Origin of oscillatory kinetics of respiratory gas exchange in chronic heart failure

Periodic breathing during exercise in heart failure: beyond the classic risk factors

Periodic breathing is a peculiar ventilatory pattern in patients with heart failure (HF), characterized by cyclic oscillations in minute ventilation. This phenomenon has been observed in awake patients, during sleep, and during exercise. Periodic breathing during exercise, also known as exercise oscillatory ventilation (EOV), is an important marker of clinical and functional status, morbidity, and mortality in HF patients. However, a clear understanding of the meaning, causes, and possible occurrence of different forms of EOV is still currently lacking. This review focuses on what is known, likely known, or unknown about EOV in HF, including topics such as the definition of EOV, pathophysiological mechanisms, EOV phenotypes, treatment modalities, and the prognostic role of EOV in patients with HF. Finally, some perspectives on research opportunities and clinical practice are presented, to increase the knowledge of EOV, and the application of tools for its assessment, which may improve the chances of identifying and treating EOV, with a positive impact on patients with HF.

Exercise Oscillatory Ventilation Improves Heart Failure Prognostic Scores

BACKGROUND

Several heart failure (HF) prognostic risk scores are available to guide the ideal time for listing candidates for a heart transplant (HTx). The detection of exercise oscillatory ventilation (EOV) during cardiopulmonary exercise testing (CPET) is associated with advanced HF and a worse prognosis, and yet it is not accounted for in these risk scores. Therefore, this study aimed to assess whether EOV further adds prognostic value to HF scores.

METHODS

A single-centre retrospective cohort study was undertaken of consecutive HF patients with reduced ejection fraction (HFrEF) who underwent CPET from 1996 to 2018. The Heart Failure Survival Score (HFSS), Seattle Heart Failure Model (SHFM), Meta-analysis Global Group In Chronic Heart Failure (MAGGIC), and Metabolic Exercise Cardiac Kidney Index (MECKI) were calculated. The added value of EOV on top of those scores was assessed using a Cox proportional hazard model. The added discriminative power was also assessed by receiver operating characteristic curve comparison.

RESULTS

A total of 390 HF patients with a median age of 58 (IQR 50-65) years were investigated, of whom 78% were male and 54% had ischaemic heart disease. The median peak oxygen consumption was 15.7 mL/kg/min (IQR 12.8-20.1). Exercise oscillatory ventilation was detected in 153 (39.2%) patients. Over a median follow-up of 2 years, 61 patients died (49 due to a cardiovascular reason) and 54 had a HTx. Exercise oscillatory ventilation independently predicted the composite outcome of all-cause death and HTx. Furthermore, the presence of this ventilatory pattern significantly improved the prognostic performance of both HFSS and MAGGIC scores.

CONCLUSION

Exercise oscillatory ventilation was often found in a cohort of HF patients with reduced LVEF who underwent CPET. It was found that EOV added further prognostic value to contemporary HF scores, suggesting that this easily obtained parameter should be included in future modified HF scores.

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.

Roles of periodic breathing and isocapnic buffering period during exercise in heart failure

In heart failure, exercise - induced periodic breathing and end tidal carbon dioxide pressure value during the isocapnic buffering period are two features identified at cardiopulmonary exercise testing strictly related to sympathetic activation. In the present review we analysed the physiology behind periodic breathing and the isocapnic buffering period and present the relevant prognostic value of both periodic breathing and the presence/absence of the identifiable isocapnic buffering period.

Exertional Periodic Breathing in Heart Failure: Mechanisms and Clinical Implications

Periodic breathing (PB) during exercise is a slow, prominent, consistent fluctuation in ventilation and derived parameters that may be persistent for the entire exercise or present only in the early phases of exercise. It is associated with a negative prognosis, particularly if concomitant with PB during sleep. Little is known about exercise-induced PB physiology, but hyperventilation is likely due to an increased sympathetic activity combined with an enhanced stimulation of intrapulmonary, chemoreceptors and metaboreceptors, low cardiac output leading to increased circulatory delay, and cerebrovascular reactivity to CO2, all with have a definite role.

Exercise Oscillatory Ventilation: Interreviewer Agreement and a Novel Determination

INTRODUCTION

Determination of exercise oscillatory ventilation (EOV) is subjective, and the interreviewer agreement has not been reported. The purposes of this study were, among patients with heart failure (HF), as follows: 1) to determine the interreviewer agreement for EOV and 2) to describe a novel, objective, and quantifiable measure of EOV.

