Peak VO2 and VE/VCO2 slope in patients with heart failure: a prognostic comparison

Exercise Capacity of Cardiac Asymptomatic Hereditary Hemochromatosis Subjects

PURPOSE

The exercise capacity of cardiac asymptomatic subjects with hereditary hemochromatosis (HH) has not been well described. In this study, we tested whether the iron overload associated with HH affected exercise capacity with a case control study design.

METHODS

Forty-three HH and 21 normal control subjects who were New York Heart Association functional class I underwent metabolic stress testing using the Bruce protocol at the clinical center of the National Institutes of Health. Exercise capacity was assessed with minute ventilation (.VE), oxygen uptake (.VO2), and carbon dioxide production (.VCO2) using a breath-by-breath respiratory gas analyzer.

RESULTS

The exercise capacity of HH subjects was not statistically different from that of control subjects (exercise time 564 +/- 135 vs 673 +/- 175 s, P = 0.191; peak .VO2 29.6 +/- 6.4 vs 32.5 +/- 6.7 mL.kg(-1).min(-1), P = 0.109; ventilatory threshold 19.0 +/- 3.4 vs 21.0 +/- 5.0 mL.min(-1).kg(-1), P = 0.099; data are for HH vs control subjects). Ventilatory efficiency was comparable between groups (.VE/.VCO2 slope 23.7 +/- 3.2 vs 23.4 +/- 4.2, P = 0.791). No significant correlation between the markers of iron levels and the markers of exercise capacity was noted. Iron depletion by 6-month phlebotomy therapy in 18 subjects who were newly diagnosed did not affect exercise testing variables (exercise time 562 +/- 119 vs 579 +/- 118 s, P = 0.691; peak .VO2 29.5 +/- 3.7 vs 29.1 +/- 4.7 mL.kg(-1).min(-1), P = 0.600; ventilatory threshold 18.5 +/- 2.8 vs 17.9 +/- 3.8 mL.kg(-1).min(-1), P = 0.651; data are from before and after phlebotomy therapy). Abnormal ischemic electrocardiographic responses and complex arrhythmias were more frequently seen in HH subjects.

CONCLUSIONS

The aerobic exercise capacity of asymptomatic HH subjects seems not to be statistically different from that of normal subjects. The iron levels do not seem to affect exercise capacity in asymptomatic HH subjects.

Comparison of the prognostic value of cardiopulmonary exercise testing between male and female patients with heart failure

BACKGROUND

Cardiopulmonary exercise testing (CPX) clearly holds prognostic value in the heart failure (HF) population. Studies investigating the prognostic value of CPX in individuals with HF have consistently examined predominantly male groups. The purpose of the present study was to examine the prognostic value of CPX in a female HF group.

METHODS

Seventy-five female and 337 male subjects diagnosed with HF participated in this study. The ability of peak oxygen consumption (VO(2)) and the minute ventilation/carbon dioxide production (VE/VCO(2)) slope to predict cardiac-related events were assessed.

RESULTS

In the year following CPX, the female group suffered 26 cardiac-related events (8 deaths/18 hospitalizations), while the male group suffered 89 cardiac-related events (20 deaths/69 hospitalizations). The hazard ratios for peak VO(2) and the VE/VCO(2) slope were 4.0 (95% confidence interval: 2.6-6.1, p<0.001) and 4.2 (95% confidence interval: 2.7-6.6, p<0.001) in the male group and 3.8 (95% confidence interval: 1.7-8.5, p<0.001) and 4.3 (95% confidence interval: 1.8-9.8, p<0.001) in the female group. In both the male and female groups, Cox multivariate analysis revealed VE/VCO(2) slope was the strongest predictor of cardiac-related events while peak VO(2) added significant predictive value and was retained in the regression.

CONCLUSION

The results of the present study indicate that the prognostic value of peak VO(2) and the VE/VCO(2) slope are similar in men and women diagnosed with HF. In both men and women, the prognostic power of the VE/VCO(2) slope is greater than that of peak VO(2).

