Identification of the human electrical impedance indifferent point: A surrogate for the volume indifferent point?

Sara S Jarvis, James A. Pawelczyk

Research output: Contribution to journalArticle

4 Scopus citations


Head-up tilt (HUT) redistributes ∼700 mL of blood to the dependent regions. In a gravitational field, hydrostatic pressure is balanced against vascular compliance, resulting in a hydrostatic indifferent point (HIP) whose location should be coincident with an indifferent point for volume (VIP). Cardiac filling is determined by the hydrostatic gradient between the HIP/VIP and right atrium. We employed segmental impedance to examine blood volume redistribution during HUT and estimate the location of the VIP. During HUT, impedance increased in the chest and decreased in the lower abdomen, presumably due to blood volume shifts. Using a non-linear model to relate blood volume shifts to the hydrostatic gradient, we estimated the location of the electrical impedance indifferent point between the xyphoid process and iliac crest, at 64.5 ± 2.6% of an individual's height. This method may provide a quantitative framework to assess the effects of blood volume distribution on tilt tolerance.

Original languageEnglish (US)
Pages (from-to)473-480
Number of pages8
JournalEuropean Journal of Applied Physiology
Issue number4
StatePublished - 2009
Externally publishedYes



  • Blood volume distribution
  • Head-up tilt
  • Segmental bioelectrical impedance
  • Volume indifferent point

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Orthopedics and Sports Medicine
  • Physiology (medical)

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