Reproducibility of cardiopulmonary exercise testing in men following myocardial infarction

Quantifying Improvement in V˙ o2peak and Exercise Thresholds in Cardiovascular Disease Using Reliable Change Indices

PURPOSE

Improving aerobic fitness through exercise training is recommended for the treatment of cardiovascular disease (CVD). However, strong justifications for the criteria of assessing improvement in key parameters of aerobic function including estimated lactate threshold (θ LT ), respiratory compensation point (RCP), and peak oxygen uptake (V˙ o2peak ) at the individual level are not established. We applied reliable change index (RCI) statistics to determine minimal meaningful change (MMC RCI ) cutoffs of θ LT , RCP, and V˙ o2peak for individual patients with CVD.

METHODS

Sixty-six stable patients post-cardiac event performed three exhaustive treadmill-based incremental exercise tests (modified Bruce) ∼1 wk apart (T1-T3). Breath-by-breath gas exchange and ventilatory variables were measured by metabolic cart and used to identify θ LT , RCP, and V˙ o2peak . Using test-retest reliability and mean difference scores to estimate error and test practice/exposure, respectively, MMC RCI values were calculated for V˙ o2 (mL·min -1. kg -1 ) at θ LT , RCP, and V˙ o2peak .

RESULTS

There were no significant between-trial differences in V˙ o2 at θ LT ( P = .78), RCP ( P = .08), or V˙ o2peak ( P = .74) and each variable exhibited excellent test-retest variability (intraclass correlation: 0.97, 0.98, and 0.99; coefficient of variation: 6.5, 5.4, and 4.9% for θ LT , RCP, and V˙ o2peak , respectively). Derived from comparing T1-T2, T1-T3, and T2-T3, the MMC RCI for θ LT were 3.91, 3.56, and 2.64 mL·min -1. kg -1 ; 4.01, 2.80, and 2.79 mL·min -1. kg -1 for RCP; and 3.61, 3.83, and 2.81 mL·min -1. kg -1 for V˙ o2peak . For each variable, MMC RCI scores were lowest for T2-T3 comparisons.

CONCLUSION

These MMC RCI scores may be used to establish cutoff criteria for determining meaningful changes for interventions designed to improve aerobic function in individuals with CVD.

The evolving role of cardiopulmonary exercise testing in ischemic heart disease - state of the art review

PURPOSE OF REVIEW

Cardiopulmonary exercise testing (CPET) is the gold standard for directly assessing cardiorespiratory fitness (CRF) and has a relatively new and evolving role in evaluating atherosclerotic heart disease, particularly in detecting cardiac dysfunction caused by ischemic heart disease. The purpose of this review is to assess the current literature on the link between cardiovascular (CV) risk factors, cardiac dysfunction and CRF assessed by CPET.

RECENT FINDINGS

We summarize the basics of exercise physiology and the key determinants of CRF. Prognostically, several studies have been published relating directly measured CRF by CPET and outcomes allowing for more precise risk assessment. Diagnostically, this review describes in detail what is considered healthy and abnormal cardiac function assessed by CPET. New studies demonstrate that cardiac dysfunction on CPET is a common finding in asymptomatic individuals and is associated with CV risk factors and lower CRF. This review covers how key CPET parameters change as individuals transition from the asymptomatic to the symptomatic stage with progressively decreasing CRF. Finally, a supplement with case studies with long-term longitudinal data demonstrating how CPET can be used in daily clinical decision making is presented.

SUMMARY

In summary, CPET is a powerful tool to provide individualized CV risk assessment, monitor the effectiveness of therapeutic interventions, and provide meaningful feedback to help patients guide their path to improve CRF when routinely used in the outpatient setting.

