A Study of Blood Pressure and Blood Supply to the Brain in Persons With a Spinal Cord Injury.
Condition: Orthostatic Hypotension; Spinal Cord Injuries
MeSH terms: Spinal Cord Injuries; Hypotension, Orthostatic; Hypotension
Study type: Interventional

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.
    

Intervention name(s): 1.25 mg enalaprilat IV; Head up tilt (HUT)
Intervention type(s): Drug; Other
Intervention description(s): an angiotensin converting enzyme (ACE) inhibitor given to lower blood pressure (BP) and measure cerebral blood flow (CBF); 45 degree head-up tilt to lower blood pressure and measure cerebral blood flow.
Intervention MeSH terms: Enalaprilat; Enalapril
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Health Services Research
Keywords: Blood Pressure, Low; Hypotension, Postural; Injuries, Spinal Cord; Spinal Cord Transection; Spinal Cord Trauma