Cardiopulmonary exercise testing for evaluation of chronic cardiac failure

Effects of 'cool-down' during exercise recovery on cardiopulmonary systems in patients with coronary artery disease

The effects of 'cool-down' during exercise recovery on cardiovascular and respiratory systems have not been fully clarified. The recovery of respiratory gasses was compared in cardiac patients after maximal exercise during which subjects either performed a cool-down or rested. Twenty-one patients (61+/-10 years) with coronary artery disease performed 2 symptom-limited incremental exercise tests on a cycle ergometer: one with a cool-down and the other without during recovery from the maximal exercise test. Expired gasses were analyzed on a breath-by-breath basis throughout the test and for 6min of recovery. Without a cool-down, the ventilatory equivalent for O2 (VE/O2) increased dramatically during recovery compared with the resting values or those of peak exercise: 44.5+/-7.7 at rest, 44.0+/-10.6 at peak exercise and 63.3+/-14.5 after 2min of recovery. End-tidal PO2 (P(ET)O2) also increased significantly during recovery. However, the overshoot phenomenon of these variables was attenuated when cool-down exercise was performed during recovery. The high ratio of VE/VO2 reflects ventilation perfusion (VA/Q) unevenness and P(ET)O2 is an index of arterial PO2. Thus, it is suggested that cool-down exercise during recovery after maximal exercise testing provides beneficial effects on the respiratory system by decreasing the VA/Q unevenness and relative hyperventilation that are observed when cool-down exercise is not performed.

Cardiopulmonary exercise parameters in relation to all-cause mortality in patients with chronic heart failure

In this study we analysed the all-cause mortality over a period of maximal 6 years in 60 male patients (age: 63.4+/-8.3 years, mean+/-S.D.), suffering from chronic heart failure with resting left ventricular ejection fraction and E/O2 slope as independent factors. We assessed functional NYHA class (II: n=36, III: n=24), radionuclide left ventricular ejection fraction (29.2+/-10.4%) and peak values of heart rate, O2, CO2, E, anaerobic threshold and exercise duration with an incremental work load test on the treadmill. O2 relative to E was based on the individual slopes of the regression of O2 on E during the first 6 min of exercise. These slopes with other exercise-related variables and factors such as etiology, medication, and NYHA class were analysed with a Cox's Regression Method. A survival time analysis (Kaplan-Meier survival curve) was done to establish the influence of E/O2 slope and left ventricular ejection fraction (both split into above and below median values), as well as their interaction, on survival. From all investigated exercise-related variables. E/O2 slope is the most powerful variable regarding prediction of all-cause mortality in our group of chronic heart failure patients. Concerning risk stratification, the subgroup (n=18) with a relatively high left ventricular ejection fraction (>28%) and flat E/O2 slope (<27.6) had most survivors (77.8%) after about 3 years, while the subgroup (n=12) with a relatively high left ventricular ejection fraction (>28%), but a steep E/O2 slope (>27.6) had least survivors (33.3%). This difference in percentage is highly significant (P=0.0025). The fact that E/O2 slope and left ventricular ejection fraction show comparable main and interaction effects between measures of exercise tolerance (e.g., anaerobic threshold, peak O2, exercise duration) on the one hand, and all-cause mortality on the other, suggests the existence of common sources of variance. Based on our analysis, it is unlikely that effects on all-cause mortality are mediated through phenomena related to exercise tolerance. Therefore, we hypothesize that the effects on exercise tolerance and all-cause mortality both depend on common factors, which cause both cardiac and peripheral organ (c.q. muscular) dysfunctions. Moreover, this study clearly shows that E/O2 slope during incremental exercise is an important prognostic marker for risk stratification in chronic heart failure patients, NYHA class II and III.

Synergistic efficacy of enalapril and losartan on exercise performance and oxygen consumption at peak exercise in congestive heart failure

Oxygen consumption at peak exercise (peak VO2) is a strong independent predictor of the outcome in congestive heart failure (CHF). Renin-angiotensin system inhibition with either ACE or AT1 receptor blockers is effective on peak VO2. We evaluated whether mechanisms are similar for the 2 categories of drugs and whether their combination is able to produce a synergistic effect. Twenty CHF patients were randomized to receive, in a double-blind fashion, placebo + placebo (P+P), enalapril (20 mg/day) + placebo (E+P), losartan (50 mg/day) + placebo (L+P), and enalapril + losartan (E+L) or the same preparations in a reverse order, each for 8 weeks. Two patients did not complete the trial. Pulmonary function, cardiopulmonary exercise test, plasma neurohormones, and quality of life were assessed at the end of each treatment. Compared with P+P, E+P, and L+P similarly (16% and 15%, respectively) and significantly (p <0.01) augmented peak VO2. Enalapril improved lung function (reduced slope of ventilation vs carbon dioxide production and dead space to tidal volume ratio, and increased alveolar membrane conductance and tidal volume). Losartan likely activated the exercising muscle perfusion (raised delta VO2/delta work rate, which is a measure of aerobic work efficiency). In combination, they further increased peak VO2, 10% from E+P (p <0.05) and 11% from L+P (p <0.05). Compared with run-in, E+P and L+P significantly reduced plasma norepinephrine by 70 +/- 14 pg/ml and 100 +/- 16 pg/ml and aldosterone by 1.6 +/- 0.7 ng/dl and 1.6 +/- 0.8 ng/dl. These changes were significantly greater when the drugs were combined (140 +/- 20 pg/ml for norepinephrine, and 5.6 +/- 0.9 ng/dl for aldosterone). Quality-of-life score did not improve significantly at each treatment step. Thus, lorsartan and enalapril similarly increased peak VO2 in CHF patients, but mediators of this effect were, at least in part, different therapeutic targets that may be synergistic when the 2 drugs are combined.

Pulmonary function, cardiac function, and exercise capacity in a follow-up of patients with congestive heart failure treated with carvedilol

BACKGROUND

Chronic heart failure causes disturbances in ventilation and pulmonary gas transfer that participate in limiting peak exercise oxygen uptake (VO(2p )). The beta-adrenergic receptor blocker carvedilol improves left ventricular (LV) function and not VO(2p). This study was aimed at investigating the pulmonary response to changes in LV performance produced by carvedilol in patients with chronic heart failure.

METHODS

Twenty-one patients with New York Heart Association class II to III heart failure were randomly assigned (2 to 1) to carvedilol (25 mg twice daily, n = 14) or placebo (n = 7) for 6 months. Rest forced expiratory volume (FEV(1)), vital capacity, total lung capacity, carbon monoxide diffusing capacity, its alveolar-capillary membrane component, pulmonary venous and transmitral flows (for monitoring changes in LV end-diastolic pressure), LV diastolic and systolic dimensions, stroke volume, ejection fraction, and fiber shortening velocity were measured at baseline and at 3 and 6 months. VO(2p), peak ratio of dead space to tidal volume (VD/VT(p)), ventilatory equivalent for carbon dioxide production (VE/VCO(2)), and VO(2) at anaerobic threshold (VO(2at)) were also determined.

RESULTS

FEV(1), vital capacity, total lung capacity, carbon monoxide diffusing capacity, and the alveolar-capillary membrane component were impaired in chronic heart failure compared with 14 volunteers and did not vary with treatment. Carvedilol reduced end-diastolic pressure, end-diastolic diameter, and end-systolic diameter and increased ejection fraction, stroke volume, and fiber shortening velocity without affecting VO(2p), VO(2at), VD/VT(p), or VE/VCO(2) at 3 and 6 months. Placebo did not produce significant changes.

CONCLUSIONS

In chronic heart failure carvedilol ameliorates LV function at rest and does not significantly affect ventilation and pulmonary gas transfer or functional capacity. These results suggest that improvement in cardiac hemodynamics with carvedilol does not reverse pulmonary dysfunction. Persistent lung impairment might have some role in the failure of carvedilol to improve exercise performance.

Cardiopulmonary exercise testing as a screening test for perioperative management of major surgery in the elderly

STUDY OBJECTIVE

To develop an integrated strategy for the identification and subsequent management of high-risk patients in order to reduce both morbidity and mortality.

DESIGN

Prospective consecutive series in which all patients underwent cardiopulmonary exercise (CPX) testing.

SETTING

CPX laboratory and level 3 ICU and high-dependency unit (HDU) of a metropolitan teaching hospital.

PATIENTS

Five hundred forty-eight patients >60 years of age (or younger with known cardiopulmonary disease) scheduled for major intra-abdominal surgery.

INTERVENTIONS

The patients were assigned to one of three management strategies (ICU, HDU, or ward) based on the anaerobic threshold (deltaT) and ECG evidence of myocardial ischemia as determined by CPX testing that was performed as part of the presurgery evaluation, and by the expected oxygen demand stress of the surgical procedure.

RESULTS

Overall mortality was 3.9%. Forty-three percent of deaths were attributed to poor cardiopulmonary function, as detected preoperatively. There were no deaths related to cardiopulmonary complications in any patient deemed fit for major abdominal surgery and ward management, as determined by CPX testing.

CONCLUSIONS

In elderly patients undergoing major intra-abdominal surgery, the AT, as determined by CPX testing, is an excellent predictor of mortality from cardiopulmonary causes in the postoperative period. Preoperative screening using CPX testing allowed the identification of high-risk patients and the appropriate selection of perioperative management.

