Anaerobic threshold detection in patients with congestive heart failure

Two-Day Cardiopulmonary Exercise Testing in Females with a Severe Grade of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Comparison with Patients with Mild and Moderate Disease

Introduction: Effort intolerance along with a prolonged recovery from exercise and post-exertional exacerbation of symptoms are characteristic features of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The gold standard to measure the degree of physical activity intolerance is cardiopulmonary exercise testing (CPET). Multiple studies have shown that peak oxygen consumption is reduced in the majority of ME/CFS patients, and that a 2-day CPET protocol further discriminates between ME/CFS patients and sedentary controls. Limited information is present on ME/CFS patients with a severe form of the disease. Therefore, the aim of this study was to compare the effects of a 2-day CPET protocol in female ME/CFS patients with a severe grade of the disease to mildly and moderately affected ME/CFS patients. Methods and results: We studied 82 female patients who had undergone a 2-day CPET protocol. Measures of oxygen consumption (VO₂), heart rate (HR) and workload both at peak exercise and at the ventilatory threshold (VT) were collected. ME/CFS disease severity was graded according to the International Consensus Criteria. Thirty-one patients were clinically graded as having mild disease, 31 with moderate and 20 with severe disease. Baseline characteristics did not differ between the 3 groups. Within each severity group, all analyzed CPET parameters (peak VO₂, VO₂ at VT, peak workload and the workload at VT) decreased significantly from day-1 to day-2 (p-Value between 0.003 and <0.0001). The magnitude of the change in CPET parameters from day-1 to day-2 was similar between mild, moderate, and severe groups, except for the difference in peak workload between mild and severe patients (p = 0.019). The peak workload decreases from day-1 to day-2 was largest in the severe ME/CFS group (−19 (11) %). Conclusion: This relatively large 2-day CPET protocol study confirms previous findings of the reduction of various exercise variables in ME/CFS patients on day-2 testing. This is the first study to demonstrate that disease severity negatively influences exercise capacity in female ME/CFS patients. Finally, this study shows that the deterioration in peak workload from day-1 to day-2 is largest in the severe ME/CFS patient group.

The effects of Jilin sika Deer's (Cervus dybowski) tendon liquid supplementation on endurance drop jumps performance, biochemistry profile of free boxing players

ETHNOPHARMACOLOGICAL RELEVANCE

Risk of anterior cruciate ligament is a persistent and severe problem in athletes owing to strenuous exercise-induced lower-body injury. Tendon of deer liquid (TD) a familiar traditional Chinese medicine, has been used for strengthening the bones and muscles.

AIM OF THE STUDY

In this study, we seek to demonstrate the application of TD in improving endurance exercise performance and reducing the risk of endurance training injury for free boxing players.

MATERIALS AND METHODS

Sixteen male free boxing players were randomly assigned to the TD and placebo groups. Body composition, clinical biochemistry profiles, kinematic and physiology exercise tests were evaluated at 2 time points - pre-supplementation (pre-) and after 6 weeks post-supplementation (post-).

RESULTS

TD group exhibited significant increase in levels of serum total protein (TP) compared to the placebo group after a 6-week supplementation. Following the treadmill test, serum glucose and maximal oxygen consumption (VO₂ max) levels were increased in the TD group. In the endurance test consisting of 200 counts of drop vertical jumps (DVJs), subjects in the TD group also showed an increase in vertical jump height and reduced risk of musculoskeletal system injuries.

CONCLUSIONS

TD supplementation leads to better physiological adaptation in free boxing players and has the potential for use as a nutrient supplement toward a variety of benefits for endurance athletes.

Test-retest reliability of the oxygen uptake efficiency slope in surgical patients

