Conditions: Orthostatic Hypotension Spinal Cord Injuries
Keywords: Blood Pressure, Low Hypotension, Postural Injuries, Spinal Cord Spinal Cord Transection Spinal Cord Trauma
Allocation: NON_RANDOMIZED | Intervention model: PARALLEL
Enrollment: 30
Healthy volunteers: yes

Brief summary:
The purpose of this study is to determine how blood pressure and blood flow are controlled during head-up tilt in a semi-upright position. In this investigation we are studying blood pressure and blood flow to the brain, with and without a medication which lowers blood pressure (Vasotec). We will determine how persons with a spinal cord injury are able to maintain blood flow to the brain (not get dizzy) as they assume a more upright position and their blood pressure decreases.

Detailed description:
Individuals with tetraplegia lack normal sympathetic nervous system regulation of blood pressure and, therefore, relative hypotension is a common occurrence. This hypotension may be more pronounced with postural stress. Loss in mental acuity and sometimes even consciousness is an associated symptom of postural hypotension in individuals with tetraplegia.

There is some evidence to suggest that although mean arterial blood pressure (MAP) is relatively low in these individuals, middle cerebral arterial blood flow (CBF) may be maintained. Consequently, individuals with chronic tetraplegia often compensate and are stable in the seated upright position.

Autoregulation of CBF has been defined as the stability of cerebral blood flow throughout a range of systemic blood pressures (MAP). This proposal will examine systemic hemodynamics and middle cerebral artery blood flow during HUT with and without Vasotec, an angiotensin II inhibitor. By partially or completely ablating the renin-angiotensin system, which is postulated to play a major role in blood pressure regulation, the potential dissociation between systemic blood pressure and middle cerebral artery blood flow, in individuals with tetraplegia, may be demonstrated. The aim is to determine whether persons with chronic tetraplegia are able to maintain similar CBF, or similar CBF changes, as able-bodied controls despite a greater decrease in MAP to the same hypotensive challenge. The relationship between MAP and CBF has not been defined in this population. Understanding this relationship may lead to improved screening and treatment for prevention of postural hypotension in persons with tetraplegia.

Arms:
arm 1: Head-up tilt maneuver without drug in subjects with spinal cord injury arm 2: Head-up tilt maneuver without drug in able-bodied controls arm 3: Head-up tilt maneuver with an angiotensin converting enzyme inhibitor (1.25 mg enalaprilat) in subjects with spinal cord injury arm 4: Head-up tilt maneuver with an angiotensin converting enzyme inhibitor (1.25 mg enalaprilat) in able-bodied controls.

Interventions: intervention 1: 1.25 mg enalaprilat IV intervention 2: Head up tilt (HUT)
Intervention descriptions: intervention 1: an angiotensin converting enzyme (ACE) inhibitor given to lower blood pressure (BP) and measure cerebral blood flow (CBF) intervention 2: 45 degree head-up tilt to lower blood pressure and measure cerebral blood flow.

Protocol document: