# Question about Poisseuille's law and blood flow

1. Sep 26, 2005

### don_anon25

I know that rate of flow is equal to pi*(P1-P2)*R^4/8nL. For blood in the coronary artery, I know the pressure drop, and the radius of the artery. What is the viscosity of blood??? I can't find this value anywhere! And what value should I enter for L (distance L along a tube)? Is there an actual value somewhere for the length of the coronary artery in mm?

2. Sep 27, 2005

### FredGarvin

According to this source http://www.usc.edu/dept/biomed/bme403/Section_3/viscosity_of_blood.html
The value is approximately three times that of water. So if I use the dynamic viscosity of water at 20°C as
$$\mu_{water} = 20.92 \frac{Lb_f sec}{ft^2}$$, that would mean that $$\mu_{blood} = 3.0 \mu_{water}$$ so...

$$\mu_{blood}= 62.76 \frac{Lb_f sec}{ft^2}$$

$$\mu_{blood}= 3.0 x 10^6 cP$$

I can't really help you in terms of L in your equation. A couple of options would be to a)Leave L blank and express your answers in flow per unit length (which sounds kind of funny but is technically correct). or b)Make an estimation.

Last edited: Sep 27, 2005