Heart rate and heart rate variability during 10- and 30-minute episodes of lower body negative pressure

With the purpose of investigating joint heart rate and heart rate variability changes, the authors studied two groups of young normal subjects with a 10-min (group 1) and 30 min (group 2) lower body negative pressure (LBNP) protocol. In both studies LBNP was applied two times, the first episode at a -15 mmHg and the second episode at a -40 mmHg level. All subjects in the first study completed the protocol. However, the protocol of the second study had to be aborted several times because of presyncopal symptoms during -40 mmHg LBNP. The question of what might have caused these symptoms is addressed