Nuffield Departnent of Surgery, John Radcliffe Hospital,. Headington, Oxford OX3 9DU this correlates reasonably well with the clinical severity of. PAOD (2).
Ann R Coll Surg Engl 1998; 80: 96-98
Photoplethysmography can replace hand-held Doppler in the measurement anklelbrachial indices M S Whiteley FRCS(Gen) FRCSEd
M Horrocks MS FRCS
Hon Lecturer in Surgery
Professor of Surgery
of
A D Fox MB BS FRCS* Research Registrar in Surgery
Department of Surgery, Royal United Hospital, Bath
Key words: Photoplethysmography (PPG); Pressure indices (ABPI); Peripheral vascular disease
Ankle/brachial pressure index (ABPI) using handheld Doppler and sphygmomanometer is a standard assessment for patients with peripheral arterial occlusive disease (PAOD). Good Doppler technique is difficult to master and so we investigated replacing Doppler with photoplethysmography (PPG). Two investigators examined 52 legs in 32 vascular patients. Both used standard sphygmomanometer cuff occlusion. Restoration of flow was detected by either an 8 MHz Doppler ultrasound probe or a PPG transmitter/receiver on index finger or great toe. Doppler-derived ABPIs were compared with PPGderived ABPIs. Excellent correlation was found between both indices (correlation coefficient 0.875). Four lower limbs had unrecordable PPG traces, one also having an unrecordable Doppler signal. Excluding these four patients, the correlation coefficient rose to 0.975. PPG placed on the pulp of a digit can replace the hand-held Doppler in measuring ABPIs.
Non-invasive blood pressure measurements using a sphygmomanometer and a hand-held Doppler, have become the first line non-invasive assessment of peripheral artery occlusive disease (PAOD) (1). Measured this way, ankle pressure divided by the brachial pressure is termed the ankle/brachial pressure index (ABPI) and *Present
appointnent: Specialist Registrar,
Nuffield Depart-
ment of Surgery, John Radcliffe Hospital, Oxford Correspondence to: M S Whiteley, Clinical Lecturer in Surgery,
Nuffield Departnent of Surgery, John Radcliffe Hospital, Headington, Oxford OX3 9DU
this correlates reasonably well with the clinical severity of PAOD (2). The APBI has a 15% variability among trained personnel and double this variability in the untrained (3). Using hand-held Doppler requires both anatomical knowledge of the relevant arteries and a basic understanding of Doppler technique to ensure an appropriate angle of insonation. To simplify this technique we investigated substituting photoplethysmography (PPG) for the hand-held Doppler, as an indicator of flow restoration.
Patients and methods Thirty-two patients with PAOD on a vascular ward were studied; seven were diet-controlled diabetics. Fifty-two lower limbs were assessed, 12 were not (five lower limb amputation; four local toe/forefoot amputation; three other factors, eg ulceration, dressings). Both investigators were vascular trainees and were blinded to each other's results. Each patient was rested supine for 5 min. Arterial occlusion was standard for both investigators-a sphygmomanometer cuff at the upper arm and between the calf and ankle. Restoration of flow was detected by: Investigator 1. An 8 MHz hand-held Doppler probe (Handidop, SciMed, Bristol, UK) insonating the brachial artery within the cubital fossa and both posterior and anterior tibial arteries at the ankle. Investigator 2. A PPG transmitter/receiver (PVL-50, Sci-Med, Bristol, UK) taped to the pulp of the relevant
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Dop-ABPI Figure 1. Graph of Doppler-derived ankle/brachial pressure index (Dop/ABPI) versus photoplethysmographic-derived ankle/brachial pressure index (PPG/ABPI).
index finger or hallux and covered with black velvet to decrease background light.
Four legs had unrecordable PPG waveforms owing to severe ischaemia. Only one had unrecordable Doppler signals. The Doppler-derived ABPI was plotted against the PPG-derived ABPI (Fig. 1) and results from all 52 limbs show an excellent correlation (coefficient 0.875). Excluding the four limbs with unrecordable PPG traces (including the one with unrecordable Doppler signal), the correlation improved to an almost perfect match (coefficient 0.975). There was no difference between diabetics and non-diabetics.
pressure by Doppler-derived brachial pressure gives a 'toe index' (8). The 'toe index' differs significantly from the Doppler-derived ABPI, although there is a correlation between the two (8). We have not measured digital pressures as our wish was merely to simplify the technique of measuring ABPIs. As diabetics may have incompressible calf and ankle vessels that resist the cuff occlusion, there is unlikely to be any advantage to PPG over Doppler. In view of the excellent correlation between PPGderived APBIs and Doppler-derived ABPIs, we suggest that this technique can replace the traditional Dopplerbased method. Further advantages of this method include the ease of PPG attachment and there being no requirement of anatomical knowledge of the distal vessels. Further, the use of PPG in this way opens the way for a fully automated system for measuring ABPIs.
Discussion
References
PPG is based on a light-emitting diode (LED) that transmits and receives back-scattered infrared light from moving erythrocytes. The transmitter/receiver unit is small with a 'footprint' of less than 1 cm2. This, in addition to the pulp of the digit producing the best signal (4), makes PPG ideal as a sensor of digital perfusion. The PPG waveform has been used to assess PAOD (5), but in combination with a digital tourniquet, digital pressures produce reasonable assessments of severe ischaemia (6). These can be used as a guide to the healing of forefoot amputation (7). Division of digital
I Baker JD, Dix DE. Variability of Doppler ankle pressures with arterial occlusive disease: an evaluation of ankle index and brachial-ankle pressure gradient. Surgery 1981; 89: 134-7. 2 Anderstr6m C, Hallbook T. Resting blood pressure index in arterial occlusive disease of the lower limbs. Scand J Thorac Cardivasc Surg 1979; 13: 143-6. 3 Ray SA, Srodon PD, Taylor RS, Dormandy JA. Reliability of ankle:brachial pressure index measurement by junior doctors. Br J Surg 1994; 81: 188-90. 4 Kamal AAR, Harness JB, Irving G, Mearns AJ. Skin photoplethysmography-a review. Comput Methods and Programs Biomed 1989; 28: 257-69.
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5 Oliva I, Roztocil K. Toe pulse wave analysis in obliterating atherosclerosis. Angiology 1983; 34: 610-19. 6 McCollum PT, Stanley ST, Kent P, Grouden MC, Moore Di, Shaniek GD. Assessment of arterial disease using digital systolic pressure measurement. Ann Vasc Surg 1988; 2: 34951. 7 Bone GE, Pomajzl MJ. Toe blood pressure by photoplethys-
mography: an index of healing in forefoot amputation. Surgery 1981; 89: 569-74. 8 Duprez D, Missault L, ban Wassenhove A, Clement DL. Comparison between ankle and toe index in patients with peripheral arterial disease. Int Angiol 1987; 6: 295-7. Received 23 October 1997
