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Systems affected

1. Musculoskeletal
   • Bone demineralisation - increased urinary calcium excretion (disproportionate degree of demineralisation of load-bearing bones such as calcaneum
   • Muscular changes - reduced muscle bulk
2. Cardiovascular
   • Seen after 3 weeks prolonged bed rest
   • Increased HR
   • Reduced SV
   • Maintained CO / arterial pressure (due to increased HR, reduced SV)
3. Autonomic
   • Blunted autonomic responses
4. Fluid compartments
   • After 3 weeks may be fall in 600mls circulating blood volume (due to loss of plasma volume)
5. Body composition
   • Reduced lean body mass - increased nitrogen excretion (after 5th day of bed rest)
   • Increased adipose tissue deposition - replacement for loss of muscle mass
   • Increased potassium excretion

Risks of prolonged bed rest

1. DVT
2. Pressure ulcers: superifical bony areas