Intercostal muscle activity of the cat in the curled, semiprone sleeping posture.

We examined the effect of different sleeping postures on intercostal muscle activity in the cat. Cats assume a variety of sleeping positions, but the semiprone, curled position with one side bearing most of the weight was the posture studied in these experiments. In this posture the cat's head rests upon the forepaws and may be slightly tilted. A lateral and ventral curvature of the spine and a lateral flexion of the neck form a curl with an upward-concave side and a downward-convex side. We examined the differences in intercostal activity on the concave and convex sides in this semiprone curled position in seven adult cats. Activity was studied at 14 sites (7 showing inspiratory and 7 showing expiratory activity). Inspiratory intercostal muscle activity was in all cases greater on the concave-upward side; similarly, expiratory intercostal muscle activity was, with the exception of activity at one site, greater on the concave-upward side than on the convex downward side. This effect was evident in rapid eye-movement (REM) as well as nonrapid-eye-movement (NREM) sleep.