title: Left atrial distension and antiorthostatic decrease in arterial pressure and heart rate in humans.
abstract: It was investigated to what degree left atrial distension augments the hypotensive effects of a 15-min moderate antiorthostatic maneuver in humans. Ten healthy males underwent a posture change from upright seated (Seat, legs horizontal) to supine (Sup) or to supine with simultaneous lower body negative pressure (Sup + LBNP) to keep left atrial diameter (LAD) unchanged. After 2.5 min of Sup, mean arterial pressure (MAP) decreased from 94 +/- 3 to 86 +/- 3 mmHg (P < 0.05), whereas a similar decrease was delayed 7.5 min into Sup + LBNP. Heart rate (HR) decreased within 2.5 min of Sup from 68 +/- 2 to 60 +/- 3 beats/min (P < 0.05) and remained significantly decreased for at least 2.5 min longer than during Sup + LBNP. Aortic systolic distension (ASD) increased by 59 +/- 17% during Sup (P < 0.05) but was unchanged during Sup + LBNP. The 29 +/- 4% decrease in plasma norepinephrine (NE) during Sup (P < 0.05) was abolished during Sup + LBNP. In conclusion, the increases in LAD and ASD seem important stimuli for the prompt decrease in MAP, the 2.5-min longer-lasting decrease in HR, and the sustained decrease in NE during a 15-min moderate antiorthostatic posture change in humans.
authors.affiliation: Danish Aerospace Medical Centre of Research, Rigshospitalet, Copenhagen, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Pump
authors.forename: N J
authors.initials: NJ
authors.lastname: Christensen
authors.forename: R
authors.initials: R
authors.lastname: Videbaek
authors.forename: J
authors.initials: J
authors.lastname: Warberg
authors.forename: O
authors.initials: O
authors.lastname: Hendriksen
authors.forename: P
authors.initials: P
authors.lastname: Norsk
mesh_terms: D000328:Adult; D001021:Aortic Valve / Q000502:physiology; D016279:Atrial Function, Left / Q000502:physiology*; D001794:Blood Pressure; D006325:Heart Atria / Q000033:anatomy & histology; D006339:Heart Rate; D006801:Humans; D007024:Hypotension, Orthostatic; D008297:Male; D011187:Posture; D016683:Supine Position