below 90% oxygen saturation (B=−0.02, p=0.02), and mean duration of apnoeas (B=−0.004, p=0.016).

MVPA is associated with reduced hypoxaemia in a cohort of community dwelling males, approximately half of whom had untreated OSA. As nocturnal intermittent hypoxaemia is associated with cardiometabolic disorders, MVPA may offer protection for patients with OSA.

This study provides epidemiological evidence that moderate to vigorous physical activity is associated with less severe OSA-induced hypoxaemia. This result suggests that MVPA should be actively implemented in treatment regimens for people with OSA.https://bit.ly/3a9asiZ

Mitigation of Exercise Oscillatory Ventilation Score by Cardiac Resynchronization Therapy

BACKGROUND

Exercise oscillatory ventilation (EOV) is a consequence of ventilatory control system instability and is commonly observed in patients with advanced heart failure (HF); it is associated with adverse prognosis. The goal of this study was to evaluate the effects of cardiac resynchronization therapy (CRT) on oscillatory ventilation as quantified by a proposed EOV score.

METHODS AND RESULTS

Consecutive patients with HF (N = 35) who underwent clinically indicated CRT, cardiopulmonary exercise testing and carbon dioxide (CO₂) chemosensitivity by rebreathe before and 4-6 months after CRT were included in this post hoc analysis. With CRT, EOV scores improved in 22 patients (63%). In these patients, left ventricular ejection fraction, left atrial volume, brain natriuretic peptide concentration, and CO₂ chemosensitivity significantly improved after CRT (P < 0.05). Furthermore, minute ventilation per unit CO₂ production significantly decreased, and end-tidal CO₂ increased at rest and at peak exercise post-CRT. Multiple regression analysis showed only the change of CO₂ chemosensitivity to be significantly associated with the improvement of the EOV score (b = 0.64; F = 11.3; P = 0.004). In the group without EOV score improvement (n = 13), though left ventricular ejection fraction significantly increased with CRT (P = 0.015), no significant changes in ventilation or gas exchange were observed.

CONCLUSION

The EOV score was mitigated by CRT and was associated with decreased CO₂ chemosensitivity.

Apneas of Heart Failure and Phenotype-Guided Treatments: Part One: OSA

Sleep-disordered breathing (SDB), including OSA and central sleep apnea, is highly prevalent in patients with heart failure (HF). Multiple studies have reported this high prevalence in asymptomatic as well as symptomatic patients with reduced left ventricular ejection fraction (HFrEF), as well as in those with HF with preserved ejection fraction. The acute pathobiologic consequences of OSA, including exaggerated sympathetic activity, oxidative stress, and inflammation, eventually could lead to progressive left ventricular dysfunction, repeated hospitalization, and excessive mortality. Large numbers of observational studies and a few small randomized controlled trials have shown improvement in various cardiovascular consequences of SDB with treatment. There are no long-term randomized controlled trials to show improved survival of patients with HF and treatment of OSA. One trial of positive airway pressure treatment of OSA included patients with HF and showed no improvement in clinical outcomes. However, any conclusions derived from this trial must take into account several important pitfalls that have been extensively discussed in the literature. With the role of positive airway pressure as the sole therapy for SDB in HF increasingly questioned, a critical examination of long-accepted concepts in this field is needed. The objective of this review was to incorporate recent advances in the field into a phenotype-based approach to the management of OSA in HF.

Effect of exercise training on ventilatory efficiency in patients with heart disease: a review

The analysis of ventilatory efficiency in cardiopulmonary exercise testing has proven useful for assessing the presence and severity of cardiorespiratory diseases. During exercise, efficient pulmonary gas exchange is characterized by uniform matching of lung ventilation with perfusion. By contrast, mismatching is marked by inefficient pulmonary gas exchange, requiring increased ventilation for a given CO2 production. The etiology of increased and inefficient ventilatory response to exercise in heart disease is multifactorial, involving both peripheral and central mechanisms. Exercise training has been recommended as non-pharmacological treatment for patients with different chronic cardiopulmonary diseases. In this respect, previous studies have reported improvements in ventilatory efficiency after aerobic exercise training in patients with heart disease. Against this background, the primary objective of the present review was to discuss the pathophysiological mechanisms involved in abnormal ventilatory response to exercise, with an emphasis on both patients with heart failure syndrome and coronary artery disease. Secondly, special focus was dedicated to the role of aerobic exercise training in improving indices of ventilatory efficiency among these patients, as well as to the underlying mechanisms involved.

