QUANTITATIVE ASSESSMENT OF RESPIRATORY-FUNCTION FOLLOWING CONTUSION INJURY OF THE CERVICAL SPINAL-CORD

In this study, we describe a new method for quantitative assessment of phrenic inspiratory motor activity in two models of cervical spinal c ord contusion injury. Anesthetized rats received contusion injury eith er to the descending bulbospinal respiratory pathway on one side of th e spinal cord alone (C-2 lateralized contusion) or to both the descend ing pathway, as well as the phrenic motoneuron pool bilaterally (C-4/C -5 midline contusion). Following injury, respiratory-associated phreni c nerve motor activity was recorded under standardized and then asphyx ic conditions. Phrenic nerve efferent activity was rectified, integrat ed, and quantitated by determining the mean area under the integrated neurograms. The mean integrated area of the four inspiratory bursts re corded just before turning off the ventilator (to induce asphyxia) was determined and divided by the integrated area under the single larges t respiratory burst recorded during asphyxia. This latter value was ta ken as the maximal inspiratory motor response that the rat was capable of generating during respiratory stress. Thus, a percentage of the ma ximal inspiratory motor drive was established for breathing in control and injured rats under standardized conditions. The results indicate that noninjured rats use 52 +/- 1.8% of maximal inspiratory motor driv e under standardized conditions. In C-2-contused rats, the results sho wed that while the percentage of maximal inspiratory motor drive on th e noncontused side was similar to the control (55 +/- 4.1%), it was in creased on the contused side (78 +/- 2.6%). In C-4/5 lesions, the resu lts indicate that this percentage was increased on both sides (77 +/- 4.4%). The results show the feasibility for performing quantitative ev aluation of respiratory dysfunction in an animal model of cervical con tusion injury. These findings lend to further development of this mode l for investigations of neuroplasticity and/or therapeutic interventio ns directed at ameliorating respiratory compromise following cervical spinal cord trauma. (C) 1998 Academic Press.