Partial Angiotensin–Converting Enzyme Inhibition During Acute Orthostatic Stress in Persons With Tetraplegia

Abstract

Introduction: Individuals with tetraplegia rely on the renin-angiotensin system for orthostatic blood pressure control.Objectives: To determine the effect of partial angiotensin-converting enzyme (ACE) inhibition on heart rate (HR), active plasma renin (PR), and mean arterial blood pressure (MAP)during acute orthostasis in subjects. with tetraplegia (n = 7) and nondisabled persons (n = 8).Methods: Subjects were instructed to avoid caffeine and alcohol for 24 hours before testing and to report to the laboratory between 1 0 AM and 1 PM. Progressive head-up tilt (15°,25°, 35°, and 45°)was performed on 2 separate days; Day 1 : without ACE inhibition; Day2:after intravenous (IV) infusion of enalaprilat (0.625mg).Results: HR was reduced during orthostasis in the tetraplegia compared with the nondisabled group(P < 0.0001 ), and was unaffected by ACE inhibition in either group. PR was not increasedwith orthostasis in either group, but was increased after ACE inhibition in both groups (P < 0.001 ). MAP wasnot affected by orthostasis in either group, but was reduced with ACEinhibition in both groups (P < 0.01).In the tetraplegia group, MAP was initially reducedafter ACE inhibition, but was maintained thereafter withincreasing angles of tilt,and nosubject complainedof symptomatic orthostatic hypotension.Conclusion: Subjects with tetraplegia were tolerant of an acute bout of orthostatic stress after partial ACE inhibition. This may have clinical relevance because of the increasedprevalence of type 2 diabetes mellitus in this population and the use of ACE inhibitors for the treatment ofprogressive renal and cardiovascular disease.