Reliability and repeatability of toe pressures measured with laser Doppler and portable and stationary photoplethysmography devices.

BACKGROUND

There are two principally different methods for measuring toe pressures (TP)-photoplethysmography (PPG) and laser Doppler (LD). PPG is based on detecting changes in the blood filling of the digital arteries and arterioles, and the LD perfusion signal is derived from the Doppler shift undergone by the emitted infrared laser light after reflection from moving particles (red blood cells). The aim of the study was to compare two PPG devices and one LD device in TP measurement. The PPG devices used were the Nicolet VasoGuard (Nicolet Vascular Inc, Madison, WI; PPG1) and Systoe (Atys Medical, France; PPG2), and the LD device was the Perimed system 5000 (Perimed, Stockholm, Sweden).

MATERIALS AND METHODS

TPs were measured from 54 nonselected consecutive patients who visited the vascular surgical outpatient clinic or underwent an endovascular procedure owing to chronic lower limb ischemia. A total of 107 toes were measured. The symptoms were claudication in 51.4% (n = 55), rest pain in 4.7% (n = 5), and ulcer or gangrene in 14.0% (n = 15) of the legs. Of the measured legs, 29.9% (n = 32) were asymptomatic. Forty patients had undergone endovascular revascularization immediately before the TP measurement. The limits of agreement show the estimated range within which the differences between measurements by the two devices would fall in approximately 95% of the measurements. The approximate 95% limits of agreement were calculated as the mean difference ± 2 standard deviation and presented in the Bland-Altman scatter plots.

RESULTS

For PPG1 versus LD, the mean difference between two measurements was 14 mm Hg and the limits of agreement were 38 mm Hg. In 47% of the toes, the difference was ≥10 mm Hg, and in 37% of the toes, it was ≥15 mm Hg. For PPG2 versus LD, the mean difference between the TPs was 12 mm Hg and the limits of agreement were 24 mm Hg. In 44% of the cases, the difference was ≥10 mm Hg, and in 30%, it was ≥15 mm Hg. For PPG1 versus PPG2, the mean difference between two measurements was 14 mm Hg and the limits of agreement were 24 mm Hg. In 50% of the cases, the difference between the two machines was ≥10 mm Hg, and in 33%, it was ≥15 mm Hg. Repeatability measured with LD, PPG1, and PPG2 showed that the difference between the first and second measurement was <10 mm Hg in 93%, 86%, and 78% of the cases, respectively, and <15 mm Hg in 98%, 94%, and 88% of the cases, respectively.

CONCLUSIONS

TP values vary greatly depending on the device used. However, the repeatability seemed to be acceptable with LD and PPG1. We recommend using same device when circulation is repeatedly assessed in the same patient. Also, we emphasize the importance of clinical examination and low threshold for angiography and revascularization especially in diabetics with wound healing problems.