Measures of dyspnea in pulmonary rehabilitation

Dyspnea is the main symptom perceived by patients affected by chronic respiratory diseases. It derives from a complex interaction of signals arising in the central nervous system, which is connected through afferent pathway receptors to the peripheral respiratory system (airways, lung, and thorax). Notwithstanding the mechanism that generates the stimulus is always the same, the sensation of dyspnea is often described with different verbal descriptors: these descriptors, or linguistic 'clusters', are clearly influenced by socio-individual factors related to the patient. These factors can play an important role in identifying the etiopathogenesis of the underlying cardiopulmonary disease causing dyspnea. The main goal of rehabilitation is to improve dyspnea; hence, quantifying dyspnea through specific tools (scales) is essential in order to describe the level of chronic disability and to assess eventual changes after intervention. Improvements, even if modest, are likely to determine clinically relevant changes (minimal clinically important difference, MCID) in patients. Currently there exist a large number of scales to classify and characterize dyspnea: the most frequently used in everyday clinical practice are the clinical scales (e.g. MRC or BDI/TDI, in which information is obtained directly from the patients through interview) and psychophysical scales (such as the Borg scale or VAS, which assess symptom intensity in response to a specific stimulus, e.g. exercise). It is also possible to assess the individual's dyspnea in relation to specific situations, e.g. chronic dyspnea (with scales that classify patients according to different levels of respiratory disability); exertional dyspnea (with tools that can measure the level of dyspnea in response to a physical stimulus); and transitional (or 'follow up') dyspnea (with scales that measure the effect in time of a treatment intervention, such as rehabilitation).