| 摘要 |
A non-invasive method for determining the absolute level of oxygen saturation in blood in deep tissue including the steps of irradiating a target area of tissue with radiation of at least two distinct wavelengths at rest and after voluntarily hydrostatically perturbating the venous blood volume in the target tissue, providing a first set of signals that represents the absorption of the radiation at each wavelength at rest and a second set of signals that represents the absorption of the radiation at each wavelength after perturbation of the blood, subtracting the first set of signals from the second set of signals to provide a difference signal for each wavelength that represents the venous blood volume change as a consequence of the perturbation, and determining the ratio of the difference signals and comparing that ratio with the ratio determined in vitro to provide the absolute level of blood oxygen concentration. The method is carried out using a spectrometer (40) having three transmitting optodes (41, 42, 43) and a receiving optode (44).
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