Delirium and abnormal autonomic nervous system response to head-up tilt testing

Background: Delirium is a common condition with poorly understood pathophysiology. Various theories have been proposed including that delirious patients have reduced cerebral blood flow. We hypothesised that patients with delirium could have abnormal autonomic nervous system function, as assessed by tilt table testing, which would explain the alteration in blood flow. Methods: A prospective cohort study of medical inpatients aged 65 years and older was undertaken. Delirium was assessed using DRS-R98 and DSM-IV criteria. Beat-to-beat blood pressure (BP) was recorded during tilt testing. Differences in BP changes between the two groups (those with delirium and those without) were explored. The association between severity of delirium and magnitude of BP changes was also examined. Results: 64 participants were recruited during hospitalisation. 29 completed follow-up Head-Up Tilt testing. The mean age of participants was 80.8 years (SD 6.2 years). The control group (n = 12) had a median decrease in systolic BP of 17.5 mmHg (IQR 20.75). The delirium group (n = 17) had a median decrease in systolic BP of 1 mmHg (IQR 38.5), p = 0.04. As delirium severity scores increased, systolic BP change during tilting also increased (r_s = 0.42, p = 0.03). Conclusion: Participants in the delirium group showed different BP responses to tilt test which may represent abnormal sympathetic response. This would be consistent with other features of delirium such as treatment response to centrally acting alpha-2 blockers. Equity of access to research for older, frail and delirious cohorts is essential but feasibility and acceptability needs to be optimised and factored into study design.