Valsalva ManeuverSinus of ValsalvaHemodynamicsAutonomic Nervous SystemBlood PressureAutonomic Nervous System DiseasesHeart Septal Defects, AtrialPelvic FloorEmbolism, ParadoxicalPure Autonomic FailureUltrasonography, Doppler, TranscranialHeart RatePostureHypotension, OrthostaticSupine PositionHeadache Disorders, PrimaryBaroreflexForamen Ovale, PatentMaximal Voluntary VentilationPneumocephalusButylscopolammonium BromideUterine ProlapseKinetocardiographyBlood Flow VelocityHypovolemiaAortic AneurysmPatient PositioningTilt-Table TestVaricoceleEchocardiography, TransesophagealCentral Venous PressurePerineumRespirationVascular ResistanceReflexBlood VolumeThoraxHead-Down TiltCerebrovascular CirculationSpectroscopy, Near-InfraredMicroscopy, AcousticVeinsHemostasis, Surgical