Abstract
After standing for 1h, ten subjects (7 male, 3 female) assumed a supine position for a further hour. Whole body bioelectrical impedance increased progressively during the hour spent in the supine position: after 60 min supine the increase was 13(6 to 32)Ω. Blood and plasma volumes, estimated from haematocrit and haemoglobin concentration, increased by 8.0(6.7 to 12.4)% and 16.7(12.3 to 20.8)% (median(range)) respectively after 60 min supine. Serum potassium concentration had fallen after 10 min supine (4.1(0.1)mmol 1−1; mean(SEM)) relative to the standing value (4.6(0.1)mmol 1−1) and was unchanged thereafter. Serum osmolality (P=0.991) and sodium (P=1.000) and chloride (P=0.998) concentrations remained unchanged throughout the study. The fall in serum potassium concentration in the supine position does not appear to be a simple dilutional effect consequent upon increases in blood and plasma volume as there was no effect of postural change on serum sodium or chloride concentrations.
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Shirreffs, S.M., Maughan, R.J. The effect of posture change on blood volume, serum potassium and whole body electrical impedance. Europ. J. Appl. Physiol. 69, 461–463 (1994). https://doi.org/10.1007/BF00865413
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DOI: https://doi.org/10.1007/BF00865413