Smartphone-based photoplethysmographic applications for assessing finger perfusion insufficiency

In prehospital trauma situations, rapid assessment of distal limb perfusion is crucial. This urgency led us to investigate a practical and user-friendly approach for screening distal perfusion. Considering the widespread use of smartphones, we evaluated the potential use of smartphone applications (apps) as tools for screening ischemic limbs. An artificial ischemic model was established using data collected through a pneumatic tourniquet system tied to the arms of 40 healthy participants. After obtaining baseline systolic arterial pressure (SAP), we rounded the number up and down from the baseline SAP to the nearest 10; the higher value was represented by (+10) occlusive pressure, further increasing to (+20) and (+30), whereas the lower value was represented by (-10) occlusive pressure, then further decreased to (-20) and (-30). Occlusive pressure was applied at 10 mm Hg intervals, from (-30) to (+30), according to each subject's baseline SAP. We further compared performance between 2 smartphone apps (RhythmCam and Cardiio) and 4 established clinical assessment methods: capillary refill time (CRT), distal arterial pulse palpation, pulse oximetry, and Doppler ultrasound. All 6 assessment methods exhibited a decline in the percentage of positive results as the applied occlusive pressure varied from (-10) to (+10). Except for CRT, all other methods exhibited significant differences between the results obtained at (+10) occlusive pressure setting and those obtained at (-10) pressure setting. High sensitivity ensures that the test can accurately detect most cases of circulation insufficiency within an occlusive pressure range of (+10) and (-10) pressure settings. Despite the errors in the smartphone apps, their accuracy remained favorable (Cardiio: 92.5%; RhythmCam: 96.1%). Both apps exhibited performance comparable to that of 2 clinically well-known methods (palpation of distal pulse and Doppler ultrasound) and even outperformed 2 other methods (pulse oximetry and CRT). Our findings suggest that photoplethysmographic signal-based smartphone apps, such as RhythmCam and Cardiio, hold promise as screening tools. These apps can enable users without a health-care professional background to effectively assess the urgency of prehospital traumatic limb scenarios. Additional studies are warranted to determine the full potential of smartphone apps in clinical scenarios.