Contribution of central and peripheral factors at peak exercise in heart failure patients with progressive severity of exercise limitation

Deceived by the Fick principle: blood flow distribution in heart failure

AIMS

The Fick principle states that oxygen uptake (V̇O2) is cardiac output (Qc)*arterial-venous O2 content difference [ΔC(a-v)O2]. Blood flow distribution is hidden in Fick principle and its relevance during exercise in heart failure (HF) is undefined.To highlight the role of blood flow distribution, we evaluated peak-exercise V̇O2, Qc and ΔC(a-v)O2, before and after HF therapeutic interventions.

METHODS

Symptoms-limited cardiopulmonary exercise tests with Qc measurement (inert-gas-rebreathing) was performed in 234 HF patients before and 6 months after successful exercise training, cardiac-resynchronization therapy or percutaneous-edge-to-edge mitral valve repair.

RESULTS

Considering all tests (n=468) a direct correlation between peakV̇O2 and peakQc (R2=0.47) and workload (R2=0.70) were observed. Patients were grouped according to treatment efficacy in group 1 (peakV̇O2 increase >10%, n=93), group 2 (peakV̇O2 change between 0 and 10%, n=60) and group 3 (reduction in peakV̇O2, n=81). Post-treatment peakV̇O2 changes poorly correlated with peakQc and peakΔC(a-v)O2 changes. Differently, post-procedures peakQc vs. peakΔC(a-v)O2 changes showed a close negative correlation (R2=0.46), becoming stronger grouping patients according to peakV̇O2 improvement (R2=0.64, 0.79 and 0.58 in group 1, 2 and 3, respectively). In 76% of patients peakQc and ΔC(a-v)O2 changes diverged regardless of treatment.

CONCLUSION

The bulk of these data suggests that blood flow distribution plays a pivotal role on peakV̇O2 determination regardless of HF treatment strategies. Accordingly, for assessing HF treatment efficacy on exercise performance the sole peakV̇O2 may be deceptive and the combination of V̇O2, Qc and ΔC(a-v)O2, must be considered.

The effect of cardiac rehabilitation on cardiopulmonary function after coronary artery bypass grafting: A systematic review and meta-analysis

We carried out a meta-analysis on the effect of cardiac rehabilitation (CR) on cardiopulmonary function after coronary artery bypass grafting (CABG). Four databases were searched for studies comparing CR with control. A random-effects model was used to pool mean difference (MD). The meta-analysis showed an increase in peak oxygen consumption (peak VO2) (MD = 1.93 mL/kg/min, p = 0.0006), and 6-min walk distance (6MWD) (MD = 59.21 m, p < 0.00001), and a decrease in resting heart rate (resting HR) (MD = 5.68 bpm, p < 0.0001) in the CR group. The subgroup analysis revealed aerobic exercise could further improve resting HR and peak HR, and physical/combination with aerobic exercise could further increase 6MWD. The improvement of peak VO2, workload, resting HR, peak HR, and 6MWD regarding CR performed within one week after CABG is greater than that one week after CABG. CR after CABG can improve the cardiopulmonary function, which is reflected by the improvement of peak VO2, 6MWD, and resting HR.

Non-Invasive Cardiac Output Measurement Using Inert Gas Rebreathing Method during Cardiopulmonary Exercise Testing-A Systematic Review

BACKGROUND

The use of inert gas rebreathing for the non-invasive cardiac output measurement has produced measurements comparable to those obtained by various other methods. However, there are no guidelines for the inert gas rebreathing method during a cardiopulmonary exercise test (CPET). In addition, there is also a lack of specific standards for assessing the non-invasive measurement of cardiac output during CPET, both for healthy patients and those suffering from diseases and conditions.

AIM

This systematic review aims to describe the use of IGR for a non-invasive assessment of cardiac output during cardiopulmonary exercise testing and, based on the information extracted, to identify a proposed CPET report that includes an assessment of the cardiac output using the IGR method.

METHODS

This systematic review was conducted by PRISMA (Preferred Reporting Items for Systematic Reviews and Meta Analyses) guidelines. PubMed, Web of Science, Scopus, and Cochrane Library databases were searched from inception until 29 December 2022. The primary search returned 261 articles, of which 47 studies met the inclusion criteria for this review.