Kinetics of pulmonary gas exchange during and while recovering from exercise in patients after anterior myocardial infarction

The effect of exercise intensity on gas exchange kinetics was investigated during exercise and recovery, as well as the relationship between the kinetics during exercise and recovery. Twenty-three patients with a history of anterior myocardial infarction performed low-intensity (38.7+/-8.3 W) and high-intensity (68.8+/-15.0 W) exercise for 6 min. The time constants of oxygen uptake (VO2), carbon dioxide output (VCO2) and minute ventilation (VE) were significantly prolonged during high intensity exercise compared with low-intensity exercise (61.2+/-8.6 vs 52.3+/-10.3 s, p<0.005 for the time constant of VO2). The time constant of VO2 was similar during exercise and during recovery from exercise of high (61.2+/-8.6 vs 66.2+/-12.2 s) as well as low intensity (52.3+/-10.3 vs 55.0+/-10.1 s). However, the time constants of VCO2 and heart rate were significantly shorter during recovery than during exercise. The time constants of VCO2 and VE were significantly longer than that of VO2 during both exercise and recovery. In the present study, it was found that (1) the gas exchange kinetics were influenced by the intensity of exercise; (2) the kinetics during recovery did not necessarily reflect the kinetics during exercise except for VO2; and (3) the kinetics of VCO2 and VE were delayed as compared with the VO2 kinetics. These characteristics should be taken into account when using gas exchange kinetics to estimate cardiopulmonary responses to exercise in patients with left ventricular dysfunction.

The influence of diastolic and systolic function on exercise performance in heart failure due to dilated cardiomyopathy or ischemic heart disease

BACKGROUND

Peripheral adaptations and ventricular abnormalities influence physical performance in chronic heart failure. However, the role of the heart in determining exercise capacity has not been completely elucidated.

AIMS

To define cardiac determinants of exercise capacity in patients with dilated cardiomyopathy.

METHODS

In 101 patients with heart failure (NYHA class II-III) due to primary or ischemic dilated cardiomyopathy we measured peak exercise oxygen consumption (Pvo2), left ventricular ejection fraction (EF), left and right atrial and ventricular cavity dimensions, mitral and tricuspid flows. Patients were subdivided in class A (Pvo2 > 20 ml/min per kg; n = 44), class B (Pvo2 16-20 ml/min per kg; n = 42) and class C (Pvo2 < 16 ml/min per kg; n = 15).

RESULTS

Left ventricular diastolic and systolic dimensions, left atrial diameter, right atrial and ventricular areas were greater in class C than in class B and A; EF was lower in class C than in the other two classes; mitral peak flow velocity at early diastole (PFVE) and the ratio between early and late peak flow velocity (PFVE/PFVA) were higher in class C; mitral and tricuspid deceleration time (DT) in class B and A significantly exceeded those in class C. Peak vo2 was correlated with left and right ventricular dimensions, left atrial diameter, EF, mitral PFVE and PFVE/PFVA, mitral and tricuspid DT. Left ventricular EF, DT of the mitral valve and left ventricular diastolic diameter were independent predictors of peak vo2 at multivariate analysis.

CONCLUSIONS

In patients with dilated cardiomyopathy Pvo2 is related to left and right ventricular dimensions, left and right ventricular filling pattern and EF. Both systolic and diastolic dysfunction influence functional capacity.

Prospective, randomized comparison of effect of long-term treatment with metoprolol or carvedilol on symptoms, exercise, ejection fraction, and oxidative stress in heart failure

BACKGROUND

With beta-blocker use becoming more prevalent in treating chronic heart failure (CHF), the choice of drugs raises important theoretical and practical questions. Although the second-generation compound metoprolol is beta1-selective, the third-generation compound carvedilol is beta-nonselective, with ancillary pharmacological properties including alpha-blockade and antioxidant effects. A prospective comparison of these 2 agents can address the issue of optimal adrenergic blockade in selecting agents for therapy in CHF.

METHODS AND RESULTS

Sixty-seven patients with symptomatic stable heart failure were randomly assigned to receive either carvedilol or metoprolol in addition to standard therapy for CHF. Measured variables included symptoms, exercise, ejection fraction, and thiobarbituric acid-reactive substances (TBARS) as an indirect marker of free radical activity. Metoprolol and carvedilol were well tolerated, and both patient groups showed beneficial effects of beta-blocker therapy in each of the measured parameters, with no between-group differences. Ejection fraction increased over 6 months from 18+/-6.3% to 23+/-8.7% (P<0.005) with metoprolol and from 19+/-8.5% to 25+/-9.9% (P<0.0005) with carvedilol (P=NS between groups). With metoprolol, TBARS values decreased from 4.7+/-0.9 nmol/mL at baseline to 4.2+/-1.5 nmol/mL at month 4 to 3.9+/-1.0 nmol/mL at month 6 (P<0.0001). With carvedilol, there was a parallel decline from 4.7+/-1.4 to 4.2+/-1.3 to 4.1+/-1.2 nmol/mL over the same time frame (P<0.025), with no between-group difference in these changes.

CONCLUSIONS

Carvedilol and metoprolol showed parallel beneficial effects in the measured parameters over 6 months, with no relevant between-group differences in this heart failure population.

Oxygen uptake to work rate relation throughout peak exercise in normal subjects: relevance for rate adaptive pacemaker programming

The oxygen uptake to work rate (VO2/WR) relationship observed throughout peak exercise testing is already being applied for rate adaptive pacemaker programming. However, the detailed curve design of VO2/WR with respect to the anaerobic threshold (AT) has not yet been investigated. It was the purpose of this study to determine the VO2/WR slope below and above the AT in a healthy control group. Seventy-eight healthy control subjects (45.9 +/- 17.4 years; 34 women: 49.9 +/- 18.6 years 44 men: 43.6 +/- 16.6 years) were exercised on a treadmill with "breath-by-breath" gas exchange monitoring using the symptom limited "ramping incremental treadmill exercise" (RITE) protocol. The slope of the VO2/WR relationship from rest to peak exercise (r-p), rest to AT (slope A), and AT to peak exercise (slope B) in mL oxygen uptake per watt of external treadmill work was determined by linear regression analysis. [table: see text] The oxygen uptake to work rate relationship throughout peak exercise in the entire study group generated a significant slope change at the AT (31%, P < 0.0001) with a decreasing slope during higher work load intensities. Female subjects demonstrated a greater percentage of slope change at AT (43%), as compared to men (22%, P < 0.01). When using the oxygen uptake to work rate relationship for the programming of the pacemaker's rate response to exercise, the significant slope change at the AT should be considered to more appropriately pace during higher work intensities supported by anaerobic metabolism. Female pacemaker patients should be programmed to generate a steeper VO2/WR slope below AT with a greater slope change at AT, as compared to men. Abnormally high oxygen uptake to work rate ratios above the AT may be possibly used as an indicator of overpacing.

Relationship between exercise capacity and ventilatory equivalent for carbon dioxide in patients with stable old myocardial infarction

The aim of the present study was to evaluate the relationship between exercise capacity and ventilatory response in patients with stable old myocardial infarction. We performed cardiopulmonary exercise test in 61 patients with stable old myocardial infarction and in 30 healthy men. Each subject exercised on a bicycle ergometer until exhaustion. Patients who had anginal pain or electrocardiographic ischemic changes during exercise were excluded. The patients were classified into three groups according to peakVO2 achieved during exercise, using Weber's method: group A, peakVO2 > or = 21 ml/min/kg (n = 4); group B, 14 < or = peakVO2 < 21 ml/min/kg (n = 45); and group C, peakVO2 < 14 ml/min/kg (n = 12). With progressive increases in VCO2, VE increased linearly below the anaerobic threshold (AT) level. The slope of the linear regression line between VCO2 and VE (SLOPE) was calculated in each subject. The mean SLOPE of the healthy men (group N) and groups A, B and C were 25.8 +/- 0.5, 25.1 +/- 0.5, 28.9 +/- 0.8 and 37.1 +/- 1.7 (x 10(-3), respectively. Thus, the SLOPE was steeper in patients with lower peakVO2. It is difficult to perform a maximal exercise tolerance test on patients with chronic heart failure to evaluate their exercise capacity. We can assess exercise capacity by the slope of the linear regression line between VCO2 and VE (SLOPE) at the lower exercise level.

Exercise-induced hemoconcentration in heart failure due to dilated cardiomyopathy

Exercise-induced hemoconcentration is a useful mechanism, particularly in heart failure, because it increases oxygen content of blood, perfusing the working muscles; in 50 normal subjects and 50 patients with congestive heart failure, hemoglobin at peak exercise increased by 7 +/- 3% and 5 +/- 3%, respectively. Hemoconcentration was due to fluid flux out of the vascular bed, likely through oncotic forces related to intracellular lactate accumulation and not to red blood cell recruitment from other organs (spleen), because hemoglobin increase, as a percentage, was similar to plasma protein increase.

Exercise tolerance in asymptomatic elderly men with fluoroscopically detected coronary artery calcification

STUDY OBJECTIVE

The value of detecting coronary artery calcification (CAC), by cardiac imaging, for the diagnosis of coronary artery disease (CAD) in asymptomatic middle-aged men has been demonstrated. However, the incidence of CAC increases with age. The functional significance of CAC remains unknown in asymptomatic elderly men. The purpose of this study is to explore whether CAC in asymptomatic aging men signifies the presence of cardiovascular dysfunction during exercise.

DESIGN

This study was designed to address whether elderly asymptomatic men, selected because they have CAC, have reduced exercise tolerance due to functionally significant CAD.

PARTICIPANTS AND SETTING

Thirty-eight asymptomatic male volunteers (ages 50 to 75 years, mean [+/-SD] 64+/-7 years) with a normal resting ECG and at least one coronary risk factor, in a population study. Nineteen subjects had CAC detected by digital subtraction fluoroscopy in at least two major coronary arteries, and 19 subjects had no identifiable CAC.