The relationship of a 6-min walk to VO(2 peak) and VT in older heart failure patients

PURPOSE

To evaluate the relationship between a 6-min walk test (6-MWT) to peak oxygen consumption (VO(2 peak)) and ventilatory threshold (VT) in older heart failure (HF) patients, to validate the equation by Cahalin et al., and to develop a new equation to improve the prediction of VO(2 peak) from 6-MWT.

METHODS

Older patients (>65 yr) with systolic or diastolic HF (N=97) performed an exercise test to peak exertion on an upright bicycle ergometer using an incremental protocol. Gas exchange measures were collected along with continuous electrocardiograph monitoring. 6-MWT was performed on an indoor track at a self-selected pace under standardized conditions. The formula of Cahalin et al. was used to predict VO(2 peak) from 6-MWT, and a new equation was generated from the measured VO(2 peak)-6-MWT relationship from this investigation.

RESULTS

The correlation between 6-MWT and measured VO(2 peak) was moderate (r=0.54) with a standard error of estimate (SEE) of 2.48 mL.kg.min. The correlation between 6-MWT and VT was weak (r=0.23), whereas the correlation between VO(2 peak) and VT was strong (r=0.74). Correlations between the measured and predicted VO(2 peak) values were moderate (r=0.54) for both prediction equations, and the SEE was 2.83 versus 1.34 mL.kg.min for the Cahalin et al. and the new equation, respectively.

CONCLUSION

These results indicate that 6-MWT does not accurately predict functional capacity in older HF patients, and questions the validity of using this test to determine functional capacity in older HF patients. Predicting VO(2 peak) from equations using 6-MWT also results in substantial variability and, consequently, should not be used in older HF patients where an accurate determination of functional capacity is essential.

Prognostic value of end-tidal carbon dioxide during exercise testing in heart failure

BACKGROUND

The partial pressure of end-tidal carbon dioxide production (P(ET)CO2) at ventilatory threshold (VT) has been shown to be strongly correlated with cardiac output during exercise in patients with heart failure (HF), but few data are available regarding its prognostic utility.

AIMS

The purpose of this study was to assess the ability of P(ET)CO2 to predict cardiac-related events in a group of subjects with HF.

METHODS

One hundred and thirty subjects diagnosed with compensated HF underwent cardiopulmonary exercise testing (CPX). Peak oxygen consumption (VO2), the minute ventilation-carbon dioxide production (VE/VCO2) slope and P(ET)CO2 were determined.

RESULTS

Receiver operating characteristic (ROC) curve analysis revealed that P(ET)CO2 at the ventilatory threshold (VT) was a significant predictor of cardiac-related events (ROC area=0.82, p<0.001). The optimal P(ET)CO2 at a VT threshold value for separating high (< or =) and low (>) risk groups was 36.1 mm Hg (77% sensitivity, 69% specificity). In a multivariate Cox regression analysis, P(ET)CO2 at VT added significant predictive value to the VE/VCO2 slope and peak VO2.

CONCLUSION

These results indicate that P(ET)CO2 during CPX is a significant predictor of cardiac-related events in patients with HF. Clinical assessment of this variable in patients with HF undergoing CPX may therefore be warranted.

Effects of Gender on Peak Oxygen Consumption and the Timing of Cardiac Transplantation

OBJECTIVES

This study examines the gender effects on peak exercise oxygen consumption (VO2) and survival in heart failure (HF) patients and their implications for cardiac transplantation.

BACKGROUND

The predictive value of peak VO2 in women HF patients is poorly established but is one of the indicators used to optimally time cardiac transplantation in women.

METHODS

A total of 594 ambulatory HF patients (mean age 52 +/- 12 years, 28% women, mean left ventricular ejection fraction 26 +/- 12%, 73% on beta-blocker) underwent symptom-limited exercise tests with breath-by-breath expired gas analyses using ramped treadmill protocols. Kaplan-Meier survival curves were generated for each gender and compared using log-rank tests.

