Pulse oximeter sensor off detector

• US 20040158135A1
• Filed: 02/09/2004
• Published: 08/12/2004
• Est. Priority Date: 08/07/1995
• Status: Active Grant

• Current Assignee: Nellcor Incorporated (Medtronic Plc)
• Original Assignee: Nellcor Incorporated (Medtronic Plc)
• Inventors: Yorkey, Thomas J., Baker, Clark R. Jr.
• Granted Patent: US 7,130,671 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: H03H 21/003 KALMAN filters

Abstract

A method and apparatus for reducing the effects of noise on a system for measuring physiological parameters, such as, for example, a pulse oximeter. The method and apparatus of the invention take into account the physical limitations on various physiological parameters being monitored when weighting and averaging a series of measurements. Varying weights are assigned different measurements, measurements are rejected, and the averaging period is adjusted according to the reliability of the measurements. Similarly, calculated values derived from analyzing the measurements are also assigned varying weights and averaged over adjustable periods. More specifically, a general class of filters such as, for example, Kalman filters, is employed in processing the measurements and calculated values. The filters use mathematical models which describe how the physiological parameters change in time, and how these parameters relate to measurement in a noisy environment. The filters adaptively modify a set of averaging weights to optimally estimate the physiological parameters.

Claims

1. A method for reducing noise effects in a system for measuring a physiological parameter, the method comprising the steps of:

generating a plurality of measurements derived from at least one wavelength of electromagnetic energy transmitted through living tissue;

comparing selected measurements with at least one expected measurement characteristic;

assigning one of a plurality of variable weights to each selected measurement based on the comparing step thereby generating a plurality of differently weighted measurements, the variable weights being assigned, in part, in response to a similarity between each selected measurement and a corresponding previous measurement, the variable weights comprising a plurality of different non-zero numbers; and

averaging a plurality of the differently weighted measurements to obtain a filtered measurement for use in estimating the physiological parameter.

2. A method for reducing noise effects in a system for measuring a physiological parameter, the method comprising the steps of:

generating a plurality of measurements corresponding to a series of cardiac pulses;

comparing each measurement with at least one expected measurement characteristic;

assigning a variable weight to each measurement based on the comparing step, thereby generating a plurality of differently weighted measurements; and

averaging a plurality of the differently weighted measurements from successive pulses to obtain a filtered measurement, each differently weighted measurement corresponding to a particular filtered measurement being similarly situated in a corresponding one of the successive pulses.

3. An apparatus for reducing noise effects in a system for measuring a physiological parameter, comprising:

means for generating a plurality of measurements corresponding to a series of cardiac pulses;

means for comparing each measurement with at least one expected measurement characteristic;

means for assigning a variable weight to each measurement based on the comparing step, thereby generating a plurality of differently weighted measurements; and

means for averaging a plurality of the differently weighted measurements from successive pulses to obtain a filtered measurement, each differently weighted measurement corresponding to a particular filtered measurement being similarly situated in a corresponding one of the successive pulses.

4. A method for reducing noise effects in a system for measuring a physiological parameter, the method comprising the steps of:

generating a plurality of measurements derived from one wavelength of electromagnetic energy transmitted through living tissue;

comparing selected measurements with at least one expected measurement characteristic;

assigning one of a plurality of variable weights to each selected measurement based on the comparing step thereby generating a plurality of differently weighted measurements, the plurality of variable weights comprising a plurality of different non-zero numbers; and

averaging a plurality of the differently weighted measurements to obtain a filtered measurement.

5. A method for reducing noise effects in a system for measuring a physiological parameter, the method comprising the steps of:

generating a plurality of time-based measurements which are not event driven, the time-based measurements being derived from at least one wavelength of electromagnetic energy transmitted through living tissue;

comparing selected time-based measurements with at least one expected measurement characteristic;

assigning one of a plurality of variable weights to each selected time-based measurement based on the comparing step thereby generating a plurality of differently weighted time-based measurements, the variable weights comprising a plurality of different non-zero numbers; and

averaging a plurality of the differently weighted time-based measurements to obtain a filtered time-based measurement.

6. An apparatus for reducing noise effects in a system for measuring a physiological parameter, comprising:

means for generating a plurality of time-based measurements which are not event driven, the time-based measurements being derived from at least one wavelength of electromagnetic energy transmitted through living tissue;

means for comparing selected time-based measurements with at least one expected measurement characteristic;

means for assigning one of a plurality of variable weights to each selected time-based measurement based on the comparing step thereby generating a plurality of differently weighted time-based measurements, the variable weights comprising a plurality of different non-zero numbers; and

means for averaging a plurality of the differently weighted time-based measurements to obtain a filtered time-based measurement.

7. A method for measuring a blood constituent using data comprising a single data set, the method comprising the steps of:

determining a plurality of possible blood constituent values using a plurality of blood constituent value calculators, each of the blood constituent value calculators using the single data set, each of the possible blood constituent values having a confidence level associated therewith based on at least one quality metric; and

arbitrating between the plurality of possible blood constituent values with regard to the confidence levels to determine a measure of the blood constituent.

8. An apparatus for measuring a blood constituent using a single data set, comprising:

means for determining a plurality of possible blood constituent values using a plurality of blood constituent value calculators, each of the blood constituent value calculators using the single data set, each of the possible blood constituent values having a confidence level associated therewith based on at least one quality metric; and

means for arbitrating between the plurality of possible blood constituent values with regard to the confidence levels to determine a measure of the blood constituent.

