Doppler ultrasound testing, one step at a time

More sensitive than palpation for determining pulse rate, the Doppler ultrasound blood flow detector is especially useful when a pulse is faint or weak. Unlike palpation, which detects arterial wall expansion and retraction, this instrument detects the motion of red blood cells (RBCs).

• Apply a small amount of coupling gel or transmission gel (not water-soluble lubricant) to the ultrasound probe.
  
  
• Position the probe on the skin directly over the selected artery. In the illustration, the probe is over the posterior tibial artery.
  
  
• When using a Doppler model like the one in the illustration, turn the instrument on and, moving counterclockwise, set the volume control to the lowest setting. If your model doesn't have a speaker, plug in the earphones and slowly raise the volume. Another option is a Doppler ultrasound stethoscope, which is basically a stethoscope fitted with an audio unit, volume control, and transducer, which amplifies the movement of RBCs.
  
  
• To obtain the best signals with either device, tilt the probe 45 degrees from the artery, being sure to put gel between the skin and the probe. Slowly move the probe in a circular motion to locate the center of the artery and the Doppler signal—a hissing noise at the heartbeat. Avoid moving the probe rapidly because this distorts the signal.
  
  
• Count the signals for 60 seconds to determine the pulse rate.
  
  
• After you've measured the pulse rate, clean the probe with a soft cloth soaked in antiseptic solution or soapy water. Don't immerse the probe or bump it against a hard surface.