Heart failure and sleep disorders

Awareness of the importance of sleep-related disorders in patients with cardiovascular diseases is growing. In particular, sleep-disordered breathing, short sleep time, and low sleep quality are frequently reported by patients with heart failure (HF). Sleep-disordered breathing, which includes obstructive sleep apnoea (OSA) and central sleep apnoea (CSA), is common in patients with HF and has been suggested to increase the morbidity and mortality in these patients. Both OSA and CSA are associated with increased sympathetic activation, vagal withdrawal, altered haemodynamic loading conditions, and hypoxaemia. Moreover, OSA is strongly associated with arterial hypertension, the most common risk factor for cardiac hypertrophy and failure. Intrathoracic pressure changes are also associated with OSA, contributing to haemodynamic alterations and potentially affecting overexpression of genes involved in ventricular remodelling. HF treatment can decrease the severity of both OSA and CSA. Indeed, furosemide and spironolactone administration, exercise training, cardiac resynchronization therapy, and eventually heart transplantation have shown a positive effect on OSA and CSA in patients with HF. At present, whether CSA should be treated and, if so, which is the optimal therapy is still debated. By contrast, more evidence is available on the beneficial effects of OSA treatment in patients with HF.

Effects of continuous vs interval exercise training on oxygen uptake efficiency slope in patients with coronary artery disease

The oxygen uptake efficiency slope (OUES) is a submaximal index incorporating cardiovascular, peripheral, and pulmonary factors that determine the ventilatory response to exercise. The purpose of this study was to evaluate the effects of continuous exercise training and interval exercise training on the OUES in patients with coronary artery disease. Thirty-five patients (59.3±1.8 years old; 28 men, 7 women) with coronary artery disease were randomly divided into two groups: continuous exercise training (n=18) and interval exercise training (n=17). All patients performed graded exercise tests with respiratory gas analysis before and 3 months after the exercise-training program to determine ventilatory anaerobic threshold (VAT), respiratory compensation point, and peak oxygen consumption (peak VO₂). The OUES was assessed based on data from the second minute of exercise until exhaustion by calculating the slope of the linear relation between oxygen uptake and the logarithm of total ventilation. After the interventions, both groups showed increased aerobic fitness (P<0.05). In addition, both the continuous exercise and interval exercise training groups demonstrated an increase in OUES (P<0.05). Significant associations were observed in both groups: 1) continuous exercise training (OUES and peak VO₂ r=0.57; OUES and VO₂ VAT r=0.57); 2) interval exercise training (OUES and peak VO₂ r=0.80; OUES and VO₂ VAT r=0.67). Continuous and interval exercise training resulted in a similar increase in OUES among patients with coronary artery disease. These findings suggest that improvements in OUES among CAD patients after aerobic exercise training may be dependent on peripheral and central mechanisms.

Effect of a cardiac rehabilitation program on exercise oscillatory ventilation in Japanese patients with heart failure

Although exercise oscillatory ventilation has emerged as a potent independent risk factor for adverse prognosis in heart failure, it is not well known whether cardiac rehabilitation can improve oscillatory ventilation. In this study, we investigated the magnitude of oscillations in ventilation before and after cardiac rehabilitation in chronic heart failure patients with exercise oscillatory ventilation. Cardiac rehabilitation (5-month program) was performed in 26 patients with chronic heart failure who showed an oscillatory ventilation pattern during cardiopulmonary exercise testing (CPX). After the 5-month rehabilitation program was completed, the patients again underwent CPX. To determine the magnitude of oscillations in ventilation, the amplitude and cycle length of the oscillations were calculated and compared with several other parameters, including biomarkers that have established prognostic value in heart failure. At baseline before cardiac rehabilitation, both oscillation amplitude (R = 0.625, P < 0.01) and cycle length (R = 0.469, P < 0.05) were positively correlated with the slope of minute ventilation vs. carbon dioxide production. Plasma BNP levels were positively correlated with amplitude (R = 0.615, P < 0.01) but not cycle length (R = 0.371). Cardiac rehabilitation decreased oscillation amplitude (P < 0.01) but failed to change cycle length. The change in amplitude was positively correlated with the change in BNP levels (R = 0.760, P < 0.01). Multiple regression analysis showed that only the change in amplitude was an independent predictor of the change in BNP levels (R = 0.717, P < 0.01). A 5-month cardiac rehabilitation program improves exercise oscillatory ventilation in chronic heart failure patients by reducing the oscillation amplitude. This effect is associated with a reduction of plasma BNP levels, potentially contributing to an improvement of heart failure.