RESULTS AND CONCLUSIONS

This systematic review provides a comprehensive description of protocols, indications, technical details, and proposed reporting standards for a non-invasive cardiac output assessment using IGR during CPET. It highlights the need for standardized approaches to CPET and identifies gaps in the literature. The review critically analyzes the strengths and limitations of the studies included and offers recommendations for future research by proposing a combined report from CPET-IGR along with its clinical application.

Determinants of exercise performance in heart failure patients with extremely reduced cardiac output and left ventricular assist device

The evaluation of exercise capacity and cardiac output (QC) is fundamental in the management of patients with advanced heart failure (AdHF). QC and peak oxygen uptake (VO2) have a pivotal role in the prognostic stratification and in the definition of therapeutic interventions, including medical therapies and devices, but also specific treatments such as heart transplantation and left ventricular assist device (LVAD) implantation. Due to the intertwined relationship between exercise capacity and daily activities, exercise intolerance dramatically has impact on the quality of life of patients. It is a multifactorial process that includes alterations in central and peripheral haemodynamic regulation, anaemia and iron deficiency, pulmonary congestion, pulmonary hypertension, and peripheral O2 extraction. This paper aims to review the pathophysiological background of exercise limitations in HF patients and to examine the complex physiology of exercise in LVAD recipients, analysing the interactions between the cardiopulmonary system, the musculoskeletal system, the autonomic nervous system, and the pump. We performed a literature review to highlight the current knowledge on this topic and possible interventions that can be implemented to increase exercise capacity in AdHF patients-including administration of levosimendan, rehabilitation, and the intriguing field of LVAD speed changes. The present paper confirms the role of CPET in the follow-up of this peculiar population and the impact of exercise capacity on the quality of life of AdHF patients.

Beyond VO2: the complex cardiopulmonary exercise test

Cardiopulmonary exercise test (CPET) is a valuable diagnostic tool with a specific application in heart failure (HF) thanks to the strong prognostic value of its parameters. The most important value provided by CPET is the peak oxygen uptake (peak VO2), the maximum rate of oxygen consumption attainable during physical exertion. According to the Fick principle, VO2 equals cardiac output (Qc) times the arteriovenous content difference [C(a-v)O2], where Ca is the arterial oxygen and Cv is the mixed venous oxygen content, respectively; therefore, VO2 can be reduced both by impaired O2 delivery (reduced Qc) or extraction (reduced arteriovenous O2 content). However, standard CPET is not capable of discriminating between these different impairments, leading to the need for 'complex' CPET technologies. Among non-invasive methods for Qc measurement during CPET, inert gas rebreathing and thoracic impedance cardiography are the most used techniques, both validated in healthy subjects and patients with HF, at rest and during exercise. On the other hand, the non-invasive assessment of peripheral muscle perfusion is possible with the application of near-infrared spectroscopy, capable of measuring tissue oxygenation. Measuring Qc allows, by having haemoglobin values available, to discriminate how much any VO2 deficit depends on the muscle, anaemia or heart.

The physiological and clinical importance of cardiorespiratory fitness in people with abdominal aortic aneurysm

New Findings

What is the topic of this review?

This review focuses on the physiological impact of abdominal aortic aneurysm (AAA) on cardiorespiratory fitness and the negative consequences of low fitness on clinical outcomes in AAA. We also discuss the efficacy of exercise training for improving cardiorespiratory fitness in AAA.

What advances does it highlight?

We demonstrate the negative impact of low fitness on disease progression and clinical outcomes in AAA. We highlight potential mechanistic determinants of low fitness in AAA and present evidence that exercise training can be an effective treatment strategy for improving cardiorespiratory fitness, postoperative mortality and disease progression.

Abstract

An abdominal aortic aneurysm (AAA) is an abnormal enlargement of the aorta, below the level of the renal arteries, where the aorta diameter increases by >50%. As an aneurysm increases in size, there is a progressive increase in the risk of rupture, which ranges from 25 to 40% for aneurysms >5.5 cm in diameter. People with AAA are also at a heightened risk of cardiovascular events and associated mortality. Cardiorespiratory fitness is impaired in people with AAA and is associated with poor (postoperative) clinical outcomes, including increased length of hospital stay and postoperative mortality after open surgical or endovascular AAA repair. Although cardiorespiratory fitness is a well‐recognized prognostic marker of cardiovascular health and mortality, it is not assessed routinely, nor is it included in current clinical practice guidelines for the management of people with AAA. In this review, we discuss the physiological impact of AAA on cardiorespiratory fitness, in addition to the consequences of low cardiorespiratory fitness on clinical outcomes in people with AAA. Finally, we summarize current evidence for the effect of exercise training interventions on cardiorespiratory fitness in people with AAA, including the associated improvements in postoperative mortality, AAA growth and cardiovascular risk. Based on this review, we propose that cardiorespiratory fitness should be considered as part of the routine risk assessment and monitoring of people with AAA and that targeting improvements in cardiorespiratory fitness with exercise training might represent a viable adjunct treatment strategy for reducing postoperative mortality and disease progression.

