Muscle tensing during standing: Effects on cerebral tissue oxygenation and cerebral artery blood velocity
article
Background and Purpose - 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 (Vmean) and the near-infrared spectroscopy-determined frontal oxygenation (O2Hb) 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 Vmean declined from 67±4 to 56±3 cm/s, O2Hb 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 Vmean increased to 63±3 cm/s and O2Hb 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. Chemicals/CAS: Oxygen, 7782-44-7.
Topics
Fourier analysisOrthostaticSpectroscopy, near-infraredSyncopeUltrasonography, Doppler, transcranialbrain blood flowbrain oxygen tensionDoppler echographyheart outputhuman experimentmiddle cerebral arterymuscle tonenormal humanpriority journalstandingsympathetic toneAdultBlood Flow VelocityBlood PressureCerebral ArteriesCerebral CortexCerebrovascular CirculationFemaleHemodynamic ProcessesHumansLegMaleMuscle ContractionOxygenOxygen ConsumptionPostureRespirationSpectroscopy, Fourier Transform InfraredUltrasonography, Doppler, Transcranial
TNO Identifier
236151
ISSN
00392499
Source
Stroke, 32(7), pp. 1546-1551.
Pages
1546-1551
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