Inspiratory Muscle Strength Training in Chronic Kidney Disease

Chronic kidney disease (CKD) is a major public health concern that has reached epidemic proportions. Hypertension is a leading modifiable risk factor for cardiovascular disease (CVD) and end-stage kidney disease, yet 50-70% of adults with CKD fail to achieve blood pressure (BP) control to <130/80 mmHg. A key process linking high systolic BP (SBP) to CVD is vascular endothelial dysfunction, which is due in part to increased reactive oxygen species and decreased nitric oxide. Nitric oxide is also critical in the regulation of renal blood flow, which is intimately related to blood pressure and vascular function. High-resistance inspiratory muscle strength training (IMST) is a novel lifestyle intervention involving repeated inhalations against a resistive load using a hand-held device. This study will test whether high-resistance IMST (75% of maximal inspiratory pressure [75% PImax]; 30 breaths [5 min]/day, 6 days [30 min]/week) vs. Sham training (15% PImax) reduces resting systolic blood pressure in midlife and older adults (>50 years) with moderate-to-severe CKD and inadequately controlled hypertension. Changes in 24-hr systolic blood pressure and endothelial function (brachial artery flow-mediated dilation) are secondary outcomes. Innovative translational techniques will be used to provide mechanistic insight, including serum incubation in endothelial cell culture, metabolomics analysis, endothelial cell collections, and assessment of renal blood flow by magnetic resonance imaging. Changes and cerebrovascular and cognitive function will be assessed as part of a sub-study.

Inclusion criteria

• Aged 50 years or older; women must be post-menopausal
• Chronic kidney disease stage 3 or 4 (estimated glomerular filtration rate with the 4 CKD-EPI 2021 race-free equation: 20-59 mL/min/1.73m^2; stable renal function in the past 3 months)
• History of inadequately controlled hypertension (systolic blood pressure 120-159 mmHg on two separate days) and on a stable antihypertensive regimen for the past 6 weeks
• Weight stable in the prior 3 months (<2 kg weight change) and willing to remain weight stable throughout the study. Participants using glucagon-like peptide-1 receptor agonists or planning to start them during the study are excluded unless they have achieved weight stability for at least 3 months prior to enrollment.
• Ability to provide informed consent

Exclusion criteria

• Patients with advanced chronic kidney disease requiring chronic dialysis
• Significant pulmonary disorders including: chronic obstructive pulmonary disease, interstitial lung disease, cystic fibrosis, or uncontrolled asthma
• History of spontaneous pneumothorax, collapsed lung due to traumatic injury that has not fully healed, burst eardrum that has not fully healed, or other conditions of the eardrum
• Significant co-morbid conditions with a life expectancy of < 1 year
• History of severe congestive heart failure (i.e., ejection fraction <35%)
• History of hospitalization within the last month
• Albuminuria (albumin to creatinine ratio > 2200 mg/g
• Current smoker
• Immunosuppressant agents taken in the past 12 months. Steroids used for the treatment of gout are acceptable; however, patients should not be using steroids within 2 weeks (or 14 days) prior to the vascular testing (rationale: may confound vascular testing)
• Known malignancy
• Inability to cooperate with or clinical contraindication for magnetic resonance imaging including: severe claustrophobia, implants, devices, or non-removable body piercings (these individuals can participate in the study but are excluded from the MRI procedure)
• Illicit drug use or alcohol dependence/abuse, which in the opinion of the investigators, would prohibit compliance with the study intervention