Role of impaired iron transport on exercise performance in heart failure patients

AIMS

Impaired iron transport (IIT) occurs frequently in heart failure (HF) patients, even in the absence of anaemia and it is associated with a poor quality of life and prognosis. The impact of IIT on exercise capacity, as assessed by the cardiopulmonary exercise test (CPET), in HF is at present unknown. The aim of this article is to evaluate in HF patients the impact on exercise performance of IIT, defined as transferrin saturation (TSAT) <20%.

METHODS AND RESULTS

We collected data of 676 patients hospitalized for HF. All underwent laboratory analysis, cardiac ultrasound, and CPET. Patients were grouped by the presence/absence of IIT and anaemia (haemoglobin <13 and <12 g/dL in male and female, respectively): Group 1 (G1) no anaemia, no IIT; Group 2 (G2) anaemia, no IIT; Group 3 (G3) no anaemia, IIT; Group 4 (G4) anaemia and IIT. Peak oxygen uptake (peakVO2) reduced from G1 to G3 and from G2 to G4 (G1: 1266 ± 497 mL/min, G2: 1011 ± 385 mL/min, G3: 1041 ± 395 mL/min, G4: 833 ± 241 mL/min), whereas the ventilation to carbon dioxide relationship slope (VE/VCO2 slope) increased (G1: 31.8 ± 7.5, G2: 34.5 ± 7.4, G3: 36.1 ± 10.2, G4: 37.5 ± 8.4). At multivariate regression analysis, peakVO2 independent predictors were anaemia, brain natriuretic peptide (BNP), and left ventricular ejection fraction, whereas VE/VCO2 slope independent predictors were IIT and BNP.

CONCLUSION

In HF IIT is associated with exercise performance impairment independently from anaemia, and it is a predictor of elevated VE/VCO2 slope, a pivotal index of HF prognosis.

Listing Criteria for Heart Transplant: Role of Cardiopulmonary Exercise Test and of Prognostic Scores

Patients with advanced heart failure (AdHF) have a reduced quality of life and poor prognosis. A heart transplant (HT) is an effective treatment for such patients. Still, because of a shortage of donor organs, the final decision to place a patient without contraindications on the HT waiting list is based on detailed risk-benefit analysis. Cardiopulmonary exercise tests (CPETs) play a pivotal role in guiding selection in patients with AdHF considered for an HT. Furthermore, several validated multivariable predicting scores obtained through various techniques, including the CPETs, are available and part of the decision-making process for HT listing.

Combined use of stress echocardiography and cardiopulmonary exercise testing to assess exercise intolerance in patients treated for acute myocardial infarction

Exercise intolerance after acute myocardial infarction (AMI) is a predictor of worse prognosis, but its causes are complex and poorly studied. This study assessed the determinants of exercise intolerance using combined stress echocardiography and cardiopulmonary exercise testing (CPET-SE) in patients treated for AMI. We prospectively enrolled patients with left ventricular ejection fraction (LV EF) ≥40% for more than 4 weeks after the first AMI. Stroke volume, heart rate, and arteriovenous oxygen difference (A-VO2Diff) were assessed during symptom-limited CPET-SE. Patients were divided into four groups according to the percentage of predicted oxygen uptake (VO2) (Group 1, <50%; Group 2, 50-74%; Group 3, 75-99%; and Group 4, ≥100%). Among 81 patients (70% male, mean age 58 ± 11 years, 47% ST-segment elevation AMI) mean peak VO2 was 19.5 ± 5.4 mL/kg/min. A better exercise capacity was related to a higher percent predicted heart rate (Group 2 vs. Group 4, p <0.01), higher peak A-VO2Diff (Group 1 vs. Group 3, p <0.01) but without differences in stroke volume. Peak VO2 and percent predicted VO2 had a significant positive correlation with percent predicted heart rate at peak exercise (r = 0.28, p = 0.01 and r = 0.46, p < 0.001) and peak A-VO2Diff (r = 0.68, p <0.001 and r = 0.36, p = 0.001) but not with peak stroke volume. Exercise capacity in patients treated for AMI with LV EF ≥40% is related to heart rate response during exercise and peak peripheral oxygen extraction. CPET-SE enables non-invasive assessment of the mechanisms of exercise intolerance.

