Development of a temperature-controlled miniature enclosure for monitoring poor perfusion photoplethysmographic signals

A major issue in most optical-based physiological measurements is the effect of temperature fluctuations on the reliability of the acquired data. Studies have suggested that waveforms obtained from the photoplethysmography (PPG) method are temperature sensitive. The conventional approach to tackle these temperature induced variations is to post-signal process the waveforms in the hope of optimizing them to a minimum level for signal pattern and recognition. However, it is known such an approach may alter the PPG characteristics which can be used to identify the pathogenesis and/or pathophysiology of peripheral vascular diseases. Thus, appropriate temperature settings can then facilitate prolonged comparative clinical studies and minimize pathogenic survivability. In this study, a miniature enclosure with a temperature-control feature is proposed to enhance PPG acquisition in a more consistent environment. Eight healthy adults (six male; 26.4 +/- 3.0 yr) were recruited to perform three different test trials to assess the usefulness of the proposed system. The obtained results indicated that without the activation of the temperature-control feature, PPG characteristics acquired from cold fingers can be compromised. Conversely, improvements can be observed when the temperature feature was activated. Hence, the findings herein suggest that this system can be a valuable tool in acquiring PPG waveforms from poorly perfused fingers.