Carvedilol reduces exercise-induced hyperventilation: A benefit in normoxia and a problem with hypoxia

Exercise-induced potentiation of the acute hypoxic ventilatory response: Neural mechanisms and implications for cerebral blood flow

A given dose of hypoxia causes a greater increase in pulmonary ventilation during physical exercise than during rest, representing an exercise-induced potentiation of the acute hypoxic ventilatory response (HVR). This phenomenon occurs independently from hypoxic blood entering the contracting skeletal muscle circulation or metabolic byproducts leaving skeletal muscles, supporting the contention that neural mechanisms per se can mediate the HVR when humoral mechanisms are not at play. However, multiple neural mechanisms might be interacting intricately. First, we discuss the neural mechanisms involved in the ventilatory response to hypoxic exercise and their potential interactions. Current evidence does not support an interaction between the carotid chemoreflex and central command. In contrast, findings from some studies support synergistic interactions between the carotid chemoreflex and the muscle mechano- and metaboreflexes. Second, we propose hypotheses about potential mechanisms underlying neural interactions, including spatial and temporal summation of afferent signals into the medulla, short-term potentiation and sympathetically induced activation of the carotid chemoreceptors. Lastly, we ponder how exercise-induced potentiation of the HVR results in hyperventilation-induced hypocapnia, which influences cerebral blood flow regulation, with multifaceted potential consequences, including deleterious (increased central fatigue and impaired cognitive performance), inert (unchanged exercise) and beneficial effects (protection against excessive cerebral perfusion).

Exercise in hypoxia: a model from laboratory to on-field studies

Clinical outcome and quality of life of patients with chronic heart failure (HF) have greatly improved over the last two decades. These results and the availability of modern lifts allow many cardiac patients to spend leisure time at altitude. Heart failure per se does not impede a safe stay at altitude, but exercise at both simulated and real altitudes is associated with a reduction in performance, which is inversely proportional to HF severity. For example, in normal subjects, the reduction in functional capacity is ∼2% every 1000 m altitude increase, whereas it is 4 and 10% in HF patients with normal or slightly diminished exercise capacity and in HF patients with markedly diminished exercise capacity, respectively. Also, the on-field experience with HF patients at altitude confirms safety and shows overall similar data to that reported at simulated altitude. Even 'optimal' HF treatment in patients spending time at altitude or at hypoxic conditions is likely different from optimal treatment at sea level, particularly with regard to the selectivity of β-blockers. Furthermore, high altitude, both simulated and on-field, represents a stimulating model of hypoxia in HF patients and healthy subjects. Our data suggest that spending time at altitude (<3500 m) can be safe even for HF patients, provided that subjects are free from comorbidities that may directly interfere with the adaptation to altitude and are stable. However, HF patients experience a reduction of exercise capacity directly proportional to HF severity and altitude. Finally, HF patients should be tested for functional capacity and must undergo a specific 'hypoxic-tailored treatment' to avoid pharmacological interference with altitude adaptation mechanisms, particularly with regard to the selectivity of β-blockers.

Physiology of exercise and heart failure treatments: cardiopulmonary exercise testing as a tool for choosing the optimal therapeutic strategy

In the last decades, the pharmacological treatment of heart failure (HF) become more complex due to the availability of new highly effective drugs. Although the cardiovascular effects of HF therapies have been extensively described, less known are their effects on cardiopulmonary function considered as a whole, both at rest and in response to exercise. This is a 'holistic' approach to disease treatment that can be accurately evaluated by a cardiopulmonary exercise test. The aim of this paper is to assess the main differences in the effects of different drugs [angiotensin-converting enzyme (ACE)-inhibitors, Angiotensin II receptor blockers, β-blockers, Angiotensin receptor-neprilysin inhibitors, renal sodium-glucose co-transporter 2 inhibitors, iron supplementation] on cardiopulmonary function in patients with HF, both at rest and during exercise, and to understand how these differences can be taken into account when choosing the most appropriate treatment protocol for each individual patient leading to a precision medicine approach.

Autonomic and respiratory consequences of altered chemoreflex function: clinical and therapeutic implications in cardiovascular diseases

The importance of chemoreflex function for cardiovascular health is increasingly recognized in clinical practice. The physiological function of the chemoreflex is to constantly adjust ventilation and circulatory control to match respiratory gases to metabolism. This is achieved in a highly integrated fashion with the baroreflex and the ergoreflex. The functionality of chemoreceptors is altered in cardiovascular diseases, causing unstable ventilation and apnoeas and promoting sympathovagal imbalance, and it is associated with arrhythmias and fatal cardiorespiratory events. In the last few years, opportunities to desensitize hyperactive chemoreceptors have emerged as potential options for treatment of hypertension and heart failure. This review summarizes up to date evidence of chemoreflex physiology/pathophysiology, highlighting the clinical significance of chemoreflex dysfunction, and lists the latest proof of concept studies based on modulation of the chemoreflex as a novel target in cardiovascular diseases.

