The Global Initiative for Chronic Obstructive Lung Disease (GOLD) evidence-based guidelines published in 2001 proposed that pulmonary rehabilitation was "recommended treatment" for patients with chronic obstructive pulmonary disease (COPD) when a forced expiratory volume in 1 second (FEV₁) is less than 80% is predicted, which is considered moderate or stage IIA disease.1 Moreover, pulmonary rehabilitation was indicated as well for more advanced stages: IIB (30% <= (FEV₁) <= 50% predicted) and III (FEV₁ < 30% predicted). On the basis of these GOLD guidelines, the collective challenge is twofold: 1) to get physicians to refer such patients to pulmonary rehabilitation programs, and 2) to get patients interested in pulmonary rehabilitation participation.

Once a patient enrolls in a pulmonary rehabilitation program, the professional responsibility of clinicians is to help that individual achieve the expected benefits:

* an increase in exercise endurance

* a decrease in dyspnea

* an improvement in quality of life.

As the author sees it, clinicians must strive to make the training program not only easy to understand, but also easy to apply at home or at an exercise facility. To achieve these objectives and to enhance compliance with an exercise training program, the individual patient should be given specific instructions or strategies for monitoring "how hard it is to exercise." The other components of exercise prescription, frequency and duration, usually are straightforward.

Both healthy individuals and patients with cardiac disease typically are instructed to train at a target heart rate (THR) so they can exercise at a safe intensity and achieve a physiologic training response. However, the American College of Sports Medicine has recommended that individuals be instructed to use ratings of perceived exertion as an alternative approach for both prescribing and regulating the training intensity.2 Because many patients with respiratory disease report that dyspnea, or breathlessness, is the primary "limiting symptom" during exertion, target dyspnea ratings (TDR) have been proposed as an alternative approach for both prescribing and monitoring exercise intensity in this population.

Although TDR are being used in the practice of pulmonary rehabilitation, scientific support (ie, validity, reliability, and clinical applicability) for this approach is building. In this issue of JCR, McKeough and colleagues3 report that their patients with COPD described similar levels of dyspnea ratings on the Borg scale of 0 to 10 at the same relative percentage of peak oxygen consumption (VO₂) during unsupported arm exercise as they described for supported arm exercise and leg exercise. This type of exercise test is called an "estimation trial" because patients estimate or provide ratings of dyspnea on an instrument (eg, 0-10 Borg scale) while performing the different tasks. On the basis of their data, the authors suggest that "during training, the patients could be instructed to reach the same target dyspnea levels for unsupported arm exercise as they do for leg exercise." Yet, an important next step would be to demonstrate that patients actually can produce a desired exercise intensity (eg, VO₂) during unsupported exercise using TDR. This type of exercise test is called a "production trial" because patients are instructed to produce a dyspnea target while a corresponding physiologic variable (eg, VO₂) is measured as the dependent variable to establish the accuracy of this method.

Although the subjects investigated by McKeough and colleagues performed only estimation trials, the authors' recommendation to use TDR for unsupported arm exercise is consistent with previous studies.4-6 In 1996 Horowitz et al4 showed that 15 patients with COPD could achieve an expected VO₂ based on an individual dyspnea target on the cycle ergometer during production trials 2 and 5 weeks after the estimation trial. In a subsequent study Horowitz and Mahler5 reported that 13 patients with COPD could use TDR from an incremental cycle ergometry test (estimation trial) to regulate exercise on the treadmill (production trial) without systematic bias at an intensity of 80% of peak VO₂, but that it was less accurate at an intensity of 50% of peak VO₂. This study supported the validity of TDR for cross-modal exercise training in patients with COPD. In a more recent report, Mejia et al6 demonstrated that 22 patients were able to use TDR (2.5 +/- 1.5 on the Borg scale) and 22 patients were able to use THR (114 +/- 15 beats/min) to produce an expected exercise intensity (~75% of peak VO₂) accurately and reliably during 10 minutes of submaximal exertion. The reliability of the two different methods (TDR vs THR) was comparable, according to the results of production trials repeated 2 weeks later.

Are there limitations with this approach? Certainly there are. Borg7 estimated that approximately 10% of individuals are unable to rate or scale perception in an accurate manner. However, three studies examining the accuracy of production trials among healthy individuals showed that errors using ratings of perceived exertion to produce an expected VO₂ were similar to errors in using a THR.8-10

Thus, target dyspnea ratings provide a simple and easy method for most patients to learn and apply. When queried, most patients with COPD indicate that they usually are aware of their breathing difficulty while performing various tasks. Thus, the use of 0-10 Borg scale enables patients to quantify and to accept a certain level of breathlessness with physical exertion rather than stop a task at the onset of breathing difficulty. Obviously, patients can continuously monitor their dyspnea/exercise intensity using a TDR rather than stop to check their pulse, as might be required with the use of a THR (unless the patient is wearing a heart rate monitor). However, it has never made sense to the author why patients with respiratory disease should monitor a cardiovascular response when their primary problem is breathing. Clearly, practice sessions are helpful so patients can be given feedback information to enhance the accuracy of using dyspnea ratings as a target for monitoring their exercise training.

Do dyspnea ratings change in patients who achieve a physiologic training response, as evident by an increase in peak VO₂ after participation in a pulmonary rehabilitation program? The answer appears to be no. The authors' have shown that dyspnea ratings generally remained stable at the same relative percentage of peak VO₂ in 21 patients who exhibited improved fitness after a pulmonary rehabilitation program.11 In fact, dyspnea ratings were stable at both 50% and 75% of peakVO₂ whether patients achieved a physiologic training response or not after exercise training.

Thus, the expanding medical literature supports current clinical practice of instructing patients to "hit the dyspnea target!!"

References