METHODS AND RESULTS

Each subject underwent a symptom-limited incremental exercise test with 12-lead ECG monitoring and respiratory gas analysis. Four indexes of exercise oxygen transport were evaluated: peak oxygen uptake (VO2), lactic acidosis threshold, peak VO2/heart rate ratio, and VO2 relative to a work rate increase. Eleven of 38 subjects (28%) were found to have reduced oxygen transport, which was defined as an abnormal reduction in more than two of the above four indexes of oxygen transport. Five of the 11 subjects with reduced oxygen transport had CAC, and 6 subjects did not (not significant). Only one subject with CAC had exercise ST depression.

CONCLUSION

Significant CAC in asymptomatic men over age 50 does not signify exercise limitation due to CAD.

Effects of severity of long-standing congestive heart failure on pulmonary function

To investigate the effects of severity of long-standing congestive heart failure (CHF) on pulmonary function, we studied 53 (47 men) consecutive patients, all heart transplant candidates. Their mean (+/- SD) age and ejection fraction were 47 +/- 12 years and 23 +/- 7%, respectively. All patients underwent spirometry, lung volume, diffusion capacity (DLCO), maximum inspiratory (PImax) and expiratory pressure (PEmax) measurement. Maximum cardiopulmonary exercise test on a treadmill was also performed to determine maximum oxygen consumption (VO2max). On the basis of VO2max, the patients were then divided into those with a VO2max > 14 ml min-1 kg-1 (group 1, n = 30) and those with a VO2max < or = 14 ml min-1 kg-1 (group 2, n = 23). In comparison with group 1, group 2 patients had lower FEV1/FVC (70 +/- 8% vs 75 +/- 7%, P = 0.008), lower FEF25-75 (46 +/- 21 vs 70 +/- 26%pred, P < 0.001), lower TLC (76 +/- 15 vs 85 +/- 13%pred, P = 0.02) and lower PImax (68 +/- 20 vs 87 +/- 22 cmH2O, P = 0.003), but comparable DLCO (84 +/- 15 vs 88 +/- 20%pred, P = N.S.), and PEmax (99 +/- 25 vs 96 +/- 22 cmH2O, P = N.S.). In conclusion, our data suggest that respiratory abnormalities, such as restrictive defects, airway obstruction, and inspiratory muscle weakness, are more pronounced in patients with severe CHF than in those with mild-to-moderate disease. Further studies are required to investigate the extent to which these abnormalities contribute to dyspnoea during daily activities in patients with heart failure.

Improved oxygen utilization during mild exercise in heart failure

In heart failure with low cardiac output, exercise tolerance is reduced despite modulated regional blood distribution and oxygen extraction. However, low cardiac output does not necessarily lead to reduced exercise tolerance especially during mild exercise. In the present study, in order to understand the mechanisms regulating exercise tolerance in heart failure, we measured oxygen consumption (VO2) and cardiac output (CO) during both mild and intense exercise. Patients with heart failure were divided into 2 groups; group L (n = 8) consists of patients with low anaerobic threshold (AT) < 13 ml/min per kg and group H (n = 7) consisting of patients with AT > 13 ml/min per kg. At rest, VO2 was similar between groups L and H, whereas CO was lower in group L than in group H (3.5 + 0.3 vs 4.8 + 1.4 ml/min, p < 0.01). Increase in VO2 during warm-up exercise was not significant between the 2 groups (7.4 +/- 0.5 (group L) vs 6.2 +/- 0.3 ml/min per kg (group H), ns), but increase in CO was lower in group L than in group H (2.5 +/- 0.6 vs 3.4 +/- 0.4 ml/min, p < 0.01). After warm-up to the AT point, however, the increase in not only VO2 but also CO was markedly reduced in group L than in group H (VO2: 0.5 +/- 0.4 vs 3.7 +/- 0.8 ml/min per kg, p < 0.01, CO: 0.2 +/- 0.3 vs 1.1 +/- 0.3 L/min, p < 0.01). Based on these measurements, we calculated the arteriovenous oxygen difference (c(A-V)O2 difference) during exercise in individual patients using Fick's equation. The c(A-V)O2 difference was markedly increased in severe heart failure during the warm-up stage, but between the end of warm-up and the AT point, it remained at the same level as that of group H. These results suggest the presence of a unique mechanism regulating the c(A-V)O2 difference in severe heart failure patients, activation of which may, at least during mild exercise, contribute to efficient oxygen delivery to the peripheral tissues thus compensating for the jeopardized exercise tolerance in those patients.

Early reduction in plasma norepinephrine during beta-blocking therapy with metoprolol in chronic heart failure

BACKGROUND

The possible role exerted by modulation of sympathetic outflow in the clinical effects of beta-blockade in chronic heart failure was tested during short- and long-term treatment.

METHODS AND RESULTS

Oral metoprolol (30-150 mg/day) was added to conventional therapy in 14 patients with idiopathic dilated cardiomyopathy, left ventricular ejection fraction (LVEF) of <0.45, and New York Heart Association class II or III. Norepinephrine plasma levels, which are an index of sympathetic activation, decreased by 27.57 +/- 18.03% after 1 month (P < .005), but returned to pretreatment levels after 6 months. LVEF increased by 7.7 +/- 6.0 ejection fraction units after 6 months (P < .005 vs baseline and P < .05 vs 1 month). Long-term beta-blockade resulted in nonsignificant improvements in functional class, symptom score, and oxygen consumption at peak exercise. After 1 month, the reduction in plasma norepinephrine levels and the changes in LVEF were inversely correlated (P < .01). No other correlation emerged during short- or long-term treatment.

CONCLUSION

In conclusion, the reduction in plasma norepinephrine levels during short-term beta-blockade was not proportional to the clinical benefits and may have been attributed to the direct inhibition of sympathetic outflow. The early reduction in circulating norepinephrine levels may decrease cardiac performance through withdrawal of sympathetic support when the favorable effects of beta-blockade have not had time to occur. The role that sympathetic modulation may exert in the long-term clinical benefits of metoprolol deserves further investigation.

Breathing reserve at the lactate threshold to differentiate a pulmonary mechanical from cardiovascular limit to exercise

STUDY OBJECTIVES

Criteria used to define the respective roles of pulmonary mechanics and cardiovascular disease in limiting exercise performance are usually obtained at peak exercise, but are dependent on maximal patient effort. To differentiate heart from lung disease during a less effort-dependent domain of exercise, the predictive value of the breathing reserve index (BRI=minute ventilation [VE]/maximal voluntary ventilation [MVV]) at the lactate threshold (LT) was evaluated.

DESIGN

Thirty-two patients with COPD and a pulmonary mechanical limit (PML) to exercise defined by classic criteria at maximum oxygen uptake (VO2max) were compared with 29 patients with a cardiovascular limit (CVL) and 12 normal control subjects. Expired gases and VE were measured breath by breath using a commercially available metabolic cart (Model 2001; MedGraphics Corp; St. Paul, Minn). Arterial blood gases, pH, and lactate were sampled each minute during exercise, and cardiac output (Q) was measured by first-pass radionuclide ventriculography (System 77; Baird Corp; Bedford, Mass) at rest and peak exercise.

RESULTS

For all patients, the BRI at lactate threshold (BRILT) correlated with the BRI at VO2max (BRIMAX) (r=0.85, p<0.0001). The BRILT was higher for PML (0.73+/-0.03, mean+/-SEM) vs CVL (0.27+/-0.02, p<0.0001), and vs control subjects (0.24+/-0.03, p<0.0001). A BRILT > or = 0.42 predicted a PML at maximum exercise, with a sensitivity of 96.9%, a specificity of 95.1%, a positive predictive value of 93.9%, and a negative predictive value of 97.5%.

CONCLUSIONS

The BRILT, a variable measured during the submaximal realm of exercise, can distinguish a PML from CVL.

Effects of isosorbide dinitrate on oxygen uptake kinetics in cardiac patients

PURPOSE

Although nitrates are known to improve indices of exercise capacity in patients with coronary artery disease, their effects on oxygen uptake kinetics during the onset of exercise have not been clarified. We evaluated the acute effects of isosorbide dinitrate on the kinetics of oxygen uptake during the onset of exercise at a constant work rate in patients with coronary artery disease.

METHODS

We studied 14 patients with coronary artery disease who performed 6 min of low-intensity exercise at a constant work rate on a cycle ergometer 30 min after oral administration of 10 mg of isosorbide dinitrate or placebo in a double-blind, crossover manner. Oxygen uptake was calculated from breath-by-breath analysis of respired gases. The time constant of oxygen uptake kinetics during the onset of exercise was determined by fitting a single exponential function to the oxygen uptake response.

RESULTS

Heart rate was significantly increased at rest, and systolic blood pressure was significantly decreased both at rest and during exercise after administration of isosorbide dinitrate. The time constant of oxygen uptake was significantly shorter (the kinetics were faster) after administration of isosorbide dinitrate (39.4+/-10.1 vs 44.5+/-10.5 s, P = 0.038).

CONCLUSIONS

Isosorbide dinitrate was found to speed the kinetics of the increase in oxygen uptake during constant work-rate exercise. The time constant of oxygen uptake, which reflects the rapidity of cardiovascular adaptation at the onset of exercise, seems to be a useful parameter of the effectiveness of therapy in patients with coronary artery disease.

