Bed RestHeart RateHeartHead-Down TiltWeightlessness SimulationRestWeightlessness CountermeasuresCardiovascular DeconditioningSpace FlightBedsWeightlessnessHeart FailureHeart Rate, FetalBlood PressureTime FactorsOrthostatic IntoleranceAutonomic Nervous SystemLower Body Negative PressureHemodynamicsHeart DiseasesExerciseHeart TransplantationSympathetic Nervous SystemHeart Defects, CongenitalSupine PositionExercise TestBaroreflexPhotic StimulationFetal HeartOxygen ConsumptionMuscle, SkeletalPhysical ExertionElectrocardiographyHypotension, OrthostaticElectrocardiography, AmbulatoryHeart AtriaCardiac OutputAdrenergic beta-AntagonistsStroke VolumeMyocardiumCardiovascular SystemBed OccupancyPlasma VolumeAnalysis of VarianceHeart ValvesMyocardial ContractionPostureReaction TimeRegional Blood FlowMuscular AtrophyHeart BlockDogsHypovolemiaNorepinephrineAcoustic StimulationEarly AmbulationRespirationParasympathetic Nervous SystemAdaptation, PhysiologicalVentricular Function, LeftHeart Function TestsReference ValuesVibrationGeneralization, StimulusTelemetryPropranololElectric StimulationReflexBradycardiaRats, Sprague-DawleyPhysical StimulationMyocardial IschemiaCardiovascular Physiological PhenomenaVascular CapacitanceAction PotentialsCoronary DiseaseAtropineDose-Response Relationship, DrugImmobilizationPressoreceptorsMagnetic Resonance ImagingEpinephrineTachycardiaVisual PerceptionProspective StudiesDiscrimination LearningTreatment OutcomePropanolaminesCardiotonic AgentsAmino Acids, EssentialLegSignal Processing, Computer-AssistedDiscrimination (Psychology)Cross-Over StudiesBlood Flow VelocityRats, WistarPhysical EnduranceOxygenAttention