Comparison of Treadmill and Bicycle Exercise in Patients With Chronic Heart Failure*

Transcription

1 Comparison of Treadmill and Bicycle Exercise in Patients With Chronic Heart Failure* Eric Page, MJJ.; Alain Cohen-Solal, M.D.; Guillaume jondeau, M.D.; Herve Douard, M.D.; Gerard Raul, M.D.; jean Pierre Kantelip, M.D.; and jean Louis Bussiere, M.D. The general opm10n that treadmill exercise elicits circulatory reserve more than bicycle exercise derives from studies conducted in normal subjects or subjects with coronary artery disease. To investigate if this also occurs in patients with chronic heart failure (CHF), 40 patients (mean ejection fraction: 26 ± 9 percent) with normal pulmonary function underwent in random order both treadmill (Naughton modified protocol, holding on handrails permitted) and bicycle (10 W /min) maximal exercise over a 1-week period. Peak oxygen uptake (19.6 ± 5.3 vs 17.6 ± 5.1 ml/min/kg, p<0.0001), ventilatory threshold (14.4 ± 4.7 vs 12.0 ± 3.5 ml/min/kg, p<0.0001), and minute ventilation (59± 18 vs 55± 15 L/min, p<0.05) were greater on treadmill than on bicy- cle. Heart rate, systolic blood pressure, breathing rate, respiratory exchange ratio, perceived exertion scale, and lactate were identical. The coefficient of the correlation between oxygen uptake and time was greater with bicycle than with treadmill (r=0.97 ± 0.04 vs 0.90 ± 0.07, p<0.001). Thus, treadmill exercise is more suitable for determining peak oxygen uptake in patients with CHF. However, the increase in oxygen uptake is more regular with bicycle exercise._ (Chest 1994; 106: } I CHF=chronic heart failure I Key words: congestive heart failure; exercise; peak oxygen uptake; treadmill Exercise is now routinely performed in order to assess exercise capacity in patients with chronic heart failure (CHF). 1 4 Treadmill exercise is the way of testing generally used in the United States and in Great Britain whereas bicycle exercise is generally preferred in the rest of Europe. Both techniques have their advantages and limitations: peak oxygen uptake is dependent on body weight but exercise may appear to be dangerous for the most disabled patients with treadmill; holding on handrails may decrease the actual metabolic requirements of exercise in patients compared with normal subjects or fit subjects. Bicycle exercise yields fewer artifacts on the electrocardiogram and a more regular pattern of breathing; it recruits less body muscle mass and therefore, peak oxygen uptake has been generally found to be lower by about 10 percent than with treadmill Exercise is generally limited by leg fatigue with bicycle exercise even in patients complaining of exercising dyspnea. The increase in oxygen uptake appears to be more regular with bicycle than with treadmill exercise. Moreover, the linear relationship that may exist between oxygen uptake and bicycle exercise time may offer an additional advantage to bicycle exercise *From the Service de Cardiologie, Hopital Beaujon, Clichy Cedex, France and the Vo2 French Study Group. Supported in part by grant from INSERM. Manuscript received September 29, 1993; revision accepted March 22, 1994 Reprint requests: Dr. Cohen-Sola!, Service de Cardiologie, 100 Boulevard du General Le Clerc, CLICHY, France testing over treadmill when one wants to analyze oxygen uptake at submaximal levels of exercise. However, most of these comparisons have been conducted in normal subjects or in patients with coronary artery disease, often limited by myocardial ischemia. 12 Patients with CHF are limited by fatigue or dyspnea. They use handrails for support during treadmill exercise, which may decrease the metabolic cost of exercise. 13 Finally, results of both modes of exercise are sometimes gathered in international studies performed in patients with CHF, suggesting that oxygen requirements are considered to be identical. Therefore, the Vo2 French Study Group decided to conduct a multicenter, comparative, randomized, crossover study of treadmill and bicycle exercise in patients with CHF to address these issues_ Patients METHODS Forty patients with CHF, recruited from seven departments, participated in the study. Twenty-five were in Ne.w York Heart Association functional class II and 15 were in class III. They were 35 men and 5 women (mean age, 56± 11 years; mean body weight, 75 ± 13 kg). The etiologies were ischemic cardiomyopathy in 18 patients, idiopathic dilated cardiomyopathy in 17, alcoholic dilated cardiomyopathy in 3, and hypertensive cardiomyopathy in l. Exercise had to be limited by fatigue and/or dyspnea; patients stopping exercise for myocardial ischemia or arrhythmias were not included. All patients underwent a radionuclide or angiographic determination of their left ventricular 1002 Comparison of Treadmill and Bicycle Exercise in CHF Patients (Page eta/)