Skeletal muscle myosin heavy chains in heart failure: correlation between magnitude of the isozyme shift, exercise capacity, and gas exchange measurements

BACKGROUND

Patients with congestive heart failure (CHF) have a reduced exercise capacity because of the early appearance of fatigue and dyspnea. Qualitative changes in the skeletal muscle composition and metabolism can be responsible for the origin of symptoms

METHODS

We correlated the myosin heavy chain (MHC) composition of the gastrocnemius in 20 patients with different degrees of CHF to NYHA class, diuretic consumption, echocardiographic parameters, and expiratory gases measured during cardiopulmonary exercise testing. MHC composition was determined electrophoretically in skeletal muscle needle microbiopsies and the percent distribution was calculated by densitometry. Maximal cardiopulmonary exercise testing was performed on a treadmill with a modified Naughton protocol. A capnograph was used.

RESULTS

There was no correlation between ejection fraction, left ventricular end systolic diameter, left ventricular end diastolic diameter, and MHC composition. We found a significant positive correlation between the percentage of MHC 1 (slow aerobic isoform) and NYHA class (r2 = 0.62, p < 0.0001), peak VO2 (r2 = 0.5, p < 0.0004), ventilatory threshold (VT) (r2 = 0.33, p = 0.008) and O2 pulse (peak VO2/HR) (r2 = 0.40, p = 0.003). There was a negative correlation between both MHC2a (fast oxidative) and MHC2b (fast glycolytic) with peak VO2 (r2 = 0.38, p = 0.004 and r2 = 0.37, p = 0.004, respectively), VT (r2 = 0.2, p = 0.046 and r2 = 0.34, p = 0.007, respectively), and O2 pulse (peak VO2/HR) (r2 = 0.39, p = 0.003 and r2 = 0.23, p = 0.03). NYHA class was also correlated positively with MHC2a and MHC2b (r2 = 0.46, p = 0.001 and r2 = 0.41, p < 0.006, respectively) and negatively with the same clinical and functional parameters.

CONCLUSIONS

The correlation between the magnitude of the MHC shift from the slow aerobic to the fast glycolytic and fast oxidative with both functional and objective measurements of exercise capacity (peak VO2, VT, O2 pulse) seem to suggest that changes in skeletal muscle composition may play a determining role in exercise tolerance in patients with CHF.

Usefulness of peak oxygen consumption in predicting outcome of heart failure in women versus men

This investigation finds that percent of predicted maximum oxygen consumption, an age- and gender-adjusted measurement of exercise, capacity, describes the degree of functional impairment in women more accurately than peak oxygen consumption. This evidence must be considered when cardiopulmonary metabolic parameters are used for prognostic stratification of women with heart failure.

Relationship between intra- and postoperative oxygen transport and prolonged intensive care after cardiac surgery: a prospective study

BACKGROUND

Prolonged intensive care is a rare but serious complication of cardiac surgery. It is required in less than 10% of operated patients but they use more than 30% of all the intensive care resources needed for cardiac surgery. The aim of our study was to describe the clinical course of the patients who need prolonged intensive care following cardiac surgery and to assess whether the intra- and postoperative oxygen transport variables are different in these patients as compared to patients with an uncomplicated course.

METHODS

The study patients were divided into two groups according to the length of stay in the intensive care unit (ICU) after the operation: Group I, n = 241, ICU-stay < 5 days and Group II, n 20, ICU-stay > or = 5 days. Hemodynamic and oxygen transport data were prospectively obtained intra- and postoperatively and postoperative organ dysfunctions were recorded.

RESULTS

The patients in the prolonged intensive care group tended to be older, have lower ejection fraction and longer cardiopulmonary bypass time. Postoperatively, this group had significantly increased oxygen extraction rate (P = 0.035, repeated measures for ANOVA). In the logistic regression analysis, increased oxygen extraction (31% in Group I vs. 36% in Group II, P < 0.005) at 6 hours after arrival at the intensive care unit had the strongest independent association with the need for prolonged intensive care.

CONCLUSIONS

There was no significant relationship between the factors conventionally assumed to be risk factors for prolonged intensive care. Instead, an increase in whole body oxygen extraction, reflecting a mismatch between the whole body oxygen demand and supply, was associated with the need for prolonged intensive care. Oxygen extraction increased to compensate for the reduced oxygen delivery, which in turn was caused by a lower arterial oxygen content.

Evaluation of a new treadmill exercise protocol

STUDY OBJECTIVES

To confirm that a newly drafted treadmill exercise protocol designed on a theoretical basis to span a range of 0 to 200 W with approximately 25-W increments by alteration of either speed or grade from one stage to the next should correspond to a standard bicycle protocol consisting of 25-W steps.

DESIGN

Randomized, crossover study to compare both exercise test modes.

STUDY PARTICIPANTS

Twenty-one consecutive healthy volunteers.

INTERVENTIONS

Subjects underwent both exercise tests until either exhaustion or completion of the respective protocol, and cardiopulmonary exercise parameters were assessed during either of them. For comparison, correlation coefficients (r) were calculated.

RESULTS

Exercise tolerance time was 9% higher on the treadmill (p<0.05). Ten subjects completed the bicycle program, whereas 18 subjects did so on the treadmill. With both protocols, there were comparably linear increases in heart rate (r=0.885), oxygen uptake (r=0.925), oxygen uptake per body weight (r=0.944), carbon dioxide output (r=0.937), and minute ventilation (r=0.914). For the 2-min stage duration, a plateau in oxygen uptake was achieved with neither protocol. The ventilatory equivalent for oxygen, which is not linear, showed its minimum at comparable workloads, at the point of surpassing the anaerobic threshold. Correlation of oxygen pulse was fair (r=0.896).

CONCLUSIONS

There was an excellent correlation of the parameters with respect to both measured values at identical workloads and slopes of both protocols, thus enabling comparability of treadmill and bicycle ergometry. Due to its practical handling, the new protocol may facilitate acceptance, especially when used for elderly or disabled patients.

Clinical correlates and prognostic significance of the ventilatory response to exercise in chronic heart failure

OBJECTIVES

This study sought to investigate the clinical characteristics of patients with chronic heart failure and an increased ventilatory response to exercise and to examine the prognostic usefulness of this response.

BACKGROUND

The ventilatory response to exercise is increased in many patients with chronic heart failure and may be characterized by the regression slope relating minute ventilation to carbon dioxide output (VE-VCO2 slope) during exercise.

METHODS

One hundred seventy-three consecutive patients (155 men; mean [+/-SD] age 59.8 +/- 11.5 years; radionuclide left ventricular ejection fraction [LVEF] 28.4 +/- 14.6%) underwent cardiopulmonary exercise testing (peak oxygen consumption 18.5 +/- 7.3 ml/kg per min; VE-CO2 slope 34.8 +/- 10.6) over a 2-year period. Using 1.96 standard deviations above the mean VE-VCO2 slope of 68 healthy age-matched subjects (mean slope 26.3 +/- 4.1), we defined a high ventilatory response to exercise as a slope >34.

RESULTS

Eighty-three patients (48%) had an increased VE-VCO2 slope (mean 43.1 +/- 8.9). There was a difference in age (62.2 vs. 57.3 years, p = 0.005), New York Heart Association functional class (2.9 vs. 2.1, p < 0.001), LVEF (24.7 vs. 31.9%, p = 0.0016), peak oxygen consumption (14.9 vs. 21.7 ml/kg per min, p < 0.0001) and radiographic cardiothoracic ratio (0.58 vs. 0.55, p = 0.002) between these patients and those with a normal slope. In the univariate Cox proportional hazards model, the E-VCO2 slope was an important prognostic factor (p < 0.0001). In the multivariate Cox analyses using several variables (age, peak oxygen consumption, VE-VCO2 slope and LVEF), the VE-VCO2 slope gave additional prognostic information (p = 0.018) beyond peak oxygen consumption (p = 0.022). Kaplan-Meier survival curves at 18 months demonstrated a survival rate of 95% in patients with a normal VE-VCO2 slope compared with 69% in those with a high slope (p < 0.0001).

CONCLUSIONS

A high VE-VCO2 slope selects patients with more severe heart failure and is an independent prognostic marker. The VE-VCO2 slope may be used as a supplementary index in the assessment of patients with chronic heart failure.

Exercise tolerance in patients with Ebstein's anomaly

OBJECTIVES

The purpose of this study was to identify the determinants of exercise tolerance in patients with Ebstein's anomaly.

BACKGROUND

Patients with Ebstein's anomaly of the tricuspid valve may have exercise limitation that improves after surgical repair.

METHODS

One hundred seventeen patients performed cycle ergometry for a total of 124 tests (preoperative test in 76 patients, postoperative test in 23, test but no operation in 18, preoperative and postoperative test in 7). Multiple linear regression analysis was used to identify predictors of maximal oxygen uptake, oxygen saturation and heart rate at peak exercise.

RESULTS

Age at the time of exercise ranged from 6 to 60 years (median 15). An atrial septal defect was present in 67 patients (88%) preoperatively. Compared with the preoperative group, the postoperative group had significantly higher maximal oxygen uptake (mean [+/- SD] 20.5 +/- 7.4 vs. 25.3 +/- 7.0 ml/kg body weight per min, p = 0.006). Postoperative rest and exercise blood oxygen saturation was higher than that measured preoperatively (p = 0.0001). Six of seven patients tested before and after the operation showed improved exercise tolerance. Preoperatively, major predictors of maximal oxygen uptake were oxygen saturation at rest (p = 0.01) and age (p = 0.0001). Preoperatively, the major predictor of oxygen saturation at peak exercise was rest oxygen saturation (p = 0.0001), and major predictors of peak exercise heart rate were rest heart rate (p = 0.01) and rest oxygen saturation (p = 0.01). In the postoperative group, predictors of maximal oxygen uptake included age at exercise testing, male gender and heart size.

CONCLUSIONS

Definitive operation for Ebstein's anomaly results in improved exercise tolerance. Before the operation, rest oxygen saturation is the major predictor of exercise tolerance, oxygen saturation at peak exercise and peak heart rate. Postoperatively, age, gender and heart size influenced maximal oxygen uptake.