The oxygen uptake efficiency slope is a measure of cardiopulmonary fitness, that can be obtained from a sub-maximal cardiopulmonary exercise test. It has been evaluated in medical patients but its reliability in surgical populations remains uncertain. We conducted a test-retest study with the aim of establishing the reliability of the oxygen uptake efficiency slope in relation to that of the anaerobic threshold and peak oxygen uptake, in general surgical patients. Twenty-six patients over 60 years old completed two symptom-limited, incremental cycle ergometry tests within 7 days. The mean (SD) anaerobic threshold was 13.0 (3.0) mlO(2) .kg(-1) .min(-1) . There were no significant differences between mean test and retest values of anaerobic threshold (p = 0.50), peak oxygen uptake (p = 0.76) or oxygen uptake efficiency slope (p = 0.42). Reliability coefficients (95% CI) for the anaerobic threshold, oxygen uptake efficiency slope and peak oxygen uptake were 66.7% (45.3-87.9%), 89.0% (81.0-96.9%) and 91.7% (85.7-97.8%), respectively. The oxygen uptake efficiency slope was determined easily in all patients and found to have excellent reliability. Its clinical utility in determining pre-operative fitness warrants further evaluation.

Noninvasive determination of anaerobic threshold by monitoring the %SpO2 changes and respiratory gas exchange

The purpose of this study was to determine the validity of noninvasive anaerobic threshold (AT) estimation using %SpO2 (arterial oxyhemoglobin saturation) changes and respiratory gas exchanges. Fifteen active, healthy males performed 2 graded exercise tests on a motor-driven treadmill in 2 separated sessions. Respiratory gas exchanges and heart rate (HR), lactate concentration, and %SpO2 were measured continuously throughout the test. Anaerobic threshold was determined based on blood lactate concentration (lactate-AT), %SpO2 changes (%SpO2-AT), respiratory exchange ratio (RER-AT), V-slope method (V-slope-AT), and ventilatory equivalent for O2 (EqO2-AT). Blood lactate measuring was considered as gold standard assessment of AT and was applied to confirm the validity of other noninvasive methods. The mean O2 corresponding to lactate-AT, %SpO2-AT, RER-AT, V-slope -AT, and EqO2-AT were 2176.6 +/- 206.4, 1909.5 +/- 221.4, 2141.2 +/- 245.6, 1933.7 +/- 216.4, and 1975 +/- 232.4, respectively. Intraclass correlation coefficient (ICC) analysis indicates a significant correlation between 4 noninvasive methods and the criterion method. Blond-Altman plots showed the good agreement between O2 corresponding to AT in each method and lactate-AT (95% confidence interval (CI). Our results indicate that a noninvasive and easy procedure of monitoring the %SpO2 is a valid method for estimation of AT. Also, in the present study, the respiratory exchange ratio (RER) method seemed to be the best respiratory index for noninvasive estimation of anaerobic threshold, and the heart rate corresponding to AT predicted by this method can be used by coaches and athletes to define training zones.

Reproducibility of the self-controlled six-minute walking test in heart failure patients

INTRODUCTION

The six-minute walk test (6WT) has been proposed to be a submaximal test, but could actually demand a high level of exercise intensity from the patient, expressed by a respiratory quotient >1.0, following the guideline recommendations. Standardizing the 6WT using the Borg scale was proposed to make sure that all patients undergo a submaximal walking test.

PURPOSE

To test the reproducibility of the six-minute treadmill cardiopulmonary walk test (6CWT) using the Borg scale and to make sure that all patients undergo a submaximal test.

METHODS

Twenty-three male heart failure patients (50+/-9 years) were included; these patients had both ischemic (5) and non-ischemic (18) heart failure with a left ventricle ejection fraction of 23+/-7%, were diagnosed as functional class NYHA II-III and were undergoing optimized drug therapy. Patients were guided to walk at a pace between "relatively easy and slightly tiring" (11 and 13 on Borg scale). The 6CWT using the Borg scale was performed two times on a treadmill with zero inclination and patient control of speed with an interval of 24 hours. During the sixth minute, we analyzed ventilation (VE, L/min), respiratory quotient, Oxygen consumption (VO2, ml/kg/min), VE/VCO2 slope, heart rate (HR, bpm), systolic blood pressure (SBP, mmHg), diastolic (DBP, mmHg) blood pressure and distance.

RESULTS

The intraclass correlation coefficients at the sixth minute were: HR (r i=0.96, p<0.0001), VE (r i=0.84, p<0.0001), SBP (r i=0.72, p=0.001), distance (r i=0.88, p<0.0001), VO2 (r i=0.92, p<0.0001), SlopeVE/VCO2 (r i=0.86, p<0.0001) and RQ<1 (r i=0.6, p=0.004).

