Does intercostal stretch alter breathing pattern and respiratory muscle activity in conscious adults?

The effects of intercostal (IC) stretch on breathing patterns and respiratory muscle activity were monitored in nine healthy subjects. Tidal volume (V_t), breathing frequency (F_b), and inspiratory (T_i) and expiratory (T_e) durations were determined from a pneumotachometer. Peak amplitudes and burst durations of activity in the diaphragm, parasternal ICs and external abdominal oblique muscles were determined from surface EMGs. The third and eighth IC spaces were stretched in phase with inspiration or expiration when supine and 60° semi recumbent. V_t increased and T_i and T_e were prolonged, resulting in a decreased F_b, independent of site of stretch, phase of breathing, or body position, during IC stretch compared to controls. Peak amplitudes and burst durations of diaphragmatic EMG and burst durations of parasternal ICs were greater when the third and eighth IC spaces were stretched during inspiration compared to controls. Peak amplitudes of parasternal ICs increased only when the third IC space was stretched during inspiration. When applied during expiration, IC stretch increased only parasternal activity in the supine position. Intercostal stretch applied in phase with inspiration resulted in a slower, deeper breathing pattern with increased activity of the diaphragm and parasternal IC muscles. IC stretch may alter breathing sufficiently to improve gas exchange in some patients with pulmonary disorders.