The effects of acute intermittent hypoxia on respiratory function in humans with spinal cord injury: a pilot study.
1Sutor T, 2Doughty K, 3Ahmed S, 3Fuller D, 3Mitchell G, 4Fox E
1University of Florida, Gainesville, Florida, United states; 2Brooks Rehabilitation, Jacksonville, Florida, United states; 3University of Florda, Gainesville, Florida, United states; 4University of Florida, Brooks Rehabilitation, Gainesville, Florida, United states
Objective: After spinal cord injury (SCI), respiratory complications are the third-leading cause of re-hospitalization, and respiratory illness such as pneumonia due to inadequate ability to cough is the leading cause of death. Standard clinical measures of respiratory strength and capacity often show decreased respiratory function in people with SCI. Exposure to brief, moderate (and safe) acute intermittent hypoxia (AIH) triggers spinal respiratory motor plasticity, and has emerged as a novel approach to restore respiratory function after incomplete cervical SCI. Studies in humans have shown that AIH increases the ability to walk and breathe after chronic, incomplete SCI. Although a few studies have examined the effects of AIH on clinical measures of respiratory capacity or strength after SCI, results have been variable, and it remains unclear whether IH can improve these outcomes. Thus, the purpose of this pilot study is to investigate the effects of AIH on respiratory capacity and strength in adults living with SCI.
Methods: Three community-dwelling, adult males with chronic (9-26 months post-injury) SCI (C4 AIS D; T11 AIS A; T8 AIS A) completed a single AIH session and sham treatment in randomized order, separated by at least 7 days. AIH consisted of 15, 1-minute periods breathing an hypoxic gas mixture (9-13% oxygen) through a face mask, interspersed with 1-minute periods breathing room air. Sham treatments simulated all aspects of the AIH protocol, but used air (21% oxygen) versus hypoxic episodes. Blood oxygen saturation was monitored. Forced vital capacity (a standard test of respiratory capacity) and maximal inspiratory and expiratory pressures (standard tests of respiratory strength) were recorded prior to and 30 minutes after AIH and sham. Percent-from-baseline changes for each condition were compared.
Results: Subjects had an average baseline blood oxygen saturation of 97 +/- 2%. During AIH, saturation decreased to an average of 85 +/- 3%, and then returned to baseline. Blood oxygen saturation remained stable during sham treatments. The effect of AIH was most evident in maximal inspiratory pressure, which tended to increase after AIH (+17.8 +/- 30.1%), but tended to decrease after sham (-11.5 +/- 8.6%). In contrast, there were no apparent changes in forced vital capacity after AIH (-5.0 +/- 9.1%) or sham (-3.0 +/- 2.5%). Average maximal expiratory pressure was also unaltered by AIH (-0.4 +/- 11.3%), and sham (+5.0 +/- 3.6%). AIH responses were individualized, with each participant increasing their value from baseline in at least one measure of respiratory strength or capacity after AIH.
Conclusion: The results of this pilot study suggest that AIH may enhance respiratory function in adults with SCI. Although outcomes were variable, either respiratory strength or capacity appeared to increase in each participant. Further research is warranted to examine response variations and to determine the therapeutic potential of AIH after SCI.
Support: Brooks-PHHP Research Collaboration; Center for Respiratory Research and Rehabilitation at the University of Florida.
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