RESULTS

Women had a significantly lower peak VO2 than men (14.0 +/- 4.9 ml/kg/min vs. 16.6 +/- 7.1 ml/kg/min; p < 0.0001), despite being younger (48.9 +/- 11.5 years vs. 53.2 +/- 12.4 years; p < 0.0001) and having a higher left ventricular ejection fraction (29 +/- 13% vs. 25 +/- 11%; p < 0.0003). However, the one-year transplant-free survival was significantly lower for men than for women (81% vs. 94%, p < 0.0001), a finding seen across each Weber class. Cox regression analyses confirmed the protective effects of female gender on transplant-free survival when controlling for peak VO2, age, race, beta-blocker use, and type of cardiomyopathy. The peak VO2 associated with 85% one-year transplant-free survival was significantly higher in men than in women (11.5 vs. 10.0 ml/kg/min).

CONCLUSIONS

Women had a significantly lower peak Vo(2) than men, but had better survival at all levels of exercise capacity. The current practice of uniform application of peak VO2 as an aid to determine cardiac transplantation timing should be re-examined.

Prognostic value of heart rate recovery in patients with heart failure

BACKGROUND

The rate in which heart rate recovers from exercise has recently been shown to be a strong predictor of mortality in patients suspected of having coronary disease, but its prognostic value in patients with heart failure (HF) has not been explored. We sought to assess the prognostic utility of heart rate recovery (HRR) in patients with HF.

METHODS

Eighty-seven subjects diagnosed with compensated HF underwent cardiopulmonary exercise testing (CPX). Mean age and ejection fraction were 50.0 (+/-13.9) years and 28.1% (+/-13.6%), respectively. Heart rate at 1-minute post-CPX was subtracted from maximal heart rate during the exercise test to produce a measure of HRR1 in beats per minute. Subjects were followed for a combined death/hospitalization end point for 1-year after CPX.

RESULTS

The mean peak respiratory exchange ratio, peak oxygen consumption (VO2), minute ventilation/carbon dioxide production (VE/VCO2) slope, and HRR1 were 1.06 (+/-0.11), 14.8 (+/-4.7) mL.kg(-1).min(-1), 36.6 (+/-8.6), and 11.0 (+/-10.4) beat/min, respectively. Although all three variables were significant univariate predictors of the composite end point (P < .001), multivariate Cox regression analysis only retained the VE/VCO2 slope (chi2 = 33.5, P < .001) and HRR1 (residual chi2 = 15.0, P < .001) in the equation. The hazard ratio for subjects having both an abnormal VE/VCO2 slope (> 34.4) and HRR1 (< 6.5 beat/min) value was 9.2 (95% CI 4.5-18.5, P < .0001).

CONCLUSIONS

These results indicate that HRR provides additional prognostic information in patients with HF undergoing CPX. Moreover, given the independent prognostic value of HRR, this variable alone may provide valuable clinical information when ventilatory expired gas analysis is not available.

Neuro-hormonal activation predicts ventilatory response to exercise and functional capacity in patients with heart failure

BACKGROUND

Heart failure (HF) is characterised by reduced tolerance to effort, associated with progressive fatigue and dyspnoea. Neuro-hormonal activation is a hallmark of HF and influences its clinical evolution.

AIM

To evaluate the relationship between neuro-hormonal activation, exercise capacity and ventilatory efficiency.

METHODS AND RESULTS

154 HF patients (127 males, 62 +/- 1 years) underwent cardiopulmonary exercise testing and resting blood sampling for assay of plasma brain natriuretic peptide (BNP), NT-proBNP, norepinephrine, epinephrine, aldosterone and plasma renin activity (PRA). BNP and NT-proBNP levels correlated with peak oxygen consumption (VO2) (both R = -0.53, p < 0.001), VE/VCO2 slope (R = 0.56; p < 0.001 and R = 0.58; p < 0.001, respectively) and maximum workload (R = -0.49; p < 0.001 and R = -0.47; p < 0.001, respectively). Norepinephrine correlated slightly less with peak VO2 (R = -0.38, p < 0.001), VE/VCO2 (R = 0.45; p < 0.001) and maximum workload (R = -0.35; p < 0.001). There was a significant inverse correlation between left ventricular ejection fraction and BNP (R = -0.48, p < 0.001), NT-proBNP (R = -0.42; p < 0.001) and norepinephrine (R = -0.43; p < 0.001). Weaker correlations were found for PRA, exercise parameters and ejection fraction. ROC curves showed that BNP was able to identify patients with peak VO2 < 14 ml/min/kg (cut-off 98 pg/ml, AUC 0.775) and a VE/VCO2 > 35 (cut-off 183 pg/ml, AUC 0.797), as well as NT-proBNP (cut-off 537 pg/ml, AUC 0.799 and cut-off 1010 pg/ml, AUC 0.768, respectively) and norepinephrine (cut-off 454 pg/ml, AUC 0.716 and cut-off 575 pg/ml, AUC 0.783, respectively).