METHODS

This was a secondary analysis of the HEART Camp: Promoting Adherence to Exercise in Patients with Heart Failure study. EOV was determined through a blinded review by six individuals on the basis of their interpretation of the EOV literature. Interreviewer agreement was assessed using Fleiss kappa (κ). Final determination of EOV was based on agreement by four of the six reviewers. A new measure (ventilation dispersion index; VDI) was calculated for each test, and its ability to predict EOV was assessed with the receiver operator characteristics curve.

RESULTS

Among 243 patients with HF (age, 60 ± 12 yr; 45% women), the interreviewer agreement for EOV was fair (κ = 0.303) with 10-s discrete data averages and significantly better, but only moderate (κ = 0.429) with 30-s rolling data averages. Prevalence rates of positive and indeterminate EOVs were 18% and 30% with the 10-s discrete averages and 14% and 13% with the 30-s rolling averages, respectively. VDI was strongly associated with EOV, with areas under the receiver operator characteristics curve of 0.852 to 0.890.

CONCLUSIONS

Interreviewer agreement for EOV in patients with HF is fair to moderate, which can negatively affect risk stratification. VDI has strong predictive validity with EOV; as such, it might be a useful measure of prognosis in patients with HF.

An overview of the applied definitions and diagnostic methods to assess exercise oscillatory ventilation--a systematic review

The variable "exercise oscillatory ventilation" (EOV), assessed during cardiopulmonary exercise test (CPET), recently became a fundamental prognostic parameter in patients with heart failure. In literature, various definitions are suggested, but an uniformly accepted description to identify EOV still lacks. We performed a systematic review of the literature in order to determine the different definitions and diagnostic techniques to assess EOV. A systematic search strategy was established and executed in seven databases (PubMed, Google Scholar, Cochrane Clinical Trials, Science Direct, Pedro, Web Of Science library and Medline (Ovid)) resulting in 605 citations after de-duplication. Full-text articles (n=124) were assessed for eligibility, resulting in 75 citations. The review accounted 17,440 patients of whom 4,638 subjects presented EOV. Seven studies described EOV in a non-heart failure population accounting 168 EOV subjects. The definitions could be categorized in nine subdivisions of which four (n=43) referred to an original description. The other subdivisions were combinations of the original definitions (n=11), quantifications (n=4), computational (n=3), vaguely described (n=8) or not defined (n=6). Symptom limited maximal exercise tests were conducted to assess EOV, however the modes, protocols, software and data sampling were divers. Heterogeneity in the numerous definitions to identify EOV and the vaguely described assessment methods are hindering the evolution to a standardized uniformly accepted definition and technique to identify this abnormal breathing pattern. Unity in definition and international adopted assessment is warranted to strengthen its validity as a prognostic marker and could promote communication. It may facilitate clinical trials on pathophysiology and origin of EOV.

Novel cardiac pacemaker-based human model of periodic breathing to develop real-time, pre-emptive technology for carbon dioxide stabilisation

BACKGROUND

Constant flow and concentration CO2 has previously been efficacious in attenuating ventilatory oscillations in periodic breathing (PB) where oscillations in CO2 drive ventilatory oscillations. However, it has the undesirable effect of increasing end-tidal CO2, and ventilation. We tested, in a model of PB, a dynamic CO2 therapy that aims to attenuate pacemaker-induced ventilatory oscillations while minimising CO2 dose.

METHODS

First, pacemakers were manipulated in 12 pacemaker recipients, 6 with heart failure (ejection fraction (EF)=23.7±7.3%) and 6 without heart failure, to experimentally induce PB. Second, we applied a real-time algorithm of pre-emptive dynamic exogenous CO2 administration, and tested different timings.

RESULTS

We found that cardiac output alternation using pacemakers successfully induced PB. Dynamic CO2 therapy, when delivered coincident with hyperventilation, attenuated 57% of the experimentally induced oscillations in end-tidal CO2: SD/mean 0.06±0.01 untreated versus 0.04±0.01 with treatment (p<0.0001) and 0.02±0.01 in baseline non-modified breathing. This translated to a 56% reduction in induced ventilatory oscillations: SD/mean 0.19±0.09 untreated versus 0.14±0.06 with treatment (p=0.001) and 0.10±0.03 at baseline. Of note, end-tidal CO2 did not significantly rise when dynamic CO2 was applied to the model (4.84±0.47 vs 4.91± 0.45 kPa, p=0.08). Furthermore, mean ventilation was also not significantly increased by dynamic CO2 compared with untreated (7.8±1.2 vs 8.4±1.2 L/min, p=0.17).

