The effect of posture change on blood volume, serum potassium and whole body electrical impedance

Abstract

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.

Austrian Moderate Altitude Study (AMAS 2000) – fluid shifts, erythropoiesis, and angiogenesis in patients with metabolic syndrome at moderate altitude (≅1700 m)

“…We are aware that application of this method has certain limitations in overnourished subjects and is also influenced by body posture and plasma sodium concentration (Kushner and Schoeller 1986;Roos et al 1992;Shirreffs and Maughan 1994). In the present study all body impedance measurements were performed in the morning between 8.00 and 11 a.m. and the values for the resistance and reactance were taken each time 15 min after the subject had taken a supine position.…”

“…a decrease in thickness of the superficial tissue. Roos et al (1992) as well as Shirreffs and Maughan (1994) studied the effect of posture change on blood volume and body impedance. In both studies it was found that body impedance is essentially influenced by alterations in body posture and by the amount and composition of extracellular fluids.…”

Errors in Dual Energy X-Ray Absorptiometry Estimation of Body Composition Induced by Hypohydration

“…All readings were obtained within 1 minute of adopting the supine posture. This procedure was to avoid erroneous impedance readings through fluid shifts that occur with prolonged periods in this position (Shirreffs & Maughan, 1994) .Following these initial measurements participants were carefully positioned for one whole body DXA scan.…”

Comparison of Wired and Wireless Bio-Electrical Impedance Fluid Status Monitoring Devices and Validation to Body Mass and Urine Specific Gravity Changes Following Mild Dehydration

“…electrode placement, side of body, posture, limb position, ambient temperature, skin temperature, hydration status, food and liquid intake, fluid shifts, sweating, and recency of exercise (Caton et al 1988;Roos et al 1992;Shirreffs and Maughan 1994;Gudivaka et al 1996;Armstrong et al 1997;Cheuvront 2005). In this current study, ambient temperature could not have been an error source because it did not change from pre-to post-practice measurements.…”

“…Fluid and electrolyte shifts occur during and immediately following exercise which effect post-exercise bio-electrical impedance measurements (Koulmann et al 2000). Additionally, many of the sources of error associated with bio-electrical impedance measurement that can be controlled in a clinical or laboratory setting may not be controllable in a field setting such as: posture, limb position, ambient temperature, hydration status, food and liquid intake, fluid shifts, sweating, and recency of exercise (Caton et al 1988;Roos et al 1992;Shirreffs and Maughan 1994;Gudivaka et al 1996;Armstrong et al 1997;Cheuvront 2005).…”