A Methodological Perspective on the Function and Assessment of Peripheral Chemoreceptors in Heart Failure: A Review of Data from Clinical Trials

Augmented peripheral chemoreceptor sensitivity (PChS) is a common feature of many sympathetically mediated diseases, among others, and it is an important mechanism of the pathophysiology of heart failure (HF). It is related not only to the greater severity of symptoms, especially to dyspnea and lower exercise tolerance but also to a greater prevalence of complications and poor prognosis. The causes, mechanisms, and impact of the enhanced activity of peripheral chemoreceptors (PChR) in the HF population are subject to intense research. Several methodologies have been established and utilized to assess the PChR function. Each of them presents certain advantages and limitations. Furthermore, numerous factors could influence and modulate the response from PChR in studied subjects. Nevertheless, even with the impressive number of studies conducted in this field, there are still some gaps in knowledge that require further research. We performed a review of all clinical trials in HF human patients, in which the function of PChR was evaluated. This review provides an extensive synthesis of studies evaluating PChR function in the HF human population, including methods used, factors potentially influencing the results, and predictors of increased PChS.

Effects of β-blocker therapy on exercise oscillatory ventilation in reduced ejection fraction heart failure patients: A case series study

BACKGROUND

Exercise oscillatory ventilation (EOV) is an abnormal breathing pattern that occurs in ~20% of patients with heart failure (HF) and is associated with poor prognosis and exercise intolerance. β-blockers (βb) are prescribed for most HF patients; however, their effect on EOV remains unclear. We evaluated the effect of βb on EOV in HF patients with reduced ejection fraction (HFrEF).

METHODS

Fifteen patients diagnosed with HF, ejection fraction < 45%, aged from 18 to 65 years, were included before starting βb therapy. Patients underwent clinical evaluation, cardiopulmonary exercise testing, echocardiography, laboratory exams (norepinephrine levels, B type natriuretic peptide) at baseline and after βb therapy optimized for six months. Presence of exercise oscillatory breathing was determined by two experienced observers who were blinded to the moment of the test (pre or post).

RESULTS

Fifteen patients (1 female), aged 49.5 ± 2.5 years, with HFrEF, NYHA I-III enrolled in the study. The etiologies of the HFrEF were idiopathic (n = 8) and hypertensive (n = 7). LVEF increased after βb therapy from 25.9 ± 2.5% to 33 ± 2.6%, P = 0.02; peak VO₂ did not significantly change (21.8 ± 1.7 vs 24.7 ± 1.9, P = 0.4); VE/VCO₂ slope changed from 32.1 ± 10.6-27.5 ± 9.1, P = 0.03. Before βb initiation, nine patients (60%) had EOV, but only two (13%) did after optimized therapy. McNemar test was used to evaluate the significance of the association between the two moments (P = 0.02).

CONCLUSION

In patients with HF, medical therapy with βb can reverse EOV. This may explain why these patients experience symptom improvement after βb therapy.

The Role of Pharmacological Treatment in the Chemoreflex Modulation

From a physiological point of view, peripheral chemoreceptors (PCh) are the main sensors of hypoxia in mammals and are responsible for adaptation to hypoxic conditions. Their stimulation causes hyperventilation—to increase oxygen uptake and increases sympathetic output in order to counteract hypoxia-induced vasodilatation and redistribute the oxygenated blood to critical organs. While this reaction promotes survival in acute settings it may be devastating when long-lasting. The permanent overfunctionality of PCh is one of the etiologic factors and is responsible for the progression of sympathetically-mediated diseases. Thus, the deactivation of PCh has been proposed as a treatment method for these disorders. We review here physiological background and current knowledge regarding the influence of widely prescribed medications on PCh acute and tonic activities.

Clinical Implications for Exercise at Altitude Among Individuals With Cardiovascular Disease: A Scientific Statement From the American Heart Association

An increasing number of individuals travel to mountainous environments for work and pleasure. However, oxygen availability declines at altitude, and hypoxic environments place unique stressors on the cardiovascular system. These stressors may be exacerbated by exercise at altitude, because exercise increases oxygen demand in an environment that is already relatively oxygen deplete compared with sea‐level conditions. Furthermore, the prevalence of cardiovascular disease, as well as diseases such as hypertension, heart failure, and lung disease, is high among individuals living in the United States. As such, patients who are at risk of or who have established cardiovascular disease may be at an increased risk of adverse events when sojourning to these mountainous locations. However, these risks may be minimized by appropriate pretravel assessments and planning through shared decision‐making between patients and their managing clinicians. This American Heart Association scientific statement provides a concise, yet comprehensive overview of the physiologic responses to exercise in hypoxic locations, as well as important considerations for minimizing the risk of adverse cardiovascular events during mountainous excursions.