Exercise Dynamic of Patients with Chronic Heart Failure and Reduced Ejection Fraction

PURPOSE OF REVIEW

Exercise causes various dynamic changes in all body parts either in healthy subject or in heart failure (HF) patients. The present review of current knowledge about HF patients with reduced ejection fraction focuses on dynamic changes along a "metabo-hemodynamic" perspective.

RECENT FINDINGS

Studies on the dynamic changes occurring during exercise span many years. Thanks to the availability of advanced methods, it is nowadays possible to properly characterize respiratory, hemodynamic, and muscular function adjustments and their mismatch with the pulmonary and systemic circulations. Exercise is a dynamic event that involves several body functions. In HF patients, it is important to know at what level the limitation takes place in order to better manage these patients and to optimize therapeutic strategies.

Relationship of end-tidal oxygen partial pressure to the determinants of anaerobic threshold in post-myocardial infarction patients

The anaerobic threshold (AT), obtained during cardiopulmonary exercise testing (CPET), is an important prognostic measure and can be used to develop an exercise prescription in patients after a myocardial infarction (post-MI). The purpose of this study was to examine the central and peripheral determinants of AT in post-MI patients end-tidal oxygen partial pressure (PETO₂) measures. We performed cardiopulmonary exercise testing (CPET) on 148 consecutively enrolled post-MI patients to determine PETO₂ measured at the AT (AT PETO₂) and ΔPETO₂ (difference between resting PETO₂ and AT PETO₂). We subsequently investigated the relationship between these measures of PETO₂ and the individual AT for each patient. Multivariate linear regression analysis indicated that AT PETO₂ and ΔPETO₂ were independently and significantly associated with the AT (β = -0.344, p < 0.001 and β = 0.228, p < 0.001, respectively). Furthermore, the independent factors of AT PETO₂ were left ventricular ejection fraction (p = 0.005), resting ventilatory equivalent for carbon dioxide (p = 0.002), and resting dead-space gas volume to tidal volume ratio (p < 0.001). However, the independent factors for ΔPETO₂ were history of diabetes (p = 0.047), estimated glomerular filtration rate (p = 0.001), and resting systolic blood pressure (p = 0.017). These findings suggested that AT PETO₂ was associated with central determinants; whereas, and ΔPETO₂ was associated with peripheral determinants, The AT PETO₂ and ΔPETO₂ provide variable insight regarding the cause of exercise intolerance and can be used to determine appropriate therapies.

Cardiac output changes during exercise in heart failure patients: focus on mid-exercise

Aims

Peak exercise oxygen uptake (VO₂) and cardiac output (CO) are strong prognostic indexes in heart failure (HF) but unrelated to real‐life physical activity, which is associated to submaximal effort.

Methods and results

We analysed maximal cardiopulmonary exercise test with rest, mid‐exercise, and peak exercise non‐invasive CO measurements (inert gas rebreathing) of 231 HF patients and 265 healthy volunteers. HF patients were grouped according to exercise capacity (peak VO₂ < 50% and ≥50% pred, Groups 1 and 2). To account for observed differences, data regarding VO₂, CO, stroke volume (SV), and artero‐venous O₂ content difference [ΔC(a‐v)O₂] were adjusted by age, gender, and body mass index. A multiple regression analysis was performed to predict peak VO₂ from mid‐exercise cardiopulmonary exercise test and CO parameters among HF patients. Rest VO₂ was lower in HF compared with healthy subjects; meanwhile, Group 1 patients had the lowest CO and highest ΔC(a‐v)O₂. At mid‐exercise, Group 1 patients achieved a lower VO₂, CO, and SV [0.69 (interquartile range 0.57–0.80) L/min; 5.59 (4.83–6.67) L/min; 62 (51–73) mL] than Group 2 [0.94 (0.83–1.1) L/min; 7.6 (6.56–9.01) L/min; 77 (66–92) mL] and healthy subjects [1.15 (0.93–1.30) L/min; 9.33 (8.07–10.81) L/min; 87 (77–102) mL]. Rest to mid‐exercise SV increase was lower in Group 1 than Group 2 (P = 0.001) and healthy subjects (P < 0.001). At mid‐exercise, ΔC(a‐v)O₂ was higher in Group 2 [13.6 (11.8–15.4) mL/100 mL] vs. healthy patients [11.6 (10.4–13.2) mL/100 mL] (P = 0.002) but not different from Group 1 [13.6 (12.0–14.9) mL/100 mL]. At peak exercise, Group 1 patients achieved a lower VO₂, CO, and SV than Group 2 and healthy subjects. ΔC(a‐v)O₂ was the highest in Group 2. At multivariate analysis, a model comprising mid‐exercise VO₂, carbon dioxide production (VCO₂), CO, haemoglobin, and weight predicted peak VO₂, P < 0.001. Mid‐exercise VO₂ and CO, haemoglobin, and weight added statistically significantly to the prediction, P < 0.050.

