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(Chest. 2003;124:511-518.)
© 2003 American College of Chest Physicians

Peak Physiologic Responses to Arm and Leg Ergometry in Male and Female Patients With Airflow Obstruction*

Rick Carter, PhD, MBA, FCCP; David B. Holiday, PhD; James Stocks, MD, FCCP and Brian Tiep, MD

* From the University of Texas Health Center at Tyler (Drs. Carter, Holiday, and Stocks), Tyler, TX; and Pulmonary Care Continuum (Dr. Tiep), Irwindale, CA.

Correspondence to: Rick Carter, PhD, MBA, FCCP, Professor of Medicine and Physiology, Center for Clinical Research, The University of Texas Health Center at Tyler, 11937 US Highway 271, Tyler, TX 75708; e-mail: Rick.Carter{at}UTHCT.EDU


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Study objective: To investigate differences in work capacity for the arms and legs in patients with moderate-to-severe COPD.

Design: Cross-sectional investigation.

Patients: One hundred twenty-four patients (90 men and 34 women) aged 45 to 81 years with moderate-to-very severe COPD. FEV1 ranged from 0.70 to 2.79 L/min (FVC, 1.73 to 5.77 L; FEV1/FVC, 24 to 69%). All patients were in stable condition at the time of testing and receiving a stable drug regime.

Measurements: Each patient completed a demographic and medical history questionnaire, pulmonary function studies (spirometry, lung volumes, and diffusion capacity), peak exercise ergometry with gas exchange for the arms and legs; they also rated their subjective assessment of perceived dyspnea and extremity fatigue using Borg scores during exercise.

Results: Patients were of comparable age, with men taller and heavier than women. Smoking history was significantly less for women (47.9 pack-years vs 66.6 pack-years for men) even though each group presented with equivalent age (p > 0.05). Women were less obstructed than men, with FEV1/FVC (mean ± SD) of 46.5 ± 10.9% vs 40.2 ± 9.3%, respectively. Ventilatory limitation during exercise was noted for all patients studied. Peak work capacity was greater for men, and leg peak responses were greater than arm values for each gender. As airway obstruction increased, work capacity became more limited. Peak arm work achieved was 38.9 ± 19.6 W, oxygen uptake (O2) was 903.9 ± 263.5 mL/min, and minute ventilation (E) was 33.7 ± 9.5 L. Peak leg work value was 62.9 ± 24.8 W, O2 was 1,091.4 ± 321.5 mL/min, and E was 39.3 ± 12.0 L. Hence, arm values were 62%, 83%, and 85% of the measured leg values, respectively. Dyspnea and extremity effort scores were similar for men and women, and for arms and legs. Regression analysis was used to derive prediction equations for arm work from measured leg ergometry testing. For watts of work, a three-variable model emerged explaining 66% of the variance; O2 yielded a four-variable model with 80% of the variance explained; and E yielded a three-variable model explaining 72% of the variance.

Conclusion: Arm work is reduced by 38% that of the legs, while more modest reductions are noted for O2 and E, suggesting greater mechanical efficiency for leg work as compared to arm work. These data also suggest greater metabolic demand for respiratory muscles and arm ergometry. Dyspnea and extremity Borg scores were equivalent for each modality and level of airway obstruction studied, suggesting that perception plays an important role in limiting exercise, and that a threshold for termination of exercise may exist. Further, peak leg ergometry results can be used with pulmonary function indexes to predict peak arm workload in watts, O2, and VE. These data may be used to assist the clinician in prescribing rehabilitation or estimating arm exercise ability when arm testing is unavailable.

Key Words: 6-min walk • COPD • functional capacity • quality of life • work capacity


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Chronic disease commonly leads to diminished functional capacity as symptomology increases. For patients with COPD, the degradation in lung function is progressive, leading to premature disability and death.1 2 As lung function decreases the ability to engage in activities of daily living (ADL) decreases and quality of life is impaired.3 Resting pulmonary function studies, while important for documenting lung function, explain only a part of the reported exercise limitation or inability to carry out ADL.