The influence of aerobic fitness status on ventilatory efficiency in patients with coronary artery disease

OBJECTIVE

To test the hypotheses that 1) coronary artery disease patients with lower aerobic fitness exhibit a lower ventilatory efficiency and 2) coronary artery disease patients with lower initial aerobic fitness exhibit greater improvements in ventilatory efficiency with aerobic exercise training.

METHOD

A total of 123 patients (61.0±0.7 years) with coronary artery disease were divided according to aerobic fitness status into 3 groups: group 1 (n = 34, peak VO₂<17.5 ml/kg/min), group 2 (n = 67, peak VO₂>17.5 and <24.5 ml/kg/min) and group 3 (n = 22, peak VO₂>24.5 ml/kg/min). All patients performed a cardiorespiratory exercise test on a treadmill. Ventilatory efficiency was determined by the lowest VE/VCO₂ ratio observed. The exercise training program comprised moderate-intensity aerobic exercise performed 3 times per week for 3 months. Clinicaltrials.gov: NCT02106533 RESULTS: Before intervention, group 1 exhibited both lower peak VO2 and lower ventilatory efficiency compared with the other 2 groups (p<0.05). After the exercise training program, group 1 exhibited greater improvements in aerobic fitness and ventilatory efficiency compared with the 2 other groups (group 1: ▵ = -2.5±0.5 units; group 2: ▵ = -0.8±0.3 units; and group 3: ▵ = -1.4±0.6 units, respectively; p<0.05).

CONCLUSIONS

Coronary artery disease patients with lower aerobic fitness status exhibited lower ventilatory efficiency during a graded exercise test. In addition, after 3 months of aerobic exercise training, only the patients with initially lower levels of aerobic fitness exhibited greater improvements in ventilatory efficiency.

Activation of the ergoreceptors in cardiac patients with and without heart failure

BACKGROUND

The presence of ergoreflex activity and its current relationship to hyperventilation and prognosis in cardiac patients is unclear. Therefore, we evaluated ergoreflex activity in cardiac patients with and without heart failure (CHF) as well as in healthy subjects, and we examined how ergoreceptor activity was related to a mortality risk score in CHF (MAGGIC).

METHODS AND RESULTS

Twenty-five healthy subjects and 76 patients were included, among whom were 25 with ischemic heart disease (IHD), 24 with stable CHF, and 27 with unstable CHF. Ergoreflex activity was measured with a dynamic handgrip exercise, followed by post-handgrip regional circulatory occlusion (PH-RCO). Ergoreflex activity contributed significantly to ventilation (median [interquartile range] %V) in unstable CHF (81 [73-91] %V without PH-RCO, 92 [82-107] %V with PH-RCO, and 11 [6-20] difference in %V; P < .001) and was positively correlated with the MAGGIC risk score (Spearman ρ = 0.431; P = .002). No ergoreflex activity was observed in healthy subjects (-4 [-10 to 5] difference in %V), IHD (0 [-8 to 3] Diff in %V) and stable CHF (-3 [-11 to 6] difference in %V).

CONCLUSIONS

Ergoreflex activity contributes to hyperventilation, but only in CHF patients with persistent symptoms, and is closely related to the MAGGIC risk score. Ergoreflex activity was not present in patients with IHD or stable CHF, suggesting other reasons for the increased ventilatory drive in those patients.

Effects of positive airway pressure therapy on exercise parameters in obstructive sleep apnea

BACKGROUND AND OBJECTIVES

Obstructive sleep apnea (OSA) is common in adult population and may cause many adverse clinical results. We aimed to investigate possible changes in cardiopulmonary exercise capacity in OSA patients after positive airway pressure treatment.

DESIGN AND SETTINGS

Patients who were admitted to Gaziantep University Pulmonary Diseases Sleep Center and diagnosed OSA were included. Studies carried out between May 2010 and July 2011. Sixty-five consecutive patients were included in this prospective study.