Effects of exercise during long-term support with a left ventricular assist device. Results of the experience with left ventricular assist device with exercise (EVADE) pilot trial

BACKGROUND

Long-term implantation of a left ventricular assist device (LVAD) may be a future alternative treatment for end-stage heart failure. The objective of the present study was to determine the hemodynamic effects of supine bicycle exercise and functional capacity during upright treadmill exercise in 10 patients after LVAD implantation placed for refractory heart failure as a bridge to cardiac transplantation.

METHODS AND RESULTS

With supine bicycle exercise, 46 +/- 25 days after device placement, heart and LVAD rates increased in parallel from 87 +/- 12 to 117 +/- 14 bpm and 82 +/- 18 to 107 +/- 21 bpm, respectively. Peak O2 consumption was 8.2 +/- 1.7 mL O2.kg-1.min-1. Fick Systemic blood flow rose from 5.0 +/- 1.2 to 7.8 +/- 2.5 L/min. Right atrial and pulmonary capillary wedge pressures increased from 6 +/- 4 and 5 +/- 3 mm Hg to 12 +/- 5 and 13 +/- 8 mm Hg, respectively. End-diastolic left ventricular dimension increased from 3.9 +/- 1.3 to 4.8 +/- 1.6 cm; however, right ventricular dimension decreased from 3.2 +/- 1.0 to 2.3 +/- 0.9 cm. With upright treadmill exercise, peak O2 consumption was 14.1 +/- 2.9 mL O2.kg-1.min-1.

CONCLUSIONS

This study indicates that exercise during long-term LVAD support is safe and is not limited by right heart decompensation. It also justifies a larger study to examine how exercise after LVAD implantation compares with that after cardiac transplantation.

Assessment of the haemodynamic response to exercise by means of electrical impedance cardiography: method, validation and clinical applications

Over the past three decades, the technique of electrical impedance cardiography (EIC) has developed into a valid and reliable instrument for the assessment of stroke volume. Recent developments have made EIC suitable for routine use during exercise testing, too. However, standardization of electrode positioning, stroke volume calculation, and data processing is lacking. In our opinion the most reliable options are, respectively, a modified semicircular electrode array, the Kubicek equation including a haematocrit-based resistivity value, and computerized signal averaging. Although EIC derived stroke volume calculation is based on several debated assumptions, numerous validation studies have shown good accuracy and reproducibility, also during exercise. Addition of EIC measurements during standard clinical exercise testing might be of benefit in occupational medicine, cardiology and pulmonary medicine. Although in the latter setting no validation studies have been performed, major methodological problems are not expected.

Cardiac output estimated noninvasively from oxygen uptake during exercise

Because gas-exchange measurements during cardiopulmonary exercise testing allow noninvasive measurement of oxygen uptake (Vo2), which is equal to cardiac output (CO) x arteriovenous oxygen content difference [C(a-vDo2),] CO and stroke volume could theoretically be estimated if the C(a-vDo2) increased in a predictable fashion as a function of % maximum Vo2 (Vo2max) during exercise. To investigate the behavior of C(a-vDo2) during progressively increasing ramp pattern cycle ergometry exercise, 5 healthy subjects performed 10 studies to exhaustion while arterial and mixed venous blood were sampled. Samples were analyzed for blood gases (pH, Pco2, Po2) and oxyhemoglobin and hemoglobin concentration with a CO-oximeter. The C(a-vDo2) (ml/100 ml) could be estimated with a linear regression [C(a-vDo2) = 5.72 + 0.105 x % Vo2max; r = 0.94]. The CO estimated from the C(a-vDo2) by using the above linear regression was well correlated with the CO determined by the direct Fick method (r = 0.96). The coefficient of variation of the estimated CO was small (7-9%) between the lactic acidosis threshold and peak Vo2. The behavior of C(a-vDo2), as related to peak Vo2, was similar regardless of cardiac function compared with similar measurements from studies in the literature performed in normal and congestive heart failure patients. In summary, CO and stroke volume can be estimated during progressive work rate exercise testing from measured Vo2 (in normal subjects and patients with congestive heart failure), and the resultant linear regression equation provides a good estimate of C(a-vDo2).

Multicenter trial of dynamic cardiomyoplasty for chronic heart failure. The American Cardiomyoplasty Group

OBJECTIVES

The purpose of this study was to prospectively assess the effect of dynamic cardiomyoplasty in patients with symptomatic chronic heart failure.

BACKGROUND

Since the first procedure was performed in 1985, dynamic cardiomyoplasty has been developed for use in patients with chronic heart failure. The aging population in developed countries has made heart failure a growing public health concern. Heart transplantation is appropriate or available for only a small proportion of these patients because of limited donor supply. Effective alternatives to transplantation are needed.

METHODS

Eight centers in North and South America performed 68 cardiomyoplasty procedures between May 1991 and September 1993. Data were prospectively collected every 6 months and compared with preoperative values using paired t tests, chi-square tests and actuarial survival analyses.

RESULTS

Patients had a mean (+/- SD) age of 57 +/- 1 years and were predominantly male (53 [78%] of 68). Heart failure etiology was classified as idiopathic in 47 (69%) of 68 patients and ischemic in 21 (31%). The in-hospital mortality rate was 12% (8 of 68), and the survival rate at 6 and 12 months was 75 +/- 5% and 68 +/- 6%, respectively. Objective improvements were seen at 6 months (n = 49) in left ventricular ejection fraction (23 +/- 1% vs. 25 +/- 1%, p = 0.05), stroke volume (50 +/- 2 vs. 56 +/- 3 ml/beat, p = 0.02) and left ventricular stroke work index (26 +/- 1 vs 30 +/- 2 g/m2 per beat, p = 0.01). Improvements in mean New York Heart Association functional class (3 +/- 0.04 vs. 1.8 +/- 0.1, p = 0.0001) and activity of daily living score (59 +/- 3 vs. 80 +/- 2, p = 0.0001) were also observed. There were no significant changes at 6 months in peak oxygen consumption (15 +/- 1 vs. 16 +/- 1 ml/kg per min), cardiac index (2.26 +/- 0.08 vs. 2.33 +/- 0.08 liters/min per m2), pulmonary capillary wedge pressure (19 +/- 2 vs. 18 +/- 1 mm Hg) or heart rate (87 +/- 2 vs. 82 +/- 3 beats/min).

CONCLUSIONS

These data suggest that dynamic cardiomyoplasty improves ventricular systolic function, reduces symptoms of heart failure and improves objective measures of quality of life in patients with congestive heart failure. This improvement occurred without changes in peak exercise capacity, ventricular filling pressure or actuarial survival.

Ventilation/carbon dioxide production ratio in early exercise predicts poor functional capacity in congestive heart failure

OBJECTIVES

To evaluate whether changes in the ventilation/carbon dioxide production ratio during early exercise could reliably serve as a surrogate marker for maximal oxygen consumption in heart failure patients. Maximal oxygen consumption is an important determinant of the severity of congestive heart failure with values > 14 ml/kg/min conferring a good 2-year survival. However, many patients undergoing cardiopulmonary exercise testing cannot exercise maximally because of other functional limitations.

METHODS

Ventilation/carbon dioxide production ratio was assessed at rest, anaerobic threshold, and peak exercise in 75 patients with chronic heart failure and in 12 healthy controls. Patients were divided into two groups on the basis of heart failure severity as judged by maximal oxygen consumption.

RESULTS

Patients with mild-moderate heart failure had a 20% reduction in the ventilation/carbon dioxide production ratio at anaerobic threshold similar to that in healthy controls. Patients with severe heart failure failed to reduce this ratio at anaerobic threshold. Furthermore, a reduction in the ventilation/carbon dioxide production ratio in early exercise of less than 10% predicted a maximal oxygen consumption of < 14 ml/kg/min with a positive predictive value of 96% and a negative predictive value of 88%.

CONCLUSIONS

A reduction of the ventilation/carbon dioxide production ratio of less then 10% with early exercise reliably predicts poor functional capacity in congestive heart failure. Changes in this ratio during early exercise may be used as a surrogate for maximal oxygen consumption in patients who cannot exercise maximally.

Influence of ACE Inhibition on Fluid Metabolism in Chronic Heart Failure and Its Pathophysiologic Relevance

BACKGROUND: In congestive heart failure with water retention, subtraction of body fluid by ultrafiltration causes greater diuresis and clinical improvement in patients who are angiotensin-converting enzyme (ACE)-inhibited, suggesting an influence of ACE inhibitors on fluid metabolism. METHODS AND RESULTS: Patients with moderate congestive heart failure were subjected to ultrafiltration (around 2000 mL) and followed up for 3 months. Usual outpatient therapy, consisting of digoxin, furosemide, and ACE inhibitors (18 patients, group A) and of digoxin and furosemide only (18 patients, group B), was continued throughout the trial. Hemodynamics, renal function, body fluid and electrolytes, plasma norepinephrine, renin activity, aldosterone, and plasma volume were monitored. At 30 and 90 days after ultrafiltration, hormones, renal function, functional capacity (based on cardiopulmonary tests), and extravascular lung water (chest radiograph score) were determined. Soon after ultrafiltration, body weight, plasma volume, and diuresis were reduced (hypovolemia) and hormones were raised (reaction to hypovolemia). In the next 4 days, all these variables reverted to the pre-ultrafiltration values in group B; in group A diuresis and plasma volume recovered, body weight was still reduced, and hormones became lower than baseline. These changes persisted in the next 3 months. An early reduction of extravascular lung water continued long term in group A only, associated with increase of exercise tolerance time and oxygen uptake and decrease of the dead space/tidal volume ratio. CONCLUSIONS: In congestive heart failure, ACE inhibition persistently prevented fluid accumulation once the excess of body fluid had been withdrawn with a nonpharmacologic method, resulting in sustained improvement in functional capacity. Reduction in circulating norepinephrine, aldosterone, and renin did not seem to be the cause but the consequence of this action, whose mechanisms remain undefined.

