Valsalva ManeuverSinus of ValsalvaAutonomic Nervous SystemAutonomic Nervous System DiseasesHeart Septal Defects, AtrialPelvic FloorEmbolism, ParadoxicalPure Autonomic FailurePostureUltrasonography, Doppler, TranscranialHypotension, OrthostaticHeadache Disorders, PrimaryBlood PressureSupine PositionHeart RateForamen Ovale, PatentBaroreflexMaximal Voluntary VentilationPneumocephalusButylscopolammonium BromideUterine ProlapseKinetocardiographyHypovolemiaAortic AneurysmPatient PositioningVaricoceleTilt-Table TestEchocardiography, TransesophagealPerineumRespirationCentral Venous PressureReflexThoraxHead-Down TiltHemostasis, SurgicalMicroscopy, Acoustic