The clinical utility of a six-minute walk test in peripheral arterial occlusive disease patients

OBJECTIVES: To determine the test-retest reliability of the distance covered and the steps taken to complete a 6-minute walk test by peripheral arterial occlusive disease (PAOD) patients with intermittent claudication. To determine the relationship between the total distance and steps covered during the 6-minute walk test and clinical measures of PAOD severity. DESIGN: Cross-sectional design. SETTING: The Claude Pepper Older Americans Independence Center at the University of Maryland at Baltimore. PARTICIPANTS: Sixty-four PAOD patients between the ages of 45 and 88 years (age = 68 +/- 7 years, ankle/brachial index (ABI) = .61 +/- .19) were recruited from the Vascular Clinic at the Baltimore Veterans Affairs Medical Center and from radio and newspaper advertisements. MEASUREMENTS: Patients were assessed on a 6-minute walk test and a treadmill graded exercise test. A second 6-minute walk test was administered approximately 1 week later. Patients also were characterized in regard to blood pressure in the arms and legs, ABI, anthropometry, body composition, and physical activity. RESULTS: The distances walked during the two 6-minute walk tests were similar (350 +/- 78 m vs 360 +/- 73 m), resulting in a high reliability coefficient (R = .94) and a low coefficient of variation (10.4%). The total steps taken during the 6-minute walk test also were similar (562 +/- 113 steps vs 587 +/- 107 steps), resulting in a high reliability coefficient (R = .90) and a low coefficient of variation (11.7%). Furthermore, the 6-minute walking distance correlated with the distances to onset (r = .346, P = .007) and with maximal claudication pain (r = .525, P < .001) during the treadmill test as well as with ABI (r = .552, P < .001). CONCLUSION: The 6-minute walk test yields highly reliable measurements, which are related to the functional and hemodynamic severity of PAOD, in patients with intermittent claudication.     

Effects of maximally tolerated oral therapy on the six-minute walking test in patients with chronic congestive heart failure secondary to either ischemic or idiopathic dilated cardiomyopathy

In patients with heart failure, therapy with "maximally tolerated" oral doses of diuretics, vasodilators, and digitalis results in a significant increase in the distance walked during the 6-minute walking test, compared with conventional therapy at "standard" doses, indicating an improvement in exercise tolerance. The 6-minute walk test is a simple, inexpensive, and well-tolerated test to measure changes in exercise tolerance induced by pharmacologic interventions, even on a short-term basis.     

Muscle oxygenation kinetics measured by near-infrared spectroscopy during recovery from exercise in chronic heart failure

The aim of the present study was to determine the kinetics of recovery of muscle oxygenation (MO) from comparable levels of exercise in chronic heart failure (CHF) patients and normal subjects and to relate MO kinetics to the level of exercise intolerance. The rationale is based on the observation that the O2 debt is increased in patients with heart failure and repayment of the debt is relatively slow. Ten patients with stable CHF (mean age 47 +/- 10 years) and nine healthy control subjects (47 +/- 6 years) were studied. All patients had ischemic cardiomyopathy (ejection fraction 33 +/- 7%). On different days, all subjects performed an upright incremental cycle ergometer exercise test with gas-exchange analysis to determine peak VO2, and a 6-minute constant work-rate (CWR) protocol at 60% of peak VO2. Oxygenation of the vastus lateralis muscle was continuously monitored during exercise and recovery using near-infrared spectroscopy (NIRS). Both MO and VO2 responses to recovery were described by a monoexponential model with a time delay. The time constant and time delay were combined to calculate a mean response time (MRT). Recovery VO2 and MO MRTs for the incremental and constant work rate exercise test were longer in CHF patients than in control subjects (p < 0.05). Both VO2 and MO MRTs were inversely related to peak VO2 (r = -0.73 and -0.52, respectively; p < 0.05 for both). However, both kinetics were not significantly different within each group between the two exercise intensities. In conclusion, the greater the cardiac dysfunction, as assessed by peak VO2, the more the recovery of muscle and total body oxygenation from both maximal and submaximal exercise is delayed.     

