Skin vasodilator response to local heating in human chronic spinal cord injury

Local heating evokes an increase in skin blood flow (SkBF), which consists of an initial peak (axon-reflex mediated) followed by a brief nadir and a secondary rise to a plateau. The aim of this study was to investigate whether heat provoked vasodilatation detects sympathetic vasomotor dysfunction and completeness of injury in patients with spinal cord injury (SCI). Twelve (seven complete, and five incomplete; level C4-L4) SCI patients, and nine healthy subjects as controls were studied. Thermostatic laser Doppler probes, which heat the skin locally, were placed on the dorsum of the hand and foot. SkBF was measured by laser Doppler flowmetry at baseline and at the first peak of vasodilatation (SkBF(max)). On the hand, SkBF at baseline and SkBF(max) were similar between the three groups. On the foot, SkBF at baseline was similar between the three groups but SkBF(max) was significantly diminished in complete SCI patients compared with controls (P < 0.01). In conclusion, heat provoked axon-reflex vasodilatation was diminished in the foot, below the level of lesion, in complete SCI. This test, that evaluates localized sympathetic vasomotor dysfunction, may be a useful non-invasive technique to detect completeness of autonomic disruption after SCI.