Valsalva ManeuverSinus of ValsalvaAutonomic Nervous SystemAutonomic Nervous System DiseasesHeart Septal Defects, AtrialPelvic FloorEmbolism, ParadoxicalPure Autonomic FailurePostureBlood PressureUltrasonography, Doppler, TranscranialHypotension, OrthostaticHeadache Disorders, PrimarySupine PositionHeart RateForamen Ovale, PatentBaroreflexMaximal Voluntary VentilationPneumocephalusButylscopolammonium BromideUterine ProlapseKinetocardiographyHypovolemiaAortic AneurysmPatient PositioningVaricoceleTilt-Table TestEchocardiography, TransesophagealPerineumRespirationCentral Venous PressureThoraxReflexHead-Down TiltBiofeedback, PsychologyHemostasis, SurgicalMicroscopy, AcousticProspective StudiesBlood Flow VelocityCough