CONCLUSION

Haemodynamic impairment (as indicated by BNP and NT-proBNP plasma values) and sympathetic activation predict exercise capacity and ventilatory efficiency in HF patients.

Cardiopulmonary exercise testing in the clinical and prognostic assessment of diastolic heart failure

OBJECTIVES

This study sought to define the relative prognostic value of cardiopulmonary exercise testing (CPET) variables in heart failure (HF) patients with preserved versus reduced systolic function.

BACKGROUND

Cardiopulmonary exercise testing has an established role in the assessment of patients with systolic heart failure (SHF). Two variables, peak Vo2 and, more recently, the VE/VCO2 slope, have been shown to be extremely valuable in risk stratification. However, data are lacking in terms of the prognostic value of CPET in patients with diastolic heart failure (DHF).

METHODS

A total of 409 HF patients underwent CPET. Patients were divided into three groups according to the following left ventricular ejection fraction (LVEF) cutoffs: > or =40%, > or =45%, and > or =50%. The CPET response and the ability of peak VO2 and the VE/VCO2 slope to predict total mortality and hospitalization were examined.

RESULTS

At univariate Cox regression analysis, both the peak VO2 and the VE/VCO2 slope were significant predictors in SHF and DHF. Multivariate analysis documented a similar prognostic power of VE/VCO2 slope and peak VO2 in all SHF groups. Conversely, in DHF patients, VE/VCO2 slope outnumbered peak VO2, remaining the only predictor regardless of LVEF. In DHF, the area under the receiver operating characteristic curve for the VE/VCO2slope identified a cutoff of 32.6 (74% sensitivity, 52% specificity), 33.1 (76% sensitivity, 62% specificity), and 33.3 (97% sensitivity, 40% specificity) for an LVEF cutoff of > or =40%, > or =45%, and > or =50%, respectively.

CONCLUSIONS

These results extend the clinical and prognostic applicability of CPET to DHF. An impairment in exercise ventilation rather than peak VO2 holds clinical and prognostic impact in this increasing subset of patients.

Influence of Heart Failure Etiology on the Prognostic Value of Peak Oxygen Consumption and Minute Ventilation/Carbon Dioxide Production Slope

BACKGROUND

Peak oxygen consumption (V(O2)) and minute ventilation (V(E))/carbon dioxide production (V(CO2)) slope have been widely demonstrated to have strong prognostic value in patients with heart failure (HF). In the present study, we investigated the effect of HF etiology on the prognostic applications of peak V(O2) and Ve/V(CO2) slope.

METHODS

Two hundred sixty-eight subjects underwent symptom-limited cardiopulmonary exercise testing (CPX). The population was divided into ischemic (115 men and 22 women) and nonischemic (108 men and 23 women) subgroups. The occurrence of cardiac-related events over the year following CPX was compared between groups using receiver operating characteristic curve (ROC) analysis

