Oxygen cost of exercise is increased in heart failure after accounting for recovery costs

STUDY OBJECTIVES: The oxygen cost during exercise has been reported to be decreased in patients with congestive heart failure (CHF), implying an increased efficiency (lower oxygen uptake [VO(2)] per Watt [VO(2)/W]); however, these studies ignored the oxygen debt that is increased in heart failure. SUBJECTS: The primary aim of this research was to evaluate the total oxygen cost (work VO(2)/W) during exercise and recovery in patients with heart failure as compared with healthy adults. DESIGN AND PATIENTS: We performed a retrospective analysis comparing the exercise VO(2)/W, the recovery VO(2)/W, the work VO(2)/W, and the VO(2)/W relationship above and below the ventilatory threshold (VT) in 11 healthy control subjects and 45 patients with CHF. RESULTS: The exercise VO(2)/W was decreased by 29% (p < 0.0001) in patients with CHF; however, the recovery VO(2)/W was increased by 167% (p < 0.0001) and the work VO(2)/W was increased by 14% in patients with CHF (p = 0.014). The VO(2)/W slope increased above the VT (+ 27%, p = 0.0017) in both normal subjects and patients with CHF, suggesting a decrease in efficiency above the VT. There was an inverse correlation (r = 0.646, p < 0.0001) between exercise VO(2)/W and recovery VO(2)/W, implying that subjects with a low exercise VO(2)/W were not efficient but rather accumulated a large oxygen debt that was repaid following completion of exercise. CONCLUSIONS: Heart failure is associated with lower exercise VO(2)/W; however, the patient with heart failure is not efficient, but rather accumulating a large oxygen debt (recovery VO(2)/W) that is repaid following exercise. In addition, the work VO(2)/W (including both exercise and recovery) is increased in patients with heart failure in comparison to control subjects, and correlates inversely with the percentage of predicted VO(2). The large recovery VO(2)/W is likely due to impaired oxygen delivery to exercising muscle during exercise. The increase in the work VO(2)/W is probably due to changes in skeletal muscle fiber type that occur in patients with heart failure (type I to type IIb).     

Oxygen uptake efficiency slope: an index of exercise performance and cardiopulmonary reserve requiring only submaximal exercise

OBJECTIVES: We sought to evaluate, in adults, the efficacy of the Oxygen Uptake Efficiency Slope (OUES), an index of cardiopulmonary functional reserve that can be based upon a submaximal exercise effort. BACKGROUND: Maximal oxygen uptake (VO2,max), the most reliable measure of exercise capacity, is seldom attained in standard exercise testing. The OUES, which relates oxygen uptake to total ventilation during exercise, was proposed by Baba and coworkers (7) in a study of pediatric cardiac patients. They felt this submaximal index of cardiopulmonary reserve might be more practical than VO2max and more appropriate than the commonly used peak oxygen consumption (VO2 peak). METHODS: Treadmill exercise tests with simultaneous respiratory gas measurement were performed in 998 older subjects free of clinically recognized cardiovascular disease and 12 male patients with congestive heart failure. During incremental exercise, oxygen uptake was plotted against the logarithm of total ventilation, and the OUES was determined. RESULTS: The OUES, when calculated only from the first 75% of the exercise test, differed by 1.9% from the OUES calculated from 100% of exercise time in subjects with a peak respiratory exchange rate > or =1.10. On serial tests the OUES was less variable than exercise duration or VO2 peak. It correlated strongly with VO2max, with forced expiratory volume in 1 s and negatively with a history of current smoking. The OUES declined linearly with age in both women and men. A small sample of patients with congestive heart failure had OUES values much lower than those of older subjects without cardiovascular disease. CONCLUSIONS: The OUES is an objective, reproducible measure of cardiopulmonary reserve that does not require a maximal exercise effort. It integrates cardiovascular, musculoskeletal and respiratory function into a single index that is largely influenced by pulmonary dead space ventilation and exercise-induced lactic acidosis.     

