Mild Intermittent Hypoxia: A Prophylactic for Autonomic Dysfunction in Individuals With Spinal Cord Injuries

Participants will breathe 8% oxygen through a non-diffusable bag that is connected to a 5-way stopcock. The inspiration side of the system is then connected to a 2-way non-rebreathing valve which is connected to a pneumotachometer that is connected to a tight fitting facemask. 100% oxygen and carbon dioxide are titrated into the system to ensure the appropriate hypoxic and hypercapnic stimulus is delivered. The investigators will lower oxygen to 55-60 mmHg and maintain end-tidal carbon dioxide 1-3 mmHg above individual baseline values. The protocol starts with 10 minutes of baseline breathing (room air) then followed by 10 more minutes of breathing room air with the additional carbon dioxide. Thereafter, individuals undergo 12 2-minute bouts of hypoxia with 2 minutes of normoxia (room air) interspersed between episodes. The intervention protocol concludes with 20 minutes of monitoring all breathing and cardiovascular measurements.

Participants will breathe 21% oxygen through a non-diffusable bag that is connected to a 5-way stopcock. The inspiration side of the system is then connected to a 2-way non-rebreathing valve which is connected to a pneumotachometer that is connected to a tight fitting facemask. No supplemental oxygen or carbon dioxide will be used during the sham protocol. The protocol starts with 10 minutes of baseline breathing (room air) then followed by 10 more minutes of breathing room air with the additional carbon dioxide. Thereafter, individuals undergo 12 2-minute bouts of hypoxia with 2 minutes of normoxia (room air) interspersed between episodes. The intervention protocol concludes with 20 minutes of monitoring all breathing and cardiovascular measurements.