CONCLUSIONS

Cardiac pacemaker manipulation can be used to induce PB experimentally. In this induced PB, delivering CO2 coincident with hyperventilation, ventilatory oscillations can be substantially attenuated without a significant increase in end-tidal CO2 or ventilation. Dynamic CO2 administration might be developed into a clinical treatment for PB.

TRIAL REGISTRATION NUMBER

ISRCTN29344450.

Prognostic implications of preoperative aerobic capacity and exercise oscillatory ventilation after liver transplantation

Our aim was to determine preoperative aerobic capacity (oxygen uptake [V'O2 ]) and prevalence of exercise oscillatory ventilation (EOV), underlying clinical characteristics of patients with EOV, and significance of reduced aerobic capacity and EOV in predicting mortality after liver transplantation. We prospectively studied 263 patients who underwent elective liver transplantation. Patients were followed up for 1 year. Despite minor impairment of resting cardiopulmonary function, preoperative aerobic capacity was reduced (peak V'O2 : 64 ± 19% predicted). EOV occurred in 10% of patients. Model for End-Stage Liver Disease score tended to be higher in patients with EOV compared to patients without, but failed to reach significance (p = 0.09). EOV patients had lower peak V'O2 and higher ventilatory drive. EOV was more frequent in nonsurvivors than in survivors (30% vs. 9%, p = 0.01) and was independently associated with posttransplant all-cause 1-year mortality. Reduced peak V'O2 best predicted the primary composite endpoint defined as 1-year mortality and/or prolonged hospitalization and early in-hospital mortality. Multivariate analysis revealed EOV (χ(2), 3.96; p = 0.04) and V'O2 (χ(2), 4.28; p = 0.04) as independent predictors of mortality and so-called primary composite endpoint, respectively. EOV and reduced peak V'O2 may identify high-risk candidates for liver transplantation, which would motivate a more aggressive treatment when detected.

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.

Cardiopulmonary exercise testing reflects similar pathophysiology and disease severity in heart failure patients with reduced and preserved ejection fraction

BACKGROUND

We are unaware of any previous investigation that has compared the relationship of key cardiopulmonary exercise testing (CPX) variables to various measures of pathophysiology between heart failure-reduced ejection fraction (HFrEF) and HF-preserved ejection fraction (HFpEF) cohorts that are well matched with respect to baseline characteristics and their exercise response, which is the purpose of the present study.

METHODS

Thirty-four patients with HFpEF were randomly matched to 34 subjects with HFrEF according to age and sex as well as peak oxygen consumption (VO2), ventilatory efficiency (VE/VCO2 slope), and exercise oscillatory ventilation (EOV). In addition to CPX, patients also underwent echocardiography with tissue Doppler imaging (TDI) and assessment of N-terminal pro-B-type natriuretic peptide (NT-proBNP).

RESULTS

When matched for age, sex, and CPX variables, the HFrEF and HFpEF cohorts had similar echocardiography with TDI and NT-proBNP values, indicating comparable disease severity. In addition, the correlations between key CPX measures (peak VO2 and VE/VCO2 slope) and echocardiography with TDI and NT-proBNP measures were similar between HFrEF and HFpEF groups. Of note, the correlation between the VE/VCO2 slope and pulmonary artery systolic pressure and NT-proBNP was highly significant in both groups (r ≥ 0.65, p < 0.01). Moreover, subjects with EOV in both groups had a significantly higher PASP (∼47 vs. ∼35 mmHg, p < 0.05).

CONCLUSIONS

The results of the current study indicate CPX equally represents disease severity in HFrEF and HFpEF patients. This is a novel finding supporting the key role of CPX in the clinical follow-up of HF patients irrespective of LVEF and cardiac phenotype.

Addition of inspiratory muscle training to aerobic training improves cardiorespiratory responses to exercise in patients with heart failure and inspiratory muscle weakness

BACKGROUND

This small clinical trial tested the hypothesis that the addition of inspiratory muscle training (IMT) to aerobic exercise training (AE) results in further improvement in cardiorespiratory responses to exercise than those obtained with AE in patients with chronic heart failure (CHF) and inspiratory muscle weakness (IMW).