Test-Retest Reliability of Maximal and Submaximal Gas Exchange Variables in Patients With Coronary Artery Disease

PURPOSE

Gas exchange variables derived from cardiopulmonary exercise tests (CPETs) need to be reliable for evaluating interventions and clinical decision making. Whereas peak oxygen uptake ((Equation is included in full-text article.)O2) has shown to be a highly reliable parameter in patients with coronary artery disease (CAD), little is known about the reproducibility of these parameters in patients with CAD. Therefore, the purpose of this study was to confirm the reliability of peak (Equation is included in full-text article.)O2 and to investigate the reliability of submaximal CPET variables in patients with CAD.

METHODS

Eighty-five patients with CAD (57.6 ± 8.5 years; 79 males) performed 2 CPETs within 10 days before starting a rehabilitation program. Reliability of peak and submaximal exercise variables was assessed by using intraclass correlation coefficients (ICC), coefficients of variation, Pearson correlation coefficients, paired t tests, and Bland-Altman plots.

RESULTS

Maximal and submaximal exercise parameters showed adequate reliability. Overall, there was a good correlation across both testing occasions (r = 0.63-0.95; P < .05 for all). Peak (Equation is included in full-text article.)O2 (ICC, 0.95; 95% CI, 0.92-0.97) demonstrated excellent reliability. Of the submaximal exercise variables, oxygen uptake efficiency slope (OUES) was as reliable as peak (Equation is included in full-text article.)O2 (ICC, 0.97; 95% CI, 0.95-0.98). The ventilation/carbon dioxide production ((Equation is included in full-text article.)E/(Equation is included in full-text article.)CO2) slope showed very good test-retest reliability (ICC, 0.87; 95% CI, 0.80-0.91) and the (Equation is included in full-text article.)O2/work rate slope showed good reliability (ICC, 0.76; 95% CI, 0.64-0.85).

CONCLUSIONS

Both peak (Equation is included in full-text article.)O2 and OUES show excellent test-retest reliability. Accordingly, in the case of no or unreliable peak (Equation is included in full-text article.)O2 data, we suggest using OUES to evaluate cardiorespiratory fitness in patients with CAD.

What can we learn from exercise testing beyond the detection of myocardial ischemia?

Noninvasive cardiopulmonary exercise (CPX) testing has proven useful in the assessment of heart and lung disease, including cardiac and ventilatory reserves. CPX includes the monitoring of respiratory gas exchange, O2 uptake the CO2 production, together with minute ventilation and its components--tidal volume and respiratory rate--together with surveillance of electrocardiography and blood pressure during supervised, incremental exercise. Exercise responses in anaerobic threshold and/or maximal O2 uptake are used to grade functional capacity objectively and to predict cardiac reserve (exercise cardiac output), which grades the severity of chronic cardiac or circulatory failure. CPX also serves to distinguish primary cardiac from ventilatory-based exertional dyspnea.

Short-term reproducibility of cardiopulmonary measurements during exercise testing in patients with severe chronic heart failure

Eleven men with severe chronic heart failure (peak cardiac index 4.0 +/- 0.2 L/m2/min), six on a heart transplantation waiting list, were prospectively assessed. To determine reproducibility of cardiopulmonary and hemodynamic variables for clinical purposes during ramp bicycle ergometry, the patients underwent two ramp bicycle ergometer tests (3 minutes unloaded, work rate increments of 12.5 W/min) with a 1-week interval between tests. Oxygen uptake (VO2) carbon dioxide production (VCO2), and ventilation were measured breath by breath, and calculations were performed to determine gas exchange ratio, oxygen pulse, ventilatory equivalents of oxygen and carbon dioxide, and end-tidal partial pressure for oxygen and carbon dioxide. Additionally, heart rate, blood pressure, and lactate levels were assessed. Measurements were performed at submaximum work rate levels of 25 W, 50 W, and 75 W at ventilatory threshold and at peak work rate. At all measurement points, the coefficient of variation for cardiopulmonary variables was between 1.4% and 7.1% for submaximum work rate levels, between 1.2% and 4.4% at ventilatory threshold, and between 2.4% and 7.1% at peak work rate. For heart rate, blood pressure, and lactate levels, coefficient of variation was between 2.7% and 5.7% for submaximum work rate levels, between 1.4% and 6.1% at ventilatory threshold, and between 1.2% and 5.5% at peak work rate. The data suggest high reproducibility for duplicate measurements of cardiopulmonary and hemodynamic variables during ramp bicycle ergometry in patients with severe chronic heart failure. The results may be used to determine whether any variable in a single patient is significantly different from that obtained in a previous exercise test or if the change is within experimental error.

