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01-12-2012 | Research | Uitgave 1/2012 Open Access

Journal of Foot and Ankle Research 1/2012

Interrater and intrarater reliability of photoplethysmography for measuring toe blood pressure and toe-brachial index in people with diabetes mellitus

Journal of Foot and Ankle Research > Uitgave 1/2012
Christopher Scanlon, Kris Park, David Mapletoft, Lindy Begg, Joshua Burns
Belangrijke opmerkingen

Competing interests

The research activities of JB are funded by grants from the NHMRC (National Health and Medical Research Council of Australia, Fellowship #1007569 and Centre of Research Excellence #1031893), NIH (National Institutes of Neurological Disorders and Stroke and Office of Rare Diseases, #U54NS065712), Australian Podiatry Education and Research Foundation, Podiatry Council of New South Wales, Charcot Marie Tooth Association, Muscular Dystrophy Association, CMT Association of Australia. The other authors declare that they have no competing interests.

Authors' contributions

CS participated in the design of the study, secured funding, carried out data collection, contributed to statistical analysis as well as writing and reviewing of the manuscript. KP and LB participated in the design of the study and reviewed the manuscript. DM participated in the design of the study, carried out data collection, and reviewed the manuscript. JB participated in the design of the study, conducted statistical analysis, reviewed the manuscript and provided academic support. All authors reviewed and approved the final manuscript.



A reliable tool to measure arterial flow to the feet in people with diabetes is required given that they are particularly prone to peripheral arterial disease. Traditionally, the ankle brachial index (ABI) has been used to measure arterial circulation, but its application is limited due to calcification of larger arteries. More recently, toe pressure and the toe brachial index (TBI) has been suggested as superior to ABI measurements because they assess smaller digital arteries less prone to arterial calcification. However, reliability studies for the clinical use of photoplethysmography (PPG) in people with diabetes are lacking.


Sixty people with diabetes mellitus (35 males and 25 females, mean age 59.6 yrs) consented to take part in the study. The majority (92%) had type 2 diabetes and 8% had type 1 diabetes. Forty-three percent were diagnosed as having peripheral neuropathy when tested using a biothesiometer and 15% were current smokers (10 – 40/day). A podiatrist and a diabetes educator measured toe and brachial blood pressure independently and in a random order using PPG. These measurements were repeated again seven days later, and subsequently analysed with intraclass correlation coefficients (ICC), 95% confidence intervals (CI) and standard error of measurement (SEM).


The intrarater reliability of measuring toe pressures was excellent (ICC3,1 =0.78-0.79, SEM 8 mmHg) and interrater reliability was also excellent (ICC2,2 = 0.93, SEM 4 mmHg). The intrarater reliability for measuring brachial pressures was generally poor (ICC3,1 = 0.40 – 0.42, SEM 19 mmHg) and interrater reliability was fair-good (ICC2,2. 0.65, SEM 14 mmHg). The TBI intrarater reliability was fair-good (ICC3,1 = 0.51-0.72, SEM 0.08), whilst the interrater reliability of TBI was excellent (ICC2,2 = 0.85, SEM 0.07).


Based on these results, interrater and intrarater reliability of PPG is excellent for measuring toe blood pressure, good for TBI and only fair for brachial pressures in people with diabetes mellitus.

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