Inspiratory inhibitory reflex caused by the chest wall vibration in man

The effects of chest wall vibrations on tidal volume (VT), inspiratory time (TI) and expiratory time (TE) were measured in normal man during rebreathing. Two vibrators, frequency 100 HZ, were applied bilaterally over the 7th to 10th intercostal spaces anterior to the mid-axillary line. The vibrators were triggered by chest wall movement during the inspiratory phase once or twice, intermittently, every 4-10 breaths. The VT and TI of "vibrated" breaths were decreased compared with preceding control breaths. These effects were clearly paralleled by a reduction in averaged integrated EMG recordings from the diaphragm. The initial time course of the integrated EMG activities in vibrated and non-vibrated breaths were almost equal. However, the relationship between VT and TI of vibrated breaths was shifted downward from that of the non-vibrated (control) breaths. The depression of VT was augmented as the VT of control breath increased. The findings suggest that supraspinal intercostal inhibitory reflex normally contributes to the phase switching mechanism of respiration in man.