METHODS

Twenty-four patients with CHF and IMW (maximal inspiratory pressure <70% of predicted) were randomly assigned to a 12-week program of AE plus IMT (AE + IMT, n = 12) or to AE alone (AE, n = 12). Before and after intervention, the following measures were obtained: maximal inspiratory muscle pressure (PI(max)), peak oxygen uptake (Vo(2)peak), peak circulatory power, oxygen uptake efficiency slope, ventilatory efficiency, ventilatory oscillation, oxygen uptake kinetics during recovery (T(1/2)Vo(2)), 6-minute walk test distance, and quality of life scores.

RESULTS

Compared to AE, AE + IMT resulted in additional significant improvement in PI(max) (110% vs 72%), Vo(2)peak (40% vs 21%), circulatory power, oxygen uptake efficiency slope, ventilatory efficiency, ventilatory oscillation, and T(1/2)Vo(2). Six-minute walk distance and quality of life scores improved similarly in the 2 groups.

CONCLUSION

This randomized trial demonstrates that the addition of IMT to AE results in improvement in cardiorespiratory responses to exercise in selected patients with CHF and IMW. The clinical significance of these findings should be addressed by larger randomized trials.

Prognostic ability of resting periodic breathing and ventilatory variation in closely matched patients with heart failure

PURPOSE

Periodic breathing (PB), characterized by waxing and waning oscillations of ventilation, has been reported in some patients with heart failure. Although PB is usually assessed in sleeping patients, PB has also been observed in awake patients. We tested the hypothesis that PB in awake, resting patients with heart failure predicts mortality.

METHODS

Resting gas exchange data were collected in consecutive, awake patients with heart failure referred for possible cardiac transplantation. Periodic breathing was defined as oscillations of resting ventilation, that is, 30% or more during 2 consecutive cycles. Each PB patient was matched to a comparison patient by age, gender, heart failure etiology, peak oxygen consumption, peak respiratory exchange ratio, and ventilatory efficiency slope.

RESULTS

Forty-four of 355 patients met the criteria for PB and were matched to 44 comparison patients. During an average follow-up of 4.9 +/- 0.1 years, 30 patients with PB (68%) versus 23 comparisons (52%) died or were transplanted urgently (P = NS). However, among the 88 PB patients and comparisons, ventilatory variation was an independent predictor of mortality by Cox regression analysis (P = .004). Resting ventilatory variation increased the explained variation in mortality by 44%, from 16% to 23%, in a mortality model that included ventilatory efficiency slope, peak oxygen consumption, left ventricular ejection fraction, systolic blood pressure, sex, age, heart rate, and etiology.

CONCLUSION

Resting ventilatory variation independently and powerfully predicted mortality in this cohort of patients with heart failure.

Evaluation of two methods for continuous cardiac output assessment during exercise in chronic heart failure patients

The purpose of this study was to evaluate the accuracy of two techniques for the continuous assessment of cardiac output in patients with chronic heart failure (CHF): a radial artery pulse contour analysis method that uses an indicator dilution method for calibration (LiDCO) and an impedance cardiography technique (Physioflow), using the Fick method as a reference. Ten male CHF patients (New York Heart Association class II–III) were included. At rest, cardiac output values obtained by LiDCO and Physioflow were compared with those of the direct Fick method. During exercise, the continuous Fick method was used as a reference. Exercise, performed on a cycle ergometer in upright position, consisted of two constant-load tests at 30% and 80% of the ventilatory threshold and a symptom-limited maximal test. Both at rest and during exercise LiDCO showed good agreement with reference values [bias ± limits of agreement (LOA), −1% ± 28% and 2% ± 28%, respectively]. In contrast, Physioflow overestimated reference values both at rest and during exercise (bias ± LOA, 48% ± 60% and 48% ± 52%, respectively). Exercise-related within-patient changes of cardiac output, expressed as a percent change, showed for both techniques clinically acceptable agreement with reference values (bias ± LOA: 2% ± 26% for LiDCO, and −2% ± 36% for Physioflow, respectively). In conclusion, although the limits of agreement with the Fick method are pretty broad, LiDCO provides accurate measurements of cardiac output during rest and exercise in CHF patients. Although Physioflow overestimates cardiac output, this method may still be useful to estimate relative changes during exercise.