Exercise intolerance in patients with chronic heart failure

Patients with chronic heart failure (CHF) experience significant morbidity because of dyspnea and fatigue with activities of daily living. Although central hemodynamic abnormalities are the hallmark of this disorder, investigators have not shown a relationship between left ventricular ejection fraction or exercise pulmonary capillary wedge pressure and exercise intolerance in this disorder. Recent studies have focused on the contributions of pulmonary abnormalities and alterations in peripheral vasomotor control and skeletal muscle in exercise intolerance in this disorder. Early anaerobic metabolism occurs in patients with CHF and appears to be caused by a combination of reduced skeletal muscle blood flow and decreased aerobic enzyme content in skeletal muscle. Atrophy in skeletal muscle and alterations in skeletal muscle fiber typing are accompanied by alterations in contractile function in skeletal muscle. These results suggest that exercise intolerance in patients with CHF is multifactorial, and that research efforts must consider central hemodynamic abnormalities, pulmonary abnormalities, and alterations in peripheral blood flow and skeletal muscle biochemistry and histology. The present review will explore current research in this area and develop a model for understanding exercise intolerance in CHF.

Effect on exercise performance of enalapril therapy initiated early after myocardial infarction. Nordic Enalapril exercise Trial

OBJECTIVES

The Nordic Enalapril Exercise Trial was a multicenter subtrial of the Cooperative New Scandinavian Enalapril Survival Study (CONSENSUS II) designed to evaluate the effect on maximal exercise performance of a 6-month period of enalapril treatment initiated early after myocardial infarction.

BACKGROUND

When begun early after myocardial infarction, converting enzyme inhibition therapy has been shown to attenuate infarct expansion and reduce left ventricular volume. Therapy has been associated with improved exercise performance.

METHODS

Three hundred twenty-seven men (mean age 63.3 +/- 10.9 years) with documented acute myocardial infarction were randomized to treatment with enalapril or placebo on a double-blind basis. Intravenous enalaprilat or placebo therapy was initiated within 24 h after the onset of symptoms. Oral therapy was continued at a target dose of 20 mg/day. Patients exercised maximally at 1 month and 6 months after infarction to symptom-limited end points on a cycle ergometer with a 20 W/min incremental protocol.

RESULTS

The treatment and control groups were comparable in patient age, concurrent therapy and type and site of infarction. At 1 month, for all patients, mean total work performed was 34.9 +/- 20.9 kJ in the enalapril group (n = 169) versus 28.5 +/- 20.6 kJ in the placebo group (n = 158) (difference = 18.4%, p < 0.01). This between-group difference in favor of enalapril was greatest in patients > 70 years old (difference = 41.4%, p < 0.01, n = 105) and those with clinical evidence of heart failure (difference = 33.0%, p < 0.01, n = 122). At 6 months for all patients, mean total work performed was 35.4 +/- 23.8 kJ in the enalapril group versus 34.0 +/- 23.9 kJ in the placebo group (difference = 4.1%, NS).

CONCLUSIONS

This trial found that chronic converting enzyme inhibition initiated early after myocardial infarction was associated with significantly greater exercise capacity in men tested at 1 month. This difference was independent of type or site of infarction, patient age or the presence of clinical heart failure. The difference between the treatment and control groups was not significant at 6 months because of improvement in the placebo group. Further research is needed to elucidate the potential mechanisms involved, profile those patients most likely to profit from early therapy and establish the optimal timing and duration for intervention.

