Blood pressure variability in tetraplegic patients with autonomic hyperreflexia

Autonomic hyperreflexia (AH) is a syndrome characterised by profound pressor responses, sweating and headache which occurs in tetraplegic patients in response to a variety of stimuli below the level of cord injury. The pathogenesis of this syndrome is unclear but may be associated with increased blood pressure (BP) variability in these patients. To investigate this possibility, 24 hour ambulatory BP monitoring was performed utilising the Spacelabs 5300 Ambulatory BP system in 30 patients: 10 normal subjects, 10 spinal cord injury (SCI) patients who had never experienced AH and 10 SCI patients who had experienced recent episodes of AH (but with no symptoms during the study period). There were no statistically significant differences in systolic BP (SBP), diastolic BP (DBP) or heart rate (HR) between the three groups. The average of the coefficients of variation of SBP, DBP and HR within each subject over the study period were calculated. Tetraplegic patients who had recently experienced episodes of AH had greater SBP, DBP and HR variability than normal persons (p less than 0.01, p less than 0.005, p less than 0.005) and greater DBP and HR variability than SCI patients who had never experienced AH (p less than 0.01, p less than 0.05). AH may represent the symptoms associated with the upper extremes of this BP variability. The increased variability may be the result of enhanced cardiovascular responsiveness to noradrenaline and arginine vasopressin or because of the absence of descending inhibitory pathways in the decentralised cord that would normally suppress spinal sympathetic reflexes.