CONCLUSION

Using the 6CWT with the Borg scale was reproducible, and it seems to be an appropriate method to evaluate the functional capacity of heart failure patients while making sure that they undergo a submaximal walking test.

The cardiopulmonary exercise test is safe and reliable in elderly patients with chronic heart failure

AIM

To assess safety and feasibility of cardiopulmonary exercise test (CPX) in elderly patients with chronic heart failure (CHF) and left ventricular dysfunction.

METHODS AND RESULTS

We analysed 395 cardiopulmonary exercise tests (CPXs) performed in 227 clinically stable patients with CHF [mean age 76 years, males 70%, mean New York Heart Association (NYHA) class 2.2 +/- 0.5] and impaired left ventricular function (mean ejection fraction 43 +/- 12%). Ninety-eight out of 395 CPXs (25%) were performed in patients older than 80 years. A standard bicycle exercise ramp protocol was used, with increments of 10 W/min. An expiratory exchange ratio (RER) >or= 1.05 at the peak of CPX was considered as the index of maximal exercise. Average workload was 65 +/- 23 W. No adverse reactions were observed, although one test was stopped for non-sustained ventricular tachycardia. The main reasons for stopping were exhaustion (50%), dyspnoea (30%), maximal predicted heart rate (17%), orthopaedic problems (2.5%) and significant ST segment depression (0.5%). In the overall cohort, 80% of patients achieved an RER >or= 1.05 and, in 56% of them, the RER was >or= 1.15. The anaerobic threshold (AT) was detectable in 80% of CPXs, and mean oxygen consumption (VO2) at AT was 9 +/- 6 ml/kg per min, whereas mean peak VO2 was 11 +/- 3 ml/kg per min. In the cohort of patients aged > 80 years, 71% reached an RER >or= 1.05 and 47% reached an RER >or= 1.15. In these older patients, AT was detectable in 68% of CPXs performed, and the mean peak VO2 was 10 +/- 3 ml/kg per min.

CONCLUSIONS

In elderly patients with CHF, the CPX is safe, feasible and able to provide basic information for individual risk assessment. These findings potentially extend the indications of CPX, which is currently applied to selected middle-aged patients with CHF, to the elderly population.

Low agreement of ventilatory threshold between training modes in cardiac patients

In cardiac rehabilitation, different endurance exercises such as walking and cycling are often performed. The training intensity for these modes is determined from a single treadmill or bicycle test by ventilatory threshold (VT). In this study, differences of VT between walking and cycling and agreement of VT between training modes were assessed in cardiac patients. A total of 46 cardiac rehabilitation patients (mean age 59.5+/-8.4 years, 45 males) (31 untrained and 15 trained) completed a maximal exercise test on bicycle and treadmill, with breath-by-breath analysis of oxygen uptake (VO2), carbon dioxide production and expiratory volume. VT was determined by V-slope method. Correlations of VT and VO2peak were calculated between exercise modes. Bland-Altman plots were made for determining VT agreement between modes. VT was significantly different between walking and cycling in trained patients (P<0.05), but not in untrained patients (P>0.05). When untrained and trained patients were compared, VT correlation was lower (r=0.50) in the former group, as compared to the latter group (r=0.78). Also, Bland-Altman plots showed smaller limits of agreement for VT in trained (2 SD -1.6 to 7.8 ml/min/kg), as compared to untrained patients (2 SD -7.0 to 9.6 ml/min/kg). In trained patients, VT correlates well between training methods, but is highly exercise mode specific. In untrained patients, VT is not exercise mode specific, but the VT has a low correlation between training modes. This study shows that VT should be assessed by the appropriate exercise model for determining exercise intensity in cardiac rehabilitation.

Serial measurements of peripheral vascular reactivity and exercise capacity in congestive heart failure and after heart transplantation

BACKGROUND

The regulation of nutritive blood flow to skeletal muscles during exercise seems to make an important contribution to exercise capacity. In congestive heart failure (CHF) this regulation seems to be impaired, with attenuated peripheral vasodilatory capacity. The results regarding improvement of peripheral vasoreactivity after heart transplantation (HTx) are conflicting, and the contribution of impaired peripheral vasoreactivity to the observed reduced exercise capacity among heart transplant recipients (HTR) has not been well elucidated. We therefore assessed the reversibility of impaired vasoreactivity in forearm and calf after HTx with relationship to exercise capacity.