RESULTS

Mean age +/- SD was significantly higher (61.0 +/- 10.0 years vs 50.3 +/- 16.2 years) while mean peak V(O2) was significantly lower (15.0 +/- 5.2 mL/kg/min vs 17.5 +/- 6.7 mL/kg/min) in the ischemic HF group (p < 0.05). ROC curve analysis demonstrated that both peak V(O2) and V(E)/V(CO2) slope were significant predictors of cardiac events in both the ischemic group (peak V(O2), 0.74; V(E)/V(CO2) slope, 0.76; p < 0.001) and the nonischemic group (peak V(O2), 0.75; V(E)/V(CO2) slope, 0.86; p < 0.001). Optimal prognostic threshold values for peak V(O2) were 14.1 mL/kg/min and 14.6 mL/kg/min in the ischemic and nonischemic groups, respectively. Optimal prognostic threshold values for the V(E)/V(CO2) slope were 34.2 and 34.5 in the ischemic and nonischemic groups, respectively.

CONCLUSIONS

Baseline and exercise characteristics were different between ischemic and nonischemic patients with HF. However, the prognostic power of the major CPX variables was strikingly similar. Different prognostic classification schemes based on HF etiology may therefore not be necessary when analyzing CPX responses in clinical practice.

Is Functional Capacity Related to Left Atrial Contractile Function in Nonobstructive Hypertrophic Cardiomyopathy?

The mechanisms underlying reduced exercise capacity in patients with nonobstructive hypertrophic cardiomyopathy (NHCM) could include perturbations of ventricular relaxation, diastolic compliance, or compensatory atrial systolic function. We hypothesized that a loss of atrial contractility in NHCM patients leads to reduced functional capacity. To test this hypothesis, we compared resting noninvasive left atrial ejection phase indices in 49 consecutive patients with NHCM (ages 36+/-10 years; 41% female) and normal left ventricular ejection fraction (mean, 68%+/-8%) with objective metabolic exercise parameters. Left atrial active emptying fraction, ejection force, and kinetic energy failed to predict exercise capacity. Only left atrial total and active emptying volumes correlated weakly with minute volume/CO2 production slope (r=0.31 and r=0.33; p<0.05 for both). Furthermore, when subjects were stratified by New York Heart Association symptomatology, exercise parameters--but not atrial contractility--differed between groups. These data, obtained at rest, fail to suggest that NHCM-related heart failure symptoms are due to an atrial myopathy.

Impact of time past exercise testing on prognostic variables in heart failure

BACKGROUND

Cardiopulmonary exercise testing (CPET) is considered a standard of care in heart failure (HF). The impact that duration of time post-evaluation has on the prognostic value of CPET, however, has not been explored. The purpose of this investigation was to examine the ability of peak oxygen consumption (VO(2)) and the minute ventilation-carbon dioxide production (VE/VCO(2)) slope to predict cardiac-related events at different time intervals post CPET.

METHODS

Two hundred fifty-eight subjects diagnosed with HF underwent CPET. The ability of peak VO(2) and VE/VCO(2) slope to predict cardiac-related events without a time limit, one year post CPET and greater than one year post CPET was examined.

RESULTS

Both peak VO(2) and VE/VCO(2) slope were significant predictors of cardiac-related mortality and hospitalization during the no time constraint and one year post CPET tracking scenarios (Hazard Ratio Range: 3.5-12.4, p<0.001). Peak VO(2) was no longer a significant predictor of mortality greater than one year post CPET. Generally, as time following CPET surpassed one year, the prognostic sensitivity of both variables slightly increased ( approximately 5%) while specificity sharply decreased ( approximately 20%).

CONCLUSIONS

Both peak VO(2) and VE/VCO(2) slope are significant predictors of cardiac-related events in HF. However, the prognostic characteristics of these variables following CPET appear to be time-sensitive.

Prognostic value of resting end-tidal carbon dioxide in patients with heart failure

BACKGROUND

Cardiopulmonary exercise testing (CPET) variables provide valuable prognostic information in the heart failure (HF) population. The purpose of the present study is to assess the ability of resting end-tidal carbon dioxide partial pressure (PETCO2) to predict cardiac-related events in patients with HF.

METHODS

121 subjects diagnosed with compensated HF underwent CPET on an outpatient basis. Mean age and ejection fraction were 49.3 years (+/-14.7) and 28.4% (+/-13.4), respectively. Resting P(ET)CO2 was determined immediately prior to the exercise test in the seated position. Peak oxygen consumption (VO2) and the minute ventilation-carbon dioxide production (VE/VCO2) slope were also acquired during CPET.