Exercise oscillatory breathing in diastolic heart failure: prevalence and prognostic insights

AIMS

Exercise intolerance occurs in both systolic and diastolic heart failure (HF). Exercise oscillatory breathing (EOB) is a powerful predictor of survival in patients with systolic HF. In diastolic HF, EOB prevalence and prognostic impact are unknown.

METHODS AND RESULTS

A total of 556 HF patients (405 with systolic HF and 151 with diastolic HF) underwent cardiopulmonary exercise testing (CPET). Diastolic HF was defined as signs and symptoms of HF, a left ventricular ejection fraction > or =50%, and a Doppler early (E) mitral to early mitral annulus ratio (E') > or =8. CPET responses, EOB prevalence and its ability to predict cardiac-related events were examined. EOB prevalence in systolic and diastolic HF was similar (35 vs. 31%). Compared with the patients without EOB, patients with EOB and either systolic or diastolic HF had a higher New York Heart Association class, lower peak VO(2) and higher E/E' ratio (all P < 0.01). Univariate Cox regression analysis demonstrated that peak VO(2), VE/VCO(2) slope and EOB all were significant predictors of cardiac events in both systolic and diastolic HF. Multivariable analysis revealed that EOB was retained as a prognostic marker in systolic HF and was the strongest predictor of cardiac events in diastolic HF.

CONCLUSION

EOB occurrence is similar in diastolic and systolic HF and provides relevant clues for the identification of diastolic HF patients at increased risk of adverse events.

Mechanisms of periodic breathing during exercise in patients with chronic heart failure

BACKGROUND

Periodic breathing (PB) in heart failure (HF) is attributed to many factors, including low cardiac output delaying the time it takes pulmonary venous blood to reach the central and peripheral chemoreceptors, low lung volume, lung congestion, augmented chemoreceptor sensitivity, and the narrow difference between eupneic carbon dioxide tension and apneic/hypoventilatory threshold.

METHODS AND RESULTS

We measured expired gases, ventilation, amplitude, and duration of PB in 23 patients with PB during progressive exercise tests done with 0 mL, 250 mL, or 500 mL of added dead space. Periodicity of PB remained constant despite heart rate, oxygen consumption, and minute ventilation increasing. Within each PB cycle, starting from the beginning of exercise, the largest (peak) tidal volume approached maximum observed tidal volume, while the smallest (nadir) tidal volume increased as exercise power output increased. PB ceased when nadir tidal volume reached peak tidal volume. End-tidal carbon dioxide increased with added dead space, and PB ceased progressively earlier during the exercise done with increased dead space.

CONCLUSION

Circulatory delay does not contribute to the PB observed in exercising HF patients. The pattern of gradually increasing nadir tidal volume during exercise and the effect of dead space on both PB ceasing and end-tidal carbon dioxide suggest that low tidal volume and carbon dioxide apnea threshold are important contributors to PB that occurs during exercise in HF.

Exercise oscillatory ventilation may predict sudden cardiac death in heart failure patients

OBJECTIVES

The purpose of this study was to test the ability of cardiopulmonary exercise testing (CPET)-derived variables as sudden cardiac death (SCD) predictors.

BACKGROUND

The CPET variables, such as peak oxygen uptake (VO2), ventilatory requirement to carbon dioxide (CO2) production (VE/VCO2) slope, and exercise oscillatory breathing (EOB), are strong predictors of overall mortality in chronic heart failure (CHF) patients. Even though up to 50% of CHF patients die from SCD, it is unknown whether any of these variables predicts SCD.

METHODS

One hundred fifty-six CHF patients (mean age: 60.9 +/- 9.4 years; mean ejection fraction: 34.9 +/- 10.6%) underwent CPET. Subjects were tracked for sudden versus pump-failure cardiac mortality over 27.8 +/- 25.2 months.

