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Medical Applications
Fast Oxygen Gas Sensor
Medical oxygraphy measures the oxygen respiration waveform breath-by-breath giving a qualitative indication of ventilation and cardiac output. Falling end-tidal oxygen levels indicate insufficient oxygen ventilation. Using oxygraphy together with spirometry and capnography, metabolic rates and nutritional substrate analysis can be calculated. |
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Why is Medical Oxygraphy Important?
- Interruption of oxygen respiration can be detected by oxygraphy well before being detected by blood oximetry because of circulation delays and because of the flat slope of the oxygen dissociation curve at high hemoglobin saturation.
- Falling end-tidal oxygen levels during ventilation indicate oxygen supply is not meeting demand even though end-tidal CO2 levels are constant. This can be true because the FIO2 - FETO2 difference or physiologic oxygen extraction may be sufficient metabolically while the available oxygen is being extracted or lost from the ventilation circuit.
- Oxygraphy may prove to be helpful in induction and cessation of ventilation and anesthesia.
- Oxygraphy or oxygen uptake may prove useful as a qualitative indicator of cardiac output in cardio-pulmonary resuscitation.
- Oxygraphy or oxygen uptake may prove helpful as an indicator of upper airway resistance in sleep disordered breathing.
How Does the Oxigraf Sensor Work?
- The patented Oxigraf sensor uses laser diode absorption spectroscopy in the visible spectrum, similar to the absorption method used to measure CO2, N2O, and anesthetic agents in the infrared spectrum.
- However, oxygen absorption is in a region of the visible spectrum (760 nm) where there is no interference or absorption by other ventilation or anesthetic gases.
- Also the emission line width of the laser and the absorption line width of O2 are very narrow, less than 0.01 nm, compared to perhaps 100 nm for the CO2 absorption band at atmospheric pressure.
- The spectrally pure laser is thermally tuned precisely to the oxygen absorption line.
- As the oxygen concentration increases, the light intensity is attenuated, and the photodetector response varies linearly
with the oxygen concentration.
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