RESULTS

There were 41 cardiac-related hospitalizations and 9 cardiac-related deaths in the year following CPET. Mean resting P(ET)CO2, peak VO2 and VE/VCO2 slope were 34.1 mmHg (+/-4.6), 14.5 ml*kg(-1)*min(-1) (+/-5.1) and 35.9 (+/-8.7) respectively. Univariate Cox regression analysis revealed that resting P(ET)CO2 (Chi-square=28.4, p<0.001), peak VO2 (Chi-square=21.6, p<0.001) and VE/VCO2 slope (Chi-square=54.9, p<0.001) were all significant predictors of cardiac related events. Multivariate Cox regression analysis revealed resting P(ET)CO2 added to the prognostic value of VE/VCO2 slope in predicting cardiac related events (residual Chi-square=4.4, p=0.04). Peak VO2 did not add additional value and was removed (residual Chi-square=3.2, p=0.08).

CONCLUSIONS

These results indicate a resting ventilatory expired gas variable possesses prognostic value independently and in combination with an established prognostic marker from the CPET. Resting P(ET)CO2 may therefore be a valuable objective measure to obtain during both non-exercise and exercise evaluations in patients with HF.

Nocturnal Continuous Positive Airway Pressure Improves Ventilatory Efficiency During Exercise in Patients With Chronic Heart Failure

OBJECTIVES

Chronic heart failure is closely related to impaired cardiorespiratory reflex control, including decreased ventilatory efficiency during exercise (Ve/Vco(2)-slope) and central sleep apnea (CSA). Continuous positive airway pressure (CPAP) and nocturnal oxygen therapy alleviate CSA. The aim of the present study was to compare the effects of nocturnal CPAP and oxygen therapy on Ve/Vco(2)-slope.

DESIGN AND SETTING

Prospective controlled trial at a university hospital.

PATIENTS

Twenty-six stable patients with chronic heart failure and CSA.

INTERVENTION AND MEASUREMENTS

Ten patients received nocturnal oxygen, and 16 patients were assigned to CPAP treatment. At baseline and after 12 weeks of treatment, symptom-limited cardiopulmonary exercise testing was performed on a cycle ergometer. Expiratory gas was analyzed breath by breath for evaluation of ventilation and ventilatory efficiency in combination with arteriocapillary blood gas analysis during rest and exercise.

RESULTS

CPAP treatment significantly reduced the Ve/Vco(2)-slope (31.2 +/- 1.6 vs 26.2 +/- 1.0, p = 0.005) and improved the left ventricular ejection fraction (LVEF) [31.7 +/- 2.6% vs 35.7 +/- 2.7%, p = 0.041]. CPAP treatment significantly reduced the apnea-hypopnea index (AHI) [35.9 +/- 4.0/h vs 12.2 +/- 3.6/h, p = 0.002]. Peak oxygen consumption (Vo(2)) [16.2 +/- 1.1 L/min/kg vs 16.3 +/- 1.2 L/min/kg, p = 0.755] remained similar after CPAP treatment. Oxygen therapy reduced the AHI (28.8 +/- 3.2/h vs 8.7 +/- 4.1/h, p = 0.019), but did not improve exercise capacity (peak Vo(2), 15.4 +/- 1.5 L/min/kg vs 15.6 +/- 1.9 L/min/kg, p = 0.760), LVEF (30.9 +/- 2.4% vs 32.5 +/- 2.3%, p = 0.231), or the Ve/Vco(2)-slope (30.0 +/- 1.5 vs 29.8 +/- 1.5, p = 0.646).

CONCLUSION

Nocturnal CPAP and oxygen therapy alleviate CSA to a similar degree. Only CPAP therapy may improve ventilatory efficiency during exercise and may have favorable effects on LVEF. Therefore, our data suggest that CPAP is advantageous compared to oxygen in the treatment of CSA in patients with chronic heart failure.