Blood Flow VelocityRegional Blood FlowCerebrovascular CirculationUltrasonography, Doppler, TranscranialMiddle Cerebral ArteryUltrasonography, DopplerCerebral ArteriesOphthalmic ArteryPulsatile FlowUltrasonography, Doppler, ColorCoronary CirculationUltrasonography, Doppler, PulsedBlood PressureVascular ResistanceHemodynamicsLaser-Doppler FlowmetryHypocapniaCiliary ArteriesRetinal ArteryEchocardiography, DopplerBlood CirculationEchoencephalographyRheologyUmbilical ArteriesHyperventilationMicrocirculationCarbon DioxidePulmonary CirculationDiastoleUltrasonography, PrenatalAnterior Cerebral ArteryHeart RateHyperemiaUltrasonographyCollateral CirculationModels, CardiovascularArteriesReference ValuesPlacental CirculationCoronary VesselsIntracranial PressureVasodilationSplanchnic CirculationCeliac ArteryHeart Rate, FetalSystoleHomeostasisDogsVasodilator AgentsTime FactorsGestational AgePregnancyAcetazolamideBlood Circulation TimeOxygenDoppler EffectBrainMesenteric Artery, SuperiorCarotid Artery, InternalFetal Growth RetardationCircle of WillisProspective StudiesHemorheologyEchocardiography, Doppler, ColorPosterior Cerebral ArteryReproducibility of ResultsVasomotor SystemFetal HeartTilt-Table TestHypercapniaFlow CytometryEchocardiographyLiver CirculationHypotension, OrthostaticBlood ViscosityRenal CirculationBlood VolumeVasoconstrictionPartial PressureCardiac OutputRetinal VesselsPosturePapaverineFetusOxygen ConsumptionUterusExtracorporeal CirculationCarotid ArteriesAdenosineVeinsInfant, NewbornEchocardiography, TransesophagealMicrospheresEchocardiography, Doppler, PulsedHematocritAnalysis of VarianceVentricular Function, LeftDuctus ArteriosusMitral ValveSensitivity and Specificity