Effect of timolol on cardiopulmonary exercise performance in men after myocardial infarction

The effect of the nonselective beta blocker timolol on maximal cardiopulmonary exercise performance was evaluated in 28 men with previous myocardial infarction without effort angina (mean age 63 +/- 8 years). Patients were randomized to placebo or timolol (10 mg twice daily) for 4 weeks and then crossed over to the alternative therapy in a double-blind manner. At the completion of each treatment period, patients underwent symptom-limited maximal cardiopulmonary exercise on a cycle ergometer. Exercise time, heart rate, oxygen consumption (VO2), oxygen (O2) pulse and respiratory exchange ratio were measured at peak exercise and at a submaximal exercise level defined at a respiratory exchange ratio of 1.00. Timolol treatment reduced peak heart rate from 153 +/- 11 to 102 +/- 14 beats/min (-33%, p less than 0.001). Exercise time decreased from 680 +/- 91 to 633 +/- 78 seconds (-7%, p less than 0.001). Peak VO2 decreased from 25.3 +/- 4.7 to 21.4 +/- 3.5 ml/min/kg (-15%, p less than 0.001). O2 pulse increased from 12.9 +/- 1.9 to 16.7 +/- 2.3 ml/beat (+29%, p less than 0.001). Peak respiratory exchange ratio did not change significantly, indicating comparable effort. At submaximal exercise, defined at a respiratory exchange ratio of 1.00, there was no difference in exercise time between placebo and timolol. Heart rate decreased with timolol compared with placebo, from 126 +/- 16 beats/min by 31% (p less than 0.001), VO2 decreased from 18.5 +/- 4.3 ml/min/kg by 10% (p less than 0.001), O2 pulse increased from 11.5 +/- 2.0 ml/beat by 30% (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of long-term enalapril therapy on cardiopulmonary exercise performance in men with mild heart failure and previous myocardial infarction

Forty-one men with documented myocardial infarction greater than 6 months previously were randomized to long-term (48 weeks) therapy with placebo or enalapril on a double-blind basis. All patients were receiving concurrent therapy with digitalis and a diuretic drug for symptomatic heart failure (functional class II or III). The mean age was 64 +/- 7.3 years and no patient suffered from exertional chest pain. Patients underwent maximal cardiopulmonary exertional chest pain. Patients underwent maximal cardiopulmonary exercise testing to exhaustion on an ergometer cycle nine times over the course of 48 weeks. Gas exchange data were collected on a breath by breath basis with use of a continuous ramp protocol. In the placebo group (n = 21), the mean (+/- SD) peak oxygen consumption (VO2) at baseline was 18.8 +/- 5.2 versus 18.5 +/- 5.5 ml/kg per min at 48 weeks (-1.4%, p = NS). In the enalapril group (n = 20), the corresponding values were 18.1 +/- 3.1 versus 18.3 +/- 2.6 ml/kg per min (+2.8%, p = NS). The mean VO2 at the anaerobic threshold for the placebo group at baseline study was 13.1 +/- 3.5 versus 12.8 +/- 2.1 ml/kg per min at 48 weeks (-2.2%, p = NS). The corresponding values for the enalapril group were 11.8 +/- 2.3 versus 11.8 +/- 2.4 ml/kg per min (+1.4%, p = NS). The mean total exercise duration in the placebo group at baseline study was 589 +/- 153 versus 620 +/- 181 s at 48 weeks (+5.4%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of long-term enalapril therapy on cardiopulmonary exercise performance after myocardial infarction

BACKGROUND

The Enalapril Postinfarction Exercise (EPIE) trial was designed to study the effect of enalapril treatment on peak and submaximal cardiopulmonary exercise performance over the course of 1 year in men after myocardial infarction with mild exercise intolerance.

