Short Abstract The purpose of this publication is to present our original work on a multi-muscle surface electromyographic approach to quantitatively characterize respiratory muscle activation patterns in individuals with chronic spinal cord injury using vector-based analysis. Long Abstract During breathing, activation of respiratory muscles is coordinated by integrated input from the brain, brainstem, and spinal cord. When this coordination is disrupted by spinal cord injury (SCI), control of respiratory muscles innervated below the injury level is compromised1,2 leading to respiratory muscle dysfunction and pulmonary complications. These conditions are among the leading causes of death in patients with SCI3. Standard pulmonary function tests that assess respiratory motor function include spirometrical and maximum airway pressure outcomes: Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), Maximal Inspiratory Pressure (PImax) and Maximal Expiratory Pressure (PEmax)4,5. These values provide indirect measurements of respiratorymuscle performance6. In clinical practice and research, a surface electromyography (sEMG) recorded from respiratory muscles can be used to assess respiratory motor function and help to diagnose neuromuscular pathology. However, variability in the sEMG amplitude inhibits efforts to develop objective and direct measures of respiratory motor function6. Based on a multi-muscle sEMG approach to characterize motor control of limb muscles7, known as the voluntary response index (VRI)8, we developed an analytical tool to characterize respiratory motor control directly from sEMG data recorded from multiple respiratory muscles during the voluntary respiratory tasks. We have termed this the Respiratory Motor Control Assessment (RMCA)9. This vector analysis method quantifies the amount and distribution of activity across muscles and presents it in the form of an index that relates the degree to which sEMG output within a test-subject resembles that from a group of healthy (non-injured) controls. The resulting index value has been shown to have high face validity, sensitivity and specificity9–11. We showed previously9 that the RMCA outcomes significantly correlate with levels of SCI and pulmonary function measures. We are presenting here the method to quantitatively compare post-spinal cord injury respiratory multi-muscle activation patterns to those of healthy individuals.
There are an estimated 10,000 to 12,000 spinal cord injuries (SCI) every year in the United States. Besides motor and sensory functional deficits, respiratory insufficiency is also common in individuals with SCI due to paralysis, muscle weakness and/or spastic contractions of the muscles involved in respiration. Pulmonary diseases such as pneumonia and restrictive lung disease are the number one reason for death in individuals with SCI. The aim of the study was to see how respiratory muscle training (RMT) affected the pulmonary function measured with spirometry tests. The outcomes were the forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) and surface electromyography (sEMG). The results showed that both the FVC and FEV1 improved significantly after RMT. Individuals with SCI showed significantly lower sEMG activities recorded from intercostal, diaphragm, rectus abdominis and oblique during expiratory part of spirometry test. The training increased sEMG activity during both inspiration and expiration parts of the test, and this improvement was higher in thoracic SCI compared to cervical SCI.
During breathing, activation of respiratory muscles is coordinated by integrated input from the brain, brainstem, and spinal cord. When this coordination is disrupted by spinal cord injury (SCI), control of respiratory muscles innervated below the injury level is compromised 1,2 leading to respiratory muscle dysfunction and pulmonary complications. These conditions are among the leading causes of death in patients with SCI 3 . Standard pulmonary function tests that assess respiratory motor function include spirometrical and maximum airway pressure outcomes: Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV 1 ), Maximal Inspiratory Pressure (PI max ) and Maximal Expiratory Pressure (PE max ) 4,5
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