INTRODUCTION

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Care of patients with symptomatic chronic obstructive pulmonary disease (COPD) includes smoking cessation, bronchodilator medications, oxygen therapy, and comprehensive pulmonary rehabilitation (1). Exercise training is a major component of pulmonary rehabilitation programs. Exercise intensity is prescribed as a specific percentage of maximal oxygen consumption (O₂max) during a progressive incremental exercise test (2). For monitoring purposes both healthy individuals and patients with cardiac disease are usually instructed to train at a target heart rate (THR) in order to exercise within a safe range and to attain a training response. However, this approach has at least two inherent problems for patients with respiratory disease. First, pulmonary patients are limited by ventilatory impairment and dyspnea rather than cardiovascular factors. Second, it may be difficult for some healthy adults as well as patients with cardiorespiratory disease to monitor their heart rate (HR) by palpating the radial or carotid artery (3).

An alternative approach is to use ratings of perceived exertion (RPE) for prescribing and regulating training intensity (2). RPE are the individual's internal perception of overall exercise stress. The American College of Sports Medicine has recommended that ". . . once the relationship between heart rate and RPE is known, RPE can be used in place of heart rate" for monitoring the intensity of exercise training (4). For patients with respiratory disease, dyspnea is the major perceptual distress experienced by the body rather than more general RPE. In two recent studies Horowitz and coworkers (5, 6) demonstrated that patients with moderate to severe COPD could use dyspnea ratings obtained from an incremental exercise test to reliably regulate and monitor the intensity of physical exertion. The purpose of this study was to compare the ability of patients with COPD to produce an exercise intensity using a target dyspnea rating (TDR) versus a THR. This study design considered a novel approach (i.e., dyspnea ratings) for prescribing and monitoring exercise training compared with the traditional method of HR response. We tested the null hypothesis that patients with COPD can produce a desired exercise intensity during submaximal exercise (as used in training) as accurately and as reliably using a TDR as with a THR obtained during incremental exercise (as used in testing).

	METHODS

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Study Patients

Patients were recruited from the outpatient clinics at our institution. The following inclusion criteria were used: a female or male patient 40 to 75 yr of age; a diagnosis of COPD as defined by the American Thoracic Society (1); a baseline FEV₁  65% of the predicted normal values (7); an FEV₁/FVC ratio of  70%; and dyspnea on exertion. Exclusion criteria were: inability to exercise on the cycle ergometer; an unstable respiratory status within the previous 4 wk; any clinically significant comorbid disease; and previous participation in a pulmonary rehabilitation program. None of the subjects in the present study participated in previous investigations examining the use of TDR for monitoring exercise intensity (5, 6).

Study Design

The study was a randomized, parallel group trial comparing the accuracy and reliability of patients with symptomatic COPD to produce an exercise intensity using TDR and THR. There were three visits for each participant over a 3-wk time period.

Patients were instructed not to use short-acting inhaled bronchodilators for 6 h and long-acting bronchodilators for 12 h before coming to the laboratory. At each visit spirometry was performed before and 20 min after inhalation of 2 puffs (180 µg) of albuterol. Exercise testing was then performed on the cycle ergometer (Monark-Crescent AB, Varburg, Sweeden). All testing was performed at the same time of the day for all three visits.

Visit 1. After spirometry was completed, patients read the following instructions regarding the 0 to 10 category-ratio (CR10) scale (8):

"This is a scale for rating breathlessness. The number 0 represents no breathlessness. The number 10 represents the strongest or greatest breathlessness that you have ever experienced. Each minute during the exercise test you will be asked to point to a number with your finger which represents your perceived level of breathlessness at that time. Use the written description to the right of the number to help guide your selection. I will say the number out loud to confirm your choice. During the exercise test you may have an even stronger or greater intensity of breathlessness than you have ever experienced. You should then point to the word `maximal' if the severity is greater than 10. You can tell us the number after the mouthpiece has been removed."

