Inspiratory Muscle Strength Training for Lowering Blood Pressure and Improving Endothelial Function in Postmenopausal Women: Comparison With "Standard of Care" Aerobic Exercise

High blood pressure (BP) is the major modifiable risk factor for cardiovascular diseases (CVD) and related health conditions, particularly among postmenopausal (PM) women. In adults age ≥50 years this risk is primarily driven by above-normal systolic BP (SBP ≥120 mmHg), as diastolic BP plateaus, then decreases in older adulthood. Although SBP is lower in premenopausal women vs. age-matched men, SBP reaches, then surpasses men after age 60. As such, \>75% of PM women in the U.S. have above-normal SBP, which, in turn, is responsible for a 2-fold increase in risk of hypertension and corresponding increases in risk of CVD, chronic kidney disease and many other disorders. A key process linking high SBP to CVD and related conditions is vascular endothelial dysfunction, mediated by excessive reactive oxygen species (ROS)-induced oxidative stress and reductions in nitric oxide (NO) bioavailability. As the number of PM women is rapidly growing, further increases in SBP-related CV disorders are projected without effective intervention.

* Aerobic exercise (AE) is a first-line, standard-of-care therapy for lowering BP. In PM women with baseline SBP ≥120 mmHg, AE reduces casual (resting) SBP by \~3 mmHg (back to baseline ≤4 weeks post-training), whereas 24-hour SBP is typically unchanged. However, only 25-30% of PM women meet guidelines for 150 min/week of moderate-intensity AE, citing the extensive time requirement, facility access and travel disruptions as major barriers. Another, far less recognized, limitation is that AE training consistently improves endothelial function in midlife/older men, but not in estrogen-deficient PM (PMe-) women, i.e., in \>95% of the 60+million PM women in the U.S. Thus, establishing new lifestyle therapies that induce and sustain reductions in SBP and increases in endothelial function in PMe- women with above-normal SBP is an important public health goal. * High-resistance inspiratory muscle strength training (IMST) is a time-efficient (5 minutes per session) lifestyle intervention consisting of 30 inspiratory maneuvers performed against a high resistance. Preliminary data suggest 6-weeks of IMST performed 6 days/week reduces SBP by 9 mmHg in adults with above-normal SBP (i.e., greater than 120 mmHg) at baseline. Importantly, this reduction in SBP is equal to or greater than the reduction in blood pressure typically achieved with time- and effort-intensive healthy lifestyle strategies like conventional aerobic exercise. In addition, IMST improved endothelial function in the PMe- women in a small pilot study. * To translate these promising preliminary results towards clinical practice, this randomized clinical trial is being conducted to directly compare the efficacy of a longer, clinically relevant treatment duration of IMST (3 months) against home-based, moderate-intensity (standard-of-care) AE in PMe-women. The primary outcome will be the change in casual SBP (IMST vs. AE). Changes in 24-hour SBP and endothelial function will serve as secondary outcomes. Effects on NO bioavailability, ROS/oxidative stress, and the role of "circulating factors" will provide insight into mechanisms of action. The sustained effects on SBP and endothelial function also will be assessed. * Accordingly, a randomized, blinded, sham-controlled, parallel group design clinical trial will be conducted to assess the efficacy of 3-months of IMST (75 percent maximal inspiratory pressure) vs. brisk walking (40-60% heart rate reserve; an established healthy lifestyle strategy) for lowering SBP and improving endothelial function in PMe- women age 50 years and older with above-normal SBP. It is hypothesized that IMST will lower SBP and improve endothelial function by decreasing oxidative stress and increasing nitric oxide bioavailability. It is also expect that adherence to the intervention will be excellent (over 80 percent of all training sessions completed at the appropriate intensity). * To test this hypothesis, 90 PMe- women age 50 years and older who have SBP \>/= 120 mmHg will be recruited. Participants will undergo baseline testing for casual (resting) SBP, 24-hour ambulatory SBP and endothelial function. Innovative mechanistic probes including pharmaco-dissection with vitamin C, analysis of biopsied endothelial cells, and high-throughput metabolomics, will be performed to assess oxidative stress and nitric oxide bioavailability at baseline. * After baseline testing, subjects will be randomized to perform either 3-months of high-resistance IMST or brisk walking. Subjects will train 6 days/week. Following 3 months of training, subjects will redo all the tests that were done during baseline testing to assess training-induced changes in SBP, physiological functions, and underlying mechanisms. Subjects will then cease training for 6 weeks before returning to the lab for follow-up testing to determine the persistent effects of IMST.