Comparison of oxygen uptake during bicycle exercise in patients with chronic heart failure and in normal subjects

Prediction of oxygen uptake (VO2) during exercise from relations established in normal subjects between VO2 and work load in watts (W) may be inaccurate in patients with chronic heart failure because these patients could manifest delayed VO2 kinetics at final stages of exercise. To test the hypothesis that even at low levels of work, patients exhibit a lower VO2 than do normal subjects, 77 patients with heart failure and 27 control subjects with a normal heart or with disease other than heart failure underwent bicycle exercise with respiratory gas analysis. Work load was increased by 10 W/min from an initial 20 W. VO2 (ml/min per kg) was measured every 15 s. The delta VO2/delta W ratio was significantly reduced only in the most severely impaired patients in heart failure class C-D (8.75 +/- 2.14 versus 11.05 +/- 0.38, p less than 0.05). Class B patients showed a lower ratio at a work load of greater than or equal to 80 W, whereas class C-D patients manifested a lower ratio at greater than or equal to 20 W. Even with a low incremental work rate protocol, compared with sedentary normal subjects or patients without heart failure, patients with heart failure demonstrate impaired oxygen uptake. This observation suggests the presence of anaerobic metabolism or delayed VO2 uptake, or both; accordingly, indirect estimates of VO2 requirements derived from intensity or duration of exercise in such patients are overestimated.     

Effects of active muscle mass size on cardiopulmonary responses to exercise in congestive heart failure

Previous studies from this laboratory demonstrated that in healthy young men, cardiac output is closely coupled to oxygen uptake during dynamic exercise, regardless of its mode or relative intensity, whereas other physiologic responses such as heart rate, blood pressure and ventilation are inversely related to the size of the active muscle mass when expressed as functions of oxygen uptake. The purpose of the current investigation was to determine whether congestive heart failure alters the pattern of physiologic responses to various modes of arm and leg exercise in proportion to the size of the active muscle mass. Cardiopulmonary responses to four modes of dynamic work (one arm curl, one arm cycle ergometry, one leg cycle ergometry and two leg cycle ergometry) were characterized in terms of absolute and relative intensities (oxygen uptake and mode-specific percent of peak oxygen uptake, respectively) in middle-aged men with congestive heart failure and control groups of healthy subjects and patients after myocardial infarction without heart failure. Peak oxygen uptake was reduced to the greatest extent in patients with heart failure for large muscle mass work (-13% for curl, -32% for one arm and one leg cycle ergometry and -37% for two leg cycle ergometry; p less than 0.05 versus the normal group for the three modes of ergometry). This finding was paralleled by a markedly blunted slope for the cardiac output-oxygen uptake relation for leg but not arm exercise that was only partially compensated for by a widened arteriovenous oxygen difference. Blood pressure expressed as a function of oxygen uptake remained inversely related to active muscle mass size in all groups of subjects despite attenuation of systolic pressure for heavy large muscle mass effort in the group with heart failure. Pulmonary ventilation at a given metabolic rate was not influenced by active muscle mass size. Thus, saturation of capacity for systemic oxygen transport occurs in conjunction with blunted cardiac output reserve in patients with heart failure during exercise involving a smaller muscle mass than in healthy subjects. The basic inverse relation between size of the active muscle mass and blood pressure at a given metabolic rate is not altered by aging or reduced cardiac reserve. The muscle mass effect on ventilation seen in young healthy subjects disappears with aging.     

Relative attenuation of sympathetic drive during exercise in patients with congestive heart failure

Patients with congestive heart failure have been considered to have augmented sympathetic drive both at rest and during dynamic exercise. The augmentation observed during exercise may be related to the state of near exhaustion experienced by patients with heart failure at relatively low work loads. To compare the response of the sympathetic nervous system to exercise in normal subjects and patients with heart failure when they are working in a comparable physiologic frame of reference, the data for both groups can be expressed as percent peak oxygen consumption achieved (percent peak VO2) rather than as a function of absolute oxygen consumption (VO2). Ten healthy control subjects and 31 patients with chronic clinical class II and III heart failure were studied during upright maximal bicycle exercise. Eighteen of the 31 patients had primary cardiomyopathy and 13 had ischemic cardiomyopathy. The average ejection fraction at rest was 24 +/- 10% (+/- SD) in the group with heart failure. Heart rate, systolic blood pressure, VO2 and plasma norepinephrine levels were measured at rest and throughout exercise. When the data were expressed as a function of percent peak VO2 achieved, patients with heart failure demonstrated a flatter slope (p = 0.004) than normal in the response of plasma norepinephrine to exercise, indicating a relative blunting of sympathetic drive. This was accompanied by attenuated heart rate (p = 0.001) and blood pressure (p less than 0.001) responses. These differences were not apparent when the data are expressed as a function of absolute VO2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiologic correlates of the heart rate response to upright isotonic exercise: relevance to rate-responsive pacemakers

