Peripheral Artery Disease (PAD) is one of the vascular diseases which are often asymptomatic, with studies suggesting that up to 40 % of individuals with PAD have no symptoms, about 50 % have symptoms that could be attributed to other medical conditions and only 10 % have classical PAD symptoms[1, 2]. One method of identifying undiagnosed PAD is measuring Ankle-Brachial Index (ABI).
The ABI represents the ratio of blood pressure at the ankle to blood pressure in the upper arm, known in medical parlance as brachium, hence the name ABI. Calculations use the systolic (maximum pressure during one heartbeat) value of blood pressure, which is measured on both the left and right arm and at both ankles.
In other words, the measurement shows how well blood flows through the arteries in the legs, which is outwardly observed as a slightly higher blood pressure at the ankles than in the arms. This is true in healthy individuals, while the ABI for those with PAD tells a different story.
Besides observing aforementioned symptoms which can also be present in other, non-PAD related medical conditions, the best way of detecting PAD is by taking an ABI measurement. ABI is one of the most important diagnostic tools for PAD, not least due to its non-invasive nature and cost-effectiveness. It is also valuable for assessing general cardiovascular fitness, since studies have shown that low ABI (≤ 0.90) is associated with about a four-fold increase of cardiovascular death in men and a three-fold increase in women (in comparison with individuals with healthy ABI over a 10-year period) respectively[3].
The biggest ‘selling point’ from the patient’s perspective, diagnostic value and cost-effectiveness aside, is of course the non-invasiveness of the measuring procedure in comparison with other methods such as angiography, which entails the injection, and subsequent X-ray imaging, of a special dye (contrast medium) into the bloodstream through a catheter. Another advantage is the straightforward nature of the procedure, which does not require any special preparation on the part of the patient, and the speed of its execution. There are significant differences between the established methods of measuring ABI in this regard.
Doppler method
The Doppler method involves the use of a sphygmomanometer (blood pressure meter) and a Doppler wand (a device that uses ultrasound to detect the flow of blood through the blood vessels). This requires the patient to be examined in the supine position (lying on his/her back on a flat table/surface). The examiner places the inflatable cuff of the meter in proximal to the brachial artery (upper arm) or the posterior tibial and dorsalis pedis arteries (lower leg, above the ankle) and starts inflating it until the pulse can no longer be detected with the Doppler wand in the examined artery.
The pressure cuff is then slowly deflated until the pulse is re-detected with the wand, at which point the examiner takes a measurement of the blood pressure (systolic value). The procedure is then repeated on the remaining limbs for a total of two arm and two leg (on the same leg, each artery separately) measurements. The examiner then compares the results on each arm and notes the higher blood pressure value and takes the higher value of (the two) measurements at the tibial and dorsalis pedis arteries and manually calculates the ABI value (on the basis of higher values) for the selected leg. This method, while accurate and reliable, has several drawbacks. The two most significant of these are accuracy issues when performed by an unskilled examiner and the time it takes to complete the whole procedure, which is usually about 30 minutes.
Oscillometric method (MESI ABPI MD®)
The oscillometric method is a relatively new method of measuring ABI, but has quickly established itself as superior to the Doppler method in many respects. The MESI ABPI MD®, the premiere oscillometric device for ABI measurement on the market is, for example, completely automatic and does not require special or extensive training to operate (only basic instruction into how a measurement is performed on a patient). It works on a different principle, utilizing 3 blood pressure cuffs which are placed on an arm and both legs and then automatically insufflated and desufflated in a specific sequential manner that elicits a specific response in the arterial pulse, which the machine then translates into ABI. This whole procedure takes only 1 minute. Thus the only similarity with the Doppler method is the requirement of placing the patient in a supine position.
This method is also significantly more inherently reliable than the Doppler method, since it virtually eliminates the possibility of human (examiner) error. The accuracy of the Doppler method is, on the other hand, relies upon an operator’s skill and (in)experience[4].
Furthermore, a recent study conducted in Italy has shown the superiority (time, no need for dedicated operators) of the MESI ABPI MD® device for large scale PAD screening in comparison to the Doppler method[5]. With more and more healthcare facilities adopting MESI ABPI MD®, more people will know their PAD status and, together with their physicians, undertake steps to avert any possible issues on the path to good health and general wellbeing.
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References:
[1] https://www.ncbi.nlm.nih.gov/pubmed/11560536?dopt=Abstract
[2] https://www.ncbi.nlm.nih.gov/pubmed/11585483?dopt=Abstract
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2932628/
[4] https://www.ejves.com/article/S1078-5884(99)90843-2/pdf
[5] http://www.heraldopenaccess.us/fulltext/Non-Invasive-Vascular-Investigation/Comparison-of-Ankle-Brachial-Index-ABI-Measurement-between-a-New-Oscillometric-Device-MESI-ABPI-Md-and-the-Standard-Doppler-Method.pdf
