Can Controlled Hypoxia Be Beneficial After Spinal Cord Injury?

Animal studies have suggested that intermittent, repeated episodes of hypoxia after spinal cord injury may upregulate release of intrinsic neurotropic factors, which can be functionally beneficial. In this multicenter pilot study, investigators sought to translate these findings to those with remote, incomplete spinal cord injury with ambulatory difficulties. The investigators used daily acute intermittent hypoxia (dAIH), which included 15 90-second hypoxic exposures at fraction of inspired oxygen (FIO₂) of 9%, followed by 60-second normoxic intervals at FIO₂=21%, on 5 consecutive days.

Nineteen patients (mean age, 43; mean years since injury, 9; 18 American Spinal Injury Association [ASIA] grade D and 1 grade C) underwent a double-blind, randomized, crossover study of daily intermittent hypoxia to improve walking speed and endurance. Sham hypoxia was used with a 2-week washout interval between crossovers. Nine participants underwent dAIH (or sham) alone, and 10 underwent dAIH (or sham) in addition to 30 minutes of walking exercise. Walking outcomes (6-minute timed walk and 10-meter walk test) were measured 60 minutes after the study procedures at baseline and days 1, 5, 8, and 15.

For walking speed on the 10-meter test, patients showed a trend toward 15-day improvement with dAIH alone, but not with hypoxia plus 30 minutes of walking. On the 6-minute walking test, the dAIH intervention alone (but not combined with walking) improved distance significantly over baseline (but not over sham) at day 15. The combined dAIH/walking intervention did show improvements on the 6-minute test over sham at days 5 and 8.