A Breathtaking Lift: Sex and Body Mass Index Differences in Cardiopulmonary Response in a Large Cohort of Unselected Subjects with Acute Exposure to High Altitude

Vignati, Carlo, Massimo Mapelli, Benedetta Nusca, Alice Bonomi, Elisabetta Salvioni, Irene Mattavelli, Susanna Sciomer, Andrea Faini, Gianfranco Parati, and Piergiuseppe Agostoni. A breathtaking lift: sex and body mass index differences in cardiopulmonary response in a large cohort of unselected subjects with acute exposure to high altitude. High Alt Med Biol 00:000-000, 2021. Background: Every year, thousands of people travel to high altitude and experience hypoxemia. At high altitude, the partial pressure of oxygen decreases. The aim of this observational study was to determine if there is a relationship between anthropometric features and basic cardiorespiratory variables, including oxygen saturation (SpO₂), heart rate (HR), and blood pressure (BP), following acute exposure to high altitude. Materials and Methods: At the 3,466 m top of a cableway station, we installed an automated system for measuring peripheral SpO₂, HR, BP, height, weight, and body mass index (BMI). Results: Between January and October 2020, out of 4,874 volunteers (age 39.9 ± 15.4 years, male 54.4%), 3,267 provided complete data (1,808 cases during winter and 1,459 during summer). SpO₂ was 86.8% ± 6.8%. At multivariable analysis, SpO₂ was significantly associated with age, sex, season, BMI, and HR but not with BP. We identified 391 (12%) subjects with SpO₂ ≤80%: they were older, with a higher BMI and HR but without sex or BP differences. Finally, winter season was associated with greater frequency of SpO₂ ≤80% (13.3% vs. 10.3%, p = 0.008). Conclusion: Our data show that high BMI, older age, and male sex were associated with greater degrees of hypoxemia following exposure to high altitude, particularly during the winter.

[Heart Patients and Exposure to Altitude]

Overall, heart patients should be advised individually with respect to their tolerance of altitudes. However, the historical reflex that altitude 'per se' is bad for heart patients should become a thing of the past. Adequately treated and stable patients can usually go up to an altitude of 2500 m without any restrictions. Higher altitudes are also possible for a large number of patients, but may require an adaptation of the medication and further clarification. This is especially the case when physical work is to be performed at great heights.

Minute ventilation/carbon dioxide production in chronic heart failure

In chronic heart failure, minute ventilation (V'_E) for a given carbon dioxide production (V'_CO2 ) might be abnormally high during exercise due to increased dead space ventilation, lung stiffness, chemo- and metaboreflex sensitivity, early metabolic acidosis and abnormal pulmonary haemodynamics. The V'_E versus V'_CO2 relationship, analysed either as ratio or as slope, enables us to evaluate the causes and entity of the V'_E/perfusion mismatch. Moreover, the V'_E axis intercept, i.e. when V'_CO2 is extrapolated to 0, embeds information on exercise-induced dead space changes, while the analysis of end-tidal and arterial CO₂ pressures provides knowledge about reflex activities. The V'_E versus V'_CO2 relationship has a relevant prognostic power either alone or, better, when included within prognostic scores. The V'_E versus V'_CO2 slope is reported as an absolute number with a recognised cut-off prognostic value of 35, except for specific diseases such as hypertrophic cardiomyopathy and idiopathic cardiomyopathy, where a lower cut-off has been suggested. However, nowadays, it is more appropriate to report V'_E versus V'_CO2 slope as percentage of the predicted value, due to age and gender interferences. Relevant attention is needed in V'_E versus V'_CO2 analysis in the presence of heart failure comorbidities. Finally, V'_E versus V'_CO2 abnormalities are relevant targets for treatment in heart failure.

Effects of β2-receptor stimulation by indacaterol in chronic heart failure treated with selective or non-selective β-blockers: a randomized trial

Alveolar β₂-receptor blockade worsens lung diffusion in heart failure (HF). This effect could be mitigated by stimulating alveolar β₂-receptors. We investigated the safety and the effects of indacaterol on lung diffusion, lung mechanics, sleep respiratory behavior, cardiac rhythm, welfare, and exercise performance in HF patients treated with a selective (bisoprolol) or a non-selective (carvedilol) β-blocker. Study procedures were performed before and after indacaterol and placebo treatments according to a cross-over, randomized, double-blind protocol in forty-four patients (27 on bisoprolol and 17 on carvedilol). No differences between indacaterol and placebo were observed in the whole population except for a significantly higher VE/VCO₂ slope and lower maximal P_ETCO₂ during exercise with indacaterol, entirely due to the difference in the bisoprolol group (VE/VCO₂ 31.8 ± 5.9 vs. 28.5 ± 5.6, p < 0.0001 and maximal P_ETCO₂ 36.7 ± 5.5 vs. 37.7 ± 5.8 mmHg, p < 0.02 with indacaterol and placebo, respectively). In carvedilol, indacaterol was associated with a higher peak heart rate (119 ± 34 vs. 113 ± 30 bpm, with indacaterol and placebo) and a lower prevalence of hypopnea during sleep (3.8 [0.0;6.3] vs. 5.8 [2.9;10.5] events/hour, with indacaterol and placebo). Inhaled indacaterol is well tolerated in HF patients, it does not influence lung diffusion, and, in bisoprolol, it increases ventilation response to exercise.

