The investigators will study subjects with SCI at T6 or above who are not on artificial ventilation. To characterize the sleep and breathing state of each subject, polysomnography and upper airway collapsibility will be measured at baseline. Then the following experiments will be conducted: an episodic hypoxia protocol vs normoxia will be used to determine whether cervical SCI will demonstrate greater magnitude of LTF. Experiments will be conducted to see whether dampening peripheral chemoreceptor activity in cervical SCI by giving supplemental oxygen will reduce the central respiratory events and reduce the breathing variability during sleep. A cross over experiment will be done to see whether administration of trazodone in patients with cervical SCI and central SDB decreases respiratory-related arousals and central apnea. The participant will be given the drug/placebo for one week then cross over after a 1 week wash out period to placebo.