METHODS AND RESULTS

The vasoreactivity of both forearm and calf was studied with venous occlusion plethysmography and related to exercise capacity in 64 patients with CHF and in 22 controls. Of these patients, 29 patients underwent HTx, and the same measurements were performed 10 days, 6 months and 1 year after HTx, and in a group of 15 HTR who had undergone HTx several years ago. Our main findings were (1) impaired resting blood flow in patients with CHF improved after HTx and even surpassed levels of controls; (2) peak forearm blood flow remained attenuated early after HTx, but normalized during the first year postoperatively; (3) both forearm and calf minimal resistance remained elevated after HTx; (4) vascular reactivity displays regional variations in forearm and calf both during CHF and after HTx; and (5) peripheral vascular reactivity relate to exercise performance in both patients with CHF and HTR, but the relationship seemed more pronounced in CHF.

CONCLUSION

With impaired vasoreactivity related to limited exercise capacity in CHF, improvement is evident after HTx, but both forearm and calf minimal resistance remains elevated. These findings suggest increased vasoconstrictor drive to both exercising and non-exercising muscles, possibly contributing to persistent physical limitation after HTx.

Oxygen uptake efficiency slope, a new submaximal parameter in evaluating exercise capacity in chronic heart failure patients

BACKGROUND

The oxygen uptake efficiency slope (OUES) is a new submaximal parameter which objectively predicts the maximal exercise capacity in children and healthy subjects. However, the usefulness of OUES in adult patients with and without advanced heart failure remains undetermined. The present study investigates the stability and the usefulness of OUES in adult cardiac patients with and without heart failure.

METHODS

Forty-five patients with advanced heart failure (group A) and 35 patients with ischemic heart disease but normal left ventricular ejection fraction (group B) performed a maximal exercise test. PeakVO2 and percentage of predicted peakVO2 were markers of maximal exercise capacity, whereas OUES, ventilatory anaerobic threshold (VAT), and slope VE/VCO2 were calculated as parameters of submaximal exercise.

RESULTS

Group A patients had lower peakVO2 (P < .001), lower percentage of predicted peakVO2 (P = .001), lower VAT (P < .05), steeper slope VE/VCO2 (P < .001), and lower OUES (P < .02). Within group A, significant differences were found for VAT, slope VE/VCO2, and OUES (all P < .01) between patients with peakVO2 above and below 14 mL O2/kg/min. Of all the submaximal parameters, VAT correlated best with peakVO2 (r =.814, P < .01) followed by OUES/kg (r = .781, P < .01), and slope VE/VCO2 (r = -.492, P < .001). However, VAT could not be determined in 18 (23%) patients.

CONCLUSIONS

OUES remains stable over the entire exercise duration and is significantly correlated with peakVO2 in adult cardiac patients with and without impaired LVEF. Therefore, OUES could be helpful to assess exercise performance in advanced heart failure patients unable to perform a maximal exercise test. Further studies are needed to confirm our hypothesis.

Exercise responses of elderly patients with diastolic versus systolic heart failure

PURPOSE

Little information is available regarding peak and submaximal exercise performance in elderly heart failure (HF) patients, particularly in those with diastolic dysfunction (DD). Therefore, the purpose of this investigation was to compare exercise responses of elderly patients with HF due to either systolic dysfunction (SD) or DD, to age-matched healthy volunteers (HV).

METHODS

Patients with chronic HF > or = 60 yr (N = 119) due to SD (N = 60) or primary DD (N = 59) underwent a maximal cycle ergometry test with expired gas analysis and venous lactate measurement. Twenty-eight HV > or = 60 yr served as a control group. Anaerobic threshold was determined by gas analysis (ATVEN) and by plasma lactate rise (ATLAC).

