Effect of Raised Head of the Bed on Lying Blood Pressure in Autonomic Failure

Autonomic failure (AF) is a severely disabling condition, which is characterized by orthostatic hypotension (severe drop in blood pressure upon standing), bladder and bowel dysfunction, and sexual dysfunction. Besides disabling orthostatic hypotension, however, half of these patients have supine hypertension (high blood pressure when lying). Sustained high blood pressure is a cardiac risk for heart disease, kidney disease, and stroke. Sustained supine hypertension during the night induces pressure natriuresis (increased urine production due to high blood pressure) and volume loss (due to frequent urination/high volumes of urine), worsening orthostatic hypotension the following morning (blood pressure falls even more when the blood volume has been decreased due to loss of fluids in urine) and may also complicate the treatment of orthostatic hypotension with pressor agents (giving a blood pressure pill to prevent overnight high blood pressure may make daytime standing blood pressure worse).

Upright posture induces significant gravitational pooling of blood in the lower body that is normally compensated for by sympathetic activation. Failure of compensatory sympathetic activation results in orthostatic hypotension in autonomic failure patients due to the reduction in venous return and cardiac output. This abnormality has been used in autonomic failure patients with supine hypertension to their benefit by having them sleep with the head of the bed tilted up. The recommended amount of head up tilt is 10°, or about a 9-inch elevation of the head of the bed. In the investigators' hands this degree of tilt produces a significant but only modest decrease in blood pressure. Compliance is a limiting factor because most patients (and their spouses) are not able to tolerate even this modest level of head up tilt. Participants often elevate just the torso overnight, but the effect of this approach on supine blood pressure has not been reported.The investigators would like to compare the effects of tilt versus only elevating the head on supine blood pressure.

The existing knowledge provides the rationale for the study of the elevation of the head of the bed as a non-pharmacologic approaches for the treatment of supine hypertension in these patients. Elevation of the head of the bed will decrease venous return to the heart using the effects of gravity.

• Overnight Urine Volume [Срок оценки: 10 PM to 8 AM]