Study protocol: rationale and design of the community-based prospective cohort study of kidney function and diabetes in rural New Mexico, the COMPASS study.

BACKGROUND: Rural areas in the state of New Mexico have been the "ground-zero" for the epidemic of diabetic Chronic Kidney Disease (CKD) in the United States. However, there is limited research about risk factors of diabetic CKD in this area and scarce data regarding the performance of emerging markers of renal filtration and epigenetic biomarkers of renal function and diabetes in this area with its unique ethnic/racial population. We designed the COMPASS study as a community-based program in rural New Mexico aiming to screen for CKD and to discover CKD-related translational biomarkers. METHODS/DESIGN: The study involves a prospective, longitudinal cohort design involving individuals living in rural New Mexico. Participants undergo a screening for kidney disease using markers of abnormal renal filtration (impaired glomerular filtration rate) or damage (albuminuria). Those found to have CKD on the basis of these tests or those at risk for CKD are enrolled in a prospective longitudinal cohort. We measure markers of renal function, insulin resistance and epigenetics (microRNAs) on patients. Individuals are invited to participate in interviews and focus groups in order to characterize their attitudes towards research and barriers or facilitators to participation in future research studies about kidney disease. DISCUSSION: This study will provide important data about the local epidemiology of kidney disease in a high-risk rural setting and the utility of emerging renal filtration markers (Beta 2 Microglobulin and Cystatin C), while generating data and methods for the analyses of microRNA biomarkers. The qualitative research subproject will identify factors associated with increased willingness to participate in future translational research projects. With its geographical focus, this study will address a critical disparity in kidney disease research, while generating novel epigenetic data that are relevant for future studies in the general population.

Resistant hypertension and obstructive sleep apnea in the setting of kidney disease.

OBJECTIVES: To explore the relationship between obstructive sleep apnea (OSA) and resistant hypertension in chronic kidney disease (CKD) and end-stage renal disease (ESRD). METHODS: We examined sleep parameters and blood pressure (BP) in 224 community-based, non-CKD participants from the Sleep-SCORE study: 88 nondialysis-dependent CKD and 95 ESRD participants. Unattended home polysomnography with standardized scoring protocols and automated BP monitors were used. Resistant hypertension was defined as a BP of at least 140/90  mmHg despite at least three antihypertensive drugs. RESULTS: Mean SBP of the CKD and ESRD groups were significantly higher than that of the non-CKD group [148.2 (23.8), 144.5 (26.7) vs. 132.2  mmHg (26.7), respectively; P < 0.0001] despite the use of more antihypertensive medications. The CKD and ESRD groups had higher rates of resistant hypertension than the non-CKD group (41.4, 22.6 vs. 6.7%, respectively; P < 0.0001). The severity of sleep apnea was associated with a higher risk of resistant hypertension. Although resistant hypertension was associated with severe sleep apnea in participants with ESRD [odds ratio (OR) 7.1, 95% confidence interval (CI) 2.2-23.2), there was no significant association in the non-CKD (OR 3.5, 95% CI 0.8-15.4) or CKD groups (OR 1.2, 95% CI 0.4-3.7) after accounting for case-mix. CONCLUSION: The association between resistant hypertension and sleep apnea appeared robust in ESRD. OSA may contribute to resistant hypertension or both may be linked to a common underlying process such as volume excess. Future studies in patients with kidney disease should further characterize the resistant hypertension-OSA relationship and determine whether treatment of underlying mechanisms may improve outcomes.