2 Table!-Exercise Parameters Obtained With Both Protocols (n=40)* Treadmill Bicycle p Value Time, s 819 ± ±220 < Peak Vo2, ml / min/ kg 19.6± ±7.1 < Peak Vo2fpredicted Vo2 max, % 64.4± ±15.4 < Ventilatory threshold, t ml/min/ kg 14.5± ±3.6 < Ventilatory treshold/ peak Vo2, % 64.4± ± 15.4 < Minute ventilation, (L min- 1 ) 59.2± ± 15.5 <0.02 Breathing rate, min- 1 33±7 32±7 NS VE/ Vco2 at the ventilatory threshold 35±6 35±6 NS Respiratory exchange ratio 1.09 ± ±0.10 NS Heart rate, min ± ± 19 NS Oxygen pulse, ml 02 beat ± ±3.1 < Systolic arterial pressure, mm Hg 147±24 148±28 NS Lactate, mmol l- 1 l 5.1± ±2.5 NS Perceived level of fatigue 5.6± ±2.3 NS Perceived level of dyspnea 4.9± ±2.6 NS *Values are mean±sd; NS=nonsignificant; Vo2=oxygen uptake (ml/ min/ kg); VE=minute ventilation (L min- 1 ). fn=35. ln=12. n=21 for treadmill and 19 for bicycle. ejection fraction and a pulmonary functional testing: all had a left ventricular ejection fraction <40 percent and none had significant pulmonary disease from history or spirometry (defined as FEY 1 <85 percent of the predicted value). Mean ejection fraction was 26 ± 9 percent. Informed consent was obtained in all cases. Exercise Tests Each patient performed two tests in random order on two different days over a 1-week period, at the same time of day. All were previously familiarized for a long time with the technique of respiratory gas analysis. Medication treatment was not stopped the day of the test. For treadmill exercise, the classical modified Naughton protocol, 14 because of its wide acceptance in CHF, was used, but the patient was allowed to hold on handrails. The cycle ergometer protocol was a 10-W / min stage protocol, chosen for its low initial workload of 20 W, its small and frequent increments, and thus its suitability for patients with CHF; moreover, determination of the ventilatory threshold in patients with CHF has been previously validated by our group with this protocol. 15 All patients were continuously encouraged to perform maximal exercise until exhaustion. The patients' subjective level of exhaustion was quantified from 0 to 10, both for fatigue and dyspnea, using the Borg scale. 16 Respiratory gas analyses were performed with different commercialized systems (CPX 2001 system from Medical Graphic Corporation; Oxycon Champion from Mijnhardt; EOS Sprint from Jaeger; and Qplex from Quinton). Calibration with standard gases in known concentration was performed before each test. Gas exchange variables, assessed on a breath-by-breath basis or every 15 s, were as follows: oxygen uptake (ml/ min); carbon dioxide production (ml/min); minute ventilation (L/ min); breathing rate (min- 1 ); and respiratory exchange ratio (ratio of carbon dioxide output to oxygen uptake). In order to smooth the curves and exclude erratic values often observed during irregular breathing with breath-by-breath analysis, values were reported every 15 s using a moving average of 8 to 15 breaths. Heart rate (min- 1 ) was recorded on-line and blood pressure (mm Hg) measured every minute. Peak oxygen uptake was defined as the highest value of oxygen uptake observed at the end of exercise. Predicted maximal oxygen uptake was derived from the values published by Jones et al. 17 The ventilatory threshold was detected by the physician supervising the test according to the multiple usual criteria Blood lactate level was obtained at peak exercise in a subgroup of 12 patients. In order to assess linearity of the increase in oxygen during exercise with both protocols, a regression between oxygen uptake and time was performed for the 80 tests. Statistics Values are reported as mean±sd. Comparison between the values obtained on treadmill and on bicycle was performed with a Student's t test for paired observations. A p value <0.05 was considered statistically significant. Comparison of oxygen uptake at each stage between the two protocols was performed by paired t tests, because repeated measures over time by analysis of variance led to a systematic increase in missing data. To compare the linearity of the increase in oxygen uptake between the two protocols, we plotted the value of oxygen uptake measured at the end of each