- Patent title: Bioelectrical impedance measuring apparatus constructed by one-chip integrated circuit
- Patent #: 6472888
- Patent filing date: Jan. 29, 2001
- Patent issue date: Oct. 29, 2002
- How long it took for this patent to issue: 1yr and 9mo
- Inventor(s): Oguma, Koji, Miyoshi, Tsutomu
- Assignee: Tanita Corporation
- US classification: 324/691; 324/692; 600/547
- How many claims: 9
Bioelectrical impedance apparatuses (BIA) estimate the body composition of the individual by sending a small electrical impulse through its tissues. The speed of this electrical current varies due to the water, muscle, and fat content in the tissues . Tissues containing higher water and muscle content tend to have faster electrical currents, and thus, a lower impedance; whereas, tissues containing higher fat content tend to have slower electrical currents, and thus, a higher impedance . Other factors, such as sex, height, and weight, are also considered when using this device. 
Having been available to the public since the 1980’s , this recent 2001 patent improves upon the original BIA by scaling down all the necessary processes onto a one-chip microcomputer . The essential components of a BIA include: inputting patient information, applying electrical current, integrating bioelectrical impedance, and outputting one’s body composition, all of which remain withstanding . The one-chip microcomputer is useful for 1) selectively generating and relaying an alternating-current (AC), 2) containing multiple switches that measure bioelectrical impedance, send the AC signal, and quantify the output voltage, and 3) containing devices that produce, supply, and detect voltage . Overall, the inventors sought to maintain the effectiveness of the current solution whilst minimizing the amount of compartments needed to output one’s body composition.
Figure 1. Bioelectrical Impedance Analysis Schematic. The body is composed of fat or fat-free mass and water or water-free tissues (A) . These different components result in different resistances, and thus, different impedances. Moving through water encounters less resistance than moving through fat (C) . To measure impedance, the circuit connects to 2 electrodes placed at the wrist and 2 placed at the ankle (B) .
BIA can prove to be an effective tool for quantifying one’s body composition in clinical studies, more specifically studies whose population consists of individuals from developing countries  due to its low cost, portability, ease of use, and reliability . Additionally, bioelectrical impedance analyzers are available for commercial use and offered from online retailers, such as Amazon . Like an Apple Watch or Fitbit, one may resort to purchasing a BIA in means of receiving information regarding their body constitution in a timely fashion. Using an age limit similar to a Fitbit, individuals below the age of 13 should not make use of a BIA . Moreover, the curiosity over one’s weight, body mass index, and body composition has been trending over the last decade, and is directly related to the booming health and fitness industry . Aside from its current uses, BIA deems to be a probable technique for detecting the presence of abnormalities in the body (i.e. lesions and/or tumors) .
As previously stated, BIA relies on an electrical current that passes through various regions of high to low water, muscle, or fat content in order to decipher one’s body composition. This technique assumes the body exists as conductive cylinders, uniform in material and density, and fixed in cross-sectional area .In addition, BIA assumes that the body’s conductive volume is reflective of its water composition . With these assumptions in mind, the formula that is used to estimate the contribution of a body part’s weight to the whole body resistance is as seen in equation 1.
V=p x S^2/R (1)
The variable V represents the conductive volume; p represents the receptivity of the conductor; S represents the length of the conductor; and R represents the resistance of the cross-section area .
Two electrode configurations are used to measure four impedance values in the body – one from each electrode – and to decipher whether an anomaly has occurred . The impedance analyzer makes use of a signal generator, sensor, switch, and drive and measurement electrodes in order to produce and measure a signal . The principle behind Ohm’s Law (equation 2) is used to calculate the voltage difference between the two electrode configurations as current flows through the body . For BIA measurements, electrodes are often placed at the wrist and ankle .
V=I x R (2)
Impedance is the ratio between voltage and current, V/I, and is often represented as the variable, Z . Moreover, Z is dependent upon resistance, R, and reactance, X, and can be expressed using the formula in equation 3.
Engineers often use assumptions to simplify biological processes while also attempting to retain the maximum amount of information in said processes. Based on the assumptions that make up equations 1 and 3, researchers often encounter accuracy issues when analyzing BIA measurements . To combat this, these equations can be manipulated so that they are only effective when the sample is reflective of its reference population’s impedance formula .
The one-chip microcomputer expands on prior solutions as it integrates all circuits that measure impedance onto a single platform. The inventors specifically compare their design to that of a body fat meter. In summary, the body fat meter makes use of a microcomputer, yet, continues to employ other instruments to calculate impedance, which results in 1) a large apparatus, 2) increased labor to create the circuit board, and 3) heightened likelihood of encountering noise . In synopsis, the one-chip microcomputer allows for downsizing, offers a cheaper alternative, and reduces the margin for error. Additional patents use BIA to monitor abnormalities in the body , analyze organ output , or improve instrumentation of the device .
Figure 2. Patent Drawing. The above image displays the compartments needed to measure impedance on a one-chip microcomputer .
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