Role of Sleep Apnea and Sympathetic Activity in Resistant Hypertensive Patients.

Overview

Hypertension is highly prevalent in type 2 diabetic patients (NIDDM) with nephropathy, and is the single most important determinant of the rate of renal function loss. In many of these patients, hypertension is resistant to therapy. Although increased sympathetic activity is also highly prevalent in NIDDM patients with nephropathy and chronic renal insufficiency, little attention has been paid to sleep apnea as the cause of both resistant hypertension and sympathetic hyperactivity in this population. Since the prevalence of sleep apnea is increased in patients with either NIDDM, or resistant hypertension, or chronic renal insufficiency, it is almost certain that sleep apnea has a high prevalence in patients in whom all three states co-exist, i.e. NIDDM patients with nephropathy and hypertension resistant to therapy. As a consequence of undetected and untreated sleep apnea, resistant hypertension, nocturnal hypertension, and sympathetic hyperactivity likely contribute to accelerated loss of renal function and increased cardiovascular morbidity and mortality in these patients. Hypothesis: A. Sleep apnea is highly prevalent in type 2 diabetic patients with diabetic nephropathy and hypertension resistant to therapy. Treatment with nasal continuous positive airway pressure (NCPAP) will result in a decrease in blood pressure and restore normal diurnal blood pressure pattern. B. Sleep apnea-caused hypertension is mediated by sympathetic hyperactivity and increased activity of the renin-angiotensin-aldosterone system (RAAS) in type 2 diabetic patients with nephropathy. A decrease in sympathetic hyperactivity in response to NCPAP therapy will result in a decrease in plasma renin activity and plasma aldosterone concomitant with decreases in blood pressure. Randomized, double blind, parallel comparative (two groups) one center trial. Therapeutic treatment with nasal continuous positive airway pressure (NCPAP) Sub-therapeutic treatment with nasal continuous positive airway pressure

The study will be double blind and consist of two parallel groups. Patients with type 2 diabetes with a creatinine clearance above 20 ml/min and with microalbuminuria or proteinuria who have both resistant hypertension and sleep apnea will be studied. Creatinine clearance and proteinuria will be assessed from a 24 hour urine collection not older than 6 months. Microalbuminuria will be assessed from at least 2 out of 3 positive random urine samples with the last one not older than 6 months. Blood pressure will be considered as resistive to treatment if the patient is on 3 or more antihypertensive medications with blood pressure readings of greater than 140/90 mmHg on the last 2 out of 3 office visits. Sleep apnea syndrome will be defined by the presence of at least 5 apneic or hypopneic episodes per hour during an overnight sleep study. Screening will be done in the following manner: Patients seen in the Hypertension Unit at the University of Ottawa Heart Institute, General Nephrology Clinic and Progressive Renal Insufficiency Clinic at the Ottawa Hospital, will be screened by the study coordinator. For the patients who meet the study criteria, the attending physician is asked for permission to contact each patient. If patients agree to participate, they will undergo a sleep study. Screening of patients and subsequent sleep studies will continue until 54 consecutive patients with moderate to severe sleep apnea (15 apneic or hypopneic episodes per hr) are found and enrolled into the study. The prevalence of sleep apnea in the specialty clinic population will be calculated as the number of patients with sleep apnea diagnosed based on a sleep study divided by the total number of clinic patients screened who underwent a sleep study. After the baseline visit and completion of all preliminary procedures, specific studies for microneurography, plasma renin and aldosterone will be performed. Consequently, a 24 hour blood pressure monitor and a 24 hour urine collection for creatinine clearance, microalbuminuria and proteinuria will be done. Once all the testing has been completed, the patient will be randomized to therapeutic or sub-therapeutic treatment with nasal continuous positive airway pressure for 6 weeks. After 6 weeks of treatment the specific studies, 24 hour blood pressure monitoring and 24 hour urine collection will be repeated.