The effect of posture change on blood volume, serum potassium and whole body electrical impedance.
After standing for 1 h, 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) omega. 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 l-1; mean (SEM)) relative to the standing value (4.6(0.1)mmol l-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.
Shirreffs
S M
SM
Department of Environmental and Occupational Medicine, University Medical School, Foresterhill, Aberdeen, Scotland.
Maughan
R J
RJ
D000328:Adult; D001810:Blood Volume; D017097:Electric Impedance; D004573:Electrolytes / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D010953:Plasma Volume; D011187:Posture / Q000502:physiology*; D011188:Potassium / Q000097:blood*; D012709:Serum Albumin / Q000032:analysis
D004573:Electrolytes; D012709:Serum Albumin; D011188:Potassium