Limb oxygenation during the cold pressor test in spinal cord-injured humans

To investigate changes in tissue oxygenation in the arm and leg during the cold pressor test in humans with spinal cord injury (SCI). Subjects with SCI at cervical 6 (n = 7) and subjects with SCI at thoracic 5 or thoracic 6 (n = 5) experienced 3-min cold water immersion of the foot and subsequent 10-min recovery. Changes in tissue oxygenation and blood pressure were determined. Tissue oxygenation was assessed by hemoglobin/myoglobin concentration (Hb/MbO(2)) measured using near-infrared spectroscopy. Mean arterial blood pressures increased significantly by 15 +/- A 9 and 6 +/- A 6 mmHg during cold water immersion in the cervical and thoracic SCI groups, respectively (P < 0.001). Hb/MbO(2) in the arm decreased significantly by 23 +/- A 15 mu M cm during cold water immersion only in the cervical SCI group (P < 0.001), whereas Hb/MbO(2) in the leg decreased significantly by 82 +/- A 56 mu M cm during cold water immersion only in the thoracic SCI group (P < 0.001). Afferent activity coming from below the lesion due to cold stimuli would reflexively enhance sympathetic activity in both the arm and leg in individuals with cervical SCI but only in the leg in individuals with thoracic SCI. A decrease in tissue oxygenation might have been caused by sympathetic vasoconstriction. The reduction of tissue oxygenation in the arm was marked in individuals with cervical SCI, suggesting differential control of arm oxygenation and leg oxygenation in the region below SCI.