RESULTS

Seventeen patients died from SCD, and 17 died from cardiac pump failure. Survivors showed significantly higher peak VO2 (16.8 +/- 4.5 ml x kg(-1) x min(-1)) and lower VE/VCO2 slope (32.8 +/- 6.4) and prevalence of EOB (20.3%), compared with subjects who experienced arrhythmic (13.5 +/- 3.2 ml x kg(-1) x min(-1); 41.5 +/- 11.4; 100%) or nonarrhythmic (14.1 +/- 4.7 ml x kg(-1) x min(-1); 38.1 +/- 7.3; 47.1%) deaths (p < 0.05). At Cox regression analysis, all variables were significant univariate predictors of both sudden and pump failure death (p < 0.01). Multivariate analysis, including left ventricular (LV) ejection fraction, LV end systolic volume, and LV mass selected EOB, was the strongest predictor of both overall mortality (chi-square: 38.7, p < 0.001) and SCD (chi-square: 44.7, p < 0.001), whereas VE/VCO2 slope was the strongest ventilatory predictor of pump failure death (chi-square: 11.8, p = 0.001).

CONCLUSIONS

Exercise oscillatory breathing is an independent predictor of SCD in patients with CHF and might help as an additional marker for prioritization of antiarrhythmic strategies.

Exercise oscillatory breathing and increased ventilation to carbon dioxide production slope in heart failure: an unfavorable combination with high prognostic value

BACKGROUND

Increased slope of exercise ventilation to carbon dioxide production (VE/VCO2) is an established prognosticator in patients with heart failure. Recently, the occurrence of exercise oscillatory breathing (EOB) has emerged as an additional strong indicator of survival.

OBJECTIVE

The aim of this study is to define the respective prognostic significance of these variables and whether excess risk may be identified when either respiratory disorder is present.

METHODS

In 288 stable chronic HF patients (average left ventricular ejection fraction, 33 +/- 13%) who underwent cardiopulmonary exercise testing, the prognostic relevance of VE/VCO2 slope, EOB, and peak VO2 was evaluated by multivariate Cox regression.

RESULTS

During a mean interval of 28 +/- 13 months, 62 patients died of cardiac reasons. Thirty-five percent presented with EOB. Among patients exhibiting EOB, 54% had an elevated VE/VCO2 slope. The optimal threshold value for the VE/VCO2 slope identified by receiver operating characteristic analysis was < 36.2 or > or = 36.2 (sensitivity, 77%; specificity, 64%; P < .001). Univariate predictors of death included low left ventricular ejection fraction, low peak VO2, high VE/VCO2 slope, and EOB presence. Multivariate analysis selected EOB as the strongest predictor (chi2, 46.5; P < .001). The VE/VCO2 slope (threshold, < 36.2 or > or = 36.2) was the only other exercise test variable retained in the regression (residual chi2, 5.9; P = .02). The hazard ratio for subjects with EOB and a VE/VCO2 slope > or = 36.2 was 11.4 (95% confidence interval, 4.9-26.5; P < .001).

CONCLUSION

These findings identify EOB as a strong survival predictor even more powerful than VE/VCO2 slope. Exercise oscillatory breathing presence does not necessarily imply an elevated VE/VCO2 slope, but combination of either both yields to a burden of risk remarkably high.

Effects of acute changes in pulmonary wedge pressure on periodic breathing at rest in heart failure patients

BACKGROUND

Patients with heart failure (HF) display a number of breathing abnormalities including periodic breathing (PB) at rest. Although the mechanism(s) contributing to PB remain unclear, we examined whether changes in pulmonary wedge pressure (PWP) and pulmonary vascular resistance (PVR) alter PB in patients with established HF.

METHODS

We studied 12 male patients with HF (age, 50 +/- 11 years; ejection fraction, 18.3 +/- 3.8 %; New York Heart Association class, 3.2 +/- 0.4), with PB at rest, who are undergoing right heart catheterization with infusion of nitroprusside.

RESULTS

At baseline, patients with HF displayed minute ventilation (V(E)) oscillations with amplitude of 5.5 +/- 2.7 L/min (57 +/- 34% of the average V(E)) and cycle length of 61 +/- 18 seconds. Cardiac index (CI), PVR, and mean PWP averaged 2.0 +/- 0.4 L min(-1) m(-2), 281.9 +/- 214.9 dyne/s per cm(-5), and 28.3 +/- 5.4 mm Hg, respectively. During nitroprusside infusion, CI increased to 3.1 +/- 0.6 L min(-1) m(-2), PVR decreased to 163.9 +/- 85.2 dyne/s per cm(-5), and PWP fell to 10.0 +/- 4.2 mm Hg. Nitroprusside reduced the amplitude (2.6 +/- 2.4 L/min, 23 +/- 21% of average V(E); P < .01) and cycle length (41.4 +/- 28.8 seconds; P < .01) of V(E) oscillations while abolishing oscillations in 3 patients. Although average V(E) and PaCO2 remained unchanged, there was a significant increase in the ratio of tidal volume to inspiratory time (V(T)/T(I); P < .01), suggesting an increase in ventilatory drive. The change in the amplitude of V(E) oscillations was positively correlated with the change in PWP (r = 0.75; P < .01), negatively correlated with the change in PVR (r = 0.63; P < .05), and not correlated with the change in CI.

