Cardiovascular and endocrine responses during the cold pressor test in subjects with cervical spinal cord injuries

Objective: To investigate cardiovascular regulation and endocrine responses during the cold pressor test in patients with chronic spinal cord injury (SCI). Design: Experimental and control study. Setting: University laboratory, department of rehabilitation medicine. in Japan. Participants: Eight quadriplegic subjects with complete spinal cord transection at the C6 to C8 level and 6 age-matched healthy subjects. Interventions: Cardiovascular and endocrine responses were examined during 2 minutes of control, 3 minutes of ice-water immersion of the foot, followed by a 3-minute recovery. Main Outcome Measures: Blood pressure, heart rate, the Borg 15-point Rating of Perceived Pain Scale, and blood samples for measurement of plasma norepinephrine, epinephrine, plasma renin activity, plasma aldosterone, and arginine vasopressin. Results: The rise in the mean arterial blood pressure during the cold pressor test in patients with SCI (baseline, 81.6+/-3.7mmHg. increased by 30%+/-6.1%) was significantly (P<.05) higher than that in healthy subjects (baseline, 101.2+/-4.5mn-tHg; increased by 20%+/-4.5%). The SCI subjects had no change in heart rate throughout the test, in contrast to the tachycardia noted in normal subjects. Baseline plasma norepinephrine in SCI subjects (63.0+/-18.3pg/n-LL) was significantly lower than in normal subjects (162.3+/-19.6pg/mL) and plasma norepinephrine increased significantly during the cold pressor test in both groups. Conclusions: In the SCI subjects, a reflex sympathetic discharge through the isolated spinal cord results in a more profound rise in mean blood pressure during ice-water immersion. This response was free of inhibitory impulses from supraspinal center and baroreceptor reflexes, either of which might restrain the increase in blood pressure.