Our results also demonstrated that Dsb, peak Vb2, and ASa(VAVo2 were significantly correlated with clinical ratings of dyspnea. Although most interstitial diseases are associated with restrictive ventilatory defects defined in physiologic terms by decreased lung volumes, data from this study indicated that neither FVC nor TLC was related to the experience of breathlessness in our patients. These findings suggest that impairment in gas exchange as well as in oxygen delivery or utilization, or both, influence the severity of breathlessness in patients with ILD. Fulmer et al have previously demonstrated the exercise gas exchange is the best physiologic parameter for evaluating the pathophysiology of idiopathic pulmonary fibrosis.
Clinical measures of dyspnea were unrelated to magnitude estimation of elastic loads in the ILD patients. This information is important because such patients may experience increases in pulmonary elas-tance on a daily basis during various physical activities. These results demonstrate that clinical ratings and psychophysical testing generate distinct information about the perception of respiratory sensations in these patients. Furthermore, none of the lung function variables was significantly correlated with the exponent for mouth pressure. Therefore, we believe that clinical instruments provide more relevant information about the impact of dyspnea on daily living, whereas psychophysical scaling techniques are more appropriate to examine potential mechanisms or stimuli, or both, involved in the perceived magnitude of the sensation of breathlessness. These conclusions are consistent with similar results obtained in patients with obstructive airway disease.
These data combined with results of other investigations1′ demonstrate that clinical dyspnea ratings provide valid measures of breathlessness in patients with various chronic respiratory disorders. Validity of measurement in the present study is based on significant correlations obtained among the three different scales (MRC, OCD and BDI) as well as on significant relationships among these clinical tools and diffusing capacity, exercise gas exchange and exercise capacity. These parameters reflect, at least in part, the pathophysiology of ILD. Based on these results, we believe that clinical rating scales should be used routinely to measure dyspnea in affected individuals to determine the severity of the symptom and, more importantly, to evaluate efficacy of therapy.