TY - JOUR
T1 - Identification of the human electrical impedance indifferent point
T2 - A surrogate for the volume indifferent point?
AU - Jarvis, Sara S.
AU - Pawelczyk, James A.
N1 - Funding Information:
Acknowledgments We would like to thank Jeff Banas, Bill Hen-non, Katie Homan, Kylie Kaminski, Dave Leone, Joy Lithgow, Kevin Mao, Heidi Nadeau, Adam Spinner, Kylie Weaver, and the General Clinical Research Center for their assistance with this study. We would also like to thank Don Sheriff for his advice throughout this project. This work was supported by grants from National Aeronautics and Space Administration NNJ04HF45G (to J.A. Pawelczyk), National Institutes of Health MO1RR10732 (to General Clinical Research Center), and the National Aeronautics and Space Administration Harriet G. Jenkins Pre-doctoral fellowship (to S.S. Jarvis). All procedures were performed in accordance with the Declaration of Helsinki.
PY - 2009
Y1 - 2009
N2 - 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.
AB - 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.
KW - Blood volume distribution
KW - Head-up tilt
KW - Segmental bioelectrical impedance
KW - Volume indifferent point
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U2 - 10.1007/s00421-009-1148-9
DO - 10.1007/s00421-009-1148-9
M3 - Article
C2 - 19672616
AN - SCOPUS:70350274102
SN - 1439-6319
VL - 107
SP - 473
EP - 480
JO - European Journal of Applied Physiology
JF - European Journal of Applied Physiology
IS - 4
ER -