[Role of expiratory muscles in chronic obstructive respiratory insufficiency]

We have studied the pattern of abdominal muscle (transversus abdominis, external oblique and rectus abdominis) contraction and its mechanical correlates in patients with CAO. When breathing at rest, many stable patients with severe CAO contract the abdominal muscles during expiration and this expiratory contraction is usually confined to the transversus muscle. Moreover, this contraction most often makes expiration a mechanically active process and is an important determinant of intrinsic positive end-expiratory pressure (PEEPi) in such patients. The pathophysiologic implications of these findings are discussed.