Respiratory Motor Control and Blood Pressure Regulation After Spinal Cord Injury

Overview

The proposed study is designed to answer a novel research question: Can resistive respiratory muscle training designed to improve respiratory motor control also improve blood pressure regulation impaired by spinal cord injury? Resistive breathing exercise, or respiratory muscle training, has been applied to rehabilitate breathing after spinal cord injury, but has not been evaluated as a method for increasing resting blood pressure and / or improving its regulation under stress as is planned in the proposed project. For the first time, respiratory muscle training intervention will be used as a tool to investigate the physiological relationships between pulmonary and cardiovascular function in individuals with Spinal Cord Injury (SCI). Thus, it will foster a new direction from which to address neglected issues surrounding the cardiovascular complications of spinal cord injury.

Screening: To aid in determining eligibility, participants will have a respiratory and cardiovascular function tests. The participants will also have an ASIA (American Spinal Injury Association) exam to grade the degree and level of their SCI. Enrollment: Following screening process, consenting and recruiting, the experimental recordings: 1. Pulmonary Function Test- This test measures lung volumes, airflow and airway pressure with standard equipment; 2. Respiratory Motor Control Assessment- Pulmonary function test is repeated while participant is sitting in a special hospital bed and lying on their back while the investigators record electrical impulses from their neck, chest, arms, legs, abdomen and back muscles. These impulses record how their muscles are contracting. The investigators also record how their chest and abdomen are moving by placing elastic belts around their chest and abdomen. Blood pressure will be measured using a finger cuff; 3. Orthostatic stress test- Using the same methods as above, the investigators will measure blood pressure, heart rate and chest and abdomen movements while the participant is lying down on their back and when the position is suddenly changed to sitting in the investigators' cardiac chair or to upright vertical position on a Tilt table. The investigators will measure blood samples at several intervals from a small catheter inserted into the vein in the arm. 4. Ultrasound of the heart will be performed before and after the Respiratory Muscle Training (RMT) program. RMT: During the training session, subjects will be seated in their personal wheelchair with an approximately 45° head-up tilt with nose clip on. Standard threshold Positive Expiratory Pressure Device or standard threshold Inspiratory Muscle Trainer or combination of both will be used to breathe through with adjustable resistance ranging of 20 to 41 cm of water. All of these devices are in routine clinical use. These devices will be assembled together using a T-shaped connector with flanged mouthpiece. The participants will be instructed to perform inspiratory and expiratory efforts against a resistive load. During inhalation, the subjects will be instructed to sustain the effort until their lungs feel full. During exhalation, the subjects will be instructed to sustain their effort until their lungs feel empty. This study will use two test-subject pre-training assessment sessions to provide its internal experimental group control. To match the training period (4 weeks), the pre-training assessment sessions will be performed four weeks apart and the measured parameters will be used to establish the variance in untrained subjects. The pulmonary function tests include the measurement of lung volume, airflow, and static mouth airway pressures using standard clinical methods and equipment while the SCI participant is sitting in their personal wheelchair. The investigators will also record the surface electromyogram (sEMG) activity from the trunk muscles during Maximal Inspiratory Pressure (PImax) and Maximal expiratory pressure (PEmax) measurements in supine position (PImax and PEmax tasks). The investigators will measure a Sympathetic Skin Response (SSR) by recording limb skin resistance during neural stimulations. The investigators will assess beat-to-beat systemic blood pressure, heart rate and cardiac output will be recorded during the orthostatic stress test. In addition, during the orthostatic stress test, the investigators will collect venous blood samples to measure the levels of catecholamines. In addition to the beat-to beat calculated, resting cardiac output will be measured by ultrasonic cardiac echography. After these initial tests, participants will be assigned to RMT. The participants in experimental group will complete the study after 4 weeks of training totaling 20 sessions of 45 minutes per day carried out 5 days per week. The testing battery will be repeated immediately after completing the training and repeatedly during the follow-up period. Ten matched control subjects will undergo the same procedures except training.