METHODS AND RESULTS

One hundred sixty men with a peak VO2 less than 25 ml/kg/min and without effort angina were randomized to receive enalapril 20 mg qd or placebo on a double-blind basis. The mean age was 60.3 +/- 7.6 years. All patients received concurrent beta-blocker therapy for secondary prophylaxis. Treatment began at 21 days (group 1, n = 100) or more than 6 months after infarction (group 2, n = 60). Patients underwent exercise with real-time gas-exchange analysis nine times over the course of 48 weeks. In group 1, improvement in exercise performance occurred during the course of the trial in both groups of patients receiving placebo or enalapril. The mean peak VO2 for the placebo-treated patients in group 1 increased from 18.3 +/- 3.4 ml/kg/min by 4.9% at 48 weeks (p less than 0.05). The corresponding values for enalapril-treated patients were 18.9 +/- 3.8 ml/kg/min with a 3.7% increase (p = 0.07). Total exercise time increased in the placebo-treated patients from 645 +/- 96 seconds by 7.3% (p less than 0.01). Corresponding values for enalapril-treated patients were 674 +/- 103 seconds with a 5.4% increase (p less than 0.01). In group 2, the mean peak VO2 at baseline for the placebo-treated patients of 20.3 +/- 3.8 ml/kg/min increased by 4.4% at 48 weeks (p = NS). The corresponding values for enalapril-treated patients were 19.2 +/- 3.6 ml/kg/min with a 2.6% increase (p = NS). Total exercise time increased in the placebo-treated patients from 677 +/- 114 seconds by 0.7% (p = NS). Corresponding values for enalapril-treated patients were 659 +/- 99 seconds with a 1.1% increase (p = NS). There were no significant differences between the placebo and enalapril subgroups at any time with regard to peak VO2, exercise duration, or the VO2 at the anaerobic threshold.

CONCLUSIONS

This trial demonstrates that long-term converting enzyme inhibition with enalapril had no significant effect on the peak or submaximal cardiopulmonary exercise performance over the course of 1 year in men after myocardial infarction with only mildly reduced exercise capacity.

Effect of diet therapy on maximum aerobic power in obese, hyperglycaemic men with recently diagnosed type 2 diabetes

To find out the effect of correction of hyperglycaemia on maximum aerobic power and anaerobic threshold, we studied 40 middle-aged obese men with recently diagnosed type 2 diabetes before and after 3 months diet therapy. Respiratory gas exchange was measured during maximal incremental bicycle exercise test with breath-by-breath technique at rest, at anaerobic threshold and at peak exercise. As a whole group, the diabetic men reached higher work load after therapy (+9 +/- 3 W (mean +/- SEM), p less than 0.01). A weak inverse linear correlation was found between the changes in fasting blood glucose and in maximum oxygen uptake (r = -0.29, p less than 0.05). When the patients were divided into two groups according to the median values in the change in fasting blood glucose, only those men with more than 1 mmol l-1 decrease in fasting blood glucose improved maximum oxygen uptake (+124 +/- 55 ml min-1 or +6%, p less than 0.05). Oxygen uptake at anaerobic threshold did not change significantly. These results suggest that the correction of hyperglycaemia by diet therapy may improve maximal aerobic power in obese men with recently diagnosed type 2 diabetes.

Cardiopulmonary exercise testing has limited value in diagnosing heart failure

Usefulness of cardiopulmonary exercise testing in the diagnosis of heart failure was evaluated in a study of 59 patients with clinically suspected heart failure (22 men and 37 women) and 75 healthy control persons (34 men and 41 women), aged 45-74 years. Patients were classified according to certainty of the diagnosis by the Boston criteria: 27 patients were "unlikely" to have heart failure (group I), 19 had "possible" (group II) and 13 had "definite" heart failure (group III). Oxygen consumption at peak exercise and at the appearance of the ventilatory threshold was lower in group III than in the control group (15.6 +/- 1.5 versus 26.0 +/- 0.8 ml/min/kg, p less than 0.001 and 11.8 +/- 1.5 versus 18.0 +/- 0.4 ml/min/kg, p less than 0.001, respectively). However, the distribution of oxygen consumption values was wide in both the control and patient groups, and considerable overlapping of values between study groups was observed. Thus, cardiopulmonary exercise testing appeared to be of limited value in the diagnosis of heart failure.

