The Role of Respiratory Muscles in the Hyperinflation of Bronchial Asthma1–3

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Abstract
To examine the mechanism of hyperinflation in bronchial asthma we studied lung and chest wall mechanics in 7 asymptomatic patients in whom progressive bronchoconstriction was induced by doubling the amount of inhaled aerosolized histamine. An increase in pulmonary resistance (Rl) from 2.5 ± 0.3 cmH2O · l−1 · s (mean, ± 1 SE) to 12.3 ± 0.9 cmH2 was associated with a linear increase in functional residual capacity (FRC) up to 74.7 ± 1.7 % of control total lung capacity (TLCC). The mean regression coefficient was 2.3 % TLCC · cmH2O−1 · 1. s−1. At each level of hyperinflation the most positive expiratory pleural pressures measured during spontaneous breathing were generally less than the predicted chest wall relaxation pressures, indicating persistent inspiratory muscle contraction throughout expiration. This was predominantly due to inspiratory intercostal and accessory muscle activity, because measurements of transdiaphragmatic pressure indicated complete diaphragmatic relaxation early in expiration. Recrui...

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