The Physiology of Bed Rest

Introduction to Progressive Mobility

“…1,2,[8][9][10][11] The major consequences to the respiratory system include development of compression atelectasis from the formation of dependent edema with the patient supine and impaired ability to clear the lungs because the normal lung-clearing functions of the mucociliary escalator, cough reflex, and drainage do not work as well with the patient supine. This impaired clearing places immobilized patients at greater risk for VAP or hospital-acquired pneumonia.…”

“…This loss stabilizes to 15% to 20% by the fourth week of bed rest. 1,[8][9][10][12][13][14] The result is an increase in cardiovascular workload, elevation of resting heart rate, and a decrease in stroke volume with a reduction in cardiac output. Orthostatic tolerance deteriorates rapidly with immobility.…”

“…ICU-acquired weakness is caused by many factors: the inflammatory response, glycemic control, use of myotoxic or neurotoxic medications like corticosteroids or neuromuscular blocking agents, and immobility. 1,[8][9][10] Immobility in critically ill patients leads to decreased protein synthesis in muscle, increased catabolism of the muscle, and decreased muscle mass that is more pronounced in the lower limbs. [17][18][19] Muscle groups that lose the most strength are involved in maintaining posture, transferring activities, and ambulation.…”

Effects of short-term and prolonged bed rest on the vestibulosympathetic reflex

“…Moreover, the failure to maintain blood pressure in the upright posture is associated with increased mortality (26). Head-down bed rest (BR) is used to simulate microgravity and physical deconditioning and to elicit OI (13). Mechanisms believed to contribute to the development of OI with BR include: impaired vagal baroreflex responses (5), an inadequate increase in sympathetic discharge (18,42), cardiac atrophy (24), an inability to increase peripheral vascular resistance (3,25), and hypovolemia (29).…”

“…Mechanisms believed to contribute to the development of OI with BR include: impaired vagal baroreflex responses (5), an inadequate increase in sympathetic discharge (18,42), cardiac atrophy (24), an inability to increase peripheral vascular resistance (3,25), and hypovolemia (29). Studies indicate that alterations in sympathetic nerve activity contribute to the development of OI (13,18,25,42). Hypotensive episodes during head-up tilt appear to be closely related to lack of increased muscle sympathetic nerve activity (MSNA) (25).…”