Comparison of Transmissive and Reflective Photoplethysmography for Pulse Wave Recording and Pulse Variability Analysis

This article compares two approaches to photoplethysmographic recording: a transmissive clip sensor and a reflective sensor design typical of compact wearable devices. The main criterion is not whether a visible pulse wave can be obtained, but whether the recording is suitable for producing a reliable sequence of pulse-to-pulse intervals and for subsequent HRV/PRV calculation. The transmissive clip sensor fixes the finger mechanically and transfers data through USB, which provides a more stable primary signal. The reflective sensor, in its present implementation, is suitable for approximate pulse monitoring, but it should not be treated as a reliable instrument for scientific studies of pulse variability unless it has undergone additional validation, strict signal-quality control, artifact removal, and proven agreement with a reference method.