RESULTS

Peak oxygen consumption (VO(2peak)) was significantly (P < 0.001) reduced in both SD and DD patients (13 +/- 0.4 vs 14 +/- 0.4 ml x kg(-1) x min(-1), respectively) versus HV (20 +/- 0.6 ml x kg(-1) x min(-1)). Peak heart rate was reduced in patients versus HV (131 +/- 3 bpm vs 145 +/- 4, respectively; P < or = 0.01), but heart rate at a given submaximal work rate was significantly lower (P < or = 0.01) in HV than in SD and DD patients. ATVEN of 11.8 +/- 0.3 ml x kg(-1) x min(-1) for HV was significantly higher than SD (8.9 +/- 0.2) and DD (9.2 +/- 0.3). Peak lactate concentration was 6.6 +/- 0.6 mmol x kg(-1) x l(-1) in HV and was significantly reduced in both SD and DD HF patients. ATVEN correlated well with ATLAC in HV and in DD patients, but not in SD patients.

CONCLUSIONS

Submaximal and peak exercise performance are markedly altered in elderly HF patients compared with age-matched HV but do not appear to be different between SD and DD patients.

Contribution of peak respiratory exchange ratio to peak VO2 prognostic reliability in patients with chronic heart failure and severely reduced exercise capacity

BACKGROUND

We evaluated the influence of peak respiratory exchange ratio (pRER), as an index of effort adequacy, on peak VO2 prognostic reliability in patients with chronic heart failure (CHF) and reduced exercise capacity, whose peak VO2 may be underestimated because of poor patient motivation.

METHODS

A cardiopulmonary exercise test was performed in 570 patients with CHF (age 60 +/- 10 years, ejection fraction 26% +/- 7%, New York Heart Association class 2.2 +/- 0.6), 193 of whom had a peak VO2 that was >10 but <or=14 mL/kg/min (reduced exercise capacity) and 80 of whom had a peak VO2 <or=10 mL/kg/min (severely reduced exercise capacity).

RESULTS

Seventy-eight events (72 cardiovascular deaths and 6 status I heart transplantations) occurred during follow-up (19.6 +/- 14 months). The 2-year survival rate was 69% in patients with a peak VO2 <or=10 and 83% in patients with a peak VO2 >10 but <or=14 (P <.0001). However, in the group of patients with a peak VO2 <or=10, patients who had a pRER >or=1.15 had a 2-year survival rate of 52%, and this pRER value (but not >or=1, >or=1.05, or >or=1.10) was the only independent predictor of the composite end point (chi(2) = 4.73, P =.03). Conversely, in the group of patients with a peak VO2 <or=10, patients who had a pRER value <1.15 had a survival rate of 83%, which was comparable with that of the group of patients with a peak VO2 >10 but <or=14.

CONCLUSION

Patients with CHF and severely reduced exercise capacity should be encouraged to exercise to an RER as close as possible to 1.15, to ascertain their motivation and ensure their peak VO2 prognostic reliability.

Reproducibility of cardiopulmonary exercise testing in elderly patients with congestive heart failure

Elderly patients with congestive heart failure, including those with preserved systolic function, underwent maximal cardiopulmonary exercise testing. Maximal exercise oxygen consumption, exercise time, heart rate, respiratory exchange ratio, and ventilatory anaerobic threshold showed good reproducibility.

Maximal and submaximal exercise testing in heart failure

Although reduced exercise capacity is the main complaint of patients with congestive heart failure (CHF), the best method to measure it remains controversial. Peak VO2, obtained using maximal exercise testing, is the most accurate measure of maximal functional capacity. It is related to peak exercise cardiac output and is one of the most important independent variables for the prognostic assessment of patients with CHF. It has, however, a low sensitivity for measurement of changes induced by therapy and is poorly related to everyday physical activity, patient symptoms, and quality of life. The anerobic threshold may also be regarded as a parameter of maximal functional capacity. Its value is mainly indirect, because it shows that the patient is performing a maximal effort limited by the cardiovascular system. The VO2 kinetics at the start and at the end of exercise are probably more related to patient symptoms, but it is unresolved which protocols and parameters might best be used to study this aspect of exercise performance. Duration of a submaximal exercise at a constant work rate and the distance walked during a 6-min walking test are gaining wide popularity as parameters of submaximal performance. However, when these exams are carried out up to exhaustion in patients with severe functional limitation, they may involve attainment of the anerobic threshold and therefore their clinical meaning may be similar to the one of a maximal exercise test. Moreover, tests based on the assessment of submaximal exercise capacity have been useful for assessment of therapy in single-center trials but have been often inadequate in multicenter trials.