Conclusions

Mid‐exercise VO₂ and CO portend peak exercise values and identify severe HF patients. Their evaluation could be clinically useful.

Determinants of Cardiorespiratory Fitness in Patients with Heart Failure Across a Wide Range of Ejection Fractions

Impaired cardiorespiratory fitness (CRF) in heart failure (HF) is influenced by a complex array of cardiac and extracardiac factors. The study aimed to identify clinical determinants of CRF measured as peak oxygen consumption (peak VO₂) in HF patients, and to determine a peak VO₂ prediction model using regression equations. Retrospective analysis of 200 HF patients who completed treadmill cardiopulmonary exercise testing and underwent Doppler echocardiography and/or biomarker analysis on the same day was performed. After univariate linear regression analysis, a multivariate peak VO₂ prediction model was developed using significant variables in a stepwise linear regression analysis. In subjects with repeated testing, Pearson's correlation was used to assess correlations between measured and predicted change in peak VO₂ (Δpeak VO₂) over time. Mean age was 57 years, with 55% being male. Stepwise linear regression was used to generate a weighted model for peak VO₂: 30.895 + (-0.112•age[years]) + (0.296•hemoglobin [g/dl]) + (-0.101•E/e'[unit change]) + (-0.202• body mass index [kg/m²]) + (-0.593• N-terminal pro-brain natriuretic peptide [log_N pg/ml])) + (-1.349•CRP [log mg/L]). Predicted peak VO₂ correlated strongly with measured peak VO₂ in HF with reduced ejection fraction and HF with preserved ejection fraction patients (r = +0.63, p <0.001; r = +0.64, p <0.001, respectively). Predicted Δpeak VO₂ correlated with measured Δpeak VO₂ (r = +0.23, p <0.001). In conclusion, in patients with HF across a wide range of left ventricular ejection fraction, age, systemic inflammation, oxygen carrying capacity, obesity, and elevated filling pressures are the strongest predictors of impaired CRF. The proposed CRF model allows prediction of peak VO₂ in HF patients and may be used to estimate peak VO₂ changes over time.

Type 2 Diabetes Mellitus, Glycated Hemoglobin Levels, and Cardiopulmonary Exercise Capacity in Patients With Ischemic Heart Disease

PURPOSE

Diabetes mellitus (DM) is associated with long-term cardiovascular complications, including ischemic heart disease (IHD). Nonetheless, DM may directly impair myocardial and lung structure and function. The aim of this study was to assess the impact of type 2 DM (T2DM) and glycemic control on cardiopulmonary exercise capacity in patients with IHD.

METHODS

The study involved a cross-sectional analysis of 91 consecutive patients (57 ± 10 yr, 90% men) who underwent a cardiopulmonary exercise test at the beginning of an exercise-based standard phase-II cardiac rehabilitation program, 2 to 3 mo after an acute coronary syndrome. Association of T2DM with cardiopulmonary exercise test parameters was assessed using multiple linear regression analysis controlling for prespecified potential confounders.

RESULTS

There were 26 (29%) diabetic subjects among IHD patients included in the study. After adjustment, T2DM was an independent predictor of a reduced peak oxygen uptake ((Equation is included in full-text article.)O2peak) (P = .005), a reduced pulse O2 trajectory (P = .001), a steeper minute ventilation to carbon dioxide output (VE/(Equation is included in full-text article.)CO2) slope (P = .046), and an increased dead space-to-tidal volume ratio (VD/VT) at peak exercise (P = .049). Glycated hemoglobin (HbA1c) levels were significantly associated with a reduced forced expiratory volume in the first second of expiration (FEV1) (P = .013), VE (P = .001), and VT (P = .007). (Equation is included in full-text article.)O2peak (P trend < .001), (Equation is included in full-text article.)O2 at anaerobic threshold (P trend < .001), and pulse O2 trajectory (P trend < .001) decreased among HbA1c tertiles.

