Diagnostic Performance of Photoplethysmography (PPG) for Early Vascular Compromise in a Customisable In Vitro Flap Model

Background Free flap reconstruction is a cornerstone of plastic surgery, yet vascular thrombosis, a blockage of the supporting blood vessels,(3%–5% incidence) requires early detection for salvage. Traditional clinical assessment is subjective and labour-intensive, driving the need for reliable monitoring. Photoplethysmography (PPG), a non-invasive, continuous optical sensing technology monitoring vascular volume, is highly suited for this purpose. Methods This study investigated PPG's diagnostic capability for early vascular changes utilising a custom silicone phantom as a test-bed. Vessels were fabricated to mimic human arterial and venous mechanics (compliance, ΔCSA) and embedded at depths of 3,9,15, and 21 mm. A perfusion system simulated normal, early ischemic (low arterial pressure), and early congested (high venous pressure) states. Signals were analysed using 34 pulse-wave features. Results Analysis of the diagnostic performance (AUC > 0.70) showed that PPG (IR) could successfully diagnose ischemia up to a depth of 21 mm and congestion up to 15 mm. The system was able to successfully distinguish between ischemia and congestion at all depths. Conclusion This research confirms that specific PPG features are discernible indicators of early blood flow changes. The high diagnostic accuracy achieved in this in vitro model establishes PPG as a robust platform for developing future continuous and objective free flap monitoring systems.