Choosing among β-blockers in heart failure patients according to β-receptors' location and functions in the cardiopulmonary system

Several large clinical trials showed a favorable effect of β-blocker treatment in patients with chronic heart failure (HF) as regards overall mortality, cardiovascular mortality, and hospitalizations. Indeed, the use of β-blockers is strongly recommended by current international guidelines, and it remains a cornerstone in the pharmacological treatment of HF. Although different types of β-blockers are currently approved for HF therapy, possible criteria to choose the best β-blocking agent according to HF patients' characteristics and to β-receptors' location and functions in the cardiopulmonary system are still lacking. In such a context, a growing body of literature shows remarkable differences between β-blocker types (β1-selective blockers versus β1-β2 blockers) with respect to alveolar-capillary gas diffusion and chemoreceptor response in HF patients, both factors able to impact on quality of life and, most likely, on prognosis. This review suggests an original algorithm for choosing among the currently available β-blocking agents based on the knowledge of cardiopulmonary pathophysiology. Particularly, starting from lung physiology and from some experimental models, it focuses on the mechanisms underlying lung mechanics, chemoreceptors, and alveolar-capillary unit impairment in HF. This paper also remarks the significant benefit deriving from the correct use of the different β-blockers in HF patients through a brief overview of the most important clinical trials.

The Role of Gas Exchange Variables in Cardiopulmonary Exercise Testing for Risk Stratification and Management of Heart Failure with Reduced Ejection Fraction

Heart failure with reduced ejection fraction (HFrEF) is common in the developed world and results in significant morbidity and mortality. Accurate risk assessment methods and prognostic variables are therefore needed to guide clinical decision making for medical therapy and surgical interventions with the ultimate goal of decreasing risk and improving health outcomes. The purpose of this review is to examine the role of cardiopulmonary exercise testing (CPET) and its most commonly used ventilatory gas exchange variables for the purpose of risk stratification and management of HFrEF. We evaluated five widely studied gas exchange variables from CPET in HFrEF patients based on nine previously used systematic criteria for biomarkers. This paper provides clinicians with a comprehensive and critical overview, class recommendations and evidence levels. Although some CPET variables met more criteria than others, evidence supporting the clinical assessment of variables beyond peak V̇O₂ is well-established. A multi-variable approach also including the V̇_E-V̇CO₂ slope and EOV is therefore recommended.

Upward Shift and Steepening of the Blood Pressure Response to Exercise in Hypertensive Subjects at High Altitude

BACKGROUND

Acute exposure to high-altitude hypobaric hypoxia induces a blood pressure rise in hypertensive humans, both at rest and during exercise. It is unclear whether this phenomenon reflects specific blood pressure hyperreactivity or rather an upward shift of blood pressure levels. We aimed at evaluating the extent and rate of blood pressure rise during exercise in hypertensive subjects acutely exposed to high altitude, and how these alterations can be counterbalanced by antihypertensive treatment.

METHODS AND RESULTS

Fifty-five subjects with mild hypertension, double-blindly randomized to placebo or to a fixed-dose combination of an angiotensin-receptor blocker (telmisartan 80 mg) and a calcium-channel blocker (nifedipine slow release 30 mg), performed a cardiopulmonary exercise test at sea level and after the first night's stay at 3260 m altitude. High-altitude exposure caused both an 8 mm Hg upward shift (P<0.01) and a 0.4 mm Hg/mL/kg per minute steepening (P<0.05) of the systolic blood pressure/oxygen consumption relationship during exercise, independent of treatment. Telmisartan/nifedipine did not modify blood pressure reactivity to exercise (blood pressure/oxygen consumption slope), but downward shifted (P<0.001) the relationship between systolic blood pressure and oxygen consumption by 26 mm Hg, both at sea level and at altitude. Muscle oxygen delivery was not influenced by altitude exposure but was higher on telmisartan/nifedipine than on placebo (P<0.01).

CONCLUSIONS

In hypertensive subjects exposed to high altitude, we observed a hypoxia-driven upward shift and steepening of the blood pressure response to exercise. The effect of the combination of telmisartan/nifedipine slow release outweighed these changes and was associated with better muscle oxygen delivery.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01830530.

Cardiopulmonary Exercise Test as a Tool to Choose Therapy in Heart Failure

Heart failure treatment depends on several drugs, all providing improvement in outcome, but that cannot be realistically used all together in the same patient. It would be useful to have a tool that allows the arrangement of the most appropriate therapy cocktail for each patient. The aim of this article is to show the main differences in the effects of several drugs on cardiopulmonary function in patients with heart failure, both while resting and during exercise, and to discuss how these differences can be taken into account when choosing the most appropriate therapeutic protocol. In summary, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers act synergistically to increase exercise capacity and peak oxygen uptake, but through different mechanisms: the former improving lung diffusion and exercise ventilatory efficiency, an action that is counteracted by concomitant aspirin therapy, and the latter probably by improving muscle perfusion. As for β-blockers, nonselective compounds, such as carvedilol, improve ventilation efficiency on the one hand, but interfere with lung diffusion on the other, and they are probably less tolerated under hypoxic conditions. On the contrary, β₁-selective compounds, such as bisoprolol or nebivolol, have a neutral effect on both lung diffusion and ventilation efficiency. These observations could be the basis for the choice of pharmacological therapy in patients with heart failure.

