Blood Flow VelocityRegional Blood FlowUltrasonography, Doppler, TranscranialCerebrovascular CirculationMiddle Cerebral ArteryUltrasonography, DopplerOphthalmic ArteryCerebral ArteriesPulsatile FlowUltrasonography, Doppler, ColorUltrasonography, Doppler, PulsedCoronary CirculationBlood PressureVascular ResistanceHemodynamicsLaser-Doppler FlowmetryHypocapniaCiliary ArteriesRetinal ArteryEchocardiography, DopplerEchoencephalographyRheologyUmbilical ArteriesHyperventilationMicrocirculationCarbon DioxideDiastoleUltrasonography, PrenatalAnterior Cerebral ArteryHyperemiaHeart RateUltrasonographyModels, CardiovascularArteriesReference ValuesIntracranial PressureSystoleHeart Rate, FetalCeliac ArteryCoronary VesselsTime FactorsHomeostasisVasodilationGestational AgeAcetazolamideVasodilator AgentsPregnancyDogsBrainOxygenDoppler EffectProspective StudiesMesenteric Artery, SuperiorFetal Growth RetardationCircle of WillisEchocardiography, Doppler, ColorCarotid Artery, InternalPlacental CirculationReproducibility of ResultsCollateral CirculationHemorheologyTilt-Table TestFetal HeartPosterior Cerebral ArteryEchocardiographyHypotension, OrthostaticVasomotor SystemHypercapniaSplanchnic CirculationFlow CytometryBlood ViscosityPulmonary CirculationPostureBlood Circulation TimeBlood VolumePartial PressurePapaverineUterusRetinal VesselsOxygen ConsumptionVasoconstrictionCardiac OutputEchocardiography, TransesophagealEchocardiography, Doppler, PulsedRenal CirculationAdenosineInfant, NewbornAnalysis of VarianceCarotid ArteriesAgingVentricular Function, LeftFetusMitral ValveMicrospheresOrthostatic IntoleranceHematocritInfant, PrematureSensitivity and SpecificityPredictive Value of TestsBlood Circulation