Validation of a computerized technique for detection of the gas exchange anaerobic threshold in cardiac disease

Respiratory gas exchange data were collected from 77 men greater than 6 months after acute myocardial infarction. Maximal exercise was performed on an ergometer cycle programmed for a ramp protocol of 15 W/min. The gas exchange anaerobic threshold (ATge) was determined by analysis of the carbon dioxide elimination (VCO2) vs oxygen consumption (VO2) curve below a respiratory exchange ratio of 1.00 using a computerized algorithm. This value was estimated at the inflection of VCO2 from a line with a slope of 1 which intersects the VCO2 vs VO2 curve. The relation of the ATge to the lactate acidosis threshold was studied in 29 patients. The reproducibility of the ATge method was studied in 77 patients. Mean (+/- standard deviation) VO2 for the ATge was 905 +/- 220 vs 866 +/- 299 ml/min for the lactate acidosis threshold (r = 0.86, p less than 0.001). Mean VO2 at the ATge for test 1 was 968 +/- 225 vs 952 +/- 217 ml/min for test 2 (r = 0.71, p less than 0.001). Mean peak VO2 was 1,392 +/- 379 vs 912 +/- 202 ml/min at the ATge (r = 0.76, p less than 0.001). Results demonstrate that this ATge method correlates well with the lactate acidosis threshold, is reproducible, and should be useful as an objective measure of submaximal exercise performance.

The effects of flosequinan on submaximal exercise in patients with chronic cardiac failure

1. Twenty patients with moderate to severe chronic cardiac failure were entered into a double-blind parallel group study comparing flosequinan 100 mg daily with matching placebo. 2. After at least three prior exercise tests, cardiopulmonary parameters were assessed at rest and during submaximal exercise before and after 2 and 8 weeks of active drug or placebo. 3. Resting minute ventilation and respiratory rate were reduced by flosequinan compared with placebo, but oxygen uptake was unchanged. 4. Comparison of minute ventilation, carbon dioxide production and venous lactate levels at the end of the exercise stage approximating to 50% of peak oxygen uptake demonstrated significant reductions in the flosequinan group compared with placebo at week 2 and week 8 (P less than 0.05). 5. Flosequinan increased the oxygen uptake at anaerobic threshold from 13.2 +/- 2.8 ml min-1 kg-1 to 15.9 +/- 3.4 ml min-1 kg-1 at week 2 and 15.8 +/- 3.7 ml min-1 kg-1 at week 8. These increases were significant when compared with placebo (P less than 0.05). 6. We conclude that flosequinan improves submaximal exercise performance in patients with chronic cardiac failure, probably by enhancing skeletal muscle blood flow.

Comparison of topical timolol vs betaxolol on cardiopulmonary exercise performance in healthy volunteers

The effects of topical timolol vs betaxolol on cardiopulmonary exercise performance were studied in a randomised double-masked fashion in 12 healthy male volunteers. Cardiopulmonary parameters were evaluated at the anaerobic threshold and at peak exercise. Intraocular pressure was determined before and after treatment by applanation tonometry. No differences were found in aerobic or peak exercise capacity. Maximal heart rate was slightly lower (P less than 0.05) following treatment with timolol compared with betaxolol. However, a correspondingly higher oxygen pulse (oxygen uptake/heart rate) compensated for this reduction and resulted in no difference in peak performance. At physiological work levels, it was not possible to demonstrate any influence of topical, selective or non-selective, beta-adrenergic blockade on cardiopulmonary exercise performance in these healthy volunteers.