Plethysmograph variability processor

• US 10,092,200 B2
• Filed: 04/08/2013
• Issued: 10/09/2018
• Est. Priority Date: 12/09/2006
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Al-Ali, Ammar, Weber, Walter, Majmudar, Anmol
• Primary Examiner(s): BLOCH, MICHAEL RYAN
• Application Number:
  US13/858,249
• Publication Number:
  US 20130296713A1
• Time in Patent Office: 2,010 Days
• Field of Search: None
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/4848 Monitoring or testing the effects of treatment, e.g. of medication
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

A plethysmograph variability processor inputs a plethysmograph waveform having pulses corresponding to pulsatile blood flow within a tissue site. The processor derives plethysmograph values based upon selected plethysmograph features, determines variability values, and calculates a plethysmograph variability parameter. The variability values indicate the variability of the plethysmograph features. The plethysmograph variability parameter is representative of the variability values and provides a useful indication of various physiological conditions and the efficacy of treatment for those conditions.

Claims

1. A computerized method of determining plethysmograph variability in a non-invasive electronic patient monitor using a signal processor comprising:

converting digital control signals into analog drive signals;

causing a sensor emitter to emit a plurality of wavelengths of light by communicating the analog drive signals to the sensor emitter;

receiving a sensor signal from a sensor detector in response to attenuation by pulsatile blood flow within a tissue site;

demodulating the sensor signal to generate a plethysmograph waveform having pulses corresponding to the pulsatile blood flow within the tissue site;

determining a plurality of perfusion values corresponding to the pulses, wherein said determining the plurality of perfusion values comprises;

identifying peaks and valleys of the pulses, and

calculating differential values for the pulses from the peaks and the valleys of the pulses, wherein the differential values comprise a difference between the peaks and the valleys of the pulses;

storing a first series of perfusion values of the plurality of perfusion values in a first buffer;

sorting the first series of perfusion values within the first buffer from a largest perfusion value to a smallest perfusion value;

removing at least two perfusion values from the first series of perfusion values to form a modified first series of perfusion values, wherein at least one perfusion value is removed from a set of largest perfusion values of the first series of perfusion values, and at least one perfusion value is removed from a set of smallest perfusion values of the first series of perfusion values;

determining a first variability value indicative of variability of the modified first series of perfusion values based on a difference between a first perfusion value of the modified first series of perfusion values and a second perfusion value of the modified first series of perfusion values and a normalization of the difference with the first perfusion value of the modified first series of perfusion values;

storing a second series of perfusion values of the plurality of perfusion values in a second buffer;

sorting the second series of perfusion values within the second buffer from a largest perfusion value to a smallest perfusion value;

removing at least one perfusion value from a set of largest perfusion values of the second series of perfusion values and at least one perfusion value from a set of smallest perfusion values of the second series of perfusion values to form a modified second series of perfusion values;

determining a second variability value indicative of variability of the modified second series of perfusion values based on a difference between a first perfusion value of the modified second series of perfusion values and a second perfusion value of the modified second series of perfusion values and a normalization of the difference with the first perfusion value of the modified second series of perfusion values;

determining a plethysmograph variability parameter representative of at least the first variability value and the second variability value; and

causing a display device to display the plethysmograph variability parameter.

2. The computerized method of claim 1, wherein said determining the plurality of perfusion values further comprises normalizing the calculated differential values.

3. The computerized method of claim 1, wherein said determining the first variability value and the second variability value further comprises calculating a plurality of plethysmograph variability indices from a percentage difference between a maximum perfusion value and a minimum perfusion value for each of the modified first series of perfusion values and the modified second series of perfusion values.

4. The computerized method of claim 3, wherein said determining the plethysmograph variability parameter comprises calculating a median value of the plurality of plethysmograph variability indices.

5. The computerized method of claim 4, further comprising:

identifying physiologically acceptable pulses from the pulses, wherein the pulses comprise physiologically acceptable pulses and physiologically unacceptable pulses; and

determining a minimum amount of time of acceptable data in each of the first buffer and the second buffer.

6. The computerized method of claim 5, further comprising:

verifying the physiologically acceptable pulses using a red channel,

wherein said receiving the sensor signal comprises using an IR channel.

7. A plethysmograph variability system comprising:

a sensor that emits optical radiation and detects the optical radiation after attenuation by pulsatile blood flowing within a tissue site,

a processor in communication with the sensor, the processor configured to execute one or more instructions that cause the processor to;

convert digital control signals into analog drive signals,

cause the sensor to emit the optical radiation by communicating the analog drive signals to the sensor,

receive a sensor signal from the sensor in response to the detected optical radiation after the attenuation,

demodulate the sensor signal to generate a plethysmograph waveform having pulses corresponding to the pulsatile blood flowing within the tissue site,

determine a plurality of perfusion values of pulses corresponding to the pulsatile blood flowing within the tissue site, wherein to determine the plurality of perfusion values the processor is further configured to;

identify peaks and valleys of the pulses, and

calculate differences for the pulses from the peaks and the valleys of the pulses;

store a first series of perfusion values of the plurality of perfusion values in a first buffer;

sort the first series of perfusion values within the first buffer from a largest perfusion value to a smallest perfusion value;

remove at least two perfusion values from the first series of perfusion values to form a modified first series of perfusion values, wherein at least one perfusion value is removed from a set of largest perfusion values of the first series of perfusion values and at least one perfusion value is removed from a set of smallest perfusion values of the first series of perfusion values;

determine a first variability value indicative of variability of the modