Inspiratory resistance training transiently improves endothelium-dependent dilation in young adults
Authors: Tavoian Dallin , Mazzone Josie , Craighead Daniel , Bailey E. Fiona 
Published: May 2023

Introduction: Inspiratory resistance training (IRT) is a resisted breathing exercise originally devised to improve diaphragmatic strength. We have shown IRT to be a potent non-pharmacological therapy that yields significant reductions in resting blood pressure. When performed daily for 6 weeks, systolic blood pressure is reduced by ~9 mmHg, secondary to reductions in systemic vascular resistance. Whereas the effects of IRT on the vasculature have been described over the intermediate term, the acute responses that mediate these longer-term adaptations have not been fully characterized. Purpose: Our primary aim was to quantify the acute effects of a single bout of IRT on (endothelium-dependent dilation) EDD in healthy men and women. Secondarily, our goal was to determine the acute effects of IRT on arterial stiffness. Methods: Nitric oxide-mediated EDD and ischemia-induced maximal shear rate were assessed with brachial artery flow-mediated dilation (FMD), and arterial stiffness was assessed via carotid-femoral pulse wave velocity (PWV). Twenty healthy young adults (22.9 ± 3.4 years; 10 males, 10 females) were randomized to the experimental (IRT; 5 sets of 6 breaths at 50% of maximal inspiratory pressure with 1-minute rest intervals) and control (time-matched supine rest) conditions in a crossover design, with at least 48 hours between visits. FMD and PWV were performed before, 10 minutes after, and 40 minutes after the assigned intervention. Statistical analysis included repeated measures ANOVA with Sidak post hoc analyses. Results: All values are mean difference ± SD. There were no between-day differences in EDD at baseline (mean difference: 0.08 ± 3.03%; p=0.908). EDD was significantly increased from baseline at 10 minutes post-IRT (+1.86 ± 2.75%; p=0.025), but returned to baseline levels at 40 minutes post-IRT (-0.10 ± 3.00%; p=0.998). During the control condition, EDD was unchanged from baseline at 10 minutes post-rest and 40 minutes post-rest ( p=0.136). Lastly, maximal shear rate following 5 minutes of forearm blood flow occlusion was not different from baseline at any time point following IRT ( p=0.749) and thus, the change in EDD is not a result of a modified hyperemic response. However, in the control condition maximal shear rate was significantly lower at 40 minutes post-rest, relative to baseline (mean difference -9.94 ± 2.64 per second; p=0.005), although the reduced shear rate did not impact EDD at 40 minutes post-rest. Arterial stiffness was unchanged from baseline in response to IRT ( p=0.217) or the rest intervention ( p=0.150). Conclusions: In healthy young adult men and women, a single bout of IRT elicits a transient enhancement in EDD. The effect endures for at least 10 minutes but is extinguished at 40 minutes post IRT. Repeated acute enhancements in EDD may contribute to sustained IRT-related reductions in vascular resistance after 6 weeks of traini This work was supported by NIA/NIH Grant Number: 1R01AG065346-01A1 (EFB), NIH Training Grant Number: 5T32HL007249-44 (DT), and NIH/NHLBI Grant Number: 1K01HL153326-01 (DHC) This is the full abstract presented at the American Physiology Summit 2023 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.