PATIENTS AND METHODS

Sixty-five adult sleep clinic patients diagnosed with OSA by polysomnography and in whom continuous positive airway pressure (CPAP) ventilation therapy was indicated were included. Cardiopulmonary exercise capacity was assessed by bicycle ergometry during diagnostic workup and at least 4 weeks later.

RESULTS

There were 57 (87.7%) males. The mean age was 45.29 (10.57) years, apnea-hypopnea index 38.02 (23.19 events/h, body mass index 31.72 (4.87) kg/m2. Patients were grouped with respect to compliance with CPAP. The peak oxygen consumption (VO2) did not change in the CPAP compliant group (n=33) (22.52 [6.62] mL/[min.kg] to 21.32 [5.26] mL/[min.kg]; P=.111), and decreased from 21.31 (5.66) mL/(min.kg) to 19.92 (5.40) mL/(min.kg) (P=.05) in the CPAP noncompliant group. Work rate increased from 84.0% to 85.0% in the CPAP compliant group and decreased from 79.6% to 77.1% in the noncompliant group (P=.041). In the group that used the device, ventilation (VE)/VCO2 at anaerobic threshold (AT) declined from 28.42 to 27.36; however, it increased from 27.41 to 27.81 in the group that did not use the device (P=.033).

CONCLUSIONS

Decline in the exercise capacity was prevented in patients with OSA after 4 weeks of CPAP therapy. The changes in VE/VCO2 at AT suggest the reversal of pathophysiologic changes in OSA with the CPAP therapy that may improve cardiac function and cause more efficient ventilation.

Abnormalities of the ventilatory equivalent for carbon dioxide in patients with chronic heart failure

Introduction. The relation between minute ventilation (VE) and carbon dioxide production (VCO₂) can be characterised by the instantaneous ratio of ventilation to carbon dioxide production, the ventilatory equivalent for CO₂ (VEqCO₂). We hypothesised that the time taken to achieve the lowest VEqCO₂ (time to VEqCO2 nadir) may be a prognostic marker in patients with chronic heart failure (CHF). Methods. Patients and healthy controls underwent a symptom-limited, cardiopulmonary exercise test (CPET) on a treadmill to volitional exhaustion. Results. 423 patients with CHF (mean age 63 ± 12 years; 80% males) and 78 healthy controls (62% males; age 61 ± 11 years) were recruited. Time to VEqCO2 nadir was shorter in patients than controls (327 ± 204 s versus 514 ± 187 s; P = 0.0001). Univariable predictors of all-cause mortality included peak oxygen uptake (X² = 53.0), VEqCO₂ nadir (X² = 47.9), and time to VEqCO₂ nadir (X² = 24.0). In an adjusted Cox multivariable proportional hazards model, peak oxygen uptake (X² = 16.7) and VEqCO₂ nadir (X² = 17.9) were the most significant independent predictors of all-cause mortality. Conclusion. The time to VEqCO₂ nadir was shorter in patients with CHF than in normal subjects and was a predictor of subsequent mortality.

Effect of continuous and interval exercise training on the PETCO2 response during a graded exercise test in patients with coronary artery disease

OBJECTIVE

The purpose of this study was to evaluate the following: 1) the effects of continuous exercise training and interval exercise training on the end-tidal carbon dioxide pressure (PETCO2) response during a graded exercise test in patients with coronary artery disease; and 2) the effects of exercise training modalities on the association between PETCO2 at the ventilatory anaerobic threshold (VAT) and indicators of ventilatory efficiency and cardiorespiratory fitness in patients with coronary artery disease.

METHODS

Thirty-seven patients (59.7 + 1.7 years) with coronary artery disease were randomly divided into two groups: continuous exercise training (n = 20) and interval exercise training (n = 17). All patients performed a graded exercise test with respiratory gas analysis before and after three months of the exercise training program to determine the VAT, respiratory compensation point (RCP) and peak oxygen consumption.

RESULTS

After the interventions, both groups exhibited increased cardiorespiratory fitness. Indeed, the continuous exercise and interval exercise training groups demonstrated increases in both ventilatory efficiency and PETCO2 values at VAT, RCP, and peak of exercise. Significant associations were observed in both groups: 1) continuous exercise training (PETCO2VAT and cardiorespiratory fitness r = 0.49; PETCO2VAT and ventilatory efficiency r = -0.80) and 2) interval exercise training (PETCO2VAT and cardiorespiratory fitness r = 0.39; PETCO2VAT and ventilatory efficiency r = -0.45).

