Dyspnea on exertion isone of common symptoms experienced by patients with chronic obstructive pulmonary disease (COPD).1
The measurement of dyspnea is a useful outcome measurement for assessing the symptoms and evaluating the effects of therapeutic interventions designed to relieve dyspnea. The tools most commonly used to rate the degree of dyspnea during exercise are the Borg scale and the visual analog scale.2-4Both scales have been shown to be highly reproducible in patients with COPD.5-7
The modified Borg scale, consisting of a vertical scale labeled 0 to 10 with corresponding increasing sensation of dyspnea,8
is more commonly used to measure dyspnea in clinical and study areas in China. However, many patients find it difficult to distinguish among the numbers corresponding to moderate, somewhat strong, strong, very strong, and very very strong when forced to make rapid decisions during exercise, especially for older individuals or those with limited education. The visual analog scale (VAS) consists of a horizontal line with the left end marking (0 cm) representing “no dyspnea” and the right end marking (10 cm) representing the “very severe dyspnea”; patients also need to differentiate these degrees of discomfort.
Thus, we developed a method to rate dyspnea called the counting scale (CS), in which subjects inhaled maximally and then counted from 1 to the maximum (i.e., 1, 2, 3…)
in one breath while exhaling as quickly and as clearly as they could. The highest number to which the subjects could count was defined as the counting scale number (CSN). The time spent on the counting was defined as the counting scale time (CST). The aims of the present study were to evaluate the reproducibility and sensitivity of CSN and CST as an assessment of dyspnea during exercise in patients with COPD and to compare the reproducibility and sensitivity of CSN and CST with the Borg scale.
Fourteen male patients with COPD aged (58.00±7.72) years participated in this study from December 2010 to August 2011. All subjects were clinically stable outpatients. The study was approved by the Ethics Committee of Beijing Friendship Hospital, and all subjects provided written informed consent.
Pulmonary function testing
Forced vital capacity (FVC) and forced expiratory volume in one second (FEV1
) were measured using a spirometer (MasterScreen Body, Jaeger, Germany) according to standard techniques.9
Spirometry was performed before exercise testing on each study day to determine whether individuals’ lung function had remained stable.
Patients performed a progressive incremental exercise testing to a symptom-limited maximum on an electronically braked cycle ergometer (ER 900L, Jaeger, Germany). The protocol consisted of 3 minutes of resting, 3 minutes of unloaded pedaling, and minute-by-minute increments at a work rate of 5 to 20 W/min. Minute ventilation, oxygen uptake (VO2
), and carbon dioxide were acquired breath-by-breath using a computerized system (Oxygen Delta, Jaeger). Maximal heart rate (HR) predicted for age was calculated as 220–age.10
After a 1-hour rest period, a 6-minute constant work exercise test consisting of 3 minutes of pedaling at 30% of maximal workload (Wmax) achieved and 3 minutes at 70% of Wmaxwas performed. Exercise testing was performed every 2 to 3 days for 3 times totally.
Subjects were instructed to inhale fully and then to count from 1 to as high as they could (i.e., 1, 2, 3…) in one breath while exhaling as quickly and clearly as they could. Both the maximum number the subject could speak and the time spent were recorded. The counting scales were evaluated at rest and instantly after stopping exercise in the incremental exercise test and at 30% and 70% of Wmaxin the constant work exercise test. The Borg scales were determined at the end of the incremental exercise testing and during the last 30 seconds of the two workloads (30% and 70% of Wmax) in the constant work exercise test, each of which was followed by CS measurement.
The reproducibility of the CSN, CST, and Borg test at rest and during exercise (at 30% of Wmax, 70% of Wmax, and Wmax) were assessed using repeated measures analysis of variance (ANOVA) and coefficient of variation (CV), which was calculated as the within-subject standard deviation (SD) divided by the within-subject mean. Differences between the exercise levels were compared using ANOVA with a post-hoc Tukey test. The relationship among CSN, CST, and the Borg scale was calculated by linear correlation. Continuous data are reported as mean±SD. Statistical significance was accepted atP<0.05. SPSS 13.0 software (SPSS Inc., USA) was used for data analysis.
