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An indifference point for electrical impedance in humans
1Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Denmark.
Acta Physiologica Scandinavica
|June 1, 1993
Summary
Regional electrical impedance measurements reveal fluid shifts during head-up tilt. The volume indifference point, indicating minimal fluid change, is located between the umbilicus and crista iliaca in humans.
Area of Science:
- Physiology
- Biomedical Engineering
Background:
- Understanding fluid distribution in the human body during postural changes is crucial for physiological research.
- Passive head-up tilt is a common method to study cardiovascular and fluid shifts.
Purpose of the Study:
- To determine the volume indifference point during passive head-up tilt using regional electrical impedance.
- To investigate fluid accumulation in different body segments during head-up tilt.
Main Methods:
- Regional electrical impedance was measured across eight body sections (thorax, abdomen, thigh, knee, lower leg) in eight subjects.
- Passive head-up tilt was performed in 10-degree increments from 0 to 60 degrees over 6 minutes.
Main Results:
- Thoracic electrical impedance increased with tilt angle, while abdominal impedance remained stable.
- Thigh and lower leg impedance decreased, indicating fluid shifts away from these areas.
- Minimal impedance changes were observed around the knee, suggesting limited fluid accumulation.
Conclusions:
- The volume indifference point in humans during head-up tilt is likely situated between the umbilicus and crista iliaca.
- Fluid redistribution occurs during head-up tilt, with minimal accumulation around the knee.