Inspiratory Muscle Strength Training in Adults With Type 1 Diabetes

Approximately two million Americans live with type 1 diabetes, and cardiovascular disease is the leading cause of death in this population. After glycemic control, systolic blood pressure is the leading modifiable cardiovascular risk factor. Traditional aerobic exercise lowers blood pressure and improves vascular function, but most adults with type 1 diabetes do not meet physical activity recommendations, citing time constraints and concern about exercise-associated hypoglycemia. Inspiratory muscle strength training (IMST) requires about five minutes per day, is performed seated at home with a commercially available handheld device, and is unlikely to provoke hypoglycemia. A retrospective analysis of five independent trials in 128 adults reported a 9 mmHg reduction in casual systolic blood pressure following high-resistance IMST compared with sham training, with effects that appear consistent across age, sex, health status, and baseline blood pressure. No study has examined IMST in people with type 1 diabetes. Participants are randomized in a 2:1 ratio to high-resistance IMST or very-low-resistance sham IMST. Randomization uses a computer-generated sequence held by an unmasked team member who is responsible only for setting device resistance; participants, investigators, and outcome assessors remain masked to group assignment. All participants complete approximately 56 daily training sessions over eight weeks, each consisting of five bouts of six forceful inhalations with about 30 seconds of rest between bouts. Maximal inspiratory pressure is measured at weeks 0, 2, 4, 6, and 8. For the high-resistance group, device resistance is set to a graded percentage of the participant's current maximal inspiratory pressure: 55% during weeks 1-2, 65% during weeks 3-4, and 75% during weeks 5-8. The sham group trains at 15% of maximal inspiratory pressure throughout. Participants are debriefed on their group assignment at the end of the post-training visit. Testing visits at week 0 and week 8 include laboratory blood pressure, brachial artery flow-mediated dilation and post-occlusion reactive hyperemia by high-resolution ultrasound, central blood pressure and arterial stiffness by applanation tonometry, and isometric handgrip exercise testing with post-exercise circulatory occlusion. Participants measure their blood pressure at home once weekly on a provided automated monitor during weeks without a laboratory visit. Brief check-in contacts occur on odd weeks and device adjustment visits on even weeks. An optional follow-up visit repeating all assessments is offered at week 12.