Hemodynamic responses to head-up tilt after spinal cord injury support a role for the mid-thoracic spinal cord in cardiovascular regulation

Background: Data showing a role for the mid-thoracic spinal cord (SC) in the control of hemodynamic changes is scarce despite existing evidence for its involvement in autonomic regulation. Study design: On the basis of the open label prospective series comparing three groups. Objective: To determine whether the mid-thoracic SC has a role in hemodynamic regulation during head-up tilt (HUT). Setting: Spinal Research Laboratory, Loewenstein Rehabilitation Hospital. Methods: A total of 13 healthy control subjects, 10 patients with T-4-T-6 paraplegia and 11 with C-4-C-7 tetraplegia were examined during supine rest and during HUT. Heart rate (HR), blood pressure (BP), HR spectral components (lower frequency fluctuation (LF), higher frequency fluctuations (HF) and LF/HF) and cerebral blood flow velocity (CBFV) were continuously measured or calculated. Results: BP response to HUT differed among these groups (P<0.02). During HUT, BP decreased markedly in the tetraplegia group (from a mean value of 81.65 to 67.69 mmHg), and increased in the control groups (from 92.89 to 95.44 mmHg) and in the T-4-T-6 paraplegia group (from 96.24 to 97.86 mmHg). Significant correlation was found in the control and tetraplegia groups between increases in HR LF/HF and HR at HUT (r>0.7; P<0.01). No such correlation was found in the paraplegia group. HUT effect on HR and CBFV was significant in all groups (P<0.001), but group differences were statistically non-significant. Conclusion: Findings were generally compatible with those of comparable previously published studies, but they also support a role for the mid-thoracic SC in hemodynamic regulation, which should be considered in clinical setting and in research. Spinal Cord (2011) 49, 251-256; doi: 10.1038/sc.2010.98; published online 17 August 2010