Costal and crural diaphragm and intercostal muscle activity during augmented breaths in cats

The pattern of electrical activity of the costal and crural diaphragm and the external intercostal muscles was ascertained in ten anesthetized spontaneously breathing cats during eupnea and during augmented breaths. All muscles studied manifested a biphasic activity pattern during augmented breaths. The increase in activity during the latter portion (phase II) of the augmented breaths was greater for the crural than the costal diaphragm (P less than 0.05), and greater for cranially located intercostal muscles than for the costal diaphragm (P less than 0.02) and more caudally located intercostal muscles (P less than 0.02). These results suggest that during augmented breaths, activity of different thoracic muscles is modulated in a non-uniform manner.