Repeated Exposure to Mild Intermittent Hypoxia Improves Walking Endurance in OSA Patients for 4 - 8 Weeks Post Therapy

Background: Approximately one billion adults globally are diagnosed with obstructive sleep apnea (OSA). Co-morbidities associated with sleep apnea include hypertension and increased susceptibility to fatigue linked to lower oxygen bioavailability and reduced exercise performance. Previously, we reported that daily exposure to mild intermittent hypoxia (MIH) reduces blood pressure following 3 weeks of treatment. These reductions in pressure could be coupled with improvements in microvascular function, fatigability and exercise performance. Objective: Thus, in the present investigation we explored if daily exposure to MIH improves walking endurance that is sustained for 8 weeks following treatment in individuals with OSA and hypertension (HTN). We also examined if improvements in endurance were correlated to modifications in microvascular function measured using near-infrared spectroscopy. Methods: To achieve this objective, both males and females with severe OSA and hypertension were randomly assigned to receive an MIH intervention (n=9) or Sham MIH (n=10). Half of the individuals in each group were also randomly assigned to nightly CPAP use. Based on the small sample size and the similarity of responses, the groups treated with MIH or sham MIH were combined independent of CPAP use. The MIH protocol consisted of twelve 2-minute hypoxic episodes (P ET O 2 ~ 50 mmHg), interchanged with 2 minutes of normoxia administered each day for 15 days. P ET CO 2 was sustained 2 mmHg above baseline throughout the protocol. To evaluate the impact of MIH on microvascular function, oxygen carrying capacity and fatigability, 10 minute walk tests (10 MWT) and vascular occlusion tests coupled with near infrared spectroscopy (NIRS) were performed before therapy, as well as, 5 days, 4 weeks, and 8 weeks after therapy. Results: No significant difference in distance, speed, and performance fatigue was found between the two groups during the 10 MWT before therapy. However, following therapy, the MIH group was able to walk further (p = 0.005), faster (p = 0.005), and were less fatigued (p = 0.009). These improvements were maintained for up to 8 weeks following treatment with MIH but not sham MIH. As anticipated, the total distance travelled was correlated to the performance fatigue index (r = -0.734, p < 0.0001). The Δ in performance fatigue index was correlated to the Δ in the maximal hyperemic response of oxygenated hemoglobin (HbO 2 ) (r = -0.461, p = 0.021) following treatment with MIH. Likewise, the perceived fatigability index was correlated to the Δ in the amplitude of the hyperemic HbO 2 response (relative to measures obtained at the end of occlusion) (r = -0.397, p = 0.0494) and the Δ in the time to achieve the maximum HbO 2 hyperemic response (r = 0.412, p = 0.041) following treatment with MIH. Conclusion: Our results show that distance, speed and performance fatigue are improved following treatment with MIH and that these improvements are sustained for 8 weeks. Our results also showed that correlations between improved performance, perceived fatigue and microvascular function were evident, providing the impetus to further investigate these relationships. Overall, our findings suggest that MIH may improve muscle endurance, allowing individuals with OSA and HTN to walk faster, longer, and with less fatigue for up to 8 weeks following 15 days of treatment with MIH. I01CX000125, IK6CX002287, R01HL142757, R56HL142757. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.