title: Lack of effect of moderate hypoxaemia on human postural reflexes to skeletal muscle.
abstract: The effect of moderate hypoxemia upon postural sympathetic vasoconstrictor reflexes in skeletal muscle was studied in five healthy young students, aged 20-30 years. The vasoconstrictor response to head-up tilt was studied in brachio radial muscle kept at heart level and in the anterior tibial muscle. The local sympathetic veno-arteriolar axon reflex was studied in the anterior tibial muscle placed at heart level and lowered 30-50 cm below heart level. Muscle blood flow was measured by the local 133Xe wash-out technique. The measurements were carried out with the subject breathing atmospheric air and with the subject breathing 10-11% oxygen. No sign of orthostatic intolerance was seen during hypoxaemia as arterial blood pressure remained constant in the tilted position. Hypoxaemia did not alter the head-up tilt induced vasoconstriction in brachio-radial and anterior tibial muscles. The vasoconstriction elicited by the local veno-arteriolar reflex was slightly reduced during hypoxaemia. The results suggest that central orthostatic vasoconstrictor reflexes to muscle are essentially normal during moderate hypoxaemia, but local veno-arteriolar reflexes are slightly attenuated. This does not, however, significantly alter blood pressure control during head-up tilt.
mesh_terms: D000328:Adult; D001369:Axons / Q000502:physiology; D001794:Blood Pressure; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D009132:Muscles / Q000098:blood supply* / Q000294:innervation; D011187:Posture; D012018:Reflex; D013564:Sympathetic Nervous System / Q000502:physiology; D014655:Vascular Resistance; D014661:Vasoconstriction