At the end of each treatment period, subjects will undergo noninvasive hemodynamic testing. Ultrasound will be used to measure aortic diameter and blood velocity in the ascending aorta in order to better estimate cardiac output. Then, finger plethysmography will be used to acquire beat-to-beat finger blood pressure and pulse rate. Beat-to-beat derived hemodynamic variables will be calculated by a model flow algorithm (e.g. brachial artery flow, stroke volume, cardiac output, ejection time, blood pressure rate of change, peripheral resistance). Applanation tonometry will be used to obtain pulse wave velocity and central arterial pressure. ECG will be recorded with standard ECG leads to determine heart rate variability in both time and frequency domains. Spontaneous baroreflex will be determined from beat-to-beat changes in blood pressure and pulse pressure interval. Forearm reactive hyperemia will be used to quantify endothelial dysfunction during 4 minutes of post-ischemic change. Subjects will then complete an Epworth Sleepiness Scale questionnaire (ESS) and a Functional Outcomes of Sleep Questionnaire (FOSQ) to find whether they are drowsy in the daytime and if they feel that they are compromised by not having adequate rest. Any adverse event will be recorded. They are asked about any concurrent medication over the prior period, including prescription medication, over the counter medication, and caffeine intake. Medication compliance is evaluated by pill count. Those who fail to return their pill bottle are requested to bring it in. Finally, a 24-hour ambulatory blood pressure monitor (ABPM) will be attached to automatically collect blood pressure and heart rate values every 15 minutes during the wake period and every 30 minutes during the sleep period.