Autonomic Challenges From Mild Hypovolemia and Mechanical Ventilation

"Mild hypovolemia will be induced in healthy volunteers by 12 hours fasting. Three conditions will be considered for the analysis, each of them both during spontaneous breathing and positive pressure ventilation:~1. baseline~2. after fluid shift induced by passive head down position at 15 degrees~3. after fluid challenge with Ringer acetate 15ml\*kg in head down position~A total of six steps will be considered for the analysis"

"Each previous step will be done in two respiratory conditions:~1. spontaneous breathing~2. noninvasive ventilation via facial mask in pressure support mode at 8 cmH2O above positive end expiratory pressure of 5 cmH2O, inspiratory fraction of oxygen of 0.25 In both conditions respiratory rate will be set at 18 breaths per min following a metronome"