CONCLUSIONS

Both exercise training modalities showed similar increases in PETCO2 levels during a graded exercise test in patients with coronary artery disease, which may be associated with an improvement in ventilatory efficiency and cardiorespiratory fitness.

Clinical utility of exercise training in chronic systolic heart failure

The volume of literature attesting to the clinical benefits of exercise training in patients with stable chronic heart failure (CHF) is substantial. Training can improve symptoms and exercise capacity, as well as reducing morbidity, mortality, and rates of emergency hospitalization. These benefits are apparent in all patients with stable CHF, irrespective of age or sex, or the etiology or severity of heart failure. Training regimens for patients with stable, systolic CHF should form part of a comprehensive heart-failure support effort and are best delivered using supervised in-hospital exercise combined with some training at home or in a group setting in community centers. In this Review, the modes and intensity of exercise training, selection of patients, duration of training effects, and other clinical guidance for using this treatment option are discussed.

Combined increased chemosensitivity to hypoxia and hypercapnia as a prognosticator in heart failure

OBJECTIVES

The aim of the present study was to investigate the prognostic significance of chemosensitivity to hypercapnia in chronic heart failure (HF).

BACKGROUND

Increased chemosensitivity to hypoxia and hypercapnia has been observed in HF. The potential value of enhanced chemosensitivity to hypercapnia to risk prediction in systolic HF has not been specifically evaluated.

METHODS

One hundred ten consecutive systolic HF patients (age 62 +/- 15 years, left ventricular ejection fraction [LVEF] 31 +/- 7%) underwent assessment of chemosensitivity to hypoxia and hypercapnia (rebreathing technique) and were followed up for a median period of 29 months (range 1 to 54 months). The end point was a composite of cardiac death and aborted cardiac death (ventricular tachyarrhythmia treated by cardioverter-defibrillator).

RESULTS

At baseline, 31 patients (28%) had enhanced chemosensitivity to both hypoxia and hypercapnia. Although they had the same LVEF as the 43 patients (39%) with normal chemosensitivity, they were more symptomatic (New York Heart Association functional class), had higher plasma brain natriuretic peptide and norepinephrine, steeper regression slope relating minute ventilation to carbon dioxide output (V(E)/V(CO2) slope), more Cheyne-Stokes respiration, and more ventricular arrhythmias (all p < 0.05). Four-year survival was only 49%, in marked contrast to 100% for patients with normal chemosensitivity (p < 0.001). On multivariate analysis, combined elevation in chemosensitivity was the strongest independent prognostic marker, even when adjusted for univariate predictors (V(E)/V(CO2) slope, Cheyne-Stokes respiration, LVEF, and brain natriuretic peptide, p < 0.05).

CONCLUSIONS

Increased chemosensitivity to both hypoxia and hypercapnia, eliciting neurohormonal derangement, ventilation instability, and ventricular arrhythmias, is a very serious adverse prognostic marker in HF.

Repeated experiences of air hunger and ventilatory behavior in response to hypercapnia in the standardized rebreathing test: effects of anxiety

In this study, we assessed air hunger (AH) and ventilatory responses to repeated CO(2) exposures in healthy women (N=31), scoring high or low for trait anxiety. A standardized rebreathing test, implying a gradually increasing CO(2) stimulus, was administered three times with 15-min intervals. Respiratory behavior and the intensity of AH perception were measured continuously. Across repeated exposures, maximal tolerance for AH habituated and the slope of AH (increase in AH per unit increase in CO(2)) diminished. Also the dynamics of the breathing response changed across trials. The thresholds for AH and tidal volume (V(T)) moved closer to each other, whereas the threshold for the respiratory rate (RR) was generally postponed. In addition, the association between AH and V(T) was stronger than between AH and RR, and the latter association became weaker over trials, particularly in high anxious persons. This suggests that AH perception became increasingly influenced by psychological factors, especially in high anxious persons. The results suggest that habituation of perceived air hunger is depending on a complex interplay between both changes in respiratory behavior and in perceptual-cognitive processes related to trait anxiety.

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.

Exercise hyperventilation in chronic heart failure is not caused by systemic lactic acidosis

BACKGROUND

Patients with heart failure have an abnormally high ventilatory response to exercise associated with gas exchange defects and reduced arterial pCO(2).