Safety and efficacy of epoprostenol in patients with severe congestive heart failure. Epoprostenol Multicenter Research Group

Patients with advanced heart failure often remain severely symptomatic and have a high mortality rate despite currently available therapy. We studied the safety and efficacy of a new approach to the patient with refractory heart failure: continuous intravenous treatment via a portable infusion pump with epoprostenol (prostacyclin), a potent pulmonary and systemic vasodilator. A group of 33 patients with severe heart failure (64% New York Heart Association class IV and 36% class III) and profound ventricular dysfunction (median left ventricular ejection fraction, 0.15)--despite prior treatment with diuretics (100%), digitalis (91%), angiotensin-converting enzyme inhibitors (85%), and dobutamine (30%)--underwent a baseline 6-minute walk test prior to dose titration with epoprostenol during invasive hemodynamic monitoring. Subjects responding during the dose titration were randomized, on an open basis, to receive either continuous epoprostenol infusion via an indwelling central venous catheter plus conventional therapy or conventional therapy alone for 12 weeks. The initial dose-ranging study with epoprostenol produced a significant decline in systemic and pulmonary vascular resistance and a substantial increase in cardiac index despite a fall in pulmonary capillary wedge pressure. Symptoms related to vasodilation were noted within the first week after randomization to epoprostenol in 9 of 16 patients but resolved with adjustment of the infusion and concomitant medications in all but one subject. Dose adjustments during the chronic epoprostenol infusion were infrequent after the first week and complications related to the drug delivery system were rare. The change in distance walked from baseline to the last available 6-minute walk test was significantly greater in patients who received epoprostenol compared with patients assigned to standard therapy (72 +/- 40 vs -39 +/- 32 m, mean +/- SEM; p = 0.033). Our study suggests that long-term intravenous infusion of epoprostenol is feasible in patients with severe heart failure and our hemodynamic and functional results suggest clinical benefit as well. However, until recent results indicating an adverse effect of epoprostenol on survival are fully evaluated, the role of this drug in the treatment of advanced heart failure will remain uncertain.     

In whose ''best interests''? Ethical issues involved in the moral dilemmas surrounding the removal of sexually abused adolescents from a community-based residential treatment unit to a locked, forensic adult psychiatric unit

BACKGROUND: Physiological and psychological markers of patients with congestive heart failure (CHF) who will respond to aerobic training are needed as a guide to appropriate therapy. METHODS: Seventeen of 21 patients with stable CHF completed a 16-week supervised progressive walking program 5 times per week. Cycle ergometer determinations of peak oxygen intake and peak power output at entry and 16 weeks were supplemented by a 6-minute walk, a disease-specific Quality of Life (QOL) questionnaire, and a standard gamble. RESULTS: Peak oxygen intake increased by 2.6 +/- 1.5 mL/(kgmin) over an initial value of 15.6 mL/(kgmin), with parallel gains in peak power and the 6-minute walk. Marked improvements in QOL and standard gamble scores also developed. Initial cardiorespiratory status (heart volume, ejection fraction, oxygen pulse, and peak oxygen intake) was correlated more closely (P = 0.09 to 0.18) with delta peak oxygen intake than with delta peak power or delta walking distance. Physiological gains bore little relationship to initial psychological status. Gains in CHF Questionnaire and Standard Gamble scores were strongly associated with initial scores for these variables (dyspnea, P = .02; mastery, P = .005; standard gamble, P = .001), but could not be predicted from either initial physiological status or gains in physiological condition. CONCLUSIONS: Initial cardiorespiratory status provides little indication of which patients with CHF respond well to training. Gains in QOL score are influenced by initial scores, and seem to show a "ceiling" effect.     

Paclitaxel is preferentially cytotoxic to human cervical tumor cells with low Raf-1 kinase activity: implications for paclitaxel-based chemoradiation regimens

Little is known about the association of echocardiographic estimates of right ventricular (RV) function with survival, in relation to hemodynamic and exercise-derived predictors of outcome in congestive heart failure. We prospectively studied 40 patients (age 55+/-10 years, in New York Heart Association functional class III [70%] and IV [30%]), with left ventricular (LV) ejection fraction <30%. At enrollment, all patients underwent echocardiographic evaluation of LV dimensions and function. RV shortening was measured as the difference of the end-diastolic distance - the end-systolic distance between the tricuspid annulus and the RV apex. Thirty-five patients (88%) were able to perform a maximal symptom-limited exercise test. Peak oxygen consumption (peak VO2) and percent peak age- and gender-adjusted predicted oxygen consumption (%peak VO2) were calculated. Of 40 patients, 10 died during a mean follow-up period of 14+/-10 months. On univariate analysis, nonsurvivors had lower RV shortening (p=0.0001), higher pulmonary artery wedge pressure (p=0.009), higher pulmonary vascular resistance (p=0.02), and lower mean aortic pressure (p=0.05). Cox proportional-hazards model revealed that the only independent associate of survival was RV shortening (p=0.0005), with a trend toward significance for mean aortic pressure (p=0.08). The best cutoff point of RV shortening identified by the receiver-operating curve was 1.25 cm. This value had a sensitivity of 90%, specificity of 80%, and overall predictive accuracy of 83% to distinguish survivors from nonsurvivors. In patients with advanced heart failure, preserved RV function as indicated by an echocardiographically derived RV shortening > 1.25 cm is a strong predictor of survival.     