Physiologic work capacity differences between upper and lower extremities will variably limit maximal exercise performance4 and may impact on the perception of quality of life. Maximal power output for leg exercise is limited by one or more of the central cardiorespiratory stages of the oxygen transport chain. Rhythmic arm exercise capacity is related to active muscle mass, so that central functions such as cardiac output, stroke volume, heart rate (HR), and minute ventilation (E) do not reach their maximal output.5 As a consequence to these physiologic interactions, peak arm ergometry performance will be lower than that for the legs. For pulmonary patients, peak exercise E is restricted by the underlying lung disease and associated mechanical constraints thereby limiting performance (peak oxygen uptake [O2]) and accentuating dyspnea perception. There is evidence that the muscles of respiration become compromised when arm activity is required because of the competitive recruitment of muscle groups for either respiration or arm work.6 Additionally, the respiratory muscles can become fatigued early on due to the constant increase in the work of breathing resulting from airway obstruction and mechanical deficiency in the respiratory pump.7 Thus, when these muscle groups are called on to drive ventilation as well as participate in arm movement, their ability to meet the demand becomes undermined.8 9 It is thus important to evaluate and understand imposed limitations and devise strategies to maximize the ability of the upper extremity muscles to engage in exercise and ADL activity given the limitations imposed by decrements in pulmonary function.

The aims of the present study were to measure arm ergometry peak work capacity in men and women with varying levels of airway obstruction, and to determine the differences in functional capacity of arms vs legs. A secondary objective was to determine if gas exchange measures for leg work can be used to predict arm performance in this patient group.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
Patients
One hundred twenty-four patients with COPD (90 men and 34 women; mean age, 66.8 ± 7.3 years [mean ± SD]; range, 46 to 80 years) volunteered to participate in the study. All patients gave signed informed consent prior to entering this trial according to institutional guidelines. All patients had a confirmed diagnosis of COPD prior to entrance, were receiving a stable medication regimen, and were in stable condition at the time of testing. The level of pulmonary impairment ranged from moderate to severe based on pulmonary function testing.

Pulmonary Function Tests
Spirometry was performed with a SensorMedics Vmax 20C spirometry system (SensorMedics, Yorba Linda, CA) that was calibrated prior to each study and compared to the predicted values of Crapo et al.10 Diffusion capacity of the lung for carbon monoxide (DLCO) was measured by the single-breath technique of Jones and Mead11 using a SensorMedics system (Vmax 22, Autobox; SensorMedics). Lung volumes were determined by body plethysmography (Vmax 22, Autobox: SensorMedics). DLCO was compared to the data from Miller and others,12 while normal predicted lung volumes were derived from the equations of Goldman and Becklake13 (female patients) and of Boren et al14 (male patients). All studies were performed postbronchodilation following albuterol administration via a metered-dose inhaler. The dosing protocol followed was to administer one puff (90 µg), wait 10 min, then administer one additional puff (total of 180 µg). Pulmonary function testing was performed following the standards outlined by the American Thoracic Society.15 The best flow-volume loop was used in the final analysis of the data. Severity of airway obstruction was defined according to the American Thoracic Society criteria.15

Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) were obtained from each patient according to the method of Black and Hyatt16 with modifications described elsewhere.17 MIP was measured at residual volume, and MEP was measured at total lung capacity. For both MIP and MEP, measurements were repeated until three technically satisfactory and consistent values were obtained. The highest value was used in data analysis.