Systemic blood pressure at exercise in hypoxia in hypertensive and normotensive patients

OBJECTIVES

The current study aimed to determine whether acute hypoxia exposure in laboratory conditions associated with exercise induces an increase in systemic blood pressure (BP) in normotensive and hypertensive patients, and whether hypertensive patients are more prone to develop severe acute mountain sickness (sAMS). Finally, to determine if BP changes at exercise in acute hypoxia in hypertensive patients are predictive factors for sAMS.

METHODS

From 2012 to 2015, 852 normotensive and 106 hypertensive patients went through an acute hypoxia exercise test before a sojourn at high altitude. A subgroup of 228 normotensive was selected to match age, sex ratio, body weight and BMI and compared with the hypertensive group.

RESULTS

In normotensive and hypertensive patients, for a given workload, BP was higher in hypoxia than in normoxia, whereas, for a given heart rate, it was lower in hypoxia than in normoxia. Hypertensive patients treated by beta-blockers showed lower arterial oxygen saturation (vs. other treatments) and blunted cardiac and ventilatory responses to hypoxia at exercise. Based on questionnaires filled out at high altitude, hypertensive patients were not more prone than normotensive patients to develop sAMS. During the laboratory acute hypoxic exercise test, hypertensive patients suffering from sAMS, although taking acetazolamide showed similar BP than hypertensive patients without sAMS and without acetazolamide.

DISCUSSION AND CONCLUSION

We hypothesize that acute hypoxia with exercise in laboratory conditions induces a peripheral vasodilation that balances vasoconstriction and tachycardia centrally induced through the adrenergic system. Hypertensive and normotensive patients behave similarly during exercise in acute hypoxia. Acute hypoxia does not exacerbate the exercise-induced increase in BP. BP variation, during the acute hypoxia exercise test, is not a useful predictor of intolerance to high altitude. Based on laboratory tests in acute hypoxia, hypertensive patients may not be at higher risk to develop sAMS at high altitude.

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.

Clinical usefulness of response profiles to rapidly incremental cardiopulmonary exercise testing

The advent of microprocessed "metabolic carts" and rapidly incremental protocols greatly expanded the clinical applications of cardiopulmonary exercise testing (CPET). The response normalcy to CPET is more commonly appreciated at discrete time points, for example, at the estimated lactate threshold and at peak exercise. Analysis of the response profiles of cardiopulmonary responses at submaximal exercise and recovery, however, might show abnormal physiologic functioning which would not be otherwise unraveled. Although this approach has long been advocated as a key element of the investigational strategy, it remains largely neglected in practice. The purpose of this paper, therefore, is to highlight the usefulness of selected submaximal metabolic, ventilatory, and cardiovascular variables in different clinical scenarios and patient populations. Special care is taken to physiologically justify their use to answer pertinent clinical questions and to the technical aspects that should be observed to improve responses' reproducibility and reliability. The most recent evidence in favor of (and against) these variables for diagnosis, impairment evaluation, and prognosis in systemic diseases is also critically discussed.

Lungs in heart failure

Lung function abnormalities both at rest and during exercise are frequently observed in patients with chronic heart failure, also in the absence of respiratory disease. Alterations of respiratory mechanics and of gas exchange capacity are strictly related to heart failure. Severe heart failure patients often show a restrictive respiratory pattern, secondary to heart enlargement and increased lung fluids, and impairment of alveolar-capillary gas diffusion, mainly due to an increased resistance to molecular diffusion across the alveolar capillary membrane. Reduced gas diffusion contributes to exercise intolerance and to a worse prognosis. Cardiopulmonary exercise test is considered the “gold standard” when studying the cardiovascular, pulmonary, and metabolic adaptations to exercise in cardiac patients. During exercise, hyperventilation and consequent reduction of ventilation efficiency are often observed in heart failure patients, resulting in an increased slope of ventilation/carbon dioxide (VE/VCO₂) relationship. Ventilatory efficiency is as strong prognostic and an important stratification marker. This paper describes the pulmonary abnormalities at rest and during exercise in the patients with heart failure, highlighting the principal diagnostic tools for evaluation of lungs function, the possible pharmacological interventions, and the parameters that could be useful in prognostic assessment of heart failure patients.