Reproducibility of cardiopulmonary exercise parameters in patients with valvular heart disease

STUDY OBJECTIVES

To determine the degree of reproducibility of exercise parameters in patients with chronic heart failure. Parameters such as treadmill walking time (TWT), oxygen uptake (Vo2), heart rate, oxygen pulse, minute ventilation (VE) ventilatory equivalents for oxygen uptake (VE/Vo2) and carbon dioxide output (Vco2), and respiratory quotient at both anaerobic threshold (AT) and peak exercise (PE) each were assessed.

DESIGN

Using the Naughton-Weber protocol, two repeated cardiopulmonary treadmill exercise tests were performed after detailed instructions prior to the first test and on strict adherence to standardized investigational conditions, viz, at the same time of day and at the same ambient temperature, receiving constant medication, and while in a 12-h fasting state.

PATIENTS

The studies were carried out in 17 patients with chronic heart failure due to valvular heart disease considered candidates for intervention because of symptoms. According to Weber's classification of functional capacity, 10 patients were in class A (Vo2 max > 20 mL O2/min/kg), 5 patients were in class B (16 to 20 mL O2/min/kg), and the remaining 2 were in class C (10 to 16 mL O2/min/kg).

MEASUREMENTS

Parameters assessed were TWT, Vo2, heart rate, oxygen pulse, VE and ventilatory equivalents for oxygen (VE/Vo2) and carbon dioxide (VE/Vco2) both at AT and at PE. To reflect reproducibility, correlation coefficients (r) were calculated.

RESULTS

An excellent reproducibility was found for TWT (r = 0.963, p < 0.0001), Vo2 at AT in percent of predicted Vo2max (r = 0.984, p < 0.0001), Vo2 at PE (r = 0.996, p < 0.0001), heart rate at AT (r = 0.943, p < 0.0001) and at PE (r = 0.928, p < 0.0001), oxygen pulse at AT (r = 0.980, p < 0.001) and at PE (r = 0.991, p < 0.0001), VE at AT (r = 0.949, p < 0.0001) and at PE (r = 0.912, p < 0.0001) as well as VE/Vo2 at AT (r = 0.942, p < 0.0001) and at PE (r = 0.781, p < 0.0002) and VE/Vco2 at AT (r = 0.995, p < 0.0001) and at PE (r = 0.943, p < 0.0001), respectively.

CONCLUSIONS

On adherence to standardized conditions, an excellent reproducibility existed for TWT, Vo2 (reflecting cardiac output), ventilation, and heart rate as well as derived parameters, rendering cardiopulmonary exercise testing a reliable means of quantification of heart failure as a prerequisite for enabling diagnostic or therapeutic decisions.

Objective assessment of the response to treatment of severe heart failure using a 9-minute walk test on a patient-powered treadmill

BACKGROUND

No previous studies have demonstrated the changes in exercise capacity that occur during treatment of decompensated severe heart failure. The authors assessed the efficacy and safety of using a patient-powered treadmill to objectively measure exercise capacity and its relationships, if any, to symptom scores and body weight.

METHODS AND RESULTS

Changes in time-limited exercise capacity on a patient-powered treadmill were assessed during inpatient treatment of 12 patients with decompensated chronic heart failure (New York Heart Association classes III and IV). Patients performed a 9-minute walk test daily for 7 days and again at the 6-week follow-up examination. They also completed a 24-item symptom score questionnaire. After treatment, there was a rapid, significant increase in total distance walked, with the increase beginning as early as the second day after admission (mean distance walked +/- SEM, 54 +/- 27 m and 174 +/- 54 m on admission and on day 2, respectively, P < .05). Improvement was maintained throughout the period in the hospital and at 6 weeks (P < .001). Patients reported symptomatic improvement, but this did not reach significance until 4 days after admission (P < .05). Weight loss was not significant. Improved exercise capacity correlated with reduced symptoms and weight loss, but preceded these by several days.

CONCLUSIONS

In patients with decompensated chronic heart failure, this exercise test provides a safe, practical, inexpensive, and objective assessment of functional capacity, providing certain advantages over other indices of response to therapy, such as symptom scores and weight loss. Improvement of exercise capacity does not occur concurrently with relief of symptoms and weight loss.

Contribution of cardiopulmonary indices in the assessment of patients with silent and symptomatic ischemia during exercise testing

Cardiopulmonary and radionuclear indices were used to evaluate and compare cardiac function during exercise testing in patients with symptomatic and silent ischemia. The study comprised 58 patients aged 35-74 years, divided into three groups: Group I-20 patients (controls) with neither ST depression nor chest pain; Group II-22 patients with ST depression > 1 mm and no chest pain; Group III-16 patients with both ST depression and chest pain. All patients in Groups II and III demonstrated significant coronary artery disease. No antianginal medication was taken at least 24 h before testing. All patients underwent a cardiopulmonary exercise test and a multigated acquisition radionuclear study. The following variables were measured: oxygen consumption (VO2), CO2 output (VCO2), minute ventilation (VE), O2-pulse, ventilatory anaerobic threshold (VAT), left ventricular ejection fraction (LVEF) at rest (r) and at maximal effort (ex). Probability values were significant for all variables (P < 0.01-0.0001) except left ventricular ejection fraction-rest (P not significant between the three groups). No significant differences in extent of coronary artery disease were noted between Groups II and III. These findings suggest that during exercise testing patients with silent ischemia have better overall cardiac function than patients with symptomatic ischemia. Their value for both cardiopulmonary and radionuclear indices are closer to those of the control group than to the symptomatic group, regardless of the severity of the coronary artery disease Summary of results: (mean +/- 1 S.D.) Group VO2-max O2-Pulse max VAT (%) VAT (ml/min) LVEF-rest delta LVEF (ex-r) I 25.2 +/- 6.3 15.7 +/- 3.4 51.2 +/- 6.6 1075 +/- 289 54.7 +/- 7 5.4 +/- 4.85 II 22.4 +/- 2.8 14.5 +/- 2 47.0 +/- 5.3 854 +/- 136 52 +/- 10 1.2 +/- 6.7 III 16.0 +/- 2.5 11.4 +/- 2 41.6 +/- 7.7 683 +/- 105 51 +/- 8.5 -5.87 +/- 6.3

Influence of digitalis on left ventricular functional response to exercise in congestive heart failure

This was a double-blind, placebo-controlled, crossover study designed to determine the influence of digitalis treatment on left ventricular (LV) response to physical exercise in patients with congestive heart failure (CHF). In 10 patients with CHF (ejection fraction 29 +/- 2%), LV function was assessed during upright bicycle exercise using an ambulatory radionuclide detector for continuous noninvasive monitoring of cardiac function. Exercise was performed during control conditions and after a 3-week treatment with digoxin (0.25 mg/day orally) or placebo. Ten normal volunteers matched for sex and age constituted the control group. In normals, exercise ejection fraction and end-diastolic volume increased (both p <0.001), while end-systolic volume decreased progressively (p <0.001). In control conditions, patients with CHF had a sharp increase in heart rate during exercise, while ejection fraction did not change; both end-diastolic and end-systolic volumes increased significantly (both p <0.001) during exercise. During digoxin treatment, heart rate response to exercise recorded in patients with CHF was comparable to that recorded in normal subjects. In addition, a significant increase in ejection fraction during exercise was detected (P <0.001), and the increase in end-systolic volume was significantly smaller than that observed in control conditions (p <0.05). When patients received placebo, the responses of LV function to exercise were comparable to those observed in control conditions. These findings demonstrate that digitalis has a favorable influence on LV functional adaptation to exercise in CHF.

Effects of enalapril on exercise tolerance and longevity in dogs with heart failure produced by iatrogenic mitral regurgitation

This study was conducted to evaluate the effects of enalapril on exercise capacity and longevity in dogs with left-sided heart failure produced by iatrogenic mitral regurgitation. After surgical creation of mitral regurgitation, 18 dogs were allocated into replicates according to exercise capacities. One dog in each replicate received placebo, and the other received 0.5 mg/kg of enalapril sid for 9 days and bid thereafter. Exercise tolerance was studied after 10, 19, 52 to 53, and 80 to 81 days, respectively. Finally, the percentage of dogs in each group that survived 357 days was compared. The duration of exercise for dogs in the placebo and enalapril groups did not differ at baseline (P > .1) or after 19 days (P > .1). Dogs that received enalapril had significantly reduced (P < .001) exercise tolerance at day 10, and significantly increased (P = .002) exercise tolerance at days 52 to 53 and 80 to 81 when compared with controls. At 357 days, 22% of dogs receiving placebo were alive, compared with 67% of dogs receiving enalapril; however, these differences were not statistically significant (P = .124). This study shows that enalapril increases exercise tolerance in dogs with left-sided heart failure induced by iatrogenic mitral regurgitation.

Impaired cardiopulmonary exercise capacity in patients with hyperthyroidism

STUDY OBJECTIVE

Hyperthyroidism (H) has been implicated as a primary cause of decreased exercise tolerance. To our knowledge, analysis of respiratory gas exchange, an efficient noninvasive method in evaluating cardiopulmonary capacity, has not been performed in patients with H.

PATIENTS

Using cardiopulmonary exercise testing, 12 consecutive women with Graves' H were examined and controlled in euthyroidism (E). Eighteen women with E, in whom cardiac catheterization had ruled out heart disease, served as control subjects (C).

