Background: Obstructive sleep apnea (OSA) is a common sleep disorder with multiple unfavorable health outcomes, including chronic elevations in sympathetic nerve activity and peripheral endothelial dysfunction. Recently, high-intensity inspiratory muscle strength training (IMST) has gained attention as a non-pharmacological intervention to improve peripheral endothelial function. Previous studies in healthy individuals have shown that a single session of high-intensity IMST reduces muscle sympathetic nerve activity and acutely improves peripheral endothelial function. However, the acute effect of IMST on OSA patients remains unknown. Purpose: This study aimed to evaluate the acute effect of a single session of high-intensity IMST on OSA patients undergoing continuous positive airway pressure (CPAP) treatment. We hypothesized that OSA patients, who typically present with chronically elevated basal sympathetic tone, would demonstrate greater improvement in brachial endothelial function following IMST than their age-matched counterparts. Methods: Ten individuals diagnosed with OSA (8M/2F, 64 ± 8 years, apnea-hypopnea index 30.1 ± 11.2 events/h) and nine age-matched healthy controls (6M/3F, 66 ± 6 years) participated in this study. High-intensity IMST was performed at 75% of maximal inspiratory pressure, consisting of 6 breaths (2-s inspiration / 3-s expiration) per set, five total sets separated by 2-minute rest periods. Brachial flow-mediated dilation (FMD) was assessed before and 5 minutes after IMST. Brachial blood velocity and diameter were measured using duplex ultrasound during the FMD test and during IMST. FMD was calculated as the percent increase from baseline to peak diameter and was corrected to baseline diameter and shear rate area under the curve (Corrected-FMD). Results: Corrected-FMD significantly increased after high-intensity IMST in both groups (main effect of time: P < 0.01) with no interaction (P = 0.57) and no difference between groups (main effect of disease: P = 0.50). Brachial blood flow during IMST did not significantly increase from pre-IMST baseline in either group (main effect of time: P = 0.19). Conclusion: Contrary to our hypothesis, a single session of high-intensity IMST acutely improved brachial FMD to a similar extent in patients with OSA and healthy controls. This may be partly explained by the vascular benefits of CPAP, which can reduce sympathetic activity and improve endothelial function in peripheral arteries. As blood flow did not increase during IMST, reductions in sympathetic nerve activity may contribute to the observed improvement in both groups. The current findings indicate that high-intensity IMST may serve as a practical and effective strategy to improve peripheral endothelial function in individuals with OSA. Funding Information: This study was supported by JSPS KAKENHI #21K11170. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Iwamoto et al. (Fri,) studied this question.