Analysis of Trunk Motion during Electrically Stimulated Cough in Spinal Cord Injury

The feasibility of using electrical stimulation of abdominal muscles to produce or augment cough in spinal cord injury has been demonstrated. Past studies have focused exclusively on the measurement of airflow at the mouth or expiratory pressures during electrically stimulated cough. The present study examined the actual movements of the trunk during electrical stimulation of the abdominal muscles to augment cough, in order to better understand the underlying biomechanical effects of the stimulated muscle contractions. This could lead to discovering more optimal placement of electrodes and timing of stimulus delivery. While there are some similarities between subjects, there also appears to be some differences. These differences in underlying biomechanical movements may account for the variability between subjects seen in studies of cough production or augmentation. Introduction/Background The feasibility of using electrical stimulation of abdominal muscles to produce or augment cough and tidal volume during breathing in spinal cord injury has been demonstrated [1], [2]. Past studies have focused exclusively on the measurement of airflow at the mouth or pressures during electrically stimulated cough. The present study examined the actual movements of the trunk during electrical stimulation of the abdominal muscles, in order to better understand the underlying biomechanical effects of the stimulated muscle contractions, which could lead to discovering more optimal placement of electrodes and timing of stimulus delivery. In a previous study on the action of abdominal muscles on the rib cage in neurologically intact individuals, selective electrical stimulation of the rectus abdominus (RA) and external obliques (EO) showed different actions of these muscles, with RA tending to make the rib cage more elliptical along by decreasing the antero-posterior (AP) diameter and decreasing the transverse diameter [3]. In an earlier study by Estenne and DeTroyer of volitional cough in individuals with SCI, it was reported that the rib cage showed clear and consistent decrease in AP diameter of its upper portion, and after a sometimes transient increase in the AP diameter of the lower rib cage, also showed a decrease in AP diameter. In contrast, the abdomen showed an increase in AP diameter during cough [4].