MEASUREMENTS

The ventilatory anaerobic threshold was determined by means of the V-slope method. Ergometry was performed with patients in a semisupine position using a continuous ramp protocol of 20 W/min. Echocardiography at rest was performed in all patients.

RESULTS

In patients with H, heart rate at rest was higher than in patients with E (p < 0.05) and showed a markedly lower increase between rest and anaerobic threshold compared with E patients (p = 0.007) and C (p = 0.009). Work rate was reduced (H, 50% vs E, 70%; p = 0.038). In H patients, the anaerobic threshold occurred at 59.6% of maximal oxygen uptake and 72% in E patients, respectively (p = 0.024). In H patients, the linear regression of the heart rate to oxygen uptake ratio showed a reduced slope in comparison with E patients (p = 0.001) and C (p = 0.004). In patients with H, a reduced tidal volume (p = 0.021) and an increased respiratory rate (p = 0.003) in comparison to patients with E were demonstrated. Echocardiographically, H patients had an increased ejection fraction (p = 0.008) and a higher cardiac index (p = 0.008) in comparison with E patients.

CONCLUSIONS

Analysis of respiratory gas exchange showed marked alterations of cardiopulmonary exercise capacity in H patients, which are reversible in E patients. The impaired chronotropic response during exercise might be the primary limiting factor of reduced work capacity in patients with H.

Lung-heart interaction as a substrate for the improvement in exercise capacity after body fluid volume depletion in moderate congestive heart failure

We investigated exercise capacity after fluid depletion in patients with moderate congestive heart failure (CHF). Twenty-one patients underwent ultrafiltration (mean volume +/- SEM: 1,770 +/- 135 ml). Echocardiography, tests of pulmonary function, and a cardiopulmonary exercise test with hemodynamic and esophageal pressure monitoring were performed before ultrafiltration and 3 months later. Tests without invasive measurements were repeated 4 and 30 days after ultrafiltration. Twenty-one control patients followed the same protocol but did not have ultrafiltration. Patients who underwent ultrafiltration and increased their oxygen consumption at peak exercise (peak VO2) by > 10% at the 3-month evaluation (group A1, n = 9) were separated from those who did not (group A2, n = 8); 3 patients did not complete the follow-up. Four days after the procedure, peak VO2 had risen from 17.3 +/- 0.8 to 19.3 +/- 0.9 ml/min/kg in group A1, and from 11.9 +/- 0.7 to 14.1 +/- 0.7 ml/min/kg in group A2 (p < 0.01). Plasma norepinephrine and pulmonary function were consistent with a greater severity of the syndrome in group A2. At 3 months in group A1, the relations of filling pressure to cardiac index of the right and left ventricles were shifted upward; the esophageal pressure swing (differences between end-expiratory and end-inspiratory pressure) for a given tidal volume was lower; the peak exercise dynamic lung compliance had increased from 0.10 +/- 0.05 to 0.14 +/- 0.03 L/mm Hg (p < 0.01). None of these changes were detected in group A2 and control patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Excessive oxygen deficit during low-level exercise in heart failure

Although peak oxygen consumption is reduced in patients with symptomatic heart failure, the degree of limitation during routine activity often appears greater or lesser than expected from peak capacity. This study was undertaken to determine whether abnormalities could be detected during the initiation of steady-state low-level exercise, approximating routine activity, which were distinct from limitation in peak capacity. We sought to determine whether a delay in the integrated response to the increased metabolic demand caused by exercise, assessed by the oxygen deficit incurred between exercise initiation and the achievement of steady-state oxygen uptake, was present in heart failure. Low-level and symptom-limited maximal exercise tests in 33 ambulatory patients with heart failure were analyzed and compared with 9 tests in control subjects. Oxygen deficit was determined during the 8-minute low-level exercise at 20 W. During maximal exercise, as expected, patients with heart failure had lower peak oxygen uptake (16 +/- 4 vs 31 +/- 6 ml/kg/min) and anaerobic threshold (870 +/- 270 vs 1,180 +/- 370 ml/min) than controls. After 8 minutes of low-level exercise, the oxygen deficit was higher in patients than in controls (550 +/- 230 vs 270 +/- 100 ml, respectively, p < 0.01). Among patients with heart failure, the oxygen deficit did not correlate with peak oxygen uptake or anaerobic threshold. Although the time to steady-state heart rate was later in patients with heart failure, this delay did not correlate with oxygen deficit. The oxygen deficit represents a distinct abnormality of exercise response that may reflect impaired central and peripheral responses to the initiation of exercise.

Effects of nicorandil on kinetics of oxygen uptake at the onset of exercise in patients with coronary artery disease

The beneficial effects of coronary vasodilators on exercise capacity in patients with angina pectoris are well known. However, their effects on oxygen uptake (VO2) kinetics at the onset of exercise have not been elucidated. The present study was undertaken to determine the acute effects of nicorandil, a newer coronary vasodilator, on the kinetics of VO2 at the onset of exercise in patients with ischemic heart disease. Ten patients with significant coronary stenosis performed constant mild-intensity cycle exercise (32 +/- 3 W) for 6 minutes after oral administration of 10 mg of nicorandil or an identical placebo in a double-blind, crossover manner. Nicorandil had no effect on resting heart rate, blood pressure, or VO2. However, the time constant for the increase in VO2 during constant work rate exercise was significantly shorter (the kinetics of VO2 were faster) after administration of nicorandil than after placebo (46.5 +/- 13.3 vs 51.1 +/- 11.9 seconds; p = 0.039). The increase in VO2 at 6 minutes compared with 3 minutes of constant work, which reflects the VO2 kinetics, also was reduced with nicorandil (3.8 +/- 37.9 vs 27.5 +/- 27.1 ml/min; p = 0.022). Nicorandil was found to increase the rate of VO2, increase during the onset of constant work rate exercise, probably as a result of an improved response in cardiac output. Analysis of VO2 kinetics provides new and useful parameters for the evaluation of circulatory adjustments at the onset of exercise in patients with ischemic heart disease.

An evaluation of integrated cardiopulmonary exercise testing in a pulmonary function laboratory

Clinical exercise testing has been used mainly to assess the cardiac response to exercise. Integrative cardiopulmonary exercise tests (CPET) involving the measurement of the ventilatory, circulatory and metabolic response to exercise has largely been a research tool. We analysed the results of one hundred tests randomly chosen from a total of 472 exercise tests performed between January 1992 and June 1993 as clinical investigation in a pulmonary function laboratory. CPET was used (a) to identify the cause of effort limitation in patients where more than one illness could be relevant (26); (b) to obtain an objective measure of the exercise capacity of patients with respiratory or cardiac disease (31); (c) as monitor of response to treatment (11) and (d) in the investigation of unexplained dyspnoea (32). In 94 of the 100 cases CPET was able to provide an answer to the specific clinical question posed. In patients with unexplained dyspnoea (CPET identified a group who exhibit an inappropriate hyperventilatory response to exercise with no supportive evidence of cardiopulmonary disease. In a small minority of cases CPET gave non-specific results. We conclude that CPET is a useful investigation in the management of patients with cardiopulmonary disease and complements the various other investigations offered by a pulmonary function laboratory.

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.

The "low intensity treadmill exercise" protocol for appropriate rate adaptive programming of minute ventilation controlled pacemakers

The objective of rate adaptive pacemakers that measure minute ventilation by transthoracic impedance is to simulate the physiological relationship of the sensed signal to the sinus node response during exercise, thus achieving an appropriate matching of heart rate with patient effort. The purpose of this study was to determine the physiological relationship between heart rate and minute ventilation (HR/VE) during peak exercise testing in order to develop a database for appropriate rate adaptive slope programming of minute ventilation controlled pacemakers. Due to several clinical limitations of peak exercise testing, it was additionally determined whether the 35-watt "low intensity treadmill exercise" (LITE) protocol can be used as a substitute for peak exercise test using the "ramping incremental treadmill exercise" (RITE) protocol in order to assess the correct HR/VE slope below the anaerobic threshold. The stress tests were performed on a treadmill with the collection of breath-by-breath gas exchange. Linear regression analysis was used to determine the HR/VE slope below and above the anaerobic threshold and during the early, dynamic phase of low intensity exercise with the RITE and LITE protocols, respectively. The results of this testing in 41 healthy subjects demonstrated that the HR/VE relationship throughout treadmill exercise using the RITE protocol was not linear but curvilinear in nature, with a steeper HR/VE slope of 1.54 +/- 0.51 below versus 1.15 +/- 0.37 above the anaerobic threshold (P < 0.005). The HR/VE slope determined during the early, dynamic phase of the LITE protocol (1.58 +/- 0.88) did not differ from the HR/VE slope from rest to anaerobic threshold obtained using the peak exercise RITE test (1.54 +/- 0.51; P = 0.79). Rate adaptive pacing should simulate the curvilinear relationship between heart rate and minute ventilation from rest to peak exercise. The HR/VE slope determined during the early, dynamic phase of low intensity exercise represents the HR/VE slope derived from the RITE protocol below the anaerobic threshold. According to the peak exercise database, the slope above anaerobic threshold can easily be calculated as a percentage of the slope below the anaerobic threshold. The LITE protocol can, therefore, be effectively performed as a substitute for peak exercise stress tests to determine the correct pacemaker rate response factor in order to obtain a physiological heart rate to minute ventilation relationship for the appropriate matching of paced heart rate with patient effort.

Carvedilol improves left ventricular function and symptoms in chronic heart failure: a double-blind randomized study

OBJECTIVES

This study assessed the safety and efficacy of carvedilol in patients with heart failure caused by idiopathic or ischemic cardiomyopathy.

