A comparison of static and dynamic cerebral autoregulation during mild whole-body cold stress in individuals with and without cervical spinal cord injury: a pilot study

Study design: Experimental study. Objectives: To characterize static and dynamic cerebral autoregulation (CA) of individuals with cervical spinal cord injury (SCI) compared to able-bodied controls in response to moderate increases in mean arterial pressure (MAP) caused by mild whole-body cold stress. Setting: Japan Methods: Five men with complete autonomic cervical SCI (sustained>5y) and six age-matched able-bodied men participated in hemodynamic, temperature, catecholamine and respiratory measurements for 60 min during three consecutive stages: baseline (10 min; 330C water through a thin-tubed whole-body suit), mild cold stress (20 min; 250C water) and post-cold recovery (30 min; 330C water). Static CA was determined as the ratio between mean changes in middle cerebral artery blood velocity and MAP, dynamic CA as transfer function coherence, gain and phase between spontaneous changes in MAP to middle cerebral artery blood velocity. Results: MAP increased in both groups during cold and post-cold recovery (mean differences: 5 to 10 mm Hg; main effect of time: p=0.001). Static CA was not different between the able-bodied vs the cervical SCI group (mean [95% CI] of between-group difference: -4 [-11 to 3] and -2 [-5 to 1] cm/s/mmHg for cold (p=0.22) and post-cold (p=0.24), respectively). At baseline, transfer function phase was shorter in the cervical SCI group (mean [95% CI] of between-group difference: 0.6 [0.2 to 1.0] rad; p=0.006), while between-group differences in changes in phase were not different in response to the cold stress (interaction term: p=0.06). Conclusions: This pilot study suggests that static CA is similar between individuals with cervical SCI and able-bodied controls in response to moderate increases in MAP, while dynamic CA may be impaired in cervical SCI due to disturbed sympathetic control.