Rate-responsive cardiac pacing requires a sensitive physiologic variable that is closely correlated with the heart rate-oxygen uptake relation, particularly in patients with heart failure whose cardiac output response to exercise is more dependent on heart rate. Accordingly, the heart rate response to upright exercise was measured in 81 patients with heart failure or hypertension, or both, and in 27 normal subjects. Oxygen uptake (VO2), minute ventilation (VE), cardiac output, right heart pressures and the mixed venous temperature, oxygen saturation (SvO2) and pH were analyzed throughout exercise. Linear regression analysis of these variables with heart rate revealed the following: 1) There was a highly linear heart rate-VO2 relation in each subject (the average slope of this relation was greater [p less than 0.05] in patients with more severe failure). 2) VE was highly correlated with exercise heart rate, and its slope was not different between normal subjects and patients. 3) Mixed venous temperature and pH were poor predictors of exercise heart rate, particularly at low or moderate levels of work; however, SvO2 was highly correlated with heart rate for all levels of work. Thus, in normal subjects and patients with heart failure or hypertension, or both, heart rate increases linearly with isotonic leg exercise. Minute ventilation and mixed venous oxygen saturation are highly correlated with this response and may serve as potential sensors for rate-responsive pacemakers.     

Severity and pathophysiology of heart failure on the basis of anaerobic threshold (AT) and related parameters

Cardio-pulmonary exercise testing was performed in 99 normal subjects and 382 patients with cardiac disease in order to evaluate anaerobic threshold (AT) and related parameters as indices for assessing the severity of heart failure. AT could be determined easily during ergometer exercise testing with ramp protocol by monitoring minute ventilation (VE), oxygen uptake (VO2) and carbon dioxide output (VCO2). Peak VO2 and the ratio of VO2 rising to work rate increment (delta VO2/delta WR) were also determined. There was good correlation between the AT determined by respiratory measurement and that determined by arterial lactic acid concentration (r = 0.93, n = 15). The reproducibility of AT was excellent between 2 testings with a 3-hour interval. AT (ml/min/kg) and peak VO2 (ml/min/kg) declined with age, and males showed higher values than females in both indices. %AT, determined by the predicted AT values of each age and sex, decreased as NYHA class progressed as follows: 90.2 +/- 15.4% in class I, 76.9 +/- 13.8% in class II, and 59.7 +/- 11.9% in class III. Although delta VO2/delta WR was not influenced by age or sex, it also decreased as the severity of heart disease progressed. These results suggest that indices from cardiopulmonary exercise testing, especially AT, are closely related to the pathophysiology of heart failure, so that they are objective and reliable parameters for evaluation of the severity of heart failure and are sensitive enough to detect the efficacy of therapeutic intervention for heart failure.     

Cardiopulmonary exercise testing in congestive heart failure

Cardiopulmonary exercise testing includes the monitoring of respiratory gases and airflow to determine oxygen uptake, carbon dioxide (CO2) production, respiratory rate, tidal volume, and minute ventilation during a graded maximal exercise test. A plateau in oxygen uptake, which occurs despite an increase in work load, and which is termed maximal oxygen uptake (VO2 max), correlates with the maximal exercise cardiac output and can therefore be used to grade the severity of heart failure. The anaerobic threshold occurs at 60 to 70% of VO2 max and is another indicator of the severity of heart failure and, when attained, indicates that the patient is close to performing a maximal test. We have found VO2 max and anaerobic threshold to be objective measures of efficacy of both investigational and noninvestigational therapy in patients with heart failure. A pulmonary limitation to exercise can be identified by the failure to attain anaerobic threshold or VO2 max, as well as exhaustion of the ventilatory reserve, as estimated by maximal voluntary ventilation. Thus, cardiopulmonary exercise testing can be used to (1) grade the severity of heart failure, (2) objectively follow the response to therapy, and (3) differentiate a cardiac from a pulmonary limitation to exercise.     

Anaerobic metabolism as an indicator of aerobic function during exercise in cardiac patients.