Fourteen male patients with COPD from the respiratory clinic at Beijing Friendship Hospital were involved in this study between December 2010 and August 2011. All subjects completed an incremental symptom-limited exercise and a 6-minute constant work exercise test for 3 times on separate days within one week. The resting pulmonary function and maximal exercise data are shown in Table 1
Reproducibility of CSN and CST
The mean ratings of dyspnea using the CSN, CST, and Borg scale at different workloads on trial 1, trial 2, and trial 3 are presented in Figures 1, 2, and 3, respectively. No significant differences occurred across the three trials during exercise for the CSN, CST, and Borg scores. The CSN scores varied significantly at rest during the three trials (P=0.046). The CST scores were reproducible at rest, with no significant differences across the three trials.
The within-subject CV for CSN, CST, Borg scale, and FEV1 is shown in Table 2
. The CSN and CST varied more at Wmax(CV=(22.28±16.96)% for CSN, CV=(23.08±19.11)% for CST) compared to 30% of Wmax(CV=(11.92±8.78)% for CSN, CV=(11.16±9.96)% for CST) and 70% of Wmax(CV=(9.08±7.09)% for CSN, CV=(12.19±12.32)% for CST). The CV for the Borg scale considerably exceeded that for CS at sub-maximal exercise. The FEV1
was more reproducible than the CSN, CST, and Borg score.
Sensitivity of CSN and CST
Dyspnea ratings with either CSN or CST tended to decrease at higher workloads compared to lower workloads (Table 3
). Both the CSN and the CST scores at Wmaxwere significantly lower compared to 30% of Wmaxand at rest, while those at 70% of Wmaxwere significantly lower compared to at rest. No significant differences were found between at rest and during exercise at 30% of Wmax, between 30% of Wmaxand 70% of Wmax, or between 70% of Wmaxand Wmax. In contrast, significant differences were found between 30% of Wmaxand Wmaxfor the Borg scale.
Relationship among CSN, CST, and Borg scores
To assess the relationship among CSN, CST and Borg scores, the data from trials 1, 2, and 3 were combined. CSN and CST scores were highly correlated (r=0.861,P<0.001). CSN was negatively correlated with Borg scores (r=–0.363,P=0.001). Similar results were obtained for the relationship between CST and Borg scores (r=–0.345,P=0.003). The relationship among CSN, CST, and Borg scores is shown in Figures 4–6
Rating dyspnea needs to depend on what the patients feel about how difficult it is for them to breath. One method that is easy to use and simple for subjects to understand is desired in clinical practice, especially during exercise in a very short period. We developed a new method, CS (CSN and CST), to rate dyspnea during exercise. In this study, we evaluated the short-term reproducibility and sensitivity of CSN and CST measurements of dyspnea during exercise in patients with COPD. The major findings of this study were as follows: (1) neither CSN nor CST systematically varied over time during exercise, unlike the Borg scale; (2) the CSN and CST were more reproducible at sub-maximal exercise than at maximal exercise; (3) both CSN and CST tended to be lower as workload increased during exercise; and (4) CSN was highly correlated with CST. Both CSN and CST were negatively correlated with the Borg scale.
The Borg scale is widely accepted and used to rate dyspnea during exercise. Several studies have evaluated the short-term reproducibility of Borg measurements of dyspnea during exercise in patients with COPD. Muza et al5
and Silverman et al6
examined the reproducibility with six patients with stable COPD who indicated the effort to breathe during exercise; these researchers found that the variability in Borg ratings was not significantly different in exercise trials performed either within or between days. Melman et al11
showed that Borg ratings varied significantly across four subsequent study days within a ten-day period in COPD patients. In our study, we evaluated the reproducibility of the new method (i.e., CS) as well as the Borg scale to rate dyspnea during exercise. We demonstrated that both CS and the Borg scale did not vary significantly across three study days during exercise, suggesting that the CS is as reproducible as the Borg scale.
