Blood Flow VelocityUltrasonography, Doppler, TranscranialMiddle Cerebral ArteryRegional Blood FlowCerebrovascular CirculationCerebral ArteriesUltrasonography, DopplerMephenterminePulsatile FlowHypocapniaUterusEphedrineBlood PressureOphthalmic ArteryArteriesFetal Growth RetardationUltrasonography, Doppler, ColorUltrasonography, Doppler, PulsedCarbon DioxideUmbilical ArteriesHomeostasisMesenteric Artery, SuperiorPregnancyVascular ResistanceFemoral ArteryHemodynamicsCoronary CirculationLaser-Doppler FlowmetryCarotid ArteriesUltrasonographyUltrasonography, PrenatalRetinal ArteryRheologyPulmonary ArteryBronchial ArteriesCarotid Artery, InternalHeart RateCircle of WillisSplanchnic CirculationGestational AgePlacental CirculationCoronary VesselsEchoencephalographyVasodilationHyperemiaMicrocirculationDogsVasodilator AgentsHeart Rate, FetalBrachial ArteryReference ValuesUterine ArteryCiliary ArteriesEchocardiography, DopplerOxygenMesenteric ArteriesCardiac OutputRenal ArteryTime FactorsBasilar ArteryVasoconstrictionCeliac ArteryCarotid Artery, ExternalProspective StudiesHyperventilationRadial ArteryNitroglycerinDiastoleOxygen ConsumptionUltrasonography, Doppler, DuplexCarotid Artery, CommonVertebral ArteryAnterior Cerebral ArteryAnalysis of VarianceAltitudeLegModels, CardiovascularPostureFetusHypotension, OrthostaticCerebrovascular DisordersPulmonary CirculationSystoleBrainIntracranial PressureAnoxiaExerciseInfant, NewbornAcetazolamideCarotid Artery DiseasesHypercapniaPhysical ExertionCoronary AngiographyIliac ArterySympathetic Nervous SystemNitric OxideDoppler EffectArterial Occlusive DiseasesReproducibility of ResultsVasomotor System