# physiology

Given a Helium-Neon laser-based fiber optic Doppler probe at an angle of 60¡C with a blood vessel that registers a frequency shift of 63KHz, what is the velocity of the blood? Is this a reasonable number from a physiologic point of view when compared to the average velocity in the major and minor blood vessels in the human body?

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1. The He-Ne laser wavelength is L = 632.8*10^-9 m and the frequency is
f = c/L = 4.74*10^14 Hz
The doppler shift ratio is
deltaf/f = Vx/c = 63*10^3/4.74*10^14
= 1.33*10^-10
where Vx is the blood flow velocity component along the laser beam direction.
Therefore the blood velocity component along the direction of the beam is
Vx = 4.0*10^-2 m/s = 4.0 cm/s.
If the true blood flow direction is inclined 60 degrees to the line of sight, the actual blood flow velocity is higher by a ratio 1/cos60 = 2.
The blood velocity is therefore 8.0 cm/s. That seem like a reasonable value to me. I suggest you check other sources about that.

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