Taking it Further

There are many ways in which you can develop your pulse oximeter. There are some ideas below that you may wish to consider, but you may also wish to identify your own areas for development and improvement based on your experience and interests.

  1. Other Physiological Parameters: Fundamentally, photoplethysmography (PPG) detects blood volume changes in the microvascular bed of tissue. Whilst it is commonly employed to measure oxygen saturation it can also be used to monitor other physiological parameters such as heart rate, heart rate variation, respiratory rate, and blood pressure. You could see which other parameters you can measure by adding additional signal processing and analysis. How might you validate these measurements?

  2. Optical Shielding: You will no doubt have observed that PPG is sensitive to motion and to ambient light conditions. Ambient light that is incident upon the phototransistor will effect the measurement of the true reflected light from the microvascular bed of tissue, in extreme cases the ambient light may saturate the phototransistor entirely. You may wish to develop different shielding approaches that minimise the amount of ambient light.

  3. Pressure Sensitivity: PPG requires that good physical contact is maintained between the optical sensor package and the surface of the skin, if this contact is time-varying then it will modulate the observed optical properties of the tissue and thus the resulting physiological measurements. The magnitude of the pressure applied to the microvascular bed of tissue is also important, if this pressure is too great then the vessels may become occluded, if the pressure is too low then the contact will be poor and ambient light may spoil the measurement. You could explore different mechanical designs for obtaining and maintaining optimal contact pressure.

  4. Signal Processing: Where possible one ought to maximise the signal quality at the point of measurement (e.g. via optical shielding or contact pressure). However, it is often the case that signal processing, in the form of averaging, smoothing, or filtering may be required to further improve signal quality or stability. You could develop a signal processing pipeline that further improves the signal quality obtained from your pulse oximeter.

  5. Visualisation: The Organic Light Emitting Diode (OLED) screen fitted to your pulse oximeter is typical of that used for portable finger-worn devices, however it has a limited screen size and can only show a subset of information about the measurements being made. You could explore how to augment or develop the data visualisation - what is the optimal design for presenting complex physiological measurements?

Citations