BACKGROUND

Carvedilol is a mildly beta 1-selective beta-adrenergic blocking agent with vasodilator properties. Beta-blockade may be beneficial in patients with heart failure, but the effects of carvedilol are not known.

METHODS

Sixty patients with heart failure (New York Heart Association functional classes II to IV) and left ventricular ejection fraction < or = 0.35 were enrolled in the study. All patients tolerated challenge with carvedilol, 3.125 mg twice a day, and were randomized to receive carvedilol (n = 36) versus placebo (n = 24). Study medication was titrated over 1 month from 6.25 to 25 mg twice a day (< 75 kg) or 50 mg twice a day (> 75 kg) and continued for 3 months. One placebo-treated and two carvedilol-treated patients did not complete the study.

RESULTS

Carvedilol therapy resulted in a significant reduction in heart rate and mean pulmonary artery and pulmonary capillary wedge pressures and a significant increase in stroke volume and left ventricular stroke work. Left ventricular ejection fraction increased 52% in the carvedilol group (from 0.21 to 0.32, p < 0.0001 vs. placebo group). Carvedilol-treated patients also reported a significant lessening of heart failure symptoms (p < 0.05 vs. placebo group). Submaximal exercise duration tended to increase with carvedilol therapy (from 688 +/- 31 s to 871 +/- 32 s), but this change was not significantly different from that with placebo therapy by between-group analysis. Peak oxygen consumption during maximal exercise did not change.

CONCLUSIONS

Long-term carvedilol therapy improves rest cardiac function and lessens symptoms in patients with heart failure.

Assessment of working skeletal muscle oxygenation in patients with chronic heart failure

Patients with chronic heart failure (CHF) are frequently limited by muscle fatigue resulting from impaired skeletal muscle blood flow. Accordingly, we assessed working skeletal muscle oxygenation in such patients using near-infrared (NIR) spectroscopy. Nine normal subjects (mean age 52 years) and 12 patients with CHF (mean age 60 years) were studied. NIR spectroscopy was used to monitor relative changes in oxygenated hemoglobin (Hb) and myoglobin (Mb) (oxy Hb/Mb), deoxygenated Hb and Mb (deoxy Hb/Mb), and total (oxy + deoxy) Hb and Mb (total Hb/Mb) contents in the vastus lateralis muscle at rest, during warm-up (0 W, 30 cycles/min for 3 min), incremental maximal supine bicycle exercise (ramp protocol, 15 W/min, 50 cycles/min), and recovery. At peak exercise the patients exhibited reduced heart rate, systolic blood pressure, peak exercise oxygen consumption (VO2; 15 +/- 3.0 ml/kg/min vs 32 +/- 8.5 ml/kg/min), and workload (99 +/- 23.4 W vs 183 +/- 68.4 W) as compared with the normal subjects. The respiratory quotient was comparable in both groups. In the normal subjects, oxy Hb/Mb was increased from the warm-up period to the early phase of exercise, followed by a progressive decrease to peak exercise. In the recovery phase, oxy Hb/Mb was increased abruptly. For these patients, change in oxy Hb/Mb followed a pattern similar to that seen in normal subjects, and oxy Hb/Mb was decreased earlier in contrast to that in the normal subjects. There was a significant difference in the change of oxy Hb/Mb during warm-up, early phase exercise, and recovery between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of exercise capacity using submaximal exercise at a constant work rate in patients with cardiovascular disease

BACKGROUND

Symptom-limited incremental exercise tests are used to estimate the severity of cardiovascular disease and the patient's daily activity. However, there is a need for objective parameters for submaximal exercise. To test the hypothesis that a decrease in maximal exercise capacity can be estimated by oxygen uptake (VO2) kinetics, we measured the time constant of VO2 both during the onset of constant work rate exercise at 50 W and during recovery from this exercise and compared it with data obtained during maximal exercise in patients with cardiovascular disease and in normal subjects.

METHODS AND RESULTS

A total of 34 patients with cardiovascular disease and 14 normal subjects performed 6 minutes of 50-W constant work rate exercise and an incremental exercise test to the symptom-limited maximum on a cycle ergometer. VO2 was calculated from respiratory gas analysis on a breath-by-breath basis. The time constant of VO2 during the onset of 50-W exercise was 61.4 +/- 15.2 seconds in patients with cardiovascular disease, significantly longer (the kinetics of VO2 were slower) than that in normal subjects (48.8 +/- 10.4 seconds, P = .008). The time constant of VO2 during the onset of exercise was significantly negatively correlated with peak VO2 (r = -.67) and maximal work rate (r = -.66). The time constant during recovery, which did not differ significantly from that of exercise, was also prolonged in patients with cardiovascular disease; it showed a negative correlation with peak VO2 (r = -.63) and maximum work rate (r = -.54).

CONCLUSIONS

The time constant of VO2 during and after recovery from 50 W of constant work rate exercise, which does not require the subject's maximal effort, is a useful and objective measure of exercise capacity in patients with mild to moderate cardiovascular disease.

Exercise-induced left ventricular dysfunction in alcoholic and non-alcoholic cirrhosis

BACKGROUND/AIMS

Autonomic and cardiac dysfunction have been reported in patients with cirrhosis. We studied left ventricular and autonomic function in 20 patients with both alcoholic and non-alcoholic cirrhosis.

METHODS

Autonomic function was assessed by a standard battery of cardiovascular reflex tests. Supine exercise radionuclide ventriculography was used to assess the cardiac response to exercise.

RESULTS

Exercise capacity was reduced in all patients in association with marked chronotropic incompetence (peak heart rates 120.5 +/- 6 bpm). Unlike normal subjects there was no increase in left ventricular ejection fraction on exercise. Stroke volume increased by 23 +/- 6%, mediated by an increase in end-diastolic.volume of > 20%. Cardiac output was subnormal at maximal exercise, increasing by only 96 +/- 14% and 97 +/- 11% in alcoholic and non-alcoholic groups respectively. The majority (83%) of our patients had autonomic reflex abnormalities.

CONCLUSIONS

Patients with cirrhosis of alcohol and non-alcohol related aetiologies have significantly impaired cardiovascular responses to exercise, which are similar to those of a denervated heart. This may have important clinical implications for the ability of these patients to withstand cardiovascular stress.

Maximal exercise tolerance in chronic congestive heart failure. Relationship to resting left ventricular function

The relationship between maximal exercise tolerance and resting radionuclide indexes of left ventricular systolic and diastolic function were evaluated in 20 ischemic and 44 idiopathic cardiomyopathy patients with New York Heart Association class 2-4 chronic congestive heart failure. Left ventricular ejection fraction, peak systolic ejection rate, peak diastolic filling rate, time to peak filling from end-systolic volume, and fractional filling in early diastole were measured from the radionuclide ventriculogram. All patients underwent symptom-limited exercise testing with on-line measurement of oxygen consumption. In the ischemic group, all of the radionuclide indexes correlated poorly with maximal exercise oxygen consumption (VO2max) except the peak systolic ejection rate which correlated modestly (r = 0.58, p < 0.05). Peak systolic ejection rate was significantly lower (p < 0.01) as were the peak diastolic filling rate and fractional filling in the first third of diastole (p < 0.05) in ischemic patients with marked exercise intolerance (VO2max < or = 14 mL/kg/min) compared with those with preserved exercise tolerance (VO2max > 14 mL/kg/min). In the idiopathic group, none of the radionuclide indexes correlated well with VO2max; and all indexes were similar in patients with and without marked exercise intolerance. These data suggest that (1) resting left ventricular ejection fraction poorly predicts maximal exercise capacity in both ischemic and idiopathic cardiomyopathy and (2) resting peak systolic ejection rate, peak diastolic filling rate, and fractional filling in early diastole may predict exercise tolerance in ischemic but not idiopathic cardiomyopathy.

Oxygen uptake kinetics are determined by cardiac function at onset of exercise rather than peak exercise in patients with prior myocardial infarction

BACKGROUND

Resting cardiac function does not necessarily affect exercise capacity. However, to determine whether it affects early dynamics of oxygen uptake (VO2) during exercise, we measured VO2 during a constant work rate and during incremental exercise testing in patients with a history of myocardial infarction. VO2 kinetics and exercise capacity were compared between patients with relatively high left ventricular ejection fractions (LVEF > or = 35%, group 1) and those with lower ejection fractions (LVEF < 35%, group 2).

METHODS AND RESULTS

Forty patients with a history of prior myocardial infarction (age, 57 +/- 10 years) were monitored during 6 minutes of moderate constant work rate testing (40 +/- 8 W) and during symptom-limited incremental exercise testing with a cycle ergometer. VO2 was calculated from respired gas analysis on a breath-by-breath basis. Cardiac output determinations were made with a computerized cadmium telluride detector every 10 seconds during exercise. The VO2 time constant during constant work rate exercise was slower in group 2 (58.0 +/- 7.6 seconds) compared with group 1 (45.8 +/- 10.5 seconds, P = .0002), indicating slower kinetics in group 2. The time constant for the rise in cardiac output during exercise was also slower in patients with lower EFs (63.0 +/- 12.8 versus 50.0 +/- 12.2 seconds). However, there were no differences in exercise capacity parameters, such as the VO2 or cardiac output at peak exercise, obtained during incremental exercise testing among the two groups.

CONCLUSIONS

The prolonged time constant of VO2, which is primarily determined during early parts of exercise, reflects delayed cardiac output response in patients with severely impaired LV function. The time constant of VO2 during submaximal constant work rate exercise can be used as a sensitive and discriminant measure of impaired cardiac reserve in these patients.