minute of exercise against time using the least square method; the r coefficients of the correlation between oxygen uptake and time were compared with a Student's t test for paired observations. RESULTS Table 1 summarizes the hemodynamic and gas exchange values obtained during exercise with both protocols. Exercise duration was, as expected from the modified Naughton protocol, longer on treadmill. Respiratory exchange ratio at peak exercise was about 1.1 in both tests, suggesting a near maximal degree of effort with both protocols. Peak oxygen uptake was greater by 10 percent with treadmill than with bicycle (19.6±5.3 vs 17.6±5.1 ml/min/ kg, p<0.001). Peak oxygen uptake was greater on bicycle in only three patients and roughly identical with both protocols ( <5 percent difference) in five patients (Fig 1). Expressed in percentage of the predicted values, the respective values of oxygen uptake were 64±16 percent vs 58±15 percent (p<o.oool). Similarly, the ventilatory threshold-determined in 35 patients-was greater in parallel with peak oxygen uptake on treadmill (14.5 ± 4.8 vs 12.0 ± 3.6 ml/min/ CHEST /106/4/ OCTOBER,

3 35, , '" !: Treadmill Bicycle FIGURE l. Peak oxygen uptake values obtained in all patients with treadmill and with bicycle ergometer. kg, p<0.0001), without change in the ratio ventilatory threshold/ peak oxygen uptake. Minute ventilation at peak exercise was also greater on treadmill (59± 18 vs 55± 15 L/ min, p<0.05). There was no difference in heart rate, blood pressure, or breathing rate. Therefore, oxygen pulse, the ratio of oxygen uptake by heart rate, was greater at peak exercise on treadmill. Gradation of fatigue or dyspnea was obtained in only one of two patients and was not different among protocols. Blood lactate level, measured in 12 patients, was also identical with the two protocols as was the ratio of minute ventilation by carbon dioxide output at the level of the ventilatory threshold, an index of ventilatory efficiency. The subject's oxygen uptake was greater during the first minutes of the test on treadmill; during the second part of test, it was lower than on bicycle, but the number of patients exercising more than 9 min fell to 9 on bicycle, compared with 20 on treadmill after this level (Fig 2); therefore, comparison of oxygen uptake values was not done after this level of exercise. The between-subject variability of oxygen uptake,as reflected by the SD, was lower at each stage with the bicycle than with the treadmill protocol. The slope of relation between oxygen uptake and time was calculated for all tests; mean value of the coefficient of correlation r was 0.90 ± 0.07 on treadmill vs 0.97 ±0.04 on bicycle (p<0.001), suggesting that the scattering of the points around the regression line was greater with treadmill than with bicycle and thus that the increase of oxygen uptake during exercise was more linear on bicycle. = e 1500 < 1000 "" Tr B (* p < 0.05) * * BICYCLE - ().-... TREADMILL o = - F = = = = = - = TIME (min) FIGURE 2. Oxygen uptake (mean± SD) obtained at each minute of exercise of the two protocols. (Asterisk=p<0.05 bicycle vs treadmill for the same time after the beginning of exercise. ) The number of patients performing each stage on bicycle or on treadmill is reported at the upper part of the figure. Statistical analysis was carried out only between patients reaching identical time of exercise with both protocols until the ninth minute. Tr=treadmill; B=bicycle Comparison of Treadmill and Bicycle Exercise in CHF Patients (Page et aq

4 DISCUSSION This study was undertaken to compare the information obtained from the two most frequently used protocols of exercise test in CHF, the modified Naughton treadmill protocol, and the 10 W /min stage incremental bicycle protocol. The aim of our study was to determine if peak oxygen uptake was greater on treadmill in these patients. The modified Naughton treadmill protocol is the most frequently used in patients with CHF because workload increments are small. Therefore, it has been recommended for therapeutic trials conducted in these patients, but duration of exercise with this protocol may be somewhat longer than generally recommended.l 1 Most of the previous studies that have shown that peak oxygen uptake was greater by 10 to 20 percent with treadmill than with bicycle exercise 5-11 commonly used the Bruce protocol, and more importantly, did not specifically address the issue of patients with CHF. To our knowledge, only two studies have compared bicycle and