We also assessed the individual variability from the CV. In this study, the within-subject CV was (22.28±16.96)% for CSN, (23.08±19.11)% for CST, and (22.12±16.92)% for the Borg scale at maximal exercise, which were greater than the Borg results observed by Muza et al5
and Silverman et al6
(CV=(3±1)%). Mador et al12
evaluated the reproducibility of the Borg scale in the moderate term (over a 6-week period) in patients with COPD and found that its CV was (13.9±9.0)% at maximal exercise and (25.0±13.6)% at sub-maximal exercise. In our study, the CV at a workload of 30% of Wmaxwas 11.92±8.78 for CSN, 11.16±9.96 for CST, and 28.27±29.31 for the Borg scale. The CV at a workload of 70% of Wmaxwas 9.08±7.09 for CSN, 12.19±12.32 for CST, and 33.52±24.19 for the Borg scale. The present study showed that both CS and the Borg scale were more varied during maximal exercise compared to sub-maximal exercise, suggesting that CS is less reliable when used at maximal exercise and more likely to be applicable to sub-maximal exercise. We also demonstrated that the Borg scores varied more than CSN and CST during sub-maximal exercise, suggesting that our patients were sometimes unable to determine the right number on the Borg scale in a short time during exercise.
Why is the variability of Borg dyspnea measurements greater than CS? Although all patients were instructed to choose a number on the Borg scale to rate their sense of respiratory effect, some subjects were unable to distinguish between very weak and weak and moderate and somewhat strong on the Borg scale, who need to indicate in a short period during exercise. In contrast, CS measurement is simple and only needs patients to say numbers at a constant speed during one exhaled breath.
Spirometry was performed prior to exercise in all subjects on each trial. The within-subject CV for FEV1
was (6.73±2.54)%, similar to that observed in previous studies,13
suggesting that the variability of the objective measurement was smaller than the subjective indices .
The sensitivity of a method to rate dyspnea during exercise is also important. We showed that CS (CSN, CST) tended to decrease as workload increased during exercise, suggesting that the CS can reflect dyspnea intensity of the subjects. We found significant differences in CS between two workloads of 70% of maximum apart. It appears that the CS method is not so sensitive. A similar result was obtained for the Borg scale.
CS scores depend on the expiratory vital capacity and expiratory time. In COPD patients with expiratory airflow limitation, the vital capacity is reduced due to air trapping and increased residual volume (RV).14
During exercise this situation is further aggravated as the respiratory rate obviously increases,15
resulting in further increases in end-expiratory lung volume and shortened expiratory time.
In this study, we found a strong linear relationship between CSN and CST (r=0.861,P<0.001). The CS (CSN, CST) was correlated with the Borg scale—not strongly, but significantly.
In conclusion, we demonstrated that the CS was shown to be as reproducible as the Borg scale when measuring dyspnea during exercise in patients with COPD. A major advantage of the CS is that it is simple and easily learned; thus, patients can control their exercise using the CS themselves in daily rehabilitation according to prescribed intensity of training in the hospital with cardiopulmonary exercise testing. The CS can also be used in the assessment of COPD patients for follow-up in community centers that have limited and inadequate resources.
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Edited by WANG Mou-yue and LIU Huan
|At maximal exercise
Continuous data are presented as mean±SD. FEV1
: forced expiratory volume in one second; FVC: forced vital capacity; VO2
: oxygen uptake; HR: heart rate.
Within-subject day-to-day variability (CV) of CSN, CST, Borg and FEV1
at different workloads (%)
||30% of Wmax
||70% of Wmax
Data are presented as mean±SD. Wmax: maximal workload; CSN: count scale number; CST: count scale time; FEV1
: forced expiratory volume in one second.
CSN, CST and Borg scores at rest and during exercise
||30% of Wmax
||70% of Wmax
Data are presented as mean±SD. Wmax: maximal workload; CSN: count scale number; CST: count scale time.