Peak exercise oxygen consumption in chronic heart failure: toward efficient use in the individual patient

OBJECTIVES

This study sought to 1) assess the short-, medium-and long-term prognostic power of peak oxygen consumption (VO2) in patients with heart failure; 2) verify the consistency of a nonmeasurable anaerobic threshold (AT) as a criterion of nonapplicability of peak VO2; 3) develop simple rules for the efficient use of peak VO2 in individualized prognostic stratification and clinical decision making.

BACKGROUND

Peak VO2, when AT is identified, is among the indicators for heart transplant eligibility. However, in clinical practice the application of defined peak VO2 cutoff values to all patients could be inappropriate and misleading.

METHODS

Six hundred fifty-three patients consecutively considered for eligibility for heart transplantation were followed up. Outcomes (cardiac death and urgent transplantation) were determined when all survivors had a minimum of 6 months of follow-up.

RESULTS

Contraindication to the exercise test identified very high risk patients. The relatively small sample of women did not allow inferences to be drawn. In men, peak VO2 stratified into three levels (< or = 10, 10 to 18 and >18 ml/kg per min) identified groups at high, medium and low risk, respectively. The prognostic power of peak VO2 < or = 10 ml/kg per min was maintained even when the AT was not detected. In patients in New York Heart Association functional class III or IV, peak VO2 did not have prognostic power. In patients in functional class I or II, peak VO2 stratification was prognostically valuable, but less so at 6 than at 12 or 24 months. Age did not influence peak VO2 prognostic stratification.

CONCLUSIONS

A contraindication to exercise testing should be considered a priority for listing patients for heart transplantation. Only in less symptomatic male patients does a peak VO2 < or = 10 ml/kg per min identify short-, medium- and long-term high risk groups. A peak VO2 >18 ml/kg per min implies good prognosis with medical therapy.

Exercise testing and training of patients with heart failure due to left ventricular systolic dysfunction

Reducing the exercise intolerance and symptoms experienced by patients with chronic heart failure remains an important focus in their clinical care. A clear shortcoming exists; however, with respect to an appreciation that in addition to standard medical therapy, selected patients with stable heart failure also can benefit from a moderate exercise training program. Improvements in central transport, regional blood flow, and skeletal muscle histology and biochemistry all likely account for the increase in exercise capacity and delay in fatigue that these patients experience. Additionally, the autonomic imbalance that is characteristic of these patients is improved. Although the number of patients with heart failure participating in an exercise program is increasing, much work still exists relative to incorporating this treatment method into the care plans established by physicians and physician extenders.

Ventilatory and lactate threshold determinations in healthy normals and cardiac patients: methodological problems

In healthy normal individuals (n = 69), coronary patients with myocardial ischaemia (n = 27) and patients with chronic heart failure (CHF, n = 33), four widely applied methods to determine ventilatory threshold (VT) were analysed: V-slope, ventilatory equivalent for O2 (EqO2), gas exchange ratio (R) and end-tidal partial pressure of oxygen. Lactate threshold [LAT, log lactate vs log oxygen uptake (VO2)] was also determined. Analysis focused on rate of success of threshold determination, comparability of threshold methods, reproducibility and interobserver variability. Cycle ergometry protocols with ramp-like mode and graded steady-state mode used in exercise testing were considered separately. In healthy normal individuals and coronary patients with myocardial ischaemia, at least three VT could be determined during ramp-like mode and two VT during graded steady-state mode, 82% of the time. For CHF patients, the rate of successful determination of VT was lower. Compared to LAT, VO2 at VT was significantly higher using R and EqO2 methods of VT determination in healthy normal subjects (P < 0.01), and significantly higher when using all four methods in coronary patients (P < 0.01 or P < 0.05, respectively). No difference was observed between VO2 at VT and LAT in CHF patients. In healthy normal individuals, day-to-day reproducibility of VT and LAT was high (error of a single determination from duplicate determinations was between 3.9% and 6.2% corresponding to a VO2 of 52.2 and 89.2 ml.min-1). Interobserver variability was low (error between 0.3% and 5% corresponding to a VO2 of 9.8 and 68 ml.min-1). In CHF patients, interobserver variability was moderately greater (error between 4.6% and 8.2%, corresponding to a VO2 of 35.1 and 62.4 ml.min-1). To optimize threshold determination, standardized procedures are suggested.

