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Cardiovascular disease (CVD) is the leading cause of death in wealthy countries, and although it鈥檚 associated with advancing age, some risk factors are modifiable. In particular, systolic blood pressure (SBP) is a prevalent yet modifiable risk factor for CVD.

According to the investigators of a new study looking at the effects of inspiratory muscle strength training (IMST) on blood pressure (BP) and other functions,¹ roughly two-thirds of individuals older than 50 in the U.S. have an SBP above 鈮�120 mm Hg.² In addition to BP, the investigators point to endothelial dysfunction and increased arterial stiffness鈥攔esulting in part from decreased nitric oxide (NO) bioavailability caused by oxidative stress鈥攁s important factors in cardiovascular aging and risk of CVD. They further note that the reduced activation of the NO-producing enzyme, endothelial NO synthase (eNOS), may play a role in cardiovascular aging, as does chronic, low-grade inflammation.

While substantial evidence has shown aerobic exercise to promote cardiovascular health, it can be time-consuming and difficult to maintain over the long term. A more convenient alternative may be IMST, which uses the diaphragm and accessory respiratory muscles to repeatedly inhale against resistance.

Evaluating the cardiovascular benefits of IMST

Daniel H. Craighead, PhD, and his university-based colleagues in Colorado and Arizona conducted a study to better characterize the impact of IMST on cardiovascular aging, noting that previous studies had looked only at potential health benefits of IMST at low or moderate resistance to inspiration (about 30% of maximal inspiratory pressure [PI_MAX]).² Sessions were a minimum of 30 minutes each, and were conducted multiple times per week. This did not drastically reduce the time commitment when compared to moderate-intensity aerobic exercise, and often required the subjects to travel to and from training sessions.

The investigators wanted to ease patients鈥� overall time commitment by increasing the PI_MAX and reducing the time of each session. So they conducted a double-blind, randomized, sham-controlled trial to investigate whether 6 weeks of IMST (30 breaths/day, 6 days/week) would improve BP, endothelial function, and arterial stiffness in 18 subjects undergoing high-resistance IMST (75% PI_MAX) compared to 18 controls undergoing low-resistance sham training (15% PI_MAX) between 50 and 79 years of age with SBP 鈮�120 mm Hg. They also analyzed potential mechanisms and long-lasting effects of high-resistance IMST.

What the investigators discovered

With IMST, casual SBP decreased from 135 卤 2 mm Hg to 126 卤 3 mm Hg (P<.01); approximately 75% of this reduction was sustained 6 weeks after IMST (P<.01). IMST modestly decreased casual diastolic BP (79 卤 2 mm Hg to 77 卤 2 mm Hg; P=.03), which was unchanged with sham training, as was BP overall with sham training (P>.05). There was also a reduction in 24-hour SBP after IMST versus sham training (P=.01), as well as improvement in brachial artery flow-mediated dilation with high-intensity IMST鈥攁bout 45% (P<.01)鈥攂ut not with sham training (P=.73).

Increased NO bioavailability, greater eNOS activation, and lower reactive oxygen species bioactivity were shown with serum cultures of human umbilical vein endothelial cells sampled after, versus before, IMST (P<.05). High-intensity IMST also resulted in decreased C-reactive protein (P=.05) and 鈥渁ltered select circulating metabolites (targeted plasma metabolomics) associated with cardiovascular function.鈥�¹ However, neither high-intensity IMST nor sham training affected arterial stiffness (P>.05).

鈥淲ith only a little over 5 minutes a day, high-resistance IMST lowered systolic blood pressure by 9 mm Hg, which if sustained in the long term would decrease risk for cardiovascular diseases,鈥� says Dr. Craighead, the study鈥檚 lead investigator and an assistant research professor in the Integrative Physiology of Aging Laboratory at the University of Colorado Boulder.

鈥淲e鈥檝e shown that IMST is effective at lowering blood pressure, and the hope is more people might actually do it because it鈥檚 so time efficient,鈥� he adds.

IMST: an add-on, not a substitute

Dr. Craighead noted that the study found additional benefits, particularly for postmenopausal women.

鈥淰ascular endothelial function, an important nontraditional risk factor for cardiovascular diseases, was improved both in the men and postmenopausal women in our study,鈥� he says. 鈥淓vidence suggests that postmenopausal women who aren鈥檛 taking hormone therapy, which is most of them, don鈥檛 get improved endothelial health with conventional exercise, such as brisk walking. Therefore, high-resistance IMST may be a particularly important intervention for improving cardiovascular health in these women.鈥�

While IMST can鈥檛 replace the cardiovascular benefits of traditional aerobic exercise, it does provide benefit to certain individuals.

鈥淐onventional aerobic exercise improves additional cardiovascular disease risk factors, such as cholesterol levels, that we didn鈥檛 see change with IMST. So, we shouldn鈥檛 look at IMST as a replacement for other forms of exercise,鈥� Dr. Craighead cautions. 鈥淭hat being said, IMST may be another tool in the toolbox that can easily be added into someone鈥檚 current lifestyle or pharmaceutical treatment regimen, because the burden is so low. It also gives us a potential lifestyle strategy to lower blood pressure for people who can鈥檛 or won鈥檛 perform other types of exercise.鈥�

More research is necessary

Future study should focus on longer-term studies and real-world scenarios. 鈥淭he most important next step is to determine what happens after people have been doing IMST for months or years,鈥� Dr. Craighead says. 鈥淲e don鈥檛 know if the effect on blood pressure will be larger with longer use, or if there are other health benefits that weren鈥檛 apparent after only 6 weeks.鈥�

鈥淲e need to figure out if IMST can lower blood pressure for the everyday person who tries to do it without the support of a research team,鈥� he concludes. 鈥淭here may be a need for instructional videos or telehealth solutions to help with public health translation.鈥�

Published: November 11, 2021