CONCLUSIONS

These data suggest that PWP (left atrial pressure) may play a direct role in the PB observed in HF at rest.

Statement on cardiopulmonary exercise testing in chronic heart failure due to left ventricular dysfunction: recommendations for performance and interpretation Part II: How to perform cardiopulmonary exercise testing in chronic heart failure

Basic and practical information related to equipment, methodology, exercise protocols, conduct of the test and quality control issues for cardiopulmonary exercise testing (CPET) will be addressed in this II part of the statement. CPET users have the responsibility for assuring that measurements remain accurate. CPT, especially when it features breath-by-breath gas exchange analysis, requires meticulous attention to calibration procedures to assure accurate and reproducible measurements. Skills and knowledge of personnel for supervision and test interpretation, as well as patient preparation and information are key features for a correct CPET conduction: all these issues will be faced. Finally, after the test, the investigator needs to format the results in a manner that optimises the ability to discriminate essential response features; that is, to establish 'interpretive clusters' of the variables of interest. An example of a cardiopulmonary summary exercise test data report will be provided, defining the most important information that should be incorporated in a final report.

Development of respiratory control instability in heart failure: a novel approach to dissect the pathophysiological mechanisms

Observational data suggest that periodic breathing is more common in subjects with low F(ETCO(2)), high apnoeic thresholds or high chemoreflex sensitivity. It is, however, difficult to determine the individual effect of each variable because they are intrinsically related. To distinguish the effect of isolated changes in chemoreflex sensitivity, mean F(ETCO(2)) and apnoeic threshold, we employed a modelling approach to break their obligatory in vivo interrelationship. We found that a change in mean CO(2) fraction from 0.035 to 0.045 increased loop gain by 70 +/- 0.083% (P < 0.0001), irrespective of chemoreflex gain or apnoea threshold. A 100% increase in the chemoreflex gain (from 800 l min(-1) (fraction CO(2))(-1)) resulted in an increase in loop gain of 275 +/- 6% (P < 0.0001) across a wide range of values of steady state CO(2) and apnoea thresholds. Increasing the apnoea threshold F(ETCO(2)) from 0.02 to 0.03 had no effect on system stability. Therefore, of the three variables the only two destabilizing factors were high gain and high mean CO(2); the apnoea threshold did not independently influence system stability. Although our results support the idea that high chemoreflex gain destabilizes ventilatory control, there are two additional potentially controversial findings. First, it is high (rather than low) mean CO(2) that favours instability. Second, high apnoea threshold itself does not create instability. Clinically the apnoea threshold appears important only because of its associations with the true determinants of stability: chemoreflex gain and mean CO(2).

Inspiratory muscle training in patients with heart failure and inspiratory muscle weakness: a randomized trial

OBJECTIVES

This study sought to evaluate the effects of inspiratory muscle training in inspiratory muscle strength, as well as in functional capacity, ventilatory responses to exercise, recovery oxygen uptake kinetics, and quality of life in patients with chronic heart failure (CHF) and inspiratory muscle weakness.

BACKGROUND

Patients with CHF may have reduced strength and endurance in inspiratory muscles, which may contribute to exercise intolerance and is associated with a poor prognosis.

METHODS

Thirty-two patients with CHF and weakness of inspiratory muscles (maximal inspiratory pressure [Pi(max)] <70% of predicted) were randomly assigned to a 12-week program of inspiratory muscle training (IMT, 16 patients) or to a placebo-inspiratory muscle training (P-IMT, 16 patients). The following measures were obtained before and after the program: Pi(max) at rest and 10 min after maximal exercise; peak oxygen uptake, circulatory power, ventilatory oscillations, and oxygen kinetics during early recovery (VO2/t-slope); 6-min walk test; and quality of life scores.

RESULTS

The IMT resulted in a 115% increment Pi(max), 17% increase in peak oxygen uptake, and 19% increase in the 6-min walk distance. Likewise, circulatory power increased and ventilatory oscillations were reduced. The VO2/t-slope was improved during the recovery period, and quality of life scores improved.

