Reliability of a portable toe pressure photoplethysmography device compared to a stationary laser doppler flowmeter.

Objective: The study aimed to investigate the reliability of a portable toe pressure (TP) photoplethysmography device (PPG) by comparing it to a stationary laser Doppler flowmeter (LD) used in the Helsinki University Hospital. The study evaluated if lower limb arterial circulation could be reliably evaluated with the portable PPG which is more affordable and mobile than the stationary LD.

Methods: TPs were measured from 102 toes of 54 patients in the vascular surgery outpatient clinic, vascular surgery ward and interventional radiology recovery ward of Helsinki University Hospital. According to the study protocol TPs were measured twice with the PPG device. If the difference between the values was over 10 mmHg, a third measurement was done and two of the closest values were selected for the final analysis. The lowest value displayed by the PPG device was 30 mmHg. Lower than 30 mmHg values were reported as 25 mmHg in the analysis. The repeatability and reliability of the PPG measurements were compared to the LD with Bland Altman plots.

Results: Most patients had rest pain (n = 29) or claudication (n = 9). Prior to TP measurement, 24 patients had undergone lower limb revascularization through either a hybrid (n = 3), open (n = 10) or endovascular (n = 11) procedure. The mean absolute difference between PPG and LD measurement values was 15 mmHg (95% confidence interval 12-18 mmHg). 87.5% of lower limbs with significant arterial insufficiency (TP <60 mmHg with LD, n = 49) had a PPG measurement value of <60 mmHg. Conversely, 84.8% of lower limbs that did not exceed the ischemia criterion of TP ≥60 mmHg with LD had a PPG measurement value of ≥60 mmHg. Mean absolute difference of two consecutive PPG measurement values was 4 mmHg (95% CI 3-5 mmHg).

Conclusions: The PPG device is a light and affordable option for the assessment of lower limb arterial circulation in primary health care. It is moderately reliable to exclude significant lower limb arterial insufficiency and may reduce unnecessary referrals to the vascular surgery clinic. The repeatability of the PPG device is satisfactory. However, it requires training to use, and the results must always be interpreted with consideration for the patient's clinical status.