Cardio-selective beta-blocker: pharmacological evidence and their influence on exercise capacity

For the past 40 years, beta-blockers have been widely used in cardiovascular medicine, reducing morbidity as well as mortality. Beta-blockers are currently used in a number of cardiovascular conditions such as systolic heart failure, postmyocardial infarction, and in prevention and treatment of arrhythmias. They are not recommended as the first line antihypertensive therapy, particularly in the elderly, unless there are specific indications. Despite the benefits of beta-blockers, tolerability concerns in patients with co-morbidities have limited their use. Some of these problems were overcome with the discovery of cardioselective beta-blockers. The third generation beta-blockers have additional properties of vasodilatation and advantages in terms of minimizing the adverse effects of beta-blockers. Some of the advantages include improvement of insulin resistance, decrease in cholesterol as well as alleviation of erectile dysfunction. Acute treatment with beta-blockers modifies local muscular metabolic properties and impairs endurance exercise capacity whereas the influence of chronic is debated controversially.

Drug and Device Effects on Peak Oxygen Consumption, 6-Minute Walk Distance, and Natriuretic Peptides as Predictors of Therapeutic Effects on Mortality in Patients With Heart Failure and Reduced Ejection Fraction

Background—

Although peak oxygen consumption (peak V o 2 ), 6-minute walk distance (6MW), and natriuretic peptides (BNP and NT-proBNP) are predictors of mortality in heart failure (HF) patients, it is not known whether therapy-induced changes in these measures can predict therapeutic effect on mortality. The objective of this analysis is to quantitatively assess the relationship between therapeutic effects on commonly proposed short-term markers in HF trials and therapeutic effects on long-term outcome in patients with HF and left ventricular dysfunction.

Methods and Results—

We identified drug or device therapies for which there exists at least 1 randomized, controlled trial (RCT) assessing mortality over at least 6 months in at least 500 patients. For each of these therapies, we identified RCTs assessing the short-term changes in V o 2 , 6MW, BNP, and NT-proBNP (few of the mortality RCTs assessed the short-term changes in markers). For each intervention, we calculated the odds ratio for mortality (using random effect meta-analysis when necessary), as well as the trial level average drug- or device-induced change in the markers. We assessed the correlation between the odds ratio for death with the placebo-corrected change in the functional parameter or biomarker across the interventions. We identified mortality RCTs of 27 distinct therapies (n=73 267 patients) with a median follow-up of 19 months, that directed the search for RCTs of the effect of those interventions on the functional markers and biomarkers. There were 54 peak V o 2 trials (n=4646 patients), 34 6MW trials (n=6995 patients), 15 BNP trials (n=7233), and 6 NT-proBNP trials (n=1946) included in this analysis. There was no significant correlation between the average therapy-induced placebo-corrected change in peak V o 2 and the odds ratio for mortality ( r =0.158, P =0.26). Increased drug or device-induced average change in 6MW was correlated with increased odds ratio for mortality ( r =0.373, P =0.036). There was no significant correlation between the average therapy-induced, placebo-corrected change in the natriuretic peptides and the odds ratio for mortality (BNP: r =−0.065, P =0.82, NT-proBNP: r =−0.667, P =0.15). There was no apparent relation between change in the functional parameter or biomarker and categorical effect on mortality.

Conclusions—

This analysis, limited to trial level data from different therapeutic eras, suggests that drug- or device-induced effects on peak V o 2 , 6MW, and natriuretic peptides found in short-term trials do not predict the corresponding average long-term therapeutic effects on mortality for patients with HF and left ventricular dysfunction.

Exercise intolerance in chronic heart failure: mechanisms and therapies. Part II

Muscular fatigue and dyspnoea on exertion are among the most common symptoms in chronic heart failure; however their origin is still poorly understood. Several studies have shown that cardiac dysfunction alone cannot fully explain their origin, but the contribution of the multiorgan failure present in this syndrome must be highlighted. We aimed to summarize the existing evidence and the most controversial aspects of the complex interplay of different factors involved in the symptom generation. In the first part of the review, six key factors were revised (the heart, the lung, the skeletal muscle, the hormonal changes, the O2 delivery to the periphery, the endothelium). In this second part, the role of the excitatory reflexes and the cardiac cachexia are presented. Finally, potential therapeutic implications are discussed here. We believe that a better knowledge of the pathophysiology of this syndrome may contribute to the management of the patients and to the improvement in their stress tolerance and quality of life.

Effects of carvedilol on oxygen uptake and heart rate kinetics in patients with chronic heart failure at simulated altitude

Background: The response to moderate exercise at altitude in heart failure (HF) is unknown.

Methods and results: We evaluated 30 HF patients, (NYHA I-III, 25 M/5 F; 59 ± 10 years; LVEF = 39.6 ± 7.1%), in stable clinical conditions, treated with carvedilol at the maximal tolerated dose. We performed a maximal cardiopulmonary exercise test (CPET) with ramp protocol at sea level to evaluate patients’ performance and two moderate intensity constant workload CPETs (50% of peak workload) at sea level (normoxia) and simulated altitude (hypoxia). Oxygen uptake ([Formula: see text]) and heart rate (HR) on-kinetics at constant workload were assessed calculating the time constant (τ) with a monoexponential equation. [Formula: see text] and HR were higher in hypoxia (0.944 ± 0.233 vs 1.031 ± 0.264 l/min; 100 ± 23 vs 108 ± 22 bpm; p < 0.001). On-kinetics showed a different behavior of τ being [Formula: see text] faster in hypoxia (67.1 ± 23.0 vs. 56.3 ± 19.7 s; p = 0.026) and HR faster in normoxia (49.3 ± 19.4 vs. 62.2 ± 22.5 s; p = 0.018). Ten patients, who lowered oxygen kinetics in hypoxia, had greater HR increase during maximal CPET suggesting lower functional betablockade. The higher τ of [Formula: see text] in hypoxia is likely to be due to a peripheral effect of carvedilol mediated either by β- or α-receptor.

