Bioimpedance phase angle, its measurement and relation to health monitoring - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: January 20, 2021, 10:46:05 pm
content: Hi,(NOTE... I don't know anything about bio-impedance or related topics)according to some papers I came across and someone working on EAV diagnostic equipment, bioimpedance phase angle is a parameter/marker used to monitor biological status (health/vitality/behaviour) of cell cultures or, to some degree, human health diagnostic for example in EAV equipment. Also in other applications such as measurement of body tissue vs fat composition. Some links at the bottom.1) Phase angle measured with respect to what reference?2) Where can I find out any basic tutorial material or resources?3) Are there any schematics or ICs that do that reliably?Links:https://content.sciendo.com/view/journals/joeb/9/1/article-p142.xml?language=en#:~:text=The%20method%20was%20called%20Electric,large%20counter%20electrode%20are%20measured.https://www.intechopen.com/books/advanced-biometric-technologies/cell-biometrics-based-on-bio-impedance-measurementshttps://www.frontiersin.org/articles/10.3389/fbioe.2019.00474/fullhttps://www.researchgate.net/publication/330318446_Applications_of_bioimpedance_measurement_techniques_in_tissue_engineeringhttps://adc.bmj.com/content/87/3/252https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723101/https://jissn.biomedcentral.com/articles/10.1186/s12970-019-0319-2#:~:text=Background,cell%20mass%2C%20and%20cellular%20integrity.Thank you

author: Benta
author_rank: Super Contributor
timestamp: January 20, 2021, 10:48:46 pm
content: Are you sane?Please post stuff like this in "general chat".

author: ejeffrey
author_rank: Super Contributor
timestamp: January 21, 2021, 12:16:10 am
content: It's just measuring the angle of the complex impedance at a pre-defined frequency and signal amplitude. I think 50 kHz is typical. It is normally used to estimate body composition metrics like fat and water %. It's used in those bathroom scales that show body fat %. AFAIK, this is mostly done by correlating impedance data with more direct measurements of body composition such as imaging scans. You fit to a model then program that into the scale and it is good enough for most people in most situations.Pretty much any circuit that can measure complex impedance at the target frequency should work fine it isn't a complex problem. Obviously you need to make sure the excitations is limited to safe levels.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: January 21, 2021, 01:18:11 am
content: https://pubmed.ncbi.nlm.nih.gov/25661454/https://sci-hub.st/10.1093/ajcn/82.1.49Presumably you apply a 100kHz voltage and measuring the phase difference between it and the resulting current. It's just classic impedance analysis but concerning sending the voltage/current through a living human. So, you ought to continue reading the various papers and find out how that's done. But here's an introduction:https://inbodyusa.com/blogs/inbodyblog/your-body-and-you-a-guide-to-phase-angle/To the skeptics: this is legit.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 21, 2021, 01:57:46 am
content: Hah, for the diversity of projects the OP is involved with: the circumstances of this thread, and the reactions therein, are fitting.This subject, is definitely one of those that makes you think "what?", but reflecting on the terms for a moment, checks out as plausible. It's not like GSR hasn't been used for over a century (for such diagnostic purposes as it is known to be useful for...and, yes, quite a lot of quackery as well, alas). That's just DC impedance, aka resistance. Now, I don't think "cell health" is so plausible, like, what about cells would you learn this way? And like, individual cells, or in aggregate? But I don't know the literature, and if that's something, cool.Tim

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: January 21, 2021, 02:10:25 am
content: Quote from: T3sl4co1l on January 21, 2021, 01:57:46 amRead the second link I gaveAlso, bioimpedance analysis is familiar to anyone who has used one of those electronic scales that give you percent body fat, water etc. e.g.,https://www.tanita.com/en/mc-780/I used one of these (well, similar) over a few years in conjunction with more traditional multipoint caliper measurements and got good agreement.

author: bson
author_rank: Unknown
timestamp: January 21, 2021, 05:50:41 am
content: Looks like the plain old impedance phase angle. I.e., the angle between voltage and current.Bioelectrical impedance analysis (BIA) is a widely used, non-invasive field method for assessing body composition, which measures the electrical characteristics of human body either at 50 kHz (single-frequency BIA) or at several frequencies in the range 1–1000 kHz (multifrequency BIA and BIS = bioimpedance spectroscopy). Impedance (Z) is the opposition of the body to an alternating current, resulting from resistance (R) to the current that flows through tissue containing water plus electrolytes, and reactance (Xc), which is associated with the capacitive component of tissues (e.g. cell membranes and tissue interfaces) . In addition, phase angle (PhA), which is also stated as the arctangent of the Xc to R ratio, describes the angular shift (phase difference) between voltage and current sinusoidal waveforms; in humans the current reaches at regular intervals its maximum/minimum peaks after the voltage (positive PhA values) and this lag is most likely due to cell membranes and tissue interfaces

author: ricko_uk
author_rank: Super Contributor
timestamp: January 23, 2021, 01:12:07 am
content: Thank you all as usual!And apologies for the quickly written hence partially incorrect OP. It was worded incorrectly as I was stating bioimpedance measurement to be the most important/relevant/comprehensive parameter. That was a misreading of a particular paper mixed with a partial misunderstanding of a conversation with a bio-engineer who has been working on bioimpedance measurement for diagnostic equipment. To be more precise EAV-type diagnostic, which is supposed to read the condition of various body organs by measuring bio-impedance of the human body meridians.As I am getting more familiar with the subject I changed the wording in the OP to a more appropriate one. And added some links.Anyway, thank you as usual for the feedback and infos, always appreaciated!!