Device and method for monitoring and controlling physiologic parameters of a dialysis patient using segmental bioimpedance

• US 20030120170A1
• Filed: 11/27/2002
• Published: 06/26/2003
• Est. Priority Date: 08/14/2000
• Status: Active Grant

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: Renal Research Institute LLC
• Inventors: Levin, Nathan W., Zhu, Fansan
• Granted Patent: US 7,228,170 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 2205/50 with microprocessors or computers

Abstract

The present invention includes a method of determining the dry body weight of a patient undergoing dialysis by means of segmental bioimpedance analysis. In preferred embodiments, dry body weight is determined by comparison to the bioimpedance values of normal subjects or by monitoring changes in bioimpedance during dialysis. One embodiment of the present invention is a device for determining dry body weight during dialysis.

Claims

1. A device for monitoring hydration status in a hemodialysis patient comprising:

a digital signal processor;

an electrical output means being in electrical communication with the digital signal processor and being attachable to a body segment, the electrical output means being adapted to apply electrical current to the body segment;

an electrical input means being in electrical communication with the digital signal processor and being attachable to a body segment, the electrical input means being adapted to receive the current transmitted through the body segment and transmit the same to the digital signal processor; and

a microprocessor being in electrical communication with the digital signal processor;

wherein the microprocessor is adapted to determine a relative change in extracellular volume in the body segment based on the current transmitted through the body segment, and to plot said relative change as a function of time.

2. The device of claim 1, wherein the microprocessor determines the relative change in extracellular volume in the body segment according to the following equation:

δ

=ECV_t/ECV₀=(ρ

×

L²/R_t)/(ρ

×

L²/R₀)=R₀/R_t

wherein δ

is the relative change in extracellular volume in the body segment, ECV_t is a variable equal to the resistivity (ρ

) times the square of the length of the body segment (L) divided by the resistance (R_t) during hemodialysis, and ECV₀ is a constant value equal to the resistivity (ρ

) times the square of the length of the body segment (L) divided by the resistance (R₀) at the beginning of dialysis.

3. A device for determining the dry weight of a hemodialysis patient comprising:

a digital signal processor;

an electrical output means being in electrical communication with the digital signal processor and being attachable to a body segment, the electrical output means being adapted to apply electrical current to the body segment;

an electrical input means being in electrical communication with the digital signal processor and being attachable to a body segment, the electrical input means being adapted to receive the current transmitted through the body segment and transmit the same to the digital signal processor; and

a microprocessor being in electrical communication with the digital signal processor;

wherein the microprocessor is adapted to determine the dry weight of a hemodialysis patient based on the current transmitted through the body segment.

4. The device of claim 3, wherein the microprocessor determines that the dry weight of a hemodialysis patient has been reached when:

Δ

δ

=(R₀/R_t−

R₀/R_t+1)*100%≦

about 2%

wherein Δ

δ

is the relative change in the extracellular volume (ECV) during dialysis;

R₀ is the resistance during dialysis at time 0;

R_t is the resistance during dialysis at time t; and

R_t+1 is the resistance during dialysis at time t+1; and

when

resistivity (ρ

)≧

ρ

N;

 

wherein ρ

N is a normal range of resistivity.

5. A method for determining a hemodialysis patient'"'"'s dry weight comprising the steps of:

periodically measuring the resistance of a body segment during hemodialysis;

comparing successive resistance measurements according to the equation

δ

=ECV_t/ECV₀=(ρ

×

L²/R_t)/(ρ

×

L²/R₀)=R₀/R_t;

 

wherein δ

is the relative change in extracellular volume in the body segment, ECV_t is a variable equal to the resistivity (ρ

) times the square of the length of the body segment (L) divided by the resistance (R_t) during hemodialysis, and ECV₀ is a constant value equal to the resistivity (ρ

) times the square of the length of the body segment (L) divided by the resistance (R₀) at the beginning of dialysis; and

identifying the hemodialysis patient'"'"'s dry weight when a substantially constant resistivity is reached wherein

Δ

δ

=(R₀/R_t−

R₀/R_t+1)*100%≦

about 2%;

 

wherein Δ

δ

is the relative change in the extracellular volume (ECV) during dialysis;

R₀ is the resistance during dialysis at time 0;

R_t is the resistance during dialysis at time t; and

R_t+1 is the resistance during dialysis at time t+1.