While seated on the cycle ergometer, each subject breathed ambient air through a mouthpiece and low resistance two-way valve (Hans-Rudolph). Expired gas was analyzed for minute ventilation (E), oxygen consumption (O₂), and carbon dioxide production (VCO₂) using breath-by-breath analysis from the Vmax system (SensorMedics, Yorba Linda, CA). After a 5-min equilibration period, the patients started exercise at zero load at a pedal speed of 50 rpm. After the first minute a load of 12.5 W/min was applied, and thereafter increased by 12.5 W every minute until the patient reached exhaustion or stopped because of symptom limitation. At each minute the patient was asked to rate the intensity of dyspnea on the CR-10 scale. There was continuous monitoring of 12-lead electrocardiograms (ECG) and oxygen saturation by pulse oximetry (Oxyshuttle; SensorMedics).

Then, each subject was randomized into: Group 1use of THR; or Group 2use of TDR. During a 30-min rest period patients assigned to Group 1 were given both written and oral instructions on how to measure HR by palpating the radial pulse (or the carotid pulse if the individual was unable to palpate the radial pulse) at rest for 10 s using the self-palpation method. A large face clock was placed 2 to 3 feet in front of the individual to be used to determine the elapsed time. Acceptable accuracy for a 10-s period was ± 6 beats/min. Patients assigned to Group 2 were given written and oral instructions on how to measure dyspnea ratings using the CR-10 scale.

For each patient in Group 1 a plot of HR versus O₂ was obtained from the incremental exercise test; using linear regression analysis the THR was calculated corresponding to ~ 75% of peak O₂. For each patient in Group 2 a plot of dyspnea ratings versus O₂ was obtained from the incremental exercise test; using linear regression analysis the TDR was calculated corresponding to ~ 75% of peak O₂. Next, each patient exercised for 10 min on the cycle ergometer at 75% of peak O₂ and practiced measuring HR by self-palpation (Group 1) or practiced providing ratings of dyspnea (Group 2). The purpose of these sessions was for familiarization and practice of the particular method. During the practice session an investigator gave feedback to each patient as to the accuracy of the HR (compared with the measured HR by the ECG) or as to the expected dyspnea ratings (compared with the value from the incremental exercise test).

Visit 2 (3 to 5 d later). After spirometry was performed each patient was instructed to perform a production task (produce a specific THR or a TDR) as calculated at Visit 1 on the cycle ergometer for approximately 15 min. At the start the patient maintained a constant pedaling speed of 50 rpm for 1 min at zero load (warm-up), and then the work load was increased by 6 to 7 W/min (or 12.5 W/min if the peak power production at Visit 1 was > 30 W) until the patient's response (HR or dyspnea rating) reached the expected target value. The patient was asked to measure and report his or her HR (Group 1) or provide a rating of dyspnea (Group 2) at each minute of exercise until the production target was reached (usually within 3 to 5 min). Once three consecutive target values were achieved (± 6 beats/min for THR or ± 1 unit on the CR-10 scale for TDR) the patient was instructed to continue the procedure for an additional 10 minutes. If the patient reported two consecutive HR or dyspnea ratings outside the acceptable range, the workload was adjusted by 6 to 7 W in the appropriate direction. E, O₂, and HR were measured throughout the exercise test as described at Visit 1.

Visit 3 (2 wk later). Patients returned for similar testing as described for Visit 2. The purposes of this Visit were to examine accuracy and reliability over a 2-wk time period for production of the exercise intensity using either THR or TDR.

Statistical Analysis

The major outcome of the study was O₂. Individual values for O₂ obtained during submaximal exercise (Visits 2 and 3) were averaged over 10 min. To assess accuracy of TDR versus THR the within- patient differences in the expected O₂ at Visit 1 and the average O₂ at Visits 2 and 3 were calculated. These differences between groups were compared using an unpaired t test. The proportion of patients whose O₂ values at Visits 2 and 3 were < and  10% of the expected O₂ at Visit 1 were computed for each group and compared using an unpaired t test.

