Relationship between the perception of breathlessness and inspiratory resistive loading: report on a clinical trial.

We investigated the relationship between the sensation of breathlessness and progressively higher resistive inspiratory loadings in nine normal subjects (31 +/- 17 yr; forced expiratory volume in one second (FEV1) = 105 +/- 9% of predicted) and in eighteen chronic obstructive pulmonary disease (COPD) patients (63 +/- 7 yr; FEV1 = 43 +/- 17% of predicted). The sensation of breathlessness correlated with mouth pressure both in normals (r = 0.94) and in COPD patients (r = 0.95), with a steeper slope in patients. On this basis we studied the effect of inspiratory muscle training on the sensation of breathlessness in sixteen COPD patients (63 +/- 8 yr; FEV1 = 52 +/- 19% of predicted). After a baseline assessment of lung function, MIP (maximal inspiratory pressure), inspiratory muscle endurance and the sensation of breathlessness (Borg scale) at different inspiratory loads, the patients were divided into two groups: the first was trained by means of resistive breathing, the second used a placebo device. At the end of the training, MIP increased more in the trained group (56 +/- 10 to 69 +/- 15 cmH2O; p less than 0.001) than in the placebo group (50 +/- 17 to 56 +/- 22 cmH2O; p = NS). The Borg score fell significantly at all the considered inspiratory loads in trained patients, but not in the placebo group. We conclude that the training with inspiratory resistances decreased the sensation of breathlessness via an increase in inspiratory muscle strength and endurance.