Conclusion: HF patients performing moderate exercise at 2000 m simulated altitude have 20% [Formula: see text] increase without trouble at the beginning of exercise when treated with carvedilol.

Excess ventilation during exercise and prognosis in chronic heart failure

Excess ventilation during exercise with accompanying dyspnea is characteristic of chronic heart failure (CHF), and these patients often exhibit increased Ve relative to the Vco(2) compared with normal subjects. This can be measured in several ways, including using such variables as the slope of Ve versus Vco(2), the lowest ratio of Ve/Vco(2), and the ratio of Ve/Vco(2) at the lactic acidosis threshold or peak exercise. There is now considerable evidence that the degree of excess ventilation during exercise in patients with CHF is a robust predictor of outcome and identifies higher-risk patients requiring aggressive treatment, including heart transplantation. The mechanism of excess ventilation in patients with CHF during exercise is not completely understood. It may be related to enhanced output of chemoreceptors or peripheral muscle ergoreceptors, increased dead space/Vt ratio due to increased contribution of high ventilation-perfusion lung regions or rapid shallow breathing caused by earlier onset of lactic acidosis, or likely resulting from a combination of these causes.

Effects of beta-blockers on ventilation efficiency in heart failure

BACKGROUND

Hyperventilation and consequent reduction of ventilation (VE) efficiency are frequently observed during exercise in heart failure (HF) patients, resulting in an increased slope of VE/carbon dioxide (VE/Vco(2)) relationship. The latter is an independent predictor of HF prognosis. beta-Blockers improve the prognosis of HF patients. We evaluated the effect on the efficiency of VE of a beta(1)-beta(2) unselective (carvedilol) versus a beta(1) selective (bisoprolol) beta-blocker.

METHODS

We analyzed consecutive maximal cardiopulmonary exercise tests performed on 572 clinically stable HF patients (New York Heart Association class I-III, left ventricle ejection fraction < or =50%) categorized in 3 groups: 81 were not treated with beta-blocker, 304 were treated with carvedilol, and 187 were treated with bisoprolol. Clinical conditions were similar.

RESULTS

The VE/Vco(2) slope was lower in carvedilol- compared with bisoprolol-treated patients (29.7 +/- 0.4 vs 31.6 +/- 0.5, P = .023, peak oxygen consumption adjusted) and with patients not receiving beta-blockers (31.6 +/- 0.7, P = .036). Maximum end-tidal CO(2) pressure during the isocapnic buffering period was higher in patients treated with carvedilol (39.0 +/- 0.3 mm Hg) than with bisoprolol (37.2 +/- 0.4 mm Hg, P < .001) and in patients not receiving beta-blockers (37.2 +/- 0.5 mm Hg, P = .001).

CONCLUSIONS

Reduction of hyperventilation, with improvement of VE efficiency during exercise (reduction of VE/Vco(2) slope and increase of maximum end-tidal CO(2) pressure), is specific to carvedilol (beta(1)-beta(2) unselective blocker) and not to bisoprolol (beta(1)-selective blocker).

Clinical updates on carvedilol: a first choice beta-blocker in the treatment of cardiovascular diseases

IMPORTANCE OF THE FIELD

Carvedilol, a non-selective beta-blocker, has recently drawn attention because of its therapeutic benefits over other prescribed analogues for the treatment of cardiovascular diseases (CVDs).

AREAS COVERED IN THIS REVIEW

The present review attempts to present the clinical efficacy of carvedilol in comparison to other available beta-blockers. The literature search was carried out in three electronic databases (Unbound Medline, Pubmed and Sciencedirect) and internet search engines (Scirus and Google Scholar) without time constraints to ensure maximum literature coverage.

WHAT THE READER WILL GAIN

A relatively large number of comparative studies have revealed that carvedilol has advantage over traditional beta-blockers with respect to hemodynamic and metabolic effects, due to its unique non-selective alpha-/beta-adrenoceptor affinity. Such results indicate its safe and effective therapeutic application particularly in patients with complicated CVDs, even in pediatric and geriatric patients.

TAKE HOME MESSAGE

The therapeutic profile of carvedilol indicates its suitability for treatment of complicated CVDs than other non-selective beta-blockers. However, there is a limitation in terms of its dose due to its low bioavailability (approximately 25%). Therefore, there is still need for bioavailability enhancement and dose reduction to further improve the therapeutic efficacy of the drug.

