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Changes in cardiac output and tibial artery flow during and after progressive LBNPA 3.0 MHz Pulsed Doppler velocity meter (PD) was used to determine blood velocities in the ascending aorta from the suprasternal notch before, during and after progressive 5 min stages of lower body negative pressure (LBNP) in 7 subjects. Changes in stroke volume were calculated from the systolic velocity integrals. A unique 20 MHz PD was used to estimate bloodflow in the posterior tibial artery. With -20 torr mean stroke volume fell 11% and then continued to decline by 48% before LBNP was terminated. Mean tibial flow fell progressively with LBNP stress, due to an increase in reverse flow component and a reduction in peak forward flow and diameter. Stroke volume increased and heart rate fell dramatically during the first 15 sec of recovery. The LBNP was terminated early in 2 subjects because of vasovagal symptons (V). During V the stroke volume rose 86% which more than compensated for the drop in heart rate. This implies that V is accompanied by a paradoxical increase in venous return and that the reduction in HR is the primary cardiovascular event. During the first 15 sec of recovery these 2 subjects had a distinctive marked rise to heart rate reminiscent of the Bainbridge reflex.
Document ID
19810012183
Acquisition Source
Legacy CDMS
Document Type
Other
Date Acquired
August 11, 2013
Publication Date
July 1, 1980
Publication Information
Publication: Spec. Physiol. Studies in Support of Manned Space Flight
Subject Category
Aerospace Medicine
Accession Number
81N20712
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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