Pulse oximeter
First Claim
1. A method for controlling optical power in a monitoring device intended for determining the amount of at least one light absorbing substance in a subject, the monitoring device comprising emitters for emitting radiation at a minimum of two wavelengths, driving means for activating said emitters, and a detector for receiving said radiation at said wavelengths and for producing an electrical signal in response to the radiation, the method comprising the steps of supplying driving pulses from said driving means to the emitters, the pulses having predetermined characteristics determining the optical power of the device, demodulating the electrical signal originating from said detector, whereby a baseband signal is obtained, monitoring a signal-to-noise ratio of the baseband signal, and controlling the duty cycle of the driving pulses in dependence on the monitored signal-to-noise ratio.
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Accused Products
Abstract
The invention relates to pulsed oximeters used to measure blood oxygenation. The current trend towards mobile oximeters has brought the problem of how to minimize power consumption without compromising on the performance of the device. To tackle this problem, the present invention provides a method for controlling optical power in a pulse oximeter. The signal-to-noise ratio of the received baseband signal is monitored,and the duty cycle of the driving pulses is controlled in dependence on the monitored signal-to-noise ratio, preferably so that the optical power is minimized within the confines of a predetermined lower threshold set for the signal-to-noise ratio. In this way the optical power is made dependent on the perfusion level of the subject, whereby the power can be controlled to a level which does not exceed that needed for the subject.
105 Citations
16 Claims
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1. A method for controlling optical power in a monitoring device intended for determining the amount of at least one light absorbing substance in a subject, the monitoring device comprising
emitters for emitting radiation at a minimum of two wavelengths, driving means for activating said emitters, and a detector for receiving said radiation at said wavelengths and for producing an electrical signal in response to the radiation, the method comprising the steps of supplying driving pulses from said driving means to the emitters, the pulses having predetermined characteristics determining the optical power of the device, demodulating the electrical signal originating from said detector, whereby a baseband signal is obtained, monitoring a signal-to-noise ratio of the baseband signal, and controlling the duty cycle of the driving pulses in dependence on the monitored signal-to-noise ratio.
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12. An apparatus for non-invasively determining the amount of at least one light absorbing substance in a subject, the apparatus comprising
emitters for emitting radiation at a minimum of two different wavelengths, driving means for activating said emitters, adapted to supply driving pulses to the emitters, the pulses having predetermined characteristics determining current optical power of the device, a detector for receiving said radiation at said wavelengths and producing an electrical signal in response to the radiation, a demodulator unit for demodulating the electrical signal originating from said detector, whereby a baseband signal is obtained from the demodulator unit, monitoring means for monitoring signal-to-noise ratio of the baseband signal, and power control means, responsive to the monitoring means, for controlling the duty cycle of the driving pulses.
Specification