Exercise Tests
All patients performed an incremental arm (5 to 15 W/min square-wave adjustment) and a ramp leg exercise test (continuous fine workload adjustments1 in resistance equating to 10 to 30 W/min based on pulmonary function, prior exercise habits, and medical history) to a symptom-limited peak work capacity. A modified Monarch arm crank ergometer (Quinton Instruments; Bothell, WA) was used to deliver precise workload adjustments every minute to the patients tested. The ergometer was mounted on a bench, so that the crankshaft was in line with the glenohumeral joint, with the subject seated with the back straight and at full arm’s length when the ergometer crank was at the farthest position away from the patient. Each patient was familiarized with arm ergometer and had practiced arm cranking prior to testing. All patients were instructed to crank at a rate between 50 revolutions per minute and 60 revolutions per minute. Cadence was maintained with the aid of an electronic metronome. Each subject was given a 3-min, 0-load accommodation period followed by a 5 to 15 W/min increment in workload adjustment to a symptom-limited peak. Gas exchange data were obtained using the instrumentation described below. Perceived arm fatigue and dyspnea data were obtained at the end of each minute of exercise with the technician standing in front of the subject with the rating of perceived dyspnea and fatigue chart. The technician would move a finger down the ratings of perceived dyspnea/fatigue scale until the subject nodded. At that time, the technician questioned the response; if a second nod was given, the number was recorded. Otherwise, the technician would repeat the process.

For leg exercise, patients exercised on an electronically braked cycle ergometer (Medical Graphics; Minneapolis, MN) according to a ramp protocol as described by Wasserman and Whipp.1 The ramp workload was individually selected to yield an exercise performance of 8 to 12 min (10 to 30 W/min) and was preset in the computer using estimated peak exercise capacity. Seat height was adjusted to ensure that full knee extension was achieved when the pedal was in the down position and the handlebars raised to maintain the patient upright. All patients were instructed to pedal at a rate of 60 revolutions per minute, and this was monitored by the patient through a light-emitting diode display. Verbal encouragement was given to all patients throughout each exercise test period. Arm and leg exercise were separated by at least 2 h of rest or were preformed on separate days. All testing was completed 30 min following bronchodilator therapy.

Gas Exchange Measurement
Following a detailed explanation of the testing procedure and a practice trial pedaling/cranking, all patients were prepared for testing. Electrodes were positioned on the thorax for ECG monitoring. The patient then sat on the cycle ergometer, and seat height was adjusted to full knee extension. For arm ergometry, the patient was positioned on the arm ergometer bench as described above. Percentage of oxygen saturation (SpO2) was continuously monitored with a forehead sensor attached to a pulse oximeter (N200; Nellcor; Haywood, CA). The mouthpiece with disposable pneumotachograph was placed in the patient’s mouth, and the nose clip was positioned to prevent air leaks. The technician observed the end-tidal carbon dioxide values; when stabilized, a 3-min resting baseline gas collection was completed. Gas exchange data were collected and analyzed using a CPX-D gas exchange system (Medical Graphics). The system was precailbrated prior to each test using known gas concentrations, and a volume syringe was used to calibrate the pneumotach. Normal predicted values were computed according to the method of Wasserman et al.18 Peak predicted E was estimated from the measured FEV1 using the method of Carter et al.19 HR was calculated using the R-R ECG intervals.

Rating of Perceived Dyspnea and Extremity Fatigue
Borg scales were used to measure perceived breathlessness/dyspnea and extremity fatigue.20 21 22 23 The modified Borg scales used in this study have been used extensively in exercise-related studies.24 25 The Borg scales used to estimate breathlessness/dyspnea and fatigue uses a category-ratio scale ranging from zero (no breathlessness/fatigue) to 10 (maximum breathlessness/fatigue). Each patient was instructed regarding the use of the scales. Patients were presented with the breathlessness scale first with the appropriate descriptors of breathlessness recorded. Following their rating, a second scale was presented with fatigue descriptors for the extremity. Each scale was presented during the last 15 s of each minute of exercise completed.