Relationship between free-living daily physical activity and ambulatory measures in older claudicants

The purpose of this study was to determine the relationship between free-living daily physical activity and ambulatory measurements in peripheral arterial occlusive disease (PAOD) patients with intermittent claudication. Thirty-four older, nonsmoking PAOD patients with intermittent claudication (age=69.0 +/- 6.0 years, ankle/brachial index [ABI] =0.63 +/- 0.18) were recruited from the Vascular Clinic at the Baltimore Veterans Affairs Medical Center and from radio and newspaper advertisements. Energy expenditure of physical activity (EEPA) was determined by using doubly labeled water and indirect calorimetry techniques. Patients were also characterized on claudication distances and peak oxygen uptake during a graded treadmill test, 6-minute walking distance, weight, body mass index, and percent body fat. The claudication patients were sedentary, as EEPA was 362 +/- 266 kcal/day. EEPA was related to the 6-minute walk distance (369 +/- 68 meters; r=0.629, P<0.001), to the number of steps taken during 6 minutes (605 +/- 99 steps; r=0.485, P=0.008), to the treadmill distance to maximal claudication (313 +/- 131 meters; r=0.470, P=0.010), and to the time to relief of pain (6:21 +/- 3:57 min:sec; r=-0.417, P=0.017). None of the other ambulatory and body composition measurements were correlated with EEPA. In conclusion, a reduction in free-living daily physical activity was associated with a decrease in ambulatory ability and with more severe intermittent claudication in older PAOD patients.     

Can the ventilatory equivalent for carbon dioxide predict the severity of functional impairment in patients with cardiac insufficiency?

OBJECTIVE: To evaluate whether the changes in the ventilatory equivalent for carbon dioxide (VE/VCO2), during the early stages of cardiopulmonary exercise testing, can predict maximal oxygen consumption (VO2max) in patients with chronic heart failure. METHODS: We studied 38 patients (30 males, mean age 56 +/- 11 years) with chronic heart failure. All patients performed maximal symptom limited, treadmill exercise test with breath-by-breath respiratory gas analysis. They were divided in two groups according to their maximal oxygen consumption (group I-VO2max above 14 ml/kg/min and group II-VO2max below 14 ml/kg/min). In both groups, we analysed VE/VCO2 at rest, at the anaerobic threshold (AT) and at peak exercise, and the percentage of VE/VCO2 reduction from rest to AT. RESULTS: Eleven patients had a VO2max below 14 ml/kg/min (group II). At rest VE/VCO2 = 53 +/- 13 in group II versus 47 +/- 10 in group I (p = 0.048), at the AT VE/VCO2 = 46 +/- 12 in group II versus 36 +/- 7 in group I (p = 0.001) and at peak exercise VE/VCO2 = 46.2 +/- 13 in group II versus 36.2 +/- 6 in group I (p = 0.0002). There was a 24% reduction in the VE/VCO2, from rest to AT in group I, compared to a 16% reduction in group II (p = 0.004). A reduction in the VE/VCO2 from rest to AT less than 16% predicted a VO2max below 14 ml/kg/min with a sensitivity of 60% and a specificity of 93%. CONCLUSIONS: Patients with severe functional impairment have higher values of VE/VCO2 in all exercise stages. A reduction of VE/VCO2 from rest to anaerobic threshold of less than 16% is a high specific predictor of a VO2max below 14 ml/kg/min.     

