Evaluation of dyspnea and health-related quality of life

Dyspnea (discomfort in the act of breathing) is a guiding sign in most respiratory and cardiac diseases. This symptom is a sensation/ perception that is analyzed by psychophysics through an exponential equation (dyspnea = K x estimulusn) where K is a constant threshold and n a characteristic potential for each specific sensation. The experiments performed by Killian et al (McMaster) allowed dyspnea to be related to distinct loads (resistance, elastance, impedance) of the entire respiratory system and to the respiratory pattern (VT/Ti and Ti/Ttot). Several clinical scales are available to evaluate the magnitude of dyspnea, among which are the Medical Research Council scale, the "basal dyspnea index" and the "transitional dyspnea index". Dyspnea is also a guiding symptom in health-related quality of life questionnaires. To evaluate chronic obstructive pulmonary disease (COPD), notable instruments are generic questionnaires, such as the Sickness Impact Profile, the Nottingham Health Profile and the SF-36, and specific questionnaires, such as the St. George's Respiratory Questionnaire and the Chronic Respiratory Questionnaire. The main reasons for the development of dyspnea in COPD can be summarized as mechanical alterations, alterations in the ventilation/perfusion ratio, chemoreceptor stimulation, use of accessory respiratory muscles, and psychological alterations.