Statistical Analysis
Analysis of variance techniques were used to test for differences among the variables of interest.26 Preplanned orthogonal contrasts were used to test for a significant difference between the two means following the overall analysis of variance.27 Orthogonal contrasts were performed using the contrast command with the general linear models procedure in Statistical Analysis System (SAS; Cary NC). Orthogonal contrast were coded using a standard coding of 0, 1, and - 1. Correlation coefficients were generated to investigate the relationship for selected variables. Regression techniques were used to explore the relationship of arm to leg work and to derive prediction equations.26 A value of p < 0.05 was considered significant. All data are presented as mean ± SD.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
Mean anthropometric and resting lung function results for men and women are presented in Table 1 . Patients were then stratified according to the level of pulmonary impairment as either moderate or severe. Table 2 presents the findings. Pearson correlations were used to investigate relationships among selected variables. There was a significant correlation between the FEV1 and peak arm work (r = 0.59, p < 0.0001) as well as between FEV1 and peak leg work (r = 0.53, p < 0.0001) [Fig 1 ]. While the slopes were equivalent, the intercepts were different. The arm intercept was 24.1 W, while that for the legs was 49.2 W. This demonstrates that greater levels of work are accomplished for the legs than for the arms at equivalent levels of airway obstruction. When the data for men and women were examined independently, arm and leg work for men was correlated to the FEV1 (r = 0.57 and r = 0.48, respectively; p < 0.0001). For women, arm work was not correlated with FEV1 while leg work was modestly, but significantly, correlated with the FEV1 (r = 0.38, p < 0.03).


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  		Table 1. Demographic and Resting Pulmonary Function Results for Male and Female Patients Overall and by Level of Airway Obstruction*

 

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  		Table 2. Peak Exercise Responses for the Combined Group*

 


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  		Figure 1. Plot of symptom-limited peak arm and leg work to degree of airway obstruction as represented by percentage of predicted (%Pred) FEV1.

 
Exercise testing was completed to peak volitional exertion for all patients under each test condition. (Table 3 ) For the entire group, peak exercise gas exchange indexes for leg work were generally greater than those for arm work. Arm work at peak exertion, measured in watts, was 63 ± 24% of the measured leg work (p < 0.0001). Peak O2 and carbon dioxide output (CO2) were 84 ± 13% and 84 ± 17%, respectively (p < 0.0001), those for leg work. Peak exercise ventilation for the arms was 89 ± 24% (p < 0.0001) that measured for the legs with an equivalent reduction noted for tidal volume (VT) and respiratory rate (RR). SpO2 for peak arm work was higher, averaging 82 ± 25% of the observed peak decrease for leg testing. The absolute SpO2 difference was 1.01 ± 0.03% (p < 0.002). Peak HR was 3.4 ± 1.0 beats/min higher during leg as compared to peak arm effort (p < 0.0009). Borg scores for perceived dyspnea were equivalent for each test modality, while Borg scores for extremity fatigue ratings were higher for the legs (p < 0.01).


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  		Table 3. Peak Exercise Test Results for Leg and Arm Ergometry by Gender with Leg-Arm Differences Calculated*

 
Because male and female patients differ in their ability to perform physical work, we analyzed the data by gender. Peak gas exchange indexes trended higher for leg as compared to arm work. Specifically, peak values for workload accomplished (watts), O2, CO2, E, and VT were higher for leg as compared to arm effort (p < 0.0001, respectively; Table 3 ). No differences were observed for RR, SpO2, or HR (p > 0.05). Female patients did not differ with respect to their ratings for leg fatigue nor perceived dyspnea (p > 0.05) for each modality. For male patients, peak exercise indexes for watts of work accomplished, O2, CO2, E, VT, and SpO2 were greater for leg as compared to arm effort (p < 0.0001) while HR was lower for peak arm effort (p < 0.01). Male patients rated perceived dyspnea equally for the arms and legs, but extremity fatigue Borg ratings were higher for the legs as compared to the arms (p < 0.01). No differences (p > 0.05) in arm or leg dyspnea or fatigue scores were observed between male and female patients with COPD.