To assess test-retest reliability for achieving an expected exercise intensity level, the within-patient differences in average O₂ from Visits 2 and 3 were computed and compared using an unpaired t test.

We calculated that 22 patients were required per group to have an 80% power to detect a mean difference of 75 ml/min in O₂ between Visits 1 and 2 (between THR and TDR groups). This number of patients also ensured more than 80% power to test reliability (± 5% in O₂) for within-group comparisons at Visits 2 and 3. 

	RESULTS

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Forty-four of the 45 patients recruited completed the study. One individual withdrew from the study after testing at Visit 1. Five patients initially assigned to the THR group at Visit 1 were unable to measure accurately their resting HR despite instruction and practice. Rather than exclude these individuals from the study, they were reassigned to the TDR group and completed the exercise practice session at Visit 1 as described. This reassignment potentially favored the final results of the THR group by eliminating subjects who had difficulty in self-palpating their pulse. Characteristics of the 22 patients in each group are reported in Table 1. There were no significant differences in anthropometric variables, lung function, exercise performance, and ratings of dyspnea or leg discomfort at peak exercise between the groups.

Selected physiologic variables and dyspnea ratings for the two groups at Visit 1 (target values) and at Visits 2 and 3 are shown in Table 2. The O₂ calculated at ~ 75% of peak O₂ at Visit 1 was 0.88 ± 0.28 L/min for the TDR group and was 0.76 ± 0.29 L/min for the THR group (p = 0.18). The corresponding TDR was 2.5 ± 1.5 on the CR-10 scale for the TDR group; the corresponding HR was 114 ± 15 beats/min for the THR group.

The TDR group had dyspnea ratings of 3.4 ± 1.7 and 2.9 ± 1.5, respectively, during 10 min of submaximal exercise at the two different visits. At Visit 2 the THR group had a palpated HR response of 114 ± 15 beats/min during 10 min of submaximal exercise compared with the recorded HR of 113 ± 20 beats/min by ECG; at Visit 3 the palpated HR was 115 ± 13, and the HR by ECG was 114 ± 20 beats/min.

Individual values for the differences in O₂ at Visits 2 and 3 compared with the expected O₂ values from Visit 1 are shown in Figures 1 and 2, respectively. The individual differences for the measured O₂ at Visit 2 compared with expected O₂ at Visit 1 were 3.9 ± 18.1% for the TDR group and 0.5 ± 23.2% for the THR group (p = 0.58). Values at Visit 3 were 2.3 ± 17.0% for the TDR group and 2.6 ± 30.6% for the THR group (p = 0.52). At Visit 2 eleven patients in the TDR group and 9 patients in the THR group achieved O₂ < 10% of the expected value calculated at Visit 1 (p = 0.38 by Fisher exact test). At Visit 3 ten patients in the TDR group and 7 patients in the THR group achieved O₂ < 10% of the expected value at Visit 1 (p = 0.27).

View larger version (10K): [in this window] [in a new window]   Figure 1.   Individual values for O2 at Visits 2 (open circle) and 3 (closed circle) for the 22 patients in the TDR group compared with the expected O2 values at Visit 1 represented by the horizontal line.

View larger version (10K): [in this window] [in a new window]   Figure 2.   Individual values for O2 at Visit 2 (open circle) and 3 (closed circle) for the 22 patients in the THR group compared with the expected O2 values at Visit 1 represented by the horizontal line.

There were no significant differences in O₂, power output, and E during submaximal exercise for each group and between the two groups at Visits 2 and 3.

