Partial angiotensin-converting enzyme inhibition during acute orthostatic stress in persons with tetraplegia.

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 10 AM and 1 PM. Progressive head-up tilt (15 degrees, 25 degrees, 35 degrees, and 45 degrees) was performed on 2 separate days; Day 1: without ACE inhibition; Day 2: after intravenous (IV) infusion of enalaprilat (0.625 mg).

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 increased with orthostasis in either group, but was increased after ACE inhibition in both groups (P < 0.001). MAP was not affected by orthostasis in either group, but was reduced with ACE inhibition in both groups (P < 0.01). In the tetraplegia group, MAP was initially reduced after ACE inhibition, but was maintained thereafter with increasing angles of tilt, and no subject complained of 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 increased prevalence of type 2 diabetes mellitus in this population and the use of ACE inhibitors for the treatment of progressive renal and cardiovascular disease.