RESPIRATORY MUSCLE COMPENSATION FOR UNILATERAL OR BILATERAL HEMIDIAPHRAGM PARALYSIS IN AWAKE CANINES

In humans and some animals, the surviving respiratory muscles are able to compensate fully for unilateral, and partially for bilateral, hemi diaphragm paralysis. To examine differential activity of individual re spiratory muscles after unilateral or bilateral diaphragm paralysis, l ength and electromyogram (EMG) of left costal and crural diaphragm seg ments, parasternal intercostal, and transversus abdominis were measure d directly in five awake canines after implantation with sonomicrometr y transducers and bipolar EMG electrodes under three conditions: durin g normal breathing (NOFRZ), after infusion of local anesthetic (bupiva caine) through a cervical phrenic nerve cuff to induce reversible cont ralateral hemidiaphragm (CNFRZ), and after bilateral diaphragm (BIFRZ) paralysis. From NOFRZ to CNFRZ, costal, crural, parasternal, and tran sversus abdominis increased shortening and EMG activity to compensate for contralateral diaphragm paralysis, but the increase in activity wa s not equivalent for each muscle. With BIFRZ, parasternal and transver sus abdominis showed further increases in activity, coordinated betwee n both inspiration and expiration. Normalized intrabreath profiles rev ealed dynamic differences in development of muscle activity within eac h breath as paralysis worsened. Review of simultaneous muscle activiti es showed coordinated interactions among the compensating muscles: pas sive shortening of transversus, and lengthening of costal and crural, coincided with increased active inspiratory shortening of parasternal. We conclude that an integrated strategy of respiratory muscle compens ation for unilateral or bilateral diaphragm paralysis occurs among che st wall, abdominal, and diaphragm segmental muscles, with relative con tributions of individual muscles adjusted according to the degree of d iaphragm dysfunction.