A Prospective Study to Determine the Effect of Positive Airway Pressure on Heart Rate Variability in Individuals With Obstructive Sleep Apnea

Visit 1: You will come to the Diabetes and Metabolic Research Center having refrained from taking your routine medications and having not eaten in the last 8 hours, avoided using caffeine-containing beverages and tobacco products in the last 10 hours, and having had no alcoholic beverages in the last 24 hours. In addition, you should refrain from taking any nonprescription drugs and avoid engaging in any vigorous exercise for 48 hours before testing.

For those individuals who have diabetes, a letter or direct verbal permission will be obtained, prior to coming to this study visit, from your eye doctor indicating that you can take part in one of the tests listed below. During this visit, an electrocardiogram (EKG, usual heart rhythm test performed in a doctor's office) will be performed. Your heart rate will also be measured for six minutes with an EKG machine while breathing as deeply as possible. This test, which will be performed twice, will tell whether or not the nerves that go to the heart are normal. You will be asked to blow into a plastic tube for 15 seconds (this is the test for which we will obtain the eye doctor's permission for individuals with diabetes). Your heart rate will be measured during and for 60 seconds after you have finished blowing. This test, which will be performed twice, will tell if the nerves that go to blood vessels are normal. Your blood pressure will be measured four times, one minute apart, while you are lying down. You will then be asked to stand up and your blood pressure will again be measured four more times, each time one minute apart. Change in your heart rate will also be determined as you go from lying down to standing. All individuals will have a fingerstick blood sugar level performed prior to the performance of the tests describe above.

You will have about 2 tablespoons of blood drawn. This blood will be stored (frozen) in case possible risk factors of reduced heart rate variability are discovered in the future. A random urine sample will be stored (frozen) for potential examination for microalbuminuria (protein in the urine) or other possible risk factors. At this visit, we will give you a container with instructions for collecting urine for 24-hours. You will also be given some dietary suggestions (e.g., eating a liberal salt diet) that we would like you to follow for 3-days prior to the 24-hour collection of urine. For individuals with diabetes, a small portion of blood will be checked to determine your blood sugar control level.

Standard medical history questions will be asked during this visit along with questions that assess the likelihood of you falling asleep in various situations. Your medical records from your pulmonary doctor will be reviewed for information about the results of the sleep study you had that determined you have a sleep disorder. You will be asked to keep a diary everyday, for the first six weeks, of how many hours per night you use the treatment for your sleep disorder. This visit will last approximately 1-1 ½ hours.

Visit 2: Within 1-48 hours of completion of the 24-hour urine collection and before you begin treatment for your sleep disorder, you will need to bring the urine specimen to the Diabetes and Metabolic Research Center. A part of this urine will be stored (frozen) for possible testing of a hormone called aldosterone, substances filtered by the kidneys (salt and creatinine), and other potential risk factors. Also at this visit, about 2 tablespoons of blood will be drawn and stored for potential testing of a protein in the blood called renin. You should continue the dietary suggestions (e.g., liberal salt diet) given for the collection of the 24-hour urine until the blood is collected. A part of the blood drawn during this visit will also be stored (frozen) in case potential risk factors of heart rate variability are discovered in the future. This visit will last approximately 15 minutes.