Building a Pulse Oximeter
Introduction
Pulse oximetry is a non-invasive medical diagnostic technique used to measure a persons oxygen saturation.
In medicine, oxygen saturation (SaO~2), measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen. A puse oximeter relies on the light absorption characteristics of oxygenated/deoxygenated hemoglobin based on an oxygen-hemoglobin dissociation curve represented by the following formula.
Deoxygenated (or reduced) hemoglobin absorbs more red light and allows more infrared light to pass through. Red light is in the 600-750 nm wavelength light band. Infrared light is in the 850-1000 nm wavelength light band.
Photodiode Characteristics
- Absoption: 627-946mm
- Issues: 628nm
Medical significance
Effects of Oxygen Saturation
| SaO2 | Effect |
|---|---|
| 85% and above | No evidence of impairment |
| 65% and less | Impaired mental function on average |
| 55% and less | Loss of consciousness on average |
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