CONCLUSIONS

In patients with CHF and inspiratory muscle weakness, IMT results in marked improvement in inspiratory muscle strength, as well as improvement in functional capacity, ventilatory response to exercise, recovery oxygen uptake kinetics, and quality of life.

Periodic breathing during incremental exercise predicts mortality in patients with chronic heart failure evaluated for cardiac transplantation

OBJECTIVES

We hypothesized that exercise-related periodic breathing (EPB) would be associated with poor prognosis in advanced chronic heart failure (CHF).

BACKGROUND

Patients with CHF might present instability of the ventilatory control system characterized by cyclic waxing and waning of tidal volume (periodic breathing [PB]). This condition is associated with several deleterious circulatory and neuro-endocrine responses; in fact, PB in awake and asleep patients has been identified as an independent risk factor for cardiac death. During exercise, however, the prognostic value of PB is still unknown in CHF patients awaiting heart transplantation.

METHODS

Eighty-four patients with established CHF (65 male, 19 female) were submitted to clinical evaluation, echocardiogram, ventricular scintigraphy, determination of resting serum norepinephrine levels, and an incremental cardiopulmonary exercise test on cycle ergometer. Patients were followed for up to 49.7 months (median = 15.3), and 26 patients (30.9%) died during this period.

RESULTS

Twenty-five of 84 patients presented EPB (29.7%). The following variables were related to mortality according to Kaplan-Meier and univariate Cox regression analysis: EPB (p = 0.004), New York Heart Association class (p = 0.04), serum norepinephrine (p = 0.06), peak oxygen uptake (ml.min(-1).kg(-1) and % predicted; p = 0.085 and p = 0.10, respectively), slope of the ratio of change in minute ventilation to change in carbon dioxide output during exercise (p = 0.10), and scintigraphic left ventricular ejection fraction (p = 0.10). Cox multivariate analysis identified EPB as the only independent variable for cardiac death prediction (p = 0.007). Therefore, EPB alone was associated with a 2.97-fold increase in risk of death in this population (95% confidence interval = 1.34 to 6.54).

CONCLUSIONS

Exercise-related periodic breathing independently predicts cardiac mortality in CHF patients considered for heart transplantation.

Physiological basis of fractal complexity properties of heart rate variability in man

The diagnostic and prognostic power of the fractal complexity measure 'alpha' of detrended fluctuation analysis (DFA) has remained mysterious because there has been no explanation of its meaning, particularly in relation to spectral analysis. First, we present a mathematical analysis of the meaning of alpha, in weighted power-spectral terms. Second, we test this hypothesis and observe correlations between DFA-based and weighted spectral methods of 0.97 (P < 0.0001) for alpha1 and 0.98 (P < 0.0001) for alpha2. Third, we predict mathematically that even in conventional (unweighted) spectral analysis there should be approximate counterparts to DFA, namely that alpha1 and alpha2 behave broadly in proportion to the conventional (unweighted) ratios LF/(HF + LF) and VLF/(LF + VLF), respectively, where HF is high frequency, LF is low frequency and VLF is very low frequency. Fourth, we test this hypothesis by physiologically manipulating spectral ratios in healthy volunteers in two ways. The effect of 0.1 Hz controlled breathing on LF/(HF + LF) correlates markedly with the effect on alpha1 (r = 0.73, P = 0.01); the effect on VLF/(LF + VLF) correlates markedly with that on alpha2 (r = 0.76, P < 0.01). Likewise, with voluntary periodic breathing the reduction in alpha2 correlates strongly with that in VLF/(LF + VLF) (r = 0.88, P < 0.001); effects on alpha1 and LF/(HF + LF) again clearly correlate (r = 0.73, P = 0.01). Finally, we examine published literature to identify previously undiscussed evidence of the relationship between alpha1 and LF/(HF + LF). We conclude that the alpha1 and alpha2 indices are simply frequency-weighted versions of the spectral ratios LF/(HF + LF) and VLF/(LF + VLF), respectively, multiplied by two (giving a range of 0-2). We can now understand fractal manifestations of physiological abnormalities: depressed baroreflex sensitivity low LF/HF low LF/(HF + LF) low alpha1, while periodic breathing high VLF/LF high VLF/(LF + VLF) high alpha2. Prognostic associations of alpha are no longer mysterious.