Equivalence of information from single versus multiple frequency bioimpedance vector analysis in hemodialysis.
BACKGROUND
In suspended cells, low-frequency current only passes through extracellular fluids, while current at higher frequencies passes through extra- and intracellular fluids. Cells in soft tissues are in contact with each other, which causes tissue anisotropy, meaning that impedance changes along different cell directions, with part of low-frequency current also passing through cells. Hence, equivalent information on body impedance change is expected at all frequencies, which we proved in a dynamic condition of fluid removal with hemodialysis.


METHODS
We performed whole-body impedance spectroscopy (496 frequencies from 4 to 1024 kHz, SEAC SFB3 analyzer; Brisbane, Australia) before and during fluid removal (0, 60, 120, 180 min, 2.5 kg) in 67 hemodialysis patients. With increasing current frequency, resistance (R) decreases and reactance (Xc) moves along the Cole's semicircle on the R-Xc plane.


RESULTS
The Cole's semicircles progressively enlarged and moved to the right on the R-Xc plane following fluid removal (increase in both R and Xc values at any given frequency). Xc values at 5 kHz (expected values close to 0 Ohm) were 70% of the maximun Xc, indicating an intracellular current flows at low frequencies. The correlation coefficient between R at 50 kHz (standard frequency) and R at other frequencies ranged from 0.96 to 0.99, and the correlation coefficient between Xc at 50 kHz and Xc at other frequencies at any time point ranged from 0.65 to 0.99.


CONCLUSIONS
From high Xc values at low frequency, tissue anisotropy is inferred. Intra- and extracellular current flow causes equivalence of information based on functions of R and Xc measurements made at 50 kHz versus other frequencies.
Piccoli
Antonio
A
Department Scienze Mediche e Chirurgiche, University of Padova, Padova, Italy. apiccoli@unipd.it
Pastori
Giordano
G
Guizzo
Marta
M
Rebeschini
Mirca
M
Naso
Agostino
A
Cascone
Carmelo
C
D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D001825:Body Fluid Compartments; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D017097:Electric Impedance; D005260:Female; D017408:Guidelines as Topic; D006801:Humans; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis