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Help! Electrical Resistance of the Heart watch

1. Ok so in my lecture notes we are given an example calculating the resistance of the heart and i will literally copy down exactly what's in my notes onto here. I missed that lecture, so i'm a bit confused. for starters, the equation doesn't even equal 25

Consider the heart in the centre of the thorax

thorax: phi=30cm (not sure what the symbol phi is)
resistivity = 2ohm m

heart: phi=50mm
length=100mm
resistivity=20ohm m
potential diff = 5mV

R = resistivity x L / a =(2 x 100 x 10^-3)/(pi x 0.625 x 10^-3) = 25ohms

they've used resistivity of the thorax, not the heart then where does 0.625 come from? it's obv in mm

thanks!!
2. phi is clearly diameter, in case you haven't worked that out.

They've done resistivity(thorax) x length(heart)/pi (radius(heart)squared)

Should have given 102.

Of course, if he had taken the diameter measurement when doing those calculations instead of radius, it would have given 25...

As to why the resistivity of the thorax has been used, no idea. Does he use the thorax measurements elsewhere? If so maybe its another misprint.

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Updated: March 31, 2011
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