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How to Determine Speed from a Pulse Probe

A pulse probe is a device that uses the Doppler Effect to detect the flow of blood through an artery. The device sends out an ultrasonic signal non-invasively into a vein or artery. The heart produces a beat frequency which is detected with a pulse probe and can be used to measure the velocity or speed of the blood flow. This creates shifts in the Doppler Effect and correlates to the velocity of the blood flow.

Things You'll Need

Calculator

Instructions

- 1
  Find the volumetric flow rate in an artery. For example, assume the flow rate (Q) is 2 pints per minute. This can be converted to cubic inches with the conversion of 1 pint equals 29 cubic inches. A flow of 2 pints per minute equals 58 cubic inches per minute. The flow rate will not change but the velocity or speed will change with a change in artery size. Therefore, if the artery is 1/8 inch in diameter (decimal diameter is 0.125 inches), the cross sectional area (A) is 0.125^2 x 3.14 / 4 or 0.0123 square inches.
- 2
  Determine the velocity (v) of the flow through the artery. This equation is v = Q / A or 58/0.0123 for a velocity of 4,715 inches per minute.
- 3
  Find the Doppler Effect shift from the pulse probe. This shift is the change in frequency as blood flows through different size arteries and it is proportional to the change in velocity. For instance, if the frequency of flow is 250 inches per second through an 1/8-inch diameter blood vessel and if the blood constricts to 1/16-inch diameter and the frequency increases to 350 inches per second, the speed of flow can be calculated.
- 4
  Calculate the velocity of the flow at the new artery size. This can be done proportionally by the equation 4,715/250 = X / 350, where X is the new flow rate. This is calculated to be 6,601 inches per minute. Therefore, a pulse probe can calculate this velocity and changes in velocity based on the frequency of flow.

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