title: The influence of sympathetic nerves on transcutaneous oxygen tension in normal and ischemic lower extremities.
abstract: The authors evaluated the relationship between sympathetic nerve activity and transcutaneous oxygen tension (TcpO2) in normal and ischemic lower extremities. Dorsal foot TcpO2 was measured by using oxygen-sensing electrodes with surface temperatures of 42 degrees C and 45 degrees C; in theory, changes in sympathetic activity should affect vasomotor tone and TcpO2 in skin beneath an electrode at 42 degrees C (submaximal vasodilation), but not at 45 degrees C (maximal vasodilation). The vasodilation index (TcpO2 at 42 degrees C/TcpO2 at 45 degrees C) was created as an index of vasomotor tone (vasodilation index increases as tone decreases). In normal limbs (n = 24) averages for TcpO2 at 42 degrees C, TcpO2 at 45 degrees C, and vasodilation index were 30.3 mmHg, 62.1 mmHg, and 0.47, respectively. In subjects (n = 5) with quadriplegia and reduced sympathetic tone secondary to cervical cord trauma, TcpO2 at 42 degrees C and vasodilation index were increased (45.0 mmHg and 0.61); TcpO2 at 45 degrees C did not change. When normal subjects (n = 7) were chilled for twenty minutes with a cooling blanket at 5 degrees C (to increase sympathetic tone) average vasodilation index dropped from 0.50 to 0.29. Among ischemic limbs (n = 34) vasodilation index was highly variable (range: 0-0.77); in general, vasodilation index fell as the ischemia worsened. In a subset of patients with ischemic limbs, the vasodilation index increased after the limb was wrapped in a warm dressing (average vasodilation index = 0.25 without dressing, 0.37 with dressing). The authors conclude: TcpO2 can be used to assess the degree of vasomotor tone (and sympathetic activity) in skin; tone generally increases as ischemia worsens; and local warmth can improve cutaneous circulation in ischemic limbs.
mesh_terms: D003080:Cold Temperature; D004566:Electrodes; D006358:Hot Temperature; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D007866:Leg / Q000098:blood supply*; D010101:Oxygen Consumption; D012867:Skin / Q000098:blood supply / Q000378:metabolism*; D012881:Skin Temperature; D013119:Spinal Cord Injuries / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014664:Vasodilation