To determine whether patients with heart disease depend more than normal subjects on anaerobic metabolism to perform the same level of exercise, the anaerobic threshold, slope of the increase in carbon dioxide output with respect to oxygen uptake (delta VCO2/delta VO2) and the slope of the increase in oxygen uptake with respect to the increase in work rate (delta VO2/delta WR) both below and above the anaerobic threshold during exercise were evaluated. A total of 106 patients with chronic heart disease and 42 healthy subjects performed a symptom-limited incremental exercise test in a ramp pattern on a cycle ergometer. Peak oxygen uptake was significantly lower in the patients with heart disease than in the normal subjects. The anaerobic threshold, which was 20 +/- 4.6 ml/min per kg in normal subjects, decreased significantly with progressing severity of functional class: 16 +/- 2.4, 14.1 +/- 2.5 and 11.3 +/- 1.5 ml/min per kg, respectively, in patients in class I, class II and class III. The slope of delta VO2/delta WR, which represents the degree of aerobic metabolism, was also decreased both below and above the anaerobic threshold with increasing severity of heart disease. delta VCO2/delta VO2 below the anaerobic threshold was approximately 0.9 (p = NS between normal subjects and patients). However, delta VCO2/delta VO2 above the anaerobic threshold became steeper with increasing severity of heart disease: 1.37 +/- 0.17 in normal subjects versus 1.55 +/- 0.24, 1.67 +/- 0.3 and 1.8 +/- 0.35 respectively, in patients in functional class I, class II and class III.(ABSTRACT TRUNCATED AT 250 WORDS)     

Response in oxygen uptake and ventilation during stair climbing in patients with chronic heart failure

To examine the level of muscular work and ventilatory response to stair climbing (mobile Stairmaster staircase, 1 step/2.5 s), respiratory gas exchange, ventilation, heart rate and arterial pressure were monitored in patients with chronic heart failure and their response compared with that of normal individuals. Aerobic capacity (maximal oxygen uptake) and anaerobic threshold during treadmill exercise were also determined and used to ascertain the metabolic cost of stair climbing. No differences were observed in the response of mean arterial blood pressure between the 12 patients and 10 normal subjects during exercise or recovery. However, the heart rate and oxygen consumption obtained during exercise were significantly lower in the patients with chronic heart failure than in the normal subjects (p less than 0.05). All patients with a maximal oxygen uptake less than 20 ml/min/kg during treadmill exercise had an oxygen uptake during stair climbing that exceeded their anaerobic threshold and, consequently, they attained a significantly (p less than 0.01) higher level of ventilation during exercise and recovery. This was not the case for those patients with greater aerobic capacity. Therefore, it is concluded that stair climbing for the 12 patients with heart failure and moderate to moderately severe impairment in aerobic capacity represents strenuous anaerobic exercise. The resultant excess ventilation may explain the limiting sensation of dyspnea that is frequently experienced by these patients during and after stair climbing.     

Quality of life and functional status in congestive heart failure]

OBJECTIVE: To assess health related quality of life of patients with congestive heart failure (CHF), to correlate quality of life with other functional parameters; maximal oxygen uptake (peak VO2) with submaximal tests (two minute walking test and shuttle walk test) and New York Heart Association (NYHA) with other clinical variables. METHODS: We evaluated 35 stable congestive heart failure patients (NYHA II-III). Functional status was assessed by NYHA classification, maximal oxygen uptake (peak VO2) and submaximal tests (two minute walk test and shuttle walk test). Health related quality of life was measured with short form 36 health survey (SF 36). RESULTS: NYHA functional class was correlated with social functioning of SF 36, peak VO2 and shuttle walk test. Peak VO2 was correlated with most of the parameters of SF 36. On the other hand 2 minute walk test and shuttle walk test were correlated with social functioning of SF 36. There was a correlation between peak VO2 and submaximal test, but there was no correlation between left ventricular ejection fraction, peak VO2 and NYHA class. CONCLUSION: Social functioning is impaired in patients with congestive heart failure. There is a correlation between maximal and submaximal tests. The maximal and submaximal tests can explain some degree of quality of life. Functional status can be explained with peak VO2 and shuttle walk test apart from NYHA class.     

Do hemodynamic indices correlate with maximum exercise capacity and oxygen consumption in chronic congestive heart failure?

The mechanism of exercise intolerance in chronic congestive heart failure remains unclear. We correlated resting haemodynamic variables with the peak exercise capacity and maximum oxygen consumption (VO2 max) in patients with congestive heart failure in 27 studies on treadmill exercise testing using the modified Bruce protocol. VO2 max was measured using breath by breath expiratory gas analysis. The patients were in severe congestive heart failure (NYHA class II and III, pulmonary artery wedge pressure 23 +/- 2 mmHg, cardiac index 2.4 +/- 0.21 l/min/m2). VO2 max was 23 +/- 2 ml/kg/min. Fatigue was the commonest symptom limiting the exercise. None of the hemodynamic variables correlated well with VO2 max. [right atrial pressure (r = 0.08), pulmonary artery pressure (r = 0.05), pulmonary artery wedge pressure (r = 0.08), aortic pressure (r = -0.3) & cardiac index (r = 0.29)]. Both uni- and multi-variate analysis failed to show any relation between VO2 max and resting hemodynamic variables. We conclude that unlike the acute heart failure syndromes, resting hemodynamic variables do not correlate with exercise capacity in patients with chronic congestive heart failure. The abnormal resting haemodynamics do not limit exercise in these patients. Peripheral mechanisms may thus be more important.     