Enlarged scale chemical synthesis and range of activity of drosocin, an O-glycosylated antibacterial peptide of Drosophila

OBJECTIVE: Poor cardiorespiratory endurance is a common finding in neuromuscular disease (NMD), and the capacity of such patients to respond to aerobic training is unclear. This study was conducted to determine if a 12-week walking program results in increased aerobic capacity in slowly progressive NMD subjects, whether such a program is safely tolerated, and whether such patients can adhere to a self-monitored, home-based training program. DESIGN: Before-after trial. SETTING: Subjects' homes. PATIENTS: A cohort of 8 slowly progressive NMD subjects (4 men, 4 women) followed in the neuromuscular disease clinic participated (age, 36.6 +/- 8.0 yrs; ht, 170 +/- 11 cm; wt, 74.3 +/- 19.0 kg) (Mean +/- SD). INTERVENTION: Subjects walked 15 to 30 min 3 to 4 days a week at 50% to 60% of their heart rate reserve. MAIN OUTCOME MEASURES: Resting, submaximal, and peak heart rates, systolic and diastolic blood pressures, oxygen uptake, and peak power output. RESULTS: Graded exercise testing to volitional fatigue using a semirecumbent cycle ergometer before and after the training program found significant decreases in submaximal heart rate by 7 +/- 3 beats/min (Mean +/- SEM) (95% CI = -23 to 9) (p = .046) and submaximal systolic blood pressure by 11 +/- 4 mmHg (95% CI = -31 to 9) (p = .019), and nonsignificant increases in peak power output and VO2. CONCLUSIONS: These results suggest that moderate-intensity aerobic exercise training is well tolerated and may provide modest improvement in aerobic capacity in slowly progressive NMD subjects.     

Differences in duration of Huntington's disease based on age at onset

OBJECTIVE: The accurate determination of limitations in physical activity is important in evaluating patients with heart failure and in assessing the efficacy of treatment. However, the conventional measures used to evaluate hemodynamics, functional class, and exercise capacity all have limitations. Our objective was to develop a simple method (The Master-Borg test) for evaluating the physical activity of patients with chronic heart failure using self-evaluation of the sensation of dyspnea at a constant workload. METHODS: Patients with NYHA class I (N = 20), class II (N = 20), and class III (N = 20) chronic heart failure performed a symptom-limited treadmill exercise test to determine peak VO2 and anaerobic threshold (AT). Patients subsequently performed Master's two-step test for 90 s and maximal dyspnea was self-rated using the visual analog Borg scale (the Master-Borg test). RESULTS: The mean workload in the Master-Borg test was 15.2+/-1.6 mL x min(-1) x kg(-1). A significant correlation was found between the Master-Borg score and peak VO2 (r = 0.87) or AT (r = 0.84). The reproducibility of the Master-Borg tests was represented by a correlation coefficient of 0.93. CONCLUSION: Although simple and inexpensive, the Master-Borg test accurately represents ordinary activity levels, relates the sensation of dyspnea to peak exercise tolerance, and can be completed by most patients with heart failure. Master-Borg scores correlated with peak VO2 and AT, and can differentiate among NYHA classes I, II, and III. The Master-Borg test appears to be clinically useful for evaluating the value of physical activity and exercise capacity of patients with chronic heart failure.     

Oxygen uptake kinetics during low level exercise in patients with heart failure: relation to neurohormones, peak oxygen consumption, and clinical findings

OBJECTIVE: To investigate whether oxygen uptake (VO2) kinetics during low intensity exercise are related to clinical signs, symptoms, and neurohumoral activation independently of peak oxygen consumption in chronic heart failure. DESIGN: Comparison of VO2 kinetics with peak VO2, neurohormones, and clinical signs of chronic heart failure. SETTING: Tertiary care centre. PATIENTS: 48 patients with mild to moderate chronic heart failure. INTERVENTIONS: Treadmill exercise testing with "breath by breath" gas exchange monitoring. Measurement of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and noradrenaline. Assessment of clinical findings by questionnaire. MAIN OUTCOME MEASURES: O2 kinetics were defined as O2 deficit (time [rest to steady state] x DeltaVO2 -sigmaVO2 [rest to steady state]; normalised to body weight) and mean response time of oxygen consumption (MRT; O2 deficit/DeltaVO2). RESULTS: VO2 kinetics were weakly to moderately correlated to the peak VO2 (O2 deficit, r = -0.37, p < 0.05; MRT, r = -0.49, p < 0.001). Natriuretic peptides were more closely correlated with MRT (ANF, r = 0.58; BNP, r = 0.53, p < 0.001) than with O2 deficit (ANF, r = 0.48, p = 0.001; BNP, r = 0.37, p < 0.01) or peak VO2 (ANF, r = -0.40; BNP, r = -0.31, p < 0.05). Noradrenaline was correlated with MRT (r = 0. 33, p < 0.05) and O2 deficit (r = 0.39, p < 0.01) but not with peak VO2 (r = -0.20, NS). Symptoms of chronic heart failure were correlated with all indices of oxygen consumption (MRT, r = 0.47, p < 0.01; O2 deficit, r = 0.39, p < 0.01; peak VO2, r = -0.48, p < 0. 01). Multivariate analysis showed that the correlation of VO2 kinetics with neurohormones and symptoms of chronic heart failure was independent of peak VO2 and other variables. CONCLUSIONS: Oxygen kinetics during low intensity exercise may provide additional information over peak VO2 in patients with chronic heart failure, given the better correlation with neurohormones which represent an index of homeostasis of the cardiovascular system.     

