A pulsometer (often mistakenly referred to as a "pulse oximeter" when concerning medical devices) measures heart rate, but the way modern medical pulse oximeters measure oxygen saturation is by shining red and infrared light through the skin and determining how much of each is absorbed. This absorption rate reveals the ratio of oxygenated hemoglobin to deoxygenated hemoglobin in the blood.
Here's a more detailed breakdown:
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Light Emission: The device emits two wavelengths of light: red light (around 660 nm) and infrared light (around 940 nm).
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Absorption Differences: Oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) absorb these wavelengths differently.
- Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through.
- Deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through.
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Detection and Calculation: A photodetector on the opposite side of the light source measures the amount of red and infrared light that passes through the tissue (usually a finger or earlobe). The device then calculates the ratio of the absorption of red light to the absorption of infrared light.
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Oxygen Saturation Determination: This ratio is then used to estimate the percentage of oxygen saturation (SpO2). The SpO2 value represents the percentage of hemoglobin in the blood that is carrying oxygen. The device uses a pre-programmed algorithm based on empirical data to convert the light absorption ratio into an SpO2 value.
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Display: The pulsometer then displays the SpO2 value (oxygen saturation percentage) and often the pulse rate (heart rate) on its screen.
Key Components and Processes:
| Component | Function |
|---|---|
| Red Light Emitter | Emits red light at approximately 660 nm. |
| Infrared Emitter | Emits infrared light at approximately 940 nm. |
| Photodetector | Measures the amount of red and infrared light that passes through tissue. |
| Microprocessor | Calculates SpO2 and pulse rate based on light absorption ratios. |
| Display | Shows SpO2 and pulse rate. |
In summary, a modern pulse oximeter leverages the different light absorption properties of oxygenated and deoxygenated hemoglobin to non-invasively estimate arterial oxygen saturation. The device measures the amount of red and infrared light that passes through a vascular bed, then applies an algorithm to compute the SpO2.
