Blood Flow VelocityRegional Blood FlowUltrasonography, Doppler, TranscranialCerebrovascular CirculationBlood PressureMiddle Cerebral ArteryUltrasonography, DopplerCerebral ArteriesOphthalmic ArteryPulsatile FlowUltrasonography, Doppler, ColorUltrasonography, Doppler, PulsedHemodynamicsCoronary CirculationVascular ResistanceLaser-Doppler FlowmetryHypocapniaSystoleCiliary ArteriesEchocardiography, DopplerRetinal ArteryHeart RateEchoencephalographyDiastoleRheologyUmbilical ArteriesHyperventilationMicrocirculationCarbon DioxideHypertensionHyperemiaUltrasonography, PrenatalAnterior Cerebral ArteryUltrasonographyArteriesReference ValuesModels, CardiovascularTime FactorsProspective StudiesVasodilationCoronary VesselsIntracranial PressureVasodilator AgentsHeart Rate, FetalHomeostasisCeliac ArteryGestational AgeHypotension, OrthostaticPregnancyAcetazolamideDogsTilt-Table TestEchocardiographyOxygenFetal Growth RetardationDoppler EffectBrainReproducibility of ResultsMesenteric Artery, SuperiorCarotid Artery, InternalPulseCircle of WillisEchocardiography, Doppler, ColorPlacental CirculationVasomotor SystemCarotid ArteriesCollateral CirculationPostureHemorheologySplanchnic CirculationFetal HeartPosterior Cerebral ArteryHypotensionBlood ViscosityAnalysis of VarianceHypercapniaFlow CytometryBlood VolumePredictive Value of TestsCardiac OutputPulmonary CirculationVasoconstrictionVentricular Function, LeftBlood Circulation TimeOxygen ConsumptionRetinal VesselsInfant, NewbornRenal CirculationRegression AnalysisCoronary DiseasePartial PressureUterusPapaverineAdenosineCerebrovascular DisordersEchocardiography, TransesophagealPlethysmographyHematocritEchocardiography, Doppler, PulsedCarotid Artery, Common