Stepwise regression modeling using the MaxR2 improvement from the Statistical Analysis System (SAS) was used to derive prediction equations for arm peak workload (watts), O2 (milliliters per minute), and E (liters). The model included demographic, resting pulmonary function, and peak cycle ergometry gas exchange data. Variables included in the model were gender, age, body weight, FEV1, FVC, DLCO, inspiratory capacity (IC), MIP, MEP, and the peak leg cycle ergometer variables, O2, and CO2, E, RR, VT, and HR, Borg dyspnea and leg fatigue scores. The resulting regression equations for predicting peak arm workload, O2 and VE are as follows:





   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
Differences between arm and leg peak exercise performance are well documented for normal younger individuals; however, there is a paucity of data for patients with COPD especially when stratified by gender and level of airway obstruction. These data are important because they may yield important insights regarding exercise limitation in these patients. For normal subjects, the main difference between arm and leg work is the amount of muscle mass involved with the effort.4 For patients with COPD, differences would be anticipated due to decreased muscle function (inefficient bioenergetics), competitive recruitment of muscle groups for ventilation and/or extremity movement, degree of airflow limitation present, detraining, and inefficient dynamic cardiopulmonary coupling with increasing work demand.28

We and others29 30 31 32 have observed a close association between peak work capacity and cardiopulmonary indexes of exertion and the severity of airway obstruction. Generally, as airway obstruction increases, maximal E decreases and a decrease in total work output is observed. Yet, the correlations presented to date, while significant, are akin to the ones observed in this trial and are in the 0.40 to 0.60 coefficient range (ours was 0.57 for men and 0.48 for women). Therefore, airway obstruction accounts for somewhere between 16% and 36% of the variance in exercise performance in the typical COPD population. This leaves a substantial percentage of variance for other factors such as mechanical efficiency, effort, differences in dyspnea perception, and attentiveness to chemoreceptor and baroreceptor input, and shifts in lung volume with increasing exercise, to mention a few.28 33 34 35 This is why exercise testing is essential for assisting individuals with COPD who complain of increased shortness of breath and exercise limitation.

For the entire group, work capacity was significantly less for arms compared to the legs. These findings are consistent with previously published data.4 Peak workload accomplished for the arms averaged 63% that of the legs while peak O2 was 84% with a peak E of 89%. The VE/maximum voluntary ventilation of 71% (breathing reserve of 21 ± 14 L) for the arms and 81% (breathing reserve of 11.5 ± 12 L) for the legs suggest limited ventilatory reserve.36 37 These findings are in agreement with data for arm work in patients with COPD.38 There are several explanations for the differences in work capacity noted. The first is a function of the volume of muscle mass involved in the performance of external work. The arms are only a fraction of the muscle mass of the legs; thus, the total work accomplished is known to be less.39 For patients with pulmonary disease, there are additional superimposed changes in physiology that promote a reduction in the ability to perform external work with the arms as well as the legs. These can include dyssynchronous breathing,38 skeletal to respiratory muscle competition and recruitment,40 pattern of exercise and prior training,41 nutritional status,42 and dynamic hyperinflation.43 Further, perception of dyspnea and/or fatigue of the active muscles of exercise may influence continued activity. We found that perception of muscle fatigue was slightly and significantly lower for the arms as compared to the legs; however, the perception of dyspnea was the same. This suggests that physiologic adjustments to exercise are providing varying levels of sensory input from arm and leg work and that these cues may be signaling the termination of effort. This response to the sensation of shortness of breath or dyspnea is consistent with prior reports.44 45 46 This finding may also explain why peak HR was 3.4 ± 1.0 beats/min higher for leg than arm exercise. There also may exist a difference in sensory cues that signal the impending limitation to exercise for arm as opposed to leg exertion. In our study, we noted a difference between arm and leg fatigue perception at equivalent levels of dyspnea sensation. Thus, for arm work, Borg fatigue scores were lower for the arms as compared to the legs. However, the real significance of this finding cannot be identified specifically from this study. More information is required to ascertain how sensory cues contribute to exercise performance in these patients.