AIMS

We examined the possibility of lactic acidosis as the stimulus to this increased ventilation that abnormally depresses pCO(2) during exercise in heart failure.

METHOD AND RESULTS

We studied 18 patients with chronic heart failure. We measured VE/VCO(2) slope during exercise, arterial blood gases and lactate concentrations during cardiopulmonary exercise testing (rest, peak exercise and one minute after the end of exercise). Neither VE/VCO(2) slope nor arterial pCO(2) were related to arterial lactate concentrations at peak exercise (r = -0.16, p = 0.65 and r = -0.15, p = 0.6). During early recovery, patients with a high VE/VCO(2) slope had a particularly pronounced rise in arterial lactate and hydrogen ion concentrations (r = 0.57, p < 0.05 and r = 0.84, p < 0.0001) and yet their arterial pCO(2) rose rather than fell (r = 0.79, p < 0.001). The rise in arterial pCO(2) correlated with the increase in arterial hydrogen concentration (r = 0.78, p < 0.001) and with arterial pCO(2) at peak exercise (r = -0.76, p < 0.001).

CONCLUSIONS

In heart failure VE/VCO(2) slope and low arterial pCO(2) at peak exercise are not related to the degree of systemic lactic acidosis. Lactic acidosis is therefore not a plausible mechanism of exercise induced hyperventilation.

Exercise tolerance, exercise hyperpnea and central chemosensitivity to carbon dioxide in sleep apnea syndrome in heart failure patients

BACKGROUND

Sleep apnea syndrome (SAS) and exercise hyperpnea are common in patients with chronic heart failure (CHF), and although it is not known whether they are both regulated by the same mechanisms, the hypothesis of the present study was that they are related to augmented central chemosensitivity.

METHODS AND RESULTS

The oxygen desaturation index (ODI) was evaluated in 29 patients and those with ODI > 5 times/h underwent polysomnography. Patients with an apnea-hypopnea index (AHI) > 15 /h without evidence of obstructive apnea were defined as central SAS (CSAS). Cardiopulmonary exercise testing was performed to determine peak oxygen uptake and the VE-VCO2 slope. A hypercapnic gas mixture (7% CO2/93% O2) was used to activate the central chemoreflex. Nine patients had central SAS (CHF-CSAS) and 20 did not have apnea (CHF-nonSAS). Patients with CHF-CSAS had a lower peak oxygen uptake than the CHF-nonSAS group (13.0+/-2.4 vs 16.9+/-4.3 ml x kg(-1) x min(-1), p < 0.05). There was a significant correlation between central chemosensitivity and the AHI (r = 0.63, p < 0.05), between central chemosensitivity and the VE - VCO2 slope (r = 0.50, p < 0.01), whereas the VE-VCO2 slope showed an insignificant tendency to correlate with AHI (r = 0.44, p = 0.07). Conclusion CHF-CSAS is associated with impaired exercise tolerance and elevated central chemosensitivity is the responsible mechanism for CSAS and exercise hyperpnea.

Rehabilitation in Cardiac Patients

This article discusses the effects of training in cardiac rehabilitation and describes the influence of various training modalities on the evolution of exercise capacity in cardiac patients. Both home- and hospital-based studies are analysed separately. From the collected studies, a very heterogeneous character of the content of the rehabilitation programmes appears. Direct comparison of the effects of the training programmes on exercise capacity remains difficult. Baseline factors for predicting a better training outcome are: low exercise capacity and peripheral oxygen extraction; presence of hibernating myocardium; high myocardial perfusion; low degree of coronary vessel occlusion; working status; and improved feelings of wellbeing. The increased work capacity as a result of rehabilitation is associated with: an increased volume density of skeletal muscle mitochondria; peripheral muscular vasodilatory capacity; cardiac output and a decreased left ventricular end-diastolic pressure; depletion of muscular phosphocreatine levels; and degree of restenosis. Home- and hospital-based interventions induce comparable training effects. More research is needed concerning the training modalities in cardiac rehabilitation. There is an influence of weekly training frequency and programme duration on the training outcome. A higher training frequency and/or duration might induce greater training effects. The evolution of the anaerobic threshold is sensitive to the training intensity and inclusion of strength training, which remains to be established for maximal exercise capacity. However, insufficient information is available on the influence of training session duration on the evolution of exercise capacity.