title: Muscle tensing during standing: effects on cerebral tissue oxygenation and cerebral artery blood velocity.
abstract: OBJECTIVE
  When standing up causes dizziness, tensing of the leg muscles may alleviate the symptoms. We tested the hypothesis that leg tensing improves orthostatic tolerance via enhanced cerebral perfusion and oxygenation.
  
  
  METHODS
  In 10 healthy young adults, the effects of leg tensing on transcranial Doppler-determined middle cerebral artery (MCA) mean blood velocity (V(mean)) and the near-infrared spectroscopy-determined frontal oxygenation (O(2)Hb) were assessed together with central circulatory variables and an arterial pressure low-frequency (LF) (0.07 to 0.15 Hz) domain evaluation of sympathetic activity.
  
  
  RESULTS
  Standing up reduced central venous pressure by (mean+/-SEM) 4.3+/-2.6 mm Hg, stroke volume by 49+/-7 mL, cardiac output by 1.9+/-0.4 L/min, and mean arterial pressure at MCA level by 9+/-4 mm Hg, whereas it increased heart rate by 30+/-4 beats per minute (P<0.05). MCA V(mean) declined from 67+/-4 to 56+/-3 cm/s, O(2)Hb decreased by 7+/-2.8%, and LF spectral power increased (P<0.05). Leg tensing increased central venous pressure by 1.4+/-2.7 mm Hg and cardiac output by 1.8+/-0.4 L/min with no significant effect on blood pressure, whereas heart rate decreased by 11+/-3 beats per minute (P<0.05). MCA V(mean) increased to 63+/-3 cm/s and O(2)Hb increased by 2.1+/-2.6%, whereas LF power declined (P<0.05). Within 2 minutes after leg tensing, these effects had disappeared.
  
  
  CONCLUSIONS
  During standing, tensing of the leg muscles attenuates a reduction in cerebral perfusion and oxygenation as it stabilizes central circulatory variables and reduces sympathetic activity.
authors.affiliation: Cardiovascular Research Institute Amsterdam, Department of Internal Medicine, Academic Medical Center, Amsterdam, the Netherlands. j.j.vanlieshout@amc.uva.nl
authors.forename: J J
authors.initials: JJ
authors.lastname: van Lieshout
authors.forename: F
authors.initials: F
authors.lastname: Pott
authors.forename: P L
authors.initials: PL
authors.lastname: Madsen
authors.forename: J
authors.initials: J
authors.lastname: van Goudoever
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002536:Cerebral Arteries / Q000000981:diagnostic imaging / Q000502:physiology*; D002540:Cerebral Cortex / Q000098:blood supply* / Q000378:metabolism; D002560:Cerebrovascular Circulation; D005260:Female; D006439:Hemodynamics; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D009119:Muscle Contraction; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D011187:Posture; D012119:Respiration; D017550:Spectroscopy, Fourier Transform Infrared; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D010100:Oxygen