双心室起搏对慢性心力衰竭患者心肺功能和生活质量的影响

目的:观察双心室起搏对慢性心力衰竭患者心肺功能和生活质量的影响。方法:慢性心力衰竭伴室内传导阻滞患者9例,植入三腔双心室起搏器,比较双心室起搏前、后患者超声心动图检查、心肺功能和生活质量的变化。结果:双心室同步起搏后.患者左室射血分数(%)由术前(21.6±6.7)%增加到(27.3±5.2)%(术后3月,P< 0.05)。(29.5±5.4)%(术后6月,P<0.05);6 min步行距离,由术前(320±97)m增加到(384±103)m(术后3月.P<0.01).(413±110)m(术后6月.P<0.01);峰值氧耗量、氧通气当量(VE/VO2)、二氧化碳通气当量(VE/VCO2)较术前均有显著增加(P<0.05～<0.01);生活质量评分分别改善30%(术后3月,P<0.01),28% (术后6月,P<0.01)。结论:双心室起搏能有效改善慢性心衰患者心肺功能,增加运动贮量,提高生活质量。     

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.     

Ventilatory drive during exercise in congestive heart failure

Background: Continuous increases in the ventilatory equivalent for carbon dioxide (the ratio of minute ventilation to carbon dioxide production, an index of ventilatory drive) during exercise in patients with congestive heart failure would suggest that factors other than carbon dioxide excessively stimulate ventilation during exercise, and may be an important factor in exercise-related dyspnea and fatigue in these patients.Methods and Results: Eighty-five patients with congestive heart failure and 17 normal control subjects underwent symptom-limited exercise testing with gas-exchange analysis. Patients were divided into four functional classes (A–D, Weber's classification) based on peak exercise oxygen consumption. In all heart failure patient groups and in control subjects the ventilatory equivalent for carbon dioxide decreased (P < .005, class D; P < .0001, all other groups) from rest to anaerobic threshold. Three isolated patients showed a continuous increase in ventilatory drive during exercise (mean peak oxygen consumption 13.7 mL/kg/ min). In the lowest functional class (D) the ventilatory equivalent for carbon dioxide was greater than in all other groups at rest, at anaerobic threshold, and at peak exercise (P < .01).Conclusions: In all heart failure groups and in normal control subjects ventilatory drive, as determined by the ventilatory equivalent for carbon dioxide, decreases during exercise. Continuous increases in ventilatory drive during exercise are infrequently seen, suggesting that factors other than carbon dioxide production do not excessively stimulate ventilation in heart failure patients during exercise.     

Forearm reactive hyperemic blood flow and arm-cranking exercise capacity in healthy and heart failure subjects

BACKGROUND: The relationship between lower limbs maximal vasodilatory capacity and exercise capacity in congestive heart failure (CHF) and healthy subjects has been well-documented. However, the relationship between upper limbs maximal vasodilatory capacity and exercise is less well-established. METHODS AND RESULTS: Twelve patients with CHF, 16 age-matched normal subjects, and 11 very fit individuals underwent an arm-cranking exercise test using maximal oxygen uptake (arm VO(2max)) and measurements of peak forearm reactive hyperemic blood flow. Despite similar forearm strength, arm VO(2max) was significantly reduced in patients with CHF when compared to normal and very fit individuals (13.9 +/- 2.9, 23.5 +/- 4.8, and 36.4 +/- 8.5 mL/kg/min, respectively, P <.05). Similarly, peak reactive hyperemia was lower in CHF patients as compared to normal and very fit individuals (18.6 +/- 5.9, 24.3 +/- 5.8, and 41.1 +/- 8.1 mL/100 mL/min, respectively, P <.05). There was a strong relationship between peak reactive hyperemic blood flow and arm VO(2max) (r =.75; P <.001) in all subjects. CONCLUSIONS: These results suggest a significant relationship between forearm vasodilatory capacity and arm-cranking VO(2max) in CHF patients, sedentary, and very fit individuals.     

