Living body impedance measurement apparatus

• US 7,079,889 B2
• Filed: 07/01/2003
• Issued: 07/18/2006
• Est. Priority Date: 07/11/2002
• Status: Active Grant

• Current Assignee: Tanita Corporation (Tanita)
• Original Assignee: Tanita Corporation (Tanita)
• Inventors: Nakada, Masato
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Rogers, Kristin D.
• Application Number:
  US10/609,555
• Publication Number:
  US 20040010205A1
• Time in Patent Office: 1,113 Days
• Field of Search: None
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/4872 Body fat

Abstract

A living body impedance measurement apparatus is provided which measures a voltage attributed to the impedance of a living body, and separates it into a voltage attributed to a resistance component and a voltage attributed to a reactance component. Then, the voltage attributed to the resistance component, the voltage attributed to the reactance component, and resistance and reactance components of an impedance of an external reference unit are substituted into an impedance calculation formula that accounts for impedance fluctuation. A fluctuation constant is thereby calculated that is a constant for a fluctuation variable representing fluctuation caused by impedance change factors. The resistance component and the reactance component of a true impedance of the living body are then calculated based on the fluctuation constant and the measured living body impedance.

Claims

1. A living body impedance measurement apparatus, comprising:

a voltage measurement unit;

a separation unit;

a calculation formula storage unit;

a fluctuation constant calculation unit;

a fluctuation constant storage unit; and

a living body impedance calculation unit, wherein

said voltage measurement unit measures a voltage attributed to an impedance of a living body or an external reference unit, or of a living body, an external reference unit or an internal reference unit,

said separation unit separates the voltage attributed to the impedance as measured by said measurement unit into a voltage attributed to its resistance component and a voltage attributed to its reactance component,

said calculation formula storage unit stores an impedance calculation formula therein in advance, said impedance calculation formula correlates a true impedance variable representing resistance component and reactance component of true impedance of the living body or the external reference unit with a fluctuation variable representing a fluctuation which may be caused in said voltage measurement unit due to any impedance change factor as well as a measured voltage variable representing the voltage attributed to resistance component and the voltage attributed to reactance component of an actually measured impedance,

said fluctuation constant calculation unit calculates a fluctuation constant that is the constant for the fluctuation variable by substituting the voltage attributed to resistance component and the voltage attributed to reactance component, which are separated from each other by said separation unit, corresponding to the voltage attributed to the impedance of the external reference unit as measured by the voltage measurement unit, as well as the resistance component and the reactance component of the impedance of the external reference unit as measured by the voltage measurement unit for terms in said impedance calculation formula stored in said calculation formula storage unit in advance,

said fluctuation constant storage unit stores the fluctuation constant calculated by said fluctuation constant calculation unit, and

said living body impedance calculation unit calculates the resistance component and the reactance component of the true living body impedance by substituting the fluctuation constant stored in the fluctuation constant storage unit and the voltage attributed to the living body impedance as measured by the voltage measurement unit for the terms in said impedance calculation formula stored in said calculation formula storage unit in advance.

2. A living body impedance measurement apparatus according to claim 1 wherein said fluctuation constant calculation unit calculates a fluctuation constant that is the constant for the fluctuation variable by substituting each voltage attributed to each resistance component and each voltage attributed to each reactance component, which are separated from each other by said separation unit, corresponding to each voltage attributed to each impedance of each of a plurality of different external reference units as measured by the voltage measurement unit, as well as each resistance component and each reactance component of each impedance of each of a plurality of different external reference units as measured by the voltage measurement unit for the terms in said impedance calculation formula stored in said calculation formula storage unit in advance.

3. A living body impedance measurement apparatus according to claim 2 wherein said impedance calculation formula includes:

fluctuation variables;

“

C_R”

representing any fluctuation based on the scale factor and the phase of resistance component;

“

C_X”

representing any fluctuation based on the scale factor and the phase of reactance component;

“

V_OSR”

representing any fluctuation based on the offset voltage to resistance component axis; and

“

V_OSX”

representing any fluctuation based on the offset voltage to reactance component axis;

measured voltage variables;

“

V_BR”

representing the voltage attributed to resistance component of the living body or the external reference unit;

“

V_BX”

representing the voltage attributed to reactance component;

“

V_RR”

representing the voltage attributed to resistance component of the internal reference unit; and

“

V_RX”

representing the voltage attributed to reactance component; and

true impedance component variables;

“

R_B”

representing resistance component of the true impedance of the living body or the external reference unit; and

“

X_B”

representing reactance component of that true impedance, and said impedance calculation formula is written as follows;