Blood volume: importance and adaptations to exercise training, environmental stresses, and trauma/sickness

This paper reviews the influence of several perturbations (physical exercis e, heat stress, terrestrial altitude, microgravity, and trauma/sickness) on adaptations of blood volume (BV), erythrocyte volume (EV), and plasma volu me (PV). Exercise training can induce BV expansion: PV expansion usually oc curs immediately, but EV expansion takes weeks. EV and PV expansion contrib ute to aerobic power improvements associated with exercise training. Repeat ed heat exposure induces PV expansion but does nor alter EV. PV expansion d oes not improve thermoregulation, but EV expansion improves thermoregulatio n during exercise in the heat. Dehydration decreases PV (and increases plas ma tonicity) which elevates heat strain and reduces exercise performance. H igh altitude exposure causes rapid (hours) plasma loss. During initial week s at altitude, EV is unaffected, but a gradual expansion occurs with extend ed acclimatization. BV adjustments contribute, but are not key, to altitude acclimatization. Microgravity decreases PV and EV which contribute to orth ostatic intolerance and decreased exercise capacity in astronauts. PV decre ases may result from Lower set points for total body water and central veno us pressure, while EV decreases may result from increased erythrocyte destr uction. Trauma, renal disease, and chronic diseases cause anemia from hemor rhage and immune activation which suppresses erythropoiesis. The reestablis hment of EV is associated with healing, improved life quality, and exercise capabilities for these injured/sick persons.