Doppler Stethoscopy in Diagnostics

Examination procedure

• The patient is in a supine position.
• Perform the measurements after at least 5 minutes of rest.

1. Palpate the pulses and the temperature of the limb. Detection of peripheral pulses or a weak pulse does not rule out mild arterial occlusive (ASO) disease, and their absence is insufficient for a diagnosis of vascular obstruction. The detection of a temperature boundary is significant in the diagnosis of embolism.
2. With the Doppler stethoscope (picture 1), find the pulse sounds of the posterior tibial artery behind the medial malleolus, and the dorsal artery on top of the foot. The sound is best located by moving the sensor of the Doppler stethoscope slowly across the direction of the artery; if the pulsation is weak, the probe should be moved very slowly. Occasionally, instead of the dorsal artery it is easier to hear the lateral tarsal artery, which is more laterally situated. The quality of the sound itself will point to a possible occlusion.
   • Normally, the sound is as sharp as a whipslash and has at least two phases (first a rapid forward flow, then a short backflow caused by the elasticity of the artery; video Normal Pulse Sounds at Pen Doppler Examination). Often a third phase is also heard, in which the blood flows slowly forward during the diastole.
   • Below an arterial obstruction the flow sound is a soft hiss and has only one phase (collateral flow; video Measurement of Ankle Pressure and Abi).
   • If the obstruction is severe, the sound can be found only by searching carefully for it.
3. Place a sphygmomanometer cuff around the ankle. Increase the cuff pressure rapidly at first until the sound becomes weaker, and then very slowly until the sound disappears (video Normal Pulse Sounds at Pen Doppler Examination). When the pressure is slowly lowered, the sound becomes audible again. The latter pressure reading is the most exact measure of the systolic pressure. However, if the sound is very weak, the reappearance of the sound may be difficult to hear: in such cases the point where the sound disappears when the pressure is increased should be recorded as the systolic pressure. Auscultate both the posterior tibial artery (ATP) and the dorsal foot artery (ADP), and record the readings for both.
   • If the pressures in ADP and ATP differ, use the higher pressure reading for the assessment of circulation in the lower extremity. When assessing the patient's overall risk of general arterial disease, use the lower reading.
4. Measure the upper extremity pressure from both upper arms. Record the higher pressure reading. Auscultate the wrist for the pulse sound preferably with a Doppler stethoscope (measurement with an ordinary stethoscope is valid too).
   • ASO occurs in the left subclavian artery, but not on the right one. Therefore, the result of the right side is used for the determination of the pressure index. The left side measurement can be used to assess also ASO in the subclavian artery.
5. Calculate the pressure index (ABI, ankle-brachial index) = lower extremity/upper extremity pressure
   • Calculating the index is required in order to determine the extent of the obstruction and to monitor the condition (the ankle pressure will vary from one measurement to another, as will the blood pressure measured from the upper extremity).
6. If the aim of the diagnostics is merely to confirm or rule out an arterial obstruction and to determine its extent, the ankle and ABI measurement is sufficient. Segmental pressure measurement may be performed later within specialized care.

Interpretation

• If the ankle pressure is lower than the upper limb pressure (ABI < 0.9), there is a high likelihood of an arterial obstruction.
• Ankle pressure below 50 mmHg and an ulcer in the foot or pain at rest are signs of critical ischaemia, which requires urgent care.
• In about one third of diabetics, the inelasticity of vessel walls may cause too high readings in ankle pressure (ABI > 1.3).
  • The absence of a two-phase pulse sound suggest an obstruction.
  • In such a case, the ankle pressure can be estimated by elevating the leg and simultaneously observing the moment when the flow sound disappears (the pole test). A height difference of one centimetre from the level of the heart is equivalent to 0.75 mmHg in ankle pressure.
  • If symptoms suggesting an occlusive arterial disease, a one-phased pulse sound or ABI < 0.9 are found in a diabetic patient with a foot ulcer, he/she should be referred to specialized care for vascular surgical evaluation.
  • Toe-brachial index (TBI) < 0.7 is suggestive of ischaemia. The measurement can be used for differential diagnosis when the ABI is high and ischaemia is suspected.
• ABI < 0.9 or > 1.3 suggests an increase in the overall cardiovascular risk and is an indication to check the patient's risk factors for arterial diseases, to lifestyle counselling and, if needed, to start medication to prevent clinical arterial disease.