treadmill exercise in CHF. In ten patients, Franciosa et al, 20 did not observe any significant difference in peak oxygen uptake, but they used a bicycle protocol different from ours (increase in workload of 150 kilopondsmeters/ min every 4 min); peak oxygen uptake was very low (13 ml/ min/ kg), suggesting that their patients were severely disabled and/ or that exercise was submaximal (small increase in respiratory exchange ratio). Myers et al, 21 compared the Bruce, the Balke, and a ramp-test treadmill protocols with three bicycle protocols (25 W /min, 50 W /min, and ramptest). Forty-one patients were studied and in a small subgroup of 10 patients with CHF, there seems to be a trend toward lower values of peak oxygen uptake with bicycle compared with treadmill. Ventilatory threshold was greater on treadmill than on bicycle, but the ratio ventilatory threshold/ peak oxygen uptake was identical with the two protocols. The greater values observed on treadmill for minute ventilation are in accordance with the observation that oxygen uptake is greater with treadmill. 22 Why does bicycle exercise result in a lower peak oxygen uptake and ventilation than treadmill exercise? Smaller exercising muscle mass, resulting in a lower peak cardiac output,6,8 or local fatigue are explanations generally advocated. Jondeau et al, 23 have recently reported that exercising with both upper and lower limbs increased peak oxygen uptake in patients with CHF, a finding in opposition with what has been reported in normal subjects Muscle atrophy, abnormalities of muscle metabolism, 26 may explain that lower limbs may represent less than 40 percent of whole body muscle mass and thus their contribution to the increase in systemic oxygen uptake is actually smaller than in normalsubjects. On the other hand, respiratory muscle fatigue 27 and short-stepping gait 28 may increase the metabolic cost of exercise on treadmill in these patients. Conversely, it is likely that oxygen uptake was slightly underestimated at submaximal stages on treadmill because patients held on handrails. Despite markedly reduced ejection fraction, our patients had only a modest reduction of peak oxygen uptake, an observation attributable in part to treatment and to the fact that they had been previously familiarized with the apparatus and the technique of respiratory gas analysis. We took care to randomize the order of the two tests because significant improvements in exercise performances may occur with serial testing. 29 Moreover, maximal respiratory exchange ratio averaged 1.1 for each protocol, suggesting that maximal effort was generally achieved. We have tried to measure the subjective level of fatigue or dyspnea by means of the Borg scale; however, it seemed that patients had some problems to clearly explain the reason for stopping the test or did not clearly understand how to rate their effort. Only one of two patients was able to rate it. Therefore, the absence of difference between the two protocols for these ratings-as treadmill exercise is generally reported by patients to be more difficult to performand the fact that fatigue did not appear more frequent than dyspnea with bicycle, two relatively surprising findings, should be interpreted with caution. Contrary to a general belief, it is not possible to indirectly evaluate submaximal oxygen uptake from the level of exercise, both on treadmill and bicycle, because the slope of the increase of oxygen uptake is decreased in patients with CHF and values obtained from tables established in normal subjects are constantly overestimated, especially when a ramp-test is used As expected, the duration of exercise was probably too long and the oxygen uptake response was not linear on the treadmill and because body weight and the way of moving affect oxygen uptake, the oxygen requirement of each stage was quite variable among patients. Obviously, the modified Naughton protocol has various limitations even in patients with CHF and there is a need for finding new treadmill exercise protocols for these patients. 32 Finally, it is clear that it is incorrect to combine the results obtained with both protocols in trials in CHF. CONCLUSION It is definitively demonstrated that a treadmill protocol as gentle as the modified Naughton protocol leads to a greater peak oxygen uptake than a cycle ergometer protocol in patients with CHF, as observed in normal subjects or in subjects with coronary artery CHEST I 4 I OCTOBER,

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