Prolonged kinetics of recovery of oxygen consumption after maximal graded exercise in patients with chronic heart failure. Analysis with gas exchange measurements and NMR spectroscopy

BACKGROUND

Patients with chronic heart failure (CHF) often complain of prolonged dyspnea after exercise. The determinants of oxygen consumption after exercise in these patients are unknown. We hypothesized that the kinetics of oxygen consumption recovery after graded exercise was prolonged in parallel with the recovery of muscle energy stores, was not affected by the exercise level, and could be used to assess the circulatory response to exercise.

METHODS AND RESULTS

Seventy-two patients with CHF in Weber's class A (n = 28), B (n = 21), and C/D (n = 23) and 13 healthy subjects performed maximal upright bicycle exercise with breath-by-breath respiratory gas analysis. Kinetics of recovery of ventilation (VE), oxygen consumption (VO2), and CO2 production (VCO2) after exercise were characterized by T1/2, the time to reach 50% of the peak value. T1/2 VO2 (seconds) increased with the severity of CHF (97 +/- 17 for CHF A [P < .05 versus CHF B, P < .05 versus CHF C/D], 119 +/- 22 for CHF B [P < .05 versus control subjects, P < .05 versus CHF A, and P < .05 versus CHF C/D], 155 +/- 55 for CHF C/D [P < .05 versus control subjects, P < .05 versus CHF A, and P < .05 versus CHF B] compared with 77 +/- 17 for control subjects). T1/2 VCO2 and T1/2 VE also increased similarly with the worsening of CHF. T1/2 VO2 was correlated negatively with peak VO2 (r = .65) and was reproducible (r = .96). To study the relation between T1/2 VO2 and the duration of exercise, 10 healthy subjects and 22 patients underwent a second graded test at 75% and/or 50% of peak workload. T1/2 VO2 was minimally shortened, at only 50% of peak workload (P = .02). Finally, 19 patients underwent 31P nuclear magnetic resonance spectroscopy of the anterior compartment of the leg during exercise; the half-time of recovery of the ratio of inorganic phosphate to creatine phosphate (T1/2 Pi/PCr), reflecting the level of involvement of oxidative metabolism in the restoration of energetic metabolites after exercise, was linearly correlated with the half-time of VO2 recovery (r = .70, P < .01).

CONCLUSIONS

Postexercise T1/2 VO2 increases when CHF worsens, perhaps in part a result of slower kinetics of recovery of muscle energy stores. The time course of oxygen consumption recovery may represent a simple new criterion for measuring the impairment of the circulatory response to exercise in CHF, even submaximal exercise.

Characterization of systemic oxygen transport in end-stage chronic congestive heart failure

Chronic congestive heart failure (CHF) is characterized by low cardiac index (CI) and low systemic oxygen delivery (DO2), which frequently are associated with lethal cardiogenic shock after acute myocardial infarction. Nevertheless, patients with severe CHF are able to survive with these low levels of systemic DO2 and CI. It was hypothesized that patients with CHF survive low CI and DO2 by downregulation of global metabolism and resting oxygen consumption (VO2) and a concomitant increase in systemic oxygen extraction ratio (O2ER). Therefore the objective of this study was to characterize the resting pattern of systemic oxygen transport (O2T) and utilization in patients with stable CHF. Seventeen patients with CHF (New York Heart Association functional class III or IV) for > or = 3 months and with left ventricular ejection fraction (EF) < 25% and whose condition was stable with conventional oral therapy were studied. The control group comprised 10 subjects (NYHA class I) who had coronary angiography and who were found to have normal left ventricular function and EF > 60%. Subjects underwent right-heart catheterization for measurement and calculation of hemodynamic and O2T variables (VO2, DO2, and O2ER). There were no significant differences in mean age (67 +/- 6 vs 64 +/- 17 years) or gender ratio (male:female 14:3 vs 7:3) between CHF and control groups, respectively. The cause of CHF was ischemic in 13 and idiopathic in 4 patients. There were 9 patients in NYHA class III and 8 in class IV.(ABSTRACT TRUNCATED AT 250 WORDS)