9. A method for generating a pulse rate of a patient using data corresponding to at least one wavelength of electromagnetic energy transmitted through tissue of the patient, the method comprising the steps of:

defining a comb filter to isolate signal energy in the data corresponding to a fundamental frequency and related higher frequency components thereof;

determining a particular frequency which optimizes energy at an output of the comb filter; and

generating a filtered pulse rate corresponding to the particular frequency.

10. An apparatus for generating a pulse rate of a patient using data corresponding to at least one wavelength of electromagnetic energy transmitted through tissue of the patient, comprising:

means for defining a comb filter to isolate signal energy in the data corresponding to a fundamental frequency and related higher frequency components thereof;

means for determining a particular frequency which optimizes energy at an output of the comb filter; and

means for generating a pulse rate corresponding to the particular frequency.

11. A method for determining a patient'"'"'s pulse rate using data comprising a single data set corresponding to energy transmitted through the tissue of a patient, the method comprising the steps of:

determining a plurality of possible pulse rates using a plurality of pulse rate finders, each of the pulse rate finders using the single data set, each of the possible pulse rates having a confidence level associated therewith based on at least one quality metric; and

arbitrating between the plurality of possible pulse rates with regard to the confidence levels to determine the patient'"'"'s pulse rate.

12. A method for determining a pulse rate of a patient using data corresponding to at least one wavelength of electromagnetic energy transmitted through tissue of the patient, the method comprising the steps of:

tracking a fundamental frequency using an adaptive comb filter to filter the data and to thereby generate a first pulse rate, the first pulse rate having a first confidence level associated therewith based on at least one quality metric;

comparing the data to a predetermined waveform template to generate a second pulse rate, the second pulse rate having a second confidence level associated therewith based on the at least one quality metric; and

arbitrating between the first and second pulse rates with regard to the first and second confidence levels to determine the patient'"'"'s pulse rate.

13. In a system for measuring a physiological parameter using at least one wavelength of electromagnetic energy transmitted through living tissue, a method for determining an operational status of the system comprising the steps of:

receiving a data signal from at least one sensor;

determining whether the received data signal is representative of the physiological parameter by sensing whether the at least one sensor is secured to the living tissue; and

generating a status signal representative of the operational status of the system based on the determining step.

14. An apparatus for reducing noise effects in a system for measuring a physiological parameter, comprising:

means for generating a plurality of measurements derived from at least one wavelength of electromagnetic energy transmitted through living tissue;

means for providing a signal indicative of the at least one wavelength of electromagnetic energy;

means for comparing selected measurements with at least one expected measurement characteristic;

means for assigning one of a plurality of variable weights to each selected measurement based on the comparing step thereby generating a plurality of differently weighted measurements for each wavelength, the variable weights being assigned, in part, in response to a similarity between each selected measurement and a corresponding previous measurement, the variable weights comprising a plurality of different non-zero numbers;

means for averaging a plurality of the differently weighted measurements to obtain a filtered measurement for use in estimating the physiological parameter; and

means for calibrating the system to measure the physiological parameter in response to the signal indicative of the at least one wavelength of electromagnetic energy.

15. A monitor for measuring a physiological parameter, the monitor being for use with a sensor having emitting means for emitting at least one wavelength of electromagnetic energy, sensing means for sensing the electromagnetic energy and for generating a first signal representative thereof, means for detachably coupling the sensor to the oximeter and for providing communication of signals between the sensor and the oximeter, and means for providing a second signal indicative of the at least one wavelength of electromagnetic energy, the monitor comprising:

means for generating a plurality of measurements derived from the first signal;

means for comparing selected measurements with at least one expected measurement characteristic;

means for assigning one of a plurality of variable weights to each selected measurement based on the comparing step thereby generating a plurality of differently weighted measurements, the variable weights being assigned, in part, in response to a similarity between each selected measurement and a corresponding previous measurement, the variable weights comprising a plurality of different non-zero numbers;

means for averaging a plurality of the differently weighted measurements to obtain a filtered measurement for use in estimating the physiological parameter; and

means for calibrating the monitor to measure the physiological parameter in response to the second signal.

16. A method for measuring a blood constituent using data corresponding to a wavelength of electromagnetic energy transmitted through tissue of a patient, the method comprising the steps of:

filtering the data such that motion and noise energy not at integer multiples of a heart rate of the patient are attenuated, thereby generating filtered data;

comparing selected filtered data with at least one expected data characteristic;

assigning one of a plurality of variable weights to each selected filtered data based on the comparing step thereby generating a plurality of differently weighted filtered data, the variable weights comprising a plurality of different non-zero numbers; and

averaging a plurality of the differently weighted filtered data to obtain a twice-filtered data for use in estimating the blood constituent.

17. A method for calculating oxygen saturation of hemoglobin in arterial blood using data corresponding to a plurality of wavelengths of electromagnetic energy transmitted through tissue of a patient, the method comprising the steps of:

determining extinction coefficients corresponding to the plurality of wavelengths; and

calculating values proportional to total hemoglobin and oxygenated hemoglobin directly from the data and the extinction coefficients.