The effects of breathing depth in attenuating induced bronchoconstriction were studied in 12 healthy subjects. On four separate, randomized occasions, the depth of a series of five breaths taken soon (∼1 min) after methacholine (MCh) inhalation was varied from spontaneous tidal volume to lung volumes terminating at ∼80, ∼90, and 100% of total lung capacity (TLC). Partial forced expiratory flow at 40% of control forced vital capacity (V̇part) and residual volume (RV) were measured at control and again at 2, 7, and 11 min after MCh. The decrease in V̇part and the increase in RV were significantly less when the depth of the five-breath series was progressively increased (P <0.001), with a linear relationship. The attenuating effects of deep breaths of any amplitude were significantly greater on RV than V̇part (P <0.01) and lasted as long as 11 min, despite a slight decrease with time when the end-inspiratory lung volume was 100% of TLC. In conclusion, in healthy subjects exposed to MCh, a series of breaths of different depth up to TLC caused a progressive and sustained attenuation of bronchoconstriction. The effects of the depth of the five-breath series were more evident on the RV than on V̇part, likely due to the different mechanisms that regulate airway closure and expiratory flow limitation.
- Airflow obstruction
- Deep breath
- Partial forced expiratory flow
- Residual volume
ASJC Scopus subject areas
- Orthopedics and Sports Medicine
- Physical Therapy, Sports Therapy and Rehabilitation