Cardiovascular DeconditioningHead-Down TiltBed RestSupine PositionHeadPostureDown SyndromeProne PositionHead and Neck NeoplasmsHead MovementsSyncope, VasovagalPatient PositioningFemur HeadGravitationSyncopeHeart RateSupinationSperm HeadRotationDizzinessBlood PressureTilt-Table TestHypotension, OrthostaticOtolithic MembraneFemur Head NecrosisHead Injuries, ClosedHypergravityAutonomic Nervous SystemCraniocerebral TraumaGravity SensingWeightlessness SimulationPelvisBaroreflexValsalva ManeuverVestibule, LabyrinthOrientationAccelerationAutonomic Nervous System DiseasesPostural Orthostatic Tachycardia SyndromeHemodynamicsRespiratory MechanicsTime FactorsSpace FlightShy-Drager SyndromeSemicircular CanalsPelvic BonesLower Body Negative PressureCardiac OutputOrthostatic IntoleranceSympathetic Nervous SystemEye MovementsLegRespirationMovementCarcinoma, Squamous CellWeightlessnessNephrostomy, PercutaneousRestRegional Blood FlowReference ValuesNeck MusclesVascular ResistanceBiomechanical PhenomenaHead Protective DevicesPulmonary CirculationReproducibility of ResultsElectrocardiographyBlood Flow VelocityFluid ShiftsProspective StudiesMidodrinePulmonary Gas ExchangeWeightlessness CountermeasuresNeckPressureFunctional Residual CapacityHip JointNystagmus, PhysiologicTomography, X-Ray ComputedHumeral HeadFludrocortisoneSensitivity and SpecificityRange of Motion, ArticularPhysical ExertionVestibular DiseasesAdaptation, PhysiologicalPlethysmographyTorsion AbnormalityPediculusHypogravityExercise TestRetrospective StudiesExerciseEsophagusPure Autonomic FailureVestibular Function TestsTachycardia