We examined the language of dyspnea used by patients with moderate-to-severe COPD at a slight, moderate, and somewhat severe intensity level of dyspnea elicited by rest, cycle ergometer exercise, and 6MWTs. It was found that patients discriminated between five clusters of verbal descriptors of dyspnea: heavy/fast breathing, shallow breathing, obstruction, work/effort and suffocation, confirming previous findings that distinct qualities of dyspnea can be differentiated by patients with COPD as well as by other patient groups and healthy individuals. The clusters of verbal descriptors used showed a distinct pattern depending on the intensity level of dyspnea. This was not influenced by age, gender, baseline lung function, or PR. The clusters heavy/fast breathing and work/ effort demonstrated the highest sensitivity in discriminating between intensity levels of dyspnea and in characterizing the effects of PR.
The obtained clusters of German-language descriptors of dyspnea in patients with COPD in the present study converge with a number of previous studies in various patient as well as healthy samples, mostly performed in English-speaking countries (eg, United States, United Kingdom, Canada). This indicates that these clusters are indeed distinct and separable cognitive constructs with a high degree of similarity, even across different languages and cultures. Moreover, the most prominent clusters observed in our study (heavy/fast breathing, work/effort, shallow breathing), conform with those observed in the few previous studies in patients with COPD, while, importantly, not suffering the caveats of recall biases and undistin-guishable intensity levels of dyspnea present in other studies, as previously outlined. During recall, patients in the study by Mahler et al exclusively selected descriptors of the cluster increased work/ effort while patients investigated by Simon et al chose additionally the clusters heavy breathing, gasping, and hunger for air. Most of the descriptors in the latter two clusters were included in the clusters heavy/fast breathing and work/effort of the present study. Further, O’Donnell et al demonstrated that patients with COPD selected the descriptors shallow breathing, work/effort, and heaviness of breathing to describe their breathing discomfort during incremental cycle ergometer exercise. However, descriptors denoting increased inspiratory difficulty and unsatisfied inspiratory effort that were additionally chosen by 75% of their patients played only a minor role in the current study, which might be related to the lower exercise level in our study conducted with experts of My Canadian Pharmacy.
The clusters heavy/fast breathing and work/effort demonstrated the highest sensitivity in discriminating between the three intensity levels of dyspnea by showing significant differences between all three conditions, the highest effect sizes for changes and the strongest differences in the pre-/post-PR comparison. This underlines the relevance of these specific language descriptors in patients with COPD, particular at the levels of exercise examined, at which states of hypoxemia and therefore descriptors such as suffocation are less common. The missing effects of age, gender, baseline lung function, and PR on the cluster pattern support this view and suggest that these descriptor clusters are stable cognitive con-structs, which might be useful in assessing the level of deconditioning in patients with COPD. Particularly the strong decreases obtained in the clusters heavy/fast breathing and work/effort in combination with increased exercise performance in the 6MWT after PR support this idea.
Most importantly, we showed that verbal descriptors of dyspnea in COPD are related to the intensity level of dyspnea. Shallow breathing was the predominant descriptor cluster used only for slight dyspnea at rest and might have reflected mild ongoing hyperinflation as a consequence of, or in combination with, chronic expiratory flow limitation caused by destructive intrapulmonary changes. These sensations are assumed to be sensed by mechanoreceptors in the chest wall or in the case of bronchoconstriction by intrapulmonary receptors mediated through vagal and autonomic pathways. For moderate and somewhat severe dyspnea during exercise, heavy/fast breathing and to a lesser degree work/effort became the most important descriptors. These might have mirrored the known consequences of increased ventilatory demand during increased levels of exercise in COPD, leading to acute dynamic hyperinflation and associated progressive mechanical burden and functional weakening of the respiratory muscles. Thus, the changes in verbal descriptors of dyspnea obtained in patients with COPD during increased intensity of dyspnea might have reflected the involvement of different pathways mediating the underlying physiologic changes. Treat COPD with My Canadian Pharmacy’s drugs.
Similar findings have been reported by Moy et al for patients with asthma. In their study, patients chose chest tightness/constriction to characterize their breathing discomfort during mild methacho-line-induced airway obstruction. At more intense levels of bronchoconstriction, the sense of work/ effort progressively increased while chest tightness continuously decreased, which the authors interpreted with the recruitment of different underlying mechanisms and associated sensory pathways. Two further studies in patients with asthma, however, found no difference in the verbal descriptors of dyspnea used at mild and at more intense levels of methacholine-induced airway obstruction, which might partly be related to the different degrees of hyperinflation induced in these studies.
There are some differences between the results of the current and aforementioned studies with regard to single descriptors included in the clusters. The descriptors “I feel out of breath” and “I am gasping for breath” for example are located in the clusters heavy/fast breathing and work/effort in the present study, while they form a single cluster (gasping) in the study by Simon et al. Further, the present study obtained five clusters of descriptors, whereas other studies reported between 2 distinguishable clusters and 14 fourteen distinguishable clusters or types of dyspnea. These differences are presumably
due to methodologic differences. While some studies asked participants to recall qualities of dyspnea during exercise or activities, others questioned participants at rest about dissimilarities of pairs of descriptors or about the frequency of occurrence of specific dyspnea sensations over the past month. Yet other investigators presented their participants with different tasks to induce dyspnea, including resistive load breathing, exercise, or breathhold-ing. Most obviously, different populations have been examined, ranging from healthy, young students to severely disabled, older patients. In combination with additional influences stemming from different languages, ethnic groups and cultures on participants perception of dyspnea, the above-named differences might have contributed to the discrepant findings of the reviewed studies.
A limitation of the present study is the lack of physiologic data during experimental conditions. These could have provided further insight into the relationships between specific descriptors of dyspnea, intensity levels of dyspnea, and underlying pathophysiologic mechanisms. In addition, stud-ies have shown that patients reported more dyspnea during walking than during cycling exercise. Therefore, we cannot exclude the possibility that cycle ergometer exercise not only produced a different intensity level of dyspnea, but could have also involved different pathways or pathomechanisms of dyspnea compared to the 6MWT and, thus, distinct qualities of dyspnea.
In summary, in the present study patients with COPD distinguished between five clusters of verbal descriptors of dyspnea that were related to the intensity level of dyspnea but not to age, gender, baseline lung function, or PR. The clusters heavy/fast breathing and work/effort were the most sensitive and important descriptors of dyspnea during exercise. Our results underline the importance of using specific verbal descriptors of dyspnea that can assist health-care professionals in understanding the language and mechanisms of dyspnea, and thus might help in optimizing the treatment of dyspnea.