Mild Intermittent Hypoxia Improves Autonomic Dysreflexia and Orthostatic Hypotension in a Participant with Motor Incomplete Spinal Cord Injury

Research Objectives: To investigate the impact of mild intermittent hypoxia (MIH) on Autonomic Dysreflexia (AD), Orthostatic Hypotension (OH), and blood pressure instability (BPI) in an individual with motor incomplete spinal cord injury (SCI).

Design: 2-arm parallel design.

Setting: Research Laboratory.

Participants: A 49-year-old Black American with a motor incomplete C4 SCI with severe obstructive sleep apnea with signs of autonomic dysfunction.

Interventions: 8 days of MIH consisting of twelve two-minute bouts of hypoxia interspersed with two-minutes of normoxic recovery. Slight hypercapnia (+2 mmHg) was maintained throughout.

Main Outcome Measures: Systolic and Diastolic blood pressure (SBP, DBP) responses to thigh occlusion (AD), sit-up test (OH), and the frequency of AD/OH over 24-hours (BPI). Comparisons were made at baseline, post-MIH, and two weeks after the MIH protocol.

Results: At baseline AD SBP increased by +18 mmHg and DBP +13 mmHg during thigh occlusion and OH SBP decreased by 28.2 mmHg and DBP decreased by 7.4 mmHg. After 8 days of MIH, the rise in BP was mitigated during AD (SBP: 18 vs 6.2 66%, DBP: 13 vs 6.5 48% improvement) and OH (SBP: -28.2 vs 4.8 117%, DBP: -7.4 vs 5.6 176%). At the 2-week follow-up BP elevation during AD remained attenuated compared to baseline (SBP: 51%, DBP: 71% improvement). Similarly, the fall in SBP during OH remained attenuated compared to baseline (32% Improvement), but not for DBP. Average BP over a 24-hour period did not differ before, after, or 2-weeks following MIH. However, the frequency of AD was reduced after MIH (SBP 2 to 0, DBP: 14 to 1), Whereas the frequency of OH did not change for SBP, it was reduced for DBP (10 to 2). At the w-week follow-up, the frequency of AD and OH returned to baseline.

Conclusions: 8 days of MIH improved the BP changes associated with both AD and OH, and these improvements may be sustained for up to 2-weeks following MIH. The improvements in autonomic function during in-lab provocation are in-line with in-home measurements of BPI.

Author(s) Disclosures: None