Postinspiratory activity of costal and crural diaphragm

Because the first stage of expiration or "postinspiration" is an active neu rorespiratory event, we expect some persistence of diaphragm electromyogram (EMG) after the cessation of inspiratory airflow, as postinspiratory inspi ratory activity (PIIA). The costal and crural segments of the mammalian dia phragm have different mechanical and proprioceptive characteristics, so pos tinspiratory activity of these two portions may be different. In six canine s, we implanted chronically EMG electrodes and sonomicrometer transducers a nd then sampled EMG activity and length of costal and crural diaphragm segm ents at 4 kHz, 10.2 days after implantation during wakeful, resting breathi ng. Costal and crural EMG were reviewed on-screen, and duration of PIIA was calculated for each breath. Crural PIIA was present in nearly every breath , with mean duration 16% of expiratory time, compared with costal PIIA. wit h duration -2.6% of expiratory Lime (P < 0.002). A Linear regression model of crural centroid frequency vs. length, which was computed during the acti ve shortening of inspiration, did not accurately predict crural EMG centroi d frequency values at equivalent length during the controlled relaxation of postinspiration. This difference in activation of crural diaphragm in insp iration and postinspiration is consistent with a different pattern of motor unit recruitment during PIIA.