decreased respiratThe act of lying down shifts 11% of the total blood volume away from the legs, with most going to the chest. Within the first three days of bed rest, plasma volume is reduced 8%-10%. The result is increased workload of the heart, elevating of resting heart rate, and a decrease stroke volume with a reduction in cardiac output. Orthostatic intolerance deteriorates quickly with immobilityory excursion and stasis of secretions