After phrenicotomy the rat alters the output of the remaining respiratory muscles without changing its sleep-waking pattern.

The respiratory activity of selected rib cage and abdominal wall muscles was studied in intact and bilaterally phrenicotomized (PNX) rats during non-rapid eye movement sleep (nREMS) and REMS. The polygraphic method was used to identify the animal's sleep-waking states before and after PNX. Electromyographic (EMG) recordings were made from the following muscles: the parasternals of the 1st, 3rd, and 5th interspaces; the external and internal intercostals of the 1st, 6th and 10th interspaces; the levator costae attaching to the 10th rib; the scalenus medius; and, the abdominal wall muscles, the external and internal obliques and rectus abdominis. After PNX, all rib cage muscles contracted exclusively during inspiration and all but one increased their activity. The exception was the internal intercostal muscle of the 10th interspace; its activity decreased. The external and internal oblique muscles, both of which were active during expiration in nREMS, also increased their output after PNX: rectus abdominis became an inspiratory muscle. The persistence of phasic activity of respiratory muscles during REMS varied not only from muscle to muscle but from one REMS epoch to another. The sleep-waking pattern of the PNX rat differed in only a minor way from that of the intact rat. Therefore, we conclude that the rat with total paralysis of its diaphragm uses mainly its neurometabolic mechanisms to achieve an adequate level of alveolar ventilation and not neurobehavioral mechanisms.