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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+/-4.5mmHg; 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/mL) 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.