Effect of metoprolol CR/XL on exercise tolerance in chronic heart failure - a substudy to the MERIT-HF trial

BACKGROUND: Beta-blockade usually causes a slight reduction in exercise capacity among healthy subjects, while more variable results have been observed in chronic heart failure (CHF), probably related to patients studied, methods and agent used. The effect of metoprolol controlled release/extended release (CR/XL) on peak oxygen uptake (peak VO(2)) in this patient population has not previously been investigated. AIMS: We examined the effect of long-term treatment with the selective beta(1)-receptor blocker metoprolol CR/XL once daily on exercise capacity in patients with CHF. METHODS: Ninety-four patients (70 males and 24 females; mean age 63.6+/-10.6 years) with chronic symptomatic heart failure in New York Heart Association (NYHA) functional class II-IV, and with ejection fraction 相似文献   

Neuroendocrine response to standing and mild exercise in patients with untreated severe congestive heart failure and chronic constrictive pericarditis.

OBJECTIVES: Plasma hormones at rest in patients with untreated severe congestive cardiac failure are similar to those occurring during heavy exercise in healthy people. This study examines the hypothesis that the neuroendocrine effects of exercise are modified in untreated congestive cardiac failure. DESIGN: The effect of lying, standing, upright exercise, and recovery on several plasma hormones was measured in healthy controls and 2 groups of patients with severe untreated heart failure. The level of exercise was the same in all groups and low enough to be within the capacity of patients with severe failure. PATIENTS: There were 12 healthy controls, 9 patients with untreated severe congestive cardiac failure caused by myocardial disease, and 12 patients with untreated constrictive pericarditis. SETTING: A tertiary referral centre in North India. RESULTS: Heart rate, noradrenaline, renin activity, aldosterone, cortisol, growth hormone and atrial natriuretic peptide (ANP) were higher in the 2 groups of patients than in the healthy controls during both rest and exercise (P < 0.01 for both comparisons). In general, the effects of this mild degree of exercise were no greater than those of standing. The increase in heart rate during exercise was greater in the group with constrictive pericarditis than in the controls (P = 0.04) and (non-significantly) in congestive heart failure. Apart from these differences the pattern of responses to standing and exercise was similar in the three groups. CONCLUSIONS: While there was evidence of a broad neuroendocrine activation in patients with congestive cardiac failure, the only abnormal increase during exercise (of marginal significance) was found for renin activity in those with myocardial disease. In patients with untreated congestive failure, a substantially normal endocrine response to exercise was superimposed on abnormal resting concentrations.     

Effect of hyperoxia on gas exchange and lactate kinetics following exercise onset in nonhypoxemic COPD patients

STUDY OBJECTIVES: The slow oxygen uptake (VO(2)) kinetics observed in COPD patients is a manifestation of skeletal muscle dysfunction of multifactorial origin. We determined whether oxygen supplementation during exercise makes the dynamic VO(2) response faster and reduces transient lactate increase. DESIGN: Ten patients with severe COPD (ie, mean [+/- SD] FEV(1), 31 +/- 10% predicted) and 7 healthy subjects of similar age performed four repetitions of the transition between rest and 10 min of moderate-intensity, constant-work rate exercise while breathing air or 40% oxygen in random order. Minute ventilation (VE), gas exchange, and heart rate (HR) were recorded breath-by-breath, and arterialized venous pH, PCO(2), and lactate levels were measured serially. RESULTS: Compared to healthy subjects, the time constants (tau) for VO(2), HR, carbon dioxide output (VCO(2)), and VE kinetic responses were significantly slower in COPD patients than in healthy subjects (70 +/- 8 vs 44 +/- 3 s, 98 +/- 14 vs 44 +/- 8 s, 86 +/- 8 vs 61 +/- 4 s, and 81 +/- 7 vs 62 +/- 4 s, respectively; p < 0.05). Hyperoxia decreased end-exercise E in the COPD group but not the healthy group. Hyperoxia did not increase the speed of VO(2) kinetics but significantly slowed VCO(2) and E response dynamics in both groups. Only small increases in lactate occurred with exercise, and this increase did not correlate with the tau for VO(2). CONCLUSION: In nonhypoxemic COPD patients performing moderate exercise, the lower ventilatory requirement induced by oxygen supplementation is not related to improved muscle function but likely stems from direct chemoreceptor inhibition.