Perindopril postmarketing surveillance: a 12 month study in 47,351 hypertensive patients

We investigated the effect of electrical cardioversion of atrial fibrillation in patients with heart failure. The study group consisted of 24 patients with mild to moderate heart failure [13 men, mean age 67+/-7 years, mean peak oxygen consumption (peak VO2) 16.3+/-2.8 ml/min/kg] and chronic atrial fibrillation (median duration 19 (1-228) months). Patients were stable on digoxin, diuretics, nitrates and angiotensin converting enzyme inhibitors; no prophylaxis with antiarrhythmics was started after cardioversion. Cardioversion was unsuccessful in 6 patients; of the 18 patients in whom sinus rhythm was obtained 9 had a relapse of atrial fibrillation within 6 weeks after cardioversion. The remaining 9 patients with maintenance of sinus rhythm and the 15 (6+9) patients with atrial fibrillation at follow-up after 6 weeks did not differ with respect to any baseline characteristic, including age, peak VO2, duration of atrial fibrillation, echocardiographic left ventricular and left atrial dimensions, plasma atrial natriuretic peptide and norepinephrine. In the patients with maintenance of sinus rhythm, baseline measurements were repeated at follow-up. Peak VO2 did not change significantly (16.7+/-2.8 to 17.6+/-3.3 ml/min/kg, P=0.29); also, echo parameters, atrial natriuretic peptide and norepinephrine were not significantly affected. These results indicate that it is difficult to achieve lasting sinus rhythm through electrical cardioversion in patients with atrial fibrillation and mild to moderate heart failure. Moreover, in patients with maintenance of sinus rhythm after cardioversion no significant benefit in terms of peak VO2, cardiac dimensions, and neurohumoral status is to be expected. Hence, indiscriminate cardioversion of atrial fibrillation in the setting of heart failure does not appear to be useful.     

Physiologic correlates to running performance in pre-pubertal distance runners

In adults, four major variables have been shown to be associated with success in distance running performance: submaximal oxygen consumption (running economy), peak oxygen consumption (Peak VO2), ventilatory threshold (VT) and fractional utilisation (FU). The primary aim of this study was to describe the relationship between the 3000 m race times of run-trained prepubertal boys to these four variables. Thirteen male run-trained pre-pubertal boys (age 11.7 +/- 1.1 yrs, mean +/- SD), volunteered to take part in a 3000 m time trial and laboratory assessment, consisting of treadmill running at four submaximal speeds (8, 9.6, 11.2 and 12.8 km.h-1) as well as a peak VO2 test. The group demonstrated a heterogeneous array of peak VO2 data. A high level of association (p < 0.05) was found between mass-relative peak VO2 and 3000 m time trial results (r = -0.83). In addition ventilatory threshold expressed as %peak VO2, VO2 at VT and estimated velocity at VT was also highly related to 3000 m time trial (r = -0.78, -0.77 and -0.77) respectively. Fractional utilisation (%peak VO2) was significantly (p < 0.05) associated with race time at the final two submaximal running speeds only (11.2 and 12.8 km.h-1) (r = 0.61 and 0.67, respectively). Respiratory Exchange Ratio (RER) was also found to be significantly (p < 0.05) associated with 3000 m race time at 11.2 and 12.8 km.h-1. Overall peak VO2 appeared to be the single most important factor associated with success at 3000 m.     

