Loss of circadian blood pressure variability in complete tetraplegia

Blood pressure (BP) and heart rate (HR) were monitored over 24 h utilising an ambulatory blood pressure monitoring (ABPM) system in 33 subjects with spinal cord injury: 11 patients with complete tetraplegia, 13 patients with incomplete tetraplegia and nine patients with complete paraplegia. Measurements were analysed for overall levels of BP and HR, presence of a physiological day/night cycle and events of autonomic dysreflexia. Paraplegic patients exhibited normal BP and HR levels with a physiological circadian rhythm. In complete tetraplegic patients the circadian rhythm was abolished for BP but preserved for HR, while in patients with incomplete tetraplegia circadian rhythm was preserved for both BP and HR. Complete tetraplegic patients with autonomic dysreflexia revealed a typical pattern in ABPM with multiple hypertensive episodes and concomitant bradycardia. Under adequate treatment these episodes could be reduced or abolished, while the disturbed circadian BP rhythm persisted. These observations shed further light on mechanisms of central BP and HR control. In tetraplegic patients ABPM is an efficient method to assess treatment for autonomic dysreflexia.