Methods in vogue for the measurement of venous refilling time (VRT), based on the photo-plethysmographic (PPG) principle, employ a feedback compensation technique to remove the influence of the colour of a patient's skin. Hence these methods require a “standardization phase” for every measurement. Based on an appropriate model for the propagation of light through skin and tissue, a novel signal processing method is proposed for the measurement of VRT. The proposed technique renders the measurement of VRT independent of not only the colour of the skin of a patient but also of source intensity and detector sensitivity. Test results obtained from a prototype unit, built under the LabVIEW virtual environment, establish the validity of the model and the proposed signal processing technique.
Dr. Madhu Mohan N., Mariappan, L., and V. Kumar, J., “A novel signal processing method for the measurement of venous refilling time”, in 2009 IEEE Instrumentation and Measurement Technology Conference, 2009.