Optical determination of blood perfusion and similar parameters
First Claim
1. A method for measuring at least one physiological parameter of tissue by means of a semiconductor light source and of a light detector, wherein said parameter affects concentration of blood constituents, in particular different forms of hemoglobin, said method comprising the steps ofa) placing said light source and said light detector such that said light detector measures an amount of light transmitted from said light source through said tissue,b) operating said light source under a first condition where it has a first temperature, and determining a first light attenuation signal by means of said light detector,c) operating said light source under a second condition where it has a second temperature different from the first temperature, and determining a second light attenuation signal by means of said light detector,d) determining said parameter using said first light attenuation signal and said second light attenuation signal,wherein said method further comprises the step of varying a current through said light source in order to create said different operating conditions by switching said current from a first level to a second, different level and determining at least part of said attenuation signals at different times after switching said current while said light source has not yet reached thermal equilibrium.
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Abstract
A parameter affecting the absorptivity or the concentration of blood in tissue is measured using a semiconductor light source (7) and a light detector (8). The semiconductor light source (7) is operated at several operating conditions, at which it has different temperatures and therefore different emission spectra. In particular, the operating conditions correspond to different time intervals after switching the light source (7) on, while the light source (7) has not yet reached thermal equilibrium. This allows to perform a spectroscopic measurement using one light source only, which increases accuracy and reduces device cost.
22 Citations
18 Claims
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1. A method for measuring at least one physiological parameter of tissue by means of a semiconductor light source and of a light detector, wherein said parameter affects concentration of blood constituents, in particular different forms of hemoglobin, said method comprising the steps of
a) placing said light source and said light detector such that said light detector measures an amount of light transmitted from said light source through said tissue, b) operating said light source under a first condition where it has a first temperature, and determining a first light attenuation signal by means of said light detector, c) operating said light source under a second condition where it has a second temperature different from the first temperature, and determining a second light attenuation signal by means of said light detector, d) determining said parameter using said first light attenuation signal and said second light attenuation signal, wherein said method further comprises the step of varying a current through said light source in order to create said different operating conditions by switching said current from a first level to a second, different level and determining at least part of said attenuation signals at different times after switching said current while said light source has not yet reached thermal equilibrium.
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17. A device for measuring in-vivo at least one physiological parameter of tissue comprising
a housing configured to be placed against said tissue, a semiconductor light source arranged in said housing, a light detector positioned to measure light transmitted from said light source transmitted through said tissue, a control unit for operating said light source under a first condition where it has a first temperature, and determining a first attenuation signal by means of said light detector, operating said light source under a second condition where it has a second temperature different from the first temperature, and determining a second attenuation signal by means of said light detector, determining said parameter using said first signal and said second attenuation signal, wherein said device is adapted to vary a current through said light source in order to create said different operating conditions by switching said current from a first level to a second, different level and determining at least part of said attenuation signals at different times after switching said current while said light source has not yet reached thermal equilibrium.
Specification