Valsalva ManeuverSinus of ValsalvaAutonomic Nervous SystemAutonomic Nervous System DiseasesHeart Septal Defects, AtrialPelvic FloorEmbolism, ParadoxicalPure Autonomic FailurePostureUltrasonography, Doppler, TranscranialHypotension, OrthostaticBlood PressureHeadache Disorders, PrimaryHeart RateSupine PositionForamen Ovale, PatentBaroreflexMaximal Voluntary VentilationPneumocephalusButylscopolammonium BromideUterine ProlapseKinetocardiographyHypovolemiaAortic AneurysmPatient PositioningTilt-Table TestVaricoceleEchocardiography, TransesophagealPerineumRespirationCentral Venous PressureReflexThoraxHemostasis, SurgicalHead-Down TiltMicroscopy, Acoustic