	DISCUSSION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION REFERENCES

Exercise training is considered an essential component of pulmonary rehabilitation. However, an important and relevant question is, "How should the exercise intensity be prescribed and monitored in patients with respiratory disease?" The traditional approach for healthy individuals and for patients with cardiac disease has been to use HR as an estimate of intensity because of the linear relationship between HR and O₂ during incremental exercise. However, self-palpation of HR typically requires the individual to stop exercise, may not be accurate, and can be influenced by various medications. For these reasons the use of RPE has been recommended for the prescription of exercise intensity and for its monitoring during training in healthy adults (2, 4). Various investigators have reported the validity of regulating exercise intensity by using RPE (9). For example, Glass and coworkers (11) demonstrated that healthy men were able to use a "target RPE" obtained during a single graded exercise test on the treadmill to accurately produce a submaximal exercise intensity.

For patients with respiratory disease the major subjective complaint and reason for stopping exercise is dyspnea rather than overall perceived exertion. In two previous studies Horowitz and coworkers (5, 6) reported that patients with COPD were able to produce an exercise intensity accurately on the cycle ergometer and on the treadmill using dyspnea ratings obtained from a prior incremental exercise test. Accuracy was better at a dyspnea target of ~ 5 (75 to 80% of peak O₂) compared with a dyspnea target of ~ 2 (50% of peak O₂).

These results led us to compare the use of TDR, a new method for prescribing exercise training intensity in patients with respiratory disease, with the established approach of THR. We hypothesized that dyspnea ratings would be as accurate and as reliable for prescribing and monitoring exercise training in this population compared with the use of a THR. We recruited patients who had no previous experience with rating dyspnea or measuring their HR and had not participated in a pulmonary rehabilitation program. Our results demonstrated that patients with COPD had comparable ability using either TDR or THR to accurately and reliably produce an exercise intensity corresponding to ~ 75% of peak O₂. Although the mean data are similar between both groups (Table 2), examination of individual results (Figures 1 and 2) showed considerable variability in accuracy with both approaches despite familiarization and a practice session.

We found that five patients initially assigned to the THR group were unable to palpate their pulse and/or count the number of "jumps" in their pulse with acceptable accuracy even at rest. Thus, statistical analysis was based on reassignment of five patients to the TDR group rather than "intent to treat." Overall, there were 22 patients per group. During an actual exercise session it is assumed that the individual will achieve a steady-state HR response in the prescribed range; however, the actual HR will likely be both above and below the prescribed range (2). Typically, the individual is instructed to stop exercise in order to measure his or her pulse; this may lead to a reduction in the HR response depending on the time required for the individual to locate the pulse and count for the required time.

Reliability for using TDR and for THR was similar over a 2-wk period (between Visits 2 and 3). Although it is unclear whether reliability is maintained over the usual 6 to 8 wk of a typical pulmonary rehabilitation program, our clinical experience suggests that patients are able to use the same dyspnea ratings to produce a desired exercise intensity over a 2-mo period.

The use of RPE or dyspnea targets may also be problematic for some individuals. It has been estimated that about 10% of individuals are unable to rate or scale perception in an accurate manner (13). However, in healthy adults the errors in using RPE to produce an expected O₂ were similar to errors using a THR (10).

We believe that TDR provide some advantages over the use of HR. First, the process is simple and easy for most patients to learn and apply. Second, many patients with COPD are constantly aware of their breathing difficulty with various tasks. Accordingly, the use of a scale for patients to rate or estimate the severity of their dyspnea enables them to accept a certain level of physical exertion rather than stopping a task at the onset of breathlessness. This approach can be used in pulmonary rehabilitation programs where patients are encouraged to continue exercise and tolerate some unpleasant breathing in an effort to train skeletal muscles. Third, patients can continuously monitor their dyspnea/exercise intensity and do not need to stop in order to "check their pulse." Thus, the technique of TDR may be applied while patients are actually performing daily activities. It is interesting that individual percent differences in O₂ were lower in the present study (which included a practice session at Visit 1) compared with our earlier results in 15 patients with COPD (range for individual differences, 4 ± 9% to 12 ± 19%) who did not practice using dyspnea targets for producing an exercise intensity (5). Therefore, practice sessions with feedback information may be helpful to enhance the accuracy of TDR.