Impaired regulation of cardiac function in sepsis, SIRS, and MODS

In sepsis, systemic inflammatory response syndrome (SIRS), and multiorgan dysfunction syndrome (MODS), a severe prognostically relevant cardiac autonomic dysfunction exists, as manifested by a strong attenuation of sympathetically and vagally mediated heart rate variability (HRV). The mechanisms underlying this attenuation are not limited to the nervous system. They also include alterations of the cardiac pacemaker cells on a cellular level. As shown in human atrial cardiomyocytes, endotoxin interacts with cardiac hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels, which mediate the pacemaker current If and play an important role in transmitting sympathetic and vagal signals on heart rate and HRV. Moreover, endotoxin sensitizes cardiac HCN channels to sympathetic signals. These findings identify endotoxin as a pertinent modulator of the autonomic nervous regulation of heart function. In MODS, the vagal pathway of the autonomic nervous system is particularly compromised, leading to an attenuation of the cholinergic antiinflammatory reflex. An amelioration of the blunted vagal activity appears to be a promising novel therapeutic target to achieve a suppression of the inflammatory state and thereby an improvement of prognosis in MODS patients. Preliminary data revealed therapeutic benefits (increased survival rates and improvements of the depressed vagal activity) of the administration of statins, beta-blockers, and angiotensin-converting enzyme inhibitors in patients with MODS.

Prevalence of cardiovascular diseases among alpine skiers and hikers in the Austrian Alps

Mountain sports, especially hiking and alpine skiing, are very popular. It is speculated that a high percentage of hikers and skiers are older and have cardiovascular diseases, but little is known about the real frequency of cardiovascular diseases in mountaineers and skiers. The goal of this study was to provide data on the prevalence of cardiovascular diseases (coronary artery disease with and without myocardial infarction, hypertension, and arrhythmias) of a representative sample of hikers and skiers in the Austrian Alps. Questionnaire results of 1431 hikers and 1043 skiers were included in the evaluation. Regarding the whole sample, 12.7% (11.0 to 14.4) of the hikers and 11.2% (9.3 to 13.1) of the skiers are afflicted with at least one type of cardiovascular disease. The frequency of cardiovascular diseases is age dependent and more pronounced in men, but only small differences were detected between hikers and skiers. It can be assumed that 4 to 5 million hikers and skiers with known cardiovascular diseases are active in the Alps annually. Scientific research should provide the basis of an optimal risk management for this large group of persons.

Lung function with carvedilol and bisoprolol in chronic heart failure: is beta selectivity relevant?

BACKGROUND

Carvedilol is a beta-blocker with similar affinity for beta1- and beta2 receptors, while bisoprolol has higher beta1 affinity. The respiratory system is characterized by beta2-receptor prevalence. Airway beta receptors regulate bronchial tone and alveolar beta receptors regulate alveolar fluid re-absorption which influences gas diffusion.

AIMS

To compare the effects of carvedilol and bisoprolol on lung function in patients with chronic heart failure (CHF).

METHODS AND RESULTS

We performed a double-blind, cross-over study in 53 CHF patients. After 2 months of full dose treatment with either carvedilol or bisoprolol, we assessed lung function by salbutamol challenge, carbon monoxide lung diffusion (DLCO), including membrane conductance (DM), and gas exchange during exercise. FEV1 and FVC were similar; after salbutamol FEV1 was higher with bisoprolol (p<0.04). DLco was 82+/-21% of predicted with carvedilol and 90+/-20% with bisoprolol (p<0.01) due to DM changes. Peak VO2 was 17.8+/-4.5 mL/min/kg on bisoprolol and 17.0+/-4.6 on carvedilol, (p<0.05) with no differences in bronchial tone (same expiratory time) throughout exercise. Differences were greater in the 22 subjects with DLCO<80%.

CONCLUSION

Carvedilol and bisoprolol have different effects on DLCO and response to salbutamol. DLCO differences, being DM related, are due to changes in active membrane transport which is under alveolar beta2-receptor control. Peak VO2 was slightly higher with bisoprolol particularly in CHF patients with reduced DLCO.

Why does chronic heart failure cause breathlessness and fatigue?

Traditional explanations for the symptoms of fatigue and breathlessness experienced by patients with chronic heart failure (CHF) focus on how reduced cardiac output on exercise leads to impaired skeletal muscle blood supply, thus causing fatigue, and on how the requirement for a raised left ventricular filling pressure to maintain cardiac output results in reduced pulmonary diffusion owing to interstitial edema, thus causing breathlessness. However, indices of left ventricular function relate poorly to exercise capacity and symptoms, suggesting that the origin of symptoms may lie elsewhere. There is a specific heart failure myopathy that is present early in the condition which may contribute largely to the sensation of fatigue. Receptors present in skeletal muscle sensitive to work (ergoreceptors) are overactive in patients with CHF, presumably as a consequence of the myopathy, and their activity is related both to the ventilatory response to exercise and breathlessness, and to the sympathetic overactivity of CHF. In the present paper, we review the systemic consequences of left ventricular dysfunction to understand how they relate to the symptoms of heart failure.