CONCLUSIONS

Patients with IHD and a previous diagnosis of T2DM had a reduced aerobic capacity and a ventilation- perfusion mismatch compared with nondiabetic patients. Poor glycemic control in men further deteriorates aerobic capacity probably due to ventilatory inefficiency.

Do rebreathing manoeuvres for non-invasive measurement of cardiac output during maximum exercise test alter the main cardiopulmonary parameters?

Background

Inert gas rebreathing has been recently described as an emergent reliable non-invasive method for cardiac output determination during exercise, allowing a relevant improvement of cardiopulmonary exercise test clinical relevance. For cardiac output measurements by inert gas rebreathing, specific respiratory manoeuvres are needed which might affect pivotal cardiopulmonary exercise test parameters, such as exercise tolerance, oxygen uptake and ventilation vs carbon dioxide output (VE/VCO2) relationship slope.

Method

We retrospectively analysed cardiopulmonary exercise testing of 181 heart failure patients who underwent both cardiopulmonary exercise testing and cardiopulmonary exercise test+cardiac output within two months (average 16 ± 15 days). All patients were in stable clinical conditions (New York Heart Association I–III) and on optimal medical therapy.

Results

The majority of patients were in New York Heart Association Class I and II (78.8%), with a mean left ventricular ejection fraction of 31 ± 10%. No difference was found between the two tests in oxygen uptake at peak exercise (1101 (interquartile range 870–1418) ml/min at cardiopulmonary exercise test vs 1103 (844–1389) at cardiopulmonary exercise test-cardiac output) and at anaerobic threshold. However, anaerobic threshold and peak heart rate, peak workload (75 (58–101) watts and 64 (42–90), p < 0.01) and carbon dioxide output were significantly higher at cardiopulmonary exercise testing than at cardiopulmonary exercise test+cardiac output, whereas VE/VCO2 slope was higher at cardiopulmonary exercise test+cardiac output (30 (27–35) vs 33 (28–37), p < 0.01).

Conclusion

The similar anaerobic threshold and peak oxygen uptake in the two tests with a lower peak workload and higher VE/VCO2 slope at cardiopulmonary exercise test+cardiac output suggest a higher respiratory work and consequent demand for respiratory muscle blood flow secondary to the ventilatory manoeuvres. Accordingly, VE/VCO2 slope and peak workload must be evaluated with caution during cardiopulmonary exercise test+cardiac output.

Association between heart rate variability and haemodynamic response to exercise in chronic heart failure

OBJECTIVES

Heart rate variability (HRV) and haemodynamic response to exercise (i.e. peak cardiac power output) are strong predictors of mortality in heart failure. The present study assessed the relationship between measures of HRV and peak cardiac power output.

DESIGN

In a prospective observational study of 33 patients (age 54 ± 16 years) with chronic heart failure with reduced left ventricular ejection fraction (29 ± 11%), measures of the HRV (i.e. R-R interval and standard deviation of normal R-R intervals, SDNN) were recorded in a supine position. All patients underwent maximal graded cardiopulmonary exercise testing with non-invasive (inert gas rebreathing) cardiac output assessment. Cardiac power output, expressed in watts, was calculated as the product of cardiac output and mean arterial blood pressure.

RESULTS

The mean RR and SDNN were 837 ± 166 and 96 ± 29 ms, peak exercise cardiac power output 2.28 ± 0.85 watts, cardiac output 10.34 ± 3.14 L/min, mean arterial blood pressure 98 ± 14 mmHg, stroke volume 91.43 ± 40.77 mL/beat, and oxygen consumption 19.0 ± 5.6 mL/kg/min. There was a significant but only moderate relationship between the RR interval and peak exercise cardiac power output (r = 0.43, p = .013), cardiac output (r = 0.35, p = .047), and mean arterial blood pressure (r = 0.45, p = .009). The SDNN correlated with peak cardiac power output (r = 0.42, p = .016), mean arterial blood arterial (r = 0.41, p = .019), and stroke volume (r = 0.35, p = .043).

CONCLUSIONS

Moderate strength of the relationship between measures of HRV and cardiac response to exercise suggests that cardiac autonomic function is not good indicator of overall function and pumping capability of the heart in chronic heart failure.