The Effect of Different Physiological Stimuli on Skin Vasomotor Reflexes above and below the Lesion in Human Chronic Spinal Cord Injury

Objective. Spinal cord injury (SCI) results in disruption of descending tonic activation of sympathetic circuits in the spinal cord. The authors determined whether different stimuli that increase sympathetic activity induced cutaneous vasoconstriction (skin vasomotor reflex, SkVR) above and below the level of lesion in subjects with clinically complete SCI. Methods. Baseline skin blood flow (SkBF) and SkVR reduction rate in the pulp of the finger and great toe was measured by laser Doppler probes in chronic complete SCI and in controls. Results. In the finger, baseline SkBF was similar in SCI and controls. The SkVR was elicited by all stimuli in controls but was significantly diminished to gasp, mental arithmetic, tactile stimulation, cutaneous cold, and deep breathing in high SCI compared to controls. In the toe, baseline SkBF was less stable in both controls and SCI. SkVR trends were identified in controls, and responses were not present or greatly reduced in high and low SCI. Conclusions. Measurements of skin vasomotor reflexes to physiological stimuli may be a noninvasive method to evaluate the extent of sympathetic adrenergic pathways in chronic SCI. This is of clinical relevance in monitoring recovery of sympathetic adrenergic function either spontaneously or following repair interventions.

Impaired skin vasomotor reflexes in patients with erythromelalgia

Erythromelalgia (EM) is a chronic disorder characterized by intermittent burning pain, warmth and erythema of the extremities. Increasing the local temperature and dependency of the affected limb(s) precipitates the symptoms, whereas direct cooling and elevation of the limb(s) can provide partial relief. Our previous findings showed that patients with EM have enhanced cutaneous vascular tone at rest and during stimulation, which may be due to an increase in sympathetic neural activity. To test this, we measured skin vasoconstrictor responses to contralateral arm cold challenge (CC) and inspiratory gasp (IG) using laser Doppler flowmetry at the toe pulp and fingertip. These areas were chosen because of their dense sympathetic innervation. An index of the vasoconstrictor response (between 0 and 1) was calculated from the change in skin perfusion from baseline following CC and IG. In control subjects, vasoconstrictor responses to CC at the toe and fingertip were both 0.70±0.02 (mean±S.E.M.), which were significantly greater (P < 0.001) than corresponding values in patients with EM (0.37±0.04 and 0.45±0.04 respectively). Similarly, vasoconstrictor responses to IG were significantly greater (P < 0.001) at the toe and fingertip in control subjects (0.70±0.03 and 0.70±0.02 respectively) compared with values in EM patients (0.27±0.03 and 0.45±0.15 respectively). These data show that, in contrast with control subjects, patients with EM have diminished sympathetic vasoconstrictor responses to both CC and IG. Denervation supersensitivity may play a part by increasing vasoconstrictor responses to circulating catecholamines, leading to a reduction in skin blood flow. Therefore an interplay between neural and vasoactive agents may be involved in the pathophysiology of EM.