title: Leg crossing improves orthostatic tolerance in healthy subjects: a placebo-controlled crossover study.
abstract: Vasovagal syncope is the most common cause of transient loss of consciousness, and recurrent vasovagal fainting has a profound impact on quality of life. Physical countermaneuvers are applied as a means of tertiary prevention but have so far only proven useful at the onset of a faint. This placebo-controlled crossover study tested the hypothesis that leg crossing increases orthostatic tolerance. Nine naïve healthy subjects [6 females, median age 25 yr (range 20-41 yr), mean body mass index 23 (SD 2)] were subjected to passive head-up tilt combined with a graded lower body negative pressure challenge (20, 40, and 60 mmHg) determining orthostatic tolerance thrice, in randomized order: 1) control, 2) with leg crossing, and 3) with oral placebo. Blood pressure (Finometer), heart rate, and changes in thoracic blood volume (impedance), stroke volume, and cardiac output (Modelflow) were followed during orthostatic stress. Primary outcome was time to presyncope (systolic blood pressure </=85 mmHg, heart rate >/=140 beats/min). With leg crossing, orthostatic tolerance increased from 26 +/- 2 to 34 +/- 2 min (placebo 23 +/- 3 min, P < 0.001). During leg crossing, mean arterial pressure (81 vs. 81 mmHg) and cardiac output (95 vs. 94% supine) remained unchanged; heart rate increase was lower (13 vs. 18 beats/min, P < 0.05); stroke volume was higher (79 vs. 74% supine, P < 0.05); and there was a trend toward lower thoracic impedance. Leg crossing increases orthostatic tolerance in healthy human subjects. As a measure of prevention, it is a worthwhile addition to the management of vasovagal syncope.
authors.affiliation: Dept. Internal Medicine, Academic Medical Center, Univ. of Amsterdam, Rm. F4-222, Meibergdreef 9 1105AZ, Postbox 22660 1100DD, Netherlands. C.T.Krediet@amc.nl
authors.forename: C T Paul
authors.initials: CT
authors.lastname: Krediet
authors.forename: Johannes J
authors.initials: JJ
authors.lastname: van Lieshout
authors.forename: Lysander W J
authors.initials: LW
authors.lastname: Bogert
authors.forename: Rogier V
authors.initials: RV
authors.lastname: Immink
authors.forename: Yu-Sok
authors.initials: YS
authors.lastname: Kim
authors.forename: Wouter
authors.initials: W
authors.lastname: Wieling
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D018592:Cross-Over Studies; D004244:Dizziness / Q000503:physiopathology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007866:Leg / Q000098:blood supply* / Q000502:physiology*; D008150:Lower Body Negative Pressure; D008297:Male; D011187:Posture; D012039:Regional Blood Flow / Q000502:physiology; D013318:Stroke Volume / Q000502:physiology; D019462:Syncope, Vasovagal / Q000503:physiopathology / Q000517:prevention & control*; D018667:Tilt-Table Test