Work capacity for male patients is typically higher than that for female patients. This difference has been attributed to differences in body size and muscle mass, the ability of the cardiopulmonary system to supply nutrients and remove waste products of muscular contraction, differences in oxygen transport capacity, and others. Because of these known differences, we grouped our patients by gender. Female patients presented with a lower ability to perform work, yet their adjustments to exercise were similar to those of the male patients. A notable difference was in perception to dyspnea and extremity fatigue. Female patients presented with similar Borg scores for the arms and the legs, while male patients reported significantly higher fatigue scores for the legs. These observations suggest several possibilities. First, female patients may perceive dyspnea and extremity fatigue cues as being equal and may react to the sum of the sensations while males are more attuned to muscle fatigue. Another possibility is that male patients terminate exercise at the same dyspnea rating even though they sense leg fatigue as being greater. Further, there may exist some slight training differences between the male and female patients in this study since training is known to alter physiology and perception. While we do not have the data to definitively ascertain why these differences exist, nor to discern their exact contribution to exercise limitation, it appears that male and female patients may differ slightly with respect to perception and exercise cessation. An important finding is that male and female patients terminated exercise at similar Borg scores for dyspnea and fatigue. This suggests that the perceived termination threshold is similar, even though female patients accomplished less work as compared to the male patients.

Through regression analysis, we were able to identify variables that predicted watts of arm work, O2 or E. While the variables selected for inclusion were each significant, they differed with respect to the variable being predicted. For workload IC, watts of leg work and leg CO2 were mathematically selected. IC also entered into the model for prediction of peak arm E, as did DLCO and peak leg E. Predictors for peak arm O2 included DLCO, MIP, MEP, and leg O2. While we can speculate as to the mathematical logic for variable inclusion in the models for some, others are more elusive. For example, IC is related to severity of lung disease and shifting lung volumes. Peak exercise E takes into account RR and VT adjustments to exercise, muscle performance, and fatigue as well as whole-body conditioning and perception; however, DLCO is a measure of gas transfer ability in the lung that is also influenced by cardiovascular, pulmonary, and gas transport abilities of the blood as well as removal of byproducts of metabolism such as CO2. MIPs and MEPs were selected and their inclusion points to their significance with respect to muscle performance, bioenergetics, and nutritional status. MIPs and MEPs, while specific measures of respiratory muscle performance, are correlated with extremity muscle performance. What is somewhat more difficult to explain is the inclusion of IC for predicting watts of work. From these data, it would appear that the IC at rest signals disease severity and may also provide information regarding dynamic adjustments to exercise indirectly—respiratory muscle ability and thus, general muscle ability. Further studies are required to specifically address influencing factors and the underlying physiology.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
We have demonstrated that gender and level of airway obstruction impact on a patient’s ability to engage in physical exercise. This study provides data relating to airway obstruction, exercise performance for the arms and legs, as well as perceived dyspnea and extremity fatigue. Arm work generally represents a fraction of the work accomplished by the legs, yet the perception of dyspnea and extremity fatigue are equivalent at peak exertion for each modality, gender, and severity category. This suggests that dyspnea and the perception of extremity fatigue may be important modulators for exercise capacity for patients with COPD. Because exercise testing is often performed using the legs, we wanted to know if these values could be used to predict arm work. We present equations for the prediction of peak arm work in watts, O2 and E. The equations use the IC and DLCO from pulmonary function testing, MIPs and MEPs as well as peak leg ergometry E, CO2, and O2. All variables mathematically selected are known to reflect pulmonary function, muscle function, nutritional status, and the ability of the lung to efficiently participate in gas exchange. These formulas can be used to estimate arm work ability and subsequently applied to derive an initial exercise prescription for rehabilitation/exercise training for the arms. Lastly, these same prediction equations can be used as benchmarks of arm performance to judge arm work ability for individuals with moderate-to-severe COPD, then compared to existing tables of metabolic load for selected activities. This comparison would aid the clinician in assessing the patient’s complaint.


   Footnotes
 
Abbreviations: ADL = activities of daily living; DLCO = diffusion capacity of the lung for carbon monoxide; HR = heart rate; IC = inspiratory capacity; MEP = maximal expiratory pressure; MIP = maximal inspiratory pressure; RR = respiratory rate; SpO2 = oxygen saturation; CO2 = carbon dioxide output; E = minute ventilation; O2 = oxygen uptake; VT = tidal volume

This project was supported by grant number R01 HS08774 from the Agency for Health Care Research and Quality.

Received for publication July 30, 2002. Accepted for publication February 18, 2003.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

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