Impairment of exercise capacity and peak oxygen consumption in patients with mild left ventricular dysfunction and coronary artery disease

AIMS: Most studies in chronic heart failure have only included patients with marked left ventricular systolic dysfunction (i.e. ejection fraction < or =0.35), and patients with mild left ventricular dysfunction are usually excluded. Further, exercise capacity strongly depends on age, but age-adjustment is usually not applied in these studies. Therefore, this study sought to establish whether (age-adjusted) peak VO2 was impaired in patients with mild left ventricular dysfunction. METHODS: Peak VO2 and ventilatory anaerobic threshold were measured in 56 male patients with mild left ventricular dysfunction (ejection fraction 0.35-0.55; study population) and in 17 male patients with a normal left ventricular function (ejection fraction >0.55; control population). All patients had an old (>4 weeks) myocardial infarction. By using age-adjusted peak VO2 values, a 'decreased' exercise capacity was defined as < or = predicted peak VO2 - 1 x SD (0.81 of predicted peak VO2), and a severely decreased exercise capacity as < or = predicted peak VO2 - 2 x SD (0.62 of predicted peak VO2). RESULTS: Patients in the study population (age 52+/-9 years; ejection fraction 0.46+/-0.06) were mostly asymptomatic (NYHA class I: n=40, 76%), while 16 patients (24%) had mild symptoms, i.e. NYHA class II. All 17 controls (age 57+/-8 years) were asymptomatic. Mean peak VO2 was lower in patients with mild left ventricular dysfunction (23.6+/-5.7 vs 27.1+/-4.6 ml x min(-1) x kg(-1) in controls, P<0.05). In 75% of the study population patients (n=42) age-adjusted peak VO2 was decreased (NYHA I/II: n=29/13) and in 18% of them severely decreased (n=10; NYHA I/II: n=6/4). In contrast, only three patients (18%) in the control population had a decreased and none a severely decreased age-adjusted peak VO2. CONCLUSION: In patients with mild left ventricular dysfunction, who have either no or only mild symptoms of chronic heart failure, a substantial proportion has an impaired exercise capacity. By using age-adjustment, impairment of exercise capacity becomes more evident in younger patients. Patients with mild left ventricular dysfunction are probably under-diagnosed, and this finding has clinical and therapeutic implications.     

DNA reactions, mutagenic action and stealth properties of polycyclic aromatic hydrocarbon carcinogens (review)

OBJECTIVE: To present a critical review and meta-analysis of studies evaluating the long-term effects of pulmonary rehabilitation in patients with asthma and chronic obstructive pulmonary disease (COPD). DATA SOURCES: A database of articles published over the last 45 years, compiled by using medical subject heading key words pulmonary, obstructive, rehabilitation, and exercise. Articles not written in English, Dutch, or German and abstracts were excluded. STUDY SELECTION: Selected studies (1) evaluated the effects of pulmonary rehabilitation, (2) included patients with asthma or COPD older than 18 years, (3) evaluated outcome measures of exercise capacity or health related quality of life (HRQL), and (4) included a control condition lacking exercise training. DATA EXTRACTION: Independent extraction by two reviewers. DATA SYNTHESIS: For each outcome, summary effects were computed by pooling standardized mean differences as well as raw mean differences. Significant improvements were found for all outcomes (p < .001). Sensitivity analyses for methodological quality of the selected studies did not change summary effect sizes. Effect sizes were significantly heterogeneous for the outcome endurance time (p < .0001). Pooling raw mean differences revealed overall effects in 6-minute walking distance (49+/-26 m) and all 4 dimensions of the chronic respiratory questionnaire (range, 0.5+/-0.3 to 0.8+/-0.3 points), indicating substantial improvements in these outcomes. Significant summary effect sizes were found up to 9 months after finishing rehabilitation for maximal exercise capacity (p < .003) and 6-minute walking distance (p < .005). CONCLUSIONS: Patients with asthma and COPD benefit from pulmonary rehabilitation.     

Estimation of VO2 in older individuals with osteoarthritis of the knee and cardiovascular disease

The American College of Sports Medicine (ACSM) equation for estimating oxygen consumption (VO2) is often inappropriately applied to non-steady-state treadmill exercise. Therefore, it was the purpose of this investigation to develop an equation to estimate VO2 that could be applied to non-steady-state treadmill exercise in a population of patients with osteoarthritis of the knee, and to assess the generalizability of this equation for estimating VO2peak in patients with cardiovascular disease. Subjects for the investigation were 414 participants in the Fitness and Arthritis in Seniors Trial (FAST), and 362 patients with cardiovascular disease. Results from the FAST subjects showed that the ACSM equation was inappropriate for estimating VO2 during non-steady-state incremental treadmill walking. We developed the following equation (FAST) using speed and the interaction between speed and grade as the predictor variables during treadmill walking: VO2(ml.kg-1.min-1) = 0.0698 x speed(m.min-1) + 0.8147 x grade(%) x speed(m.min-1) + 7.533 ml.kg-1.min-1 The generalizability of the FAST equation for estimating VO2peak was evaluated in the patients with cardiovascular disease. The measured VO2peak of these patients was 23.7 +/- 0.3 ml.kg-1.min-1, whereas the VO2peak values estimated from the FAST equation and the ACSM equation were 24.1 +/- 0.3 and 33.2 +/- 0.5 ml.kg-1.min-1, respectively. No significant differences were found between the measured VO2peak and that estimated from the FAST equation. The VO2peak estimated from the ACSM equation was significantly greater than the measured VO2peak. These results suggest it is more appropriate to use the FAST equation rather than the ACSM equation to estimate VO2 in older patients with either osteoarthritis of the knee or cardiovascular disease.     

Improved walking economy in patients with peripheral arterial occlusive disease

The effect of exercise rehabilitation on the oxygen cost of ambulation in patients with peripheral arterial occlusive disease (PAOD) was evaluated with specific emphasis on the effects of exercise rehabilitation on the slow component of VO2. Because the slow component of VO2 represents an increase in VO2 despite constant-intensity exercise, it can profoundly affect the relative energy cost of exercise in individuals with a low functional capacity. Twenty-six patients with intermittent claudication performed treadmill walking at 2.0 mph/0% grade for 20 min or until maximal claudication pain before and after 4 months of rehabilitation. The slow component of VO2 during the treadmill test was defined as the difference between the end-exercise VO2 and the VO2 observed at minute 3. Ankle/brachial systolic pressure index (ABI) was measured before and immediately following the exercise test. Rehabilitation consisted of 3 d x wk(-1) of treadmill walking for 15-30 min at 60-70% of VO2peak. The slow component of VO2 and end-exercise VO2 at pretraining (0.75 +/- 0.90 and 11.12 +/- 2.10 mL x kg[-1] x min[-1]) were significantly reduced after 4 months of exercise rehabilitation (-0.07 +/- 1.11 and 10.07 +/- 1.80 mL x kg[-1] x min[-1]; P < 0.05). Exercise rehabilitation also significantly (P < 0.05) increased the post-exercise ABI (pre-rehabilitation = 0.36 +/- 0.26, post-rehabilitation = 0.43 +/- 0.25). These data suggest that 4 months of exercise rehabilitation: 1) improves walking economy in PAOD patients because of a decreased slow component of VO2, and 2) increases post-exercise ABI.     

Physiological responses to maximal treadmill and handweighted exercise

The purpose of this investigation was to compare the peak physiological responses among four protocols that employed different amounts of handweighted exercise in 16 males (aged 26.3 +/- 4.1 years). The four protocols were (a) uphill treadmill running (UR; 3.36 m.s-1, 2.5% grade increase-3 min-1); (b) uphill treadmill walking while pumping 1.36-kg handweights (HW) (UWHW; 1.79 m.s-1, 5.0% grade increase x 3 min-1; (c) treadmill walking while pumping .91-kg HW (WHW; 1.79 m.s-1, 0% grade, .91-kg HW increase x 3 min-1); and (d) standing in place and pumping HW (SHW; arm work as described in WHW). It was hypothesized that the peak responses would be inversely proportional to the estimated muscle mass activated (i.e., UR = UWHW > WHW > SHW). Dependent variables included peak oxygen uptake (VO2 peak), peak heart rate (HRpeak), peak ventilation (Ve peak), and peak respiratory exchange ratio (RERpeak). No differences were noted between UR and UWHW with respect to any of the dependent variables. All variables (except RERpeak) were greater (p < .01) in UR and UWHW than either WHW or SHW. RERpeak was greater (p < .01) in UR and UWHW than in WHW. VO2 peak and HRpeak were greater (p < .01) in WHW when compared to SHW. Mean VO2 peak was 97.5, 69.7, and 60% of UR for UWHW, WHW, and SHW, respectively. Therefore, walking and pumping handweights provides a maximal stimulus to the oxygen transport system.     

Acute hemodynamic effects of the prostacyclin analog 15AU81 in severe congestive heart failure

This multicenter, open-label study provides the first assessment of the safety and acute hemodynamic effects of a short-term infusion of 15AU81, a chemically stable analog of prostacyclin, in patients with New York Heart Association class III or IV heart failure. Twelve patients underwent sequential dose escalation by increasing the rate of the infusion at 15-minute intervals until the drug was no longer tolerated. Patients then received a 90-minute infusion at their maximum tolerated dose. The infusion was then discontinued and the subjects were observed during a 90-minute washout segment. Serial hemodynamic measurements were made throughout the dose-ranging, maintenance, and washout segments. A significant decrease in systemic vascular resistance (1,935 +/- 774 vs 1,243 +/- 351 dynes.s.cm-5; p < 0.001) and pulmonary vascular resistance (395 +/- 335 vs 223 +/- 198 dynes.s.cm-5; p = 0.008) occurred from the infusion of vehicle to the maximum tolerated dose. During dose titration, there was a a significant increase in cardiac index (1.9 +/- 0.7 vs 2.6 +/- 0.6 liters/min/m2; p < 0.001) and a tendency for a mild reduction in pulmonary artery wedge pressure (18 +/- 7 vs 17 +/- 6; p = 0.055) for the 8 patients with values on vehicle and maximum tolerated dose. These hemodynamic changes persisted during the maintenance infusion and disappeared rapidly during the washout segment. The most common adverse event to limit dose-ranging was headache, which occurred at a mean maximum tolerated dose of 36 +/- 15 ng/kg/min. Administration of 15AU81 was associated with significant acute hemodynamic improvement in patients with severe heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Skeletal muscle function and its relation to exercise tolerance in chronic heart failure

OBJECTIVES: This study sought to define the relation between muscle function and bulk in chronic heart failure (HF) and to explore the association between muscle function and bulk and exercise capacity. BACKGROUND: Skeletal muscle abnormalities have been postulated as determinants of exercise capacity in chronic HF. Previously, muscle function in chronic HF has been evaluated in relatively small numbers of patients and with variable results, with little account being taken of the effects of muscle wasting. METHODS: One hundred male patients with chronic HF and 31 healthy male control subjects were studied. They were matched for age (59.0 +/- 1.0 vs. 58.7 +/- 1.7 years [mean +/- SEM]) and body mass index (26.6 +/- 0.4 vs. 26.3 +/- 0.7 kg/m2). We assessed maximal treadmill oxygen consumption (VO2), quadriceps maximal isometric strength, fatigue (20-min protocol, expressed in baseline maximal strength) and computed tomographic cross-sectional area (CSA) at midthigh. RESULTS: Peak VO2 was lower in patients (18.0 +/- 0.6 vs. 33.3 +/- 1.4 ml/min per kg, p < 0.0001), although both groups achieved a similar respiratory exchange ratio at peak exercise (1.15 +/- 0.01 vs. 1.19 +/- 0.03, p = 0.13). Quadriceps (582 vs. 652 cm2, p < 0.05) and total leg muscle CSA (1,153 vs. 1,304 cm2, p < 0.005) were lower in patients with chronic HF. Patients were weaker than control subjects (357 +/- 12 vs. 434 +/- 18 N, p < 0.005) and also exhibited greater fatigue at 20 min (79.1% vs. 92.1% of baseline value, p < 0.0001). After correcting strength for quadriceps CSA, significant differences persisted (5.9 +/- 0.2 vs. 7.0 +/- 0.3 N/cm2, p < 0.005), indicating reduced strength per unit muscle. In patients, but not control subjects, muscle CSA significantly correlated with peak absolute VO2 (R = 0.66, p < 0.0001) and is an independent predictor of peak absolute VO2. CONCLUSIONS: Patients with chronic HF have reduced quadriceps maximal isometric strength. This weakness occurs as a result of both quantitative and qualitative abnormalities of the muscle. With increasing exercise limitation there is increasing muscle weakness. This progressive weakness occurs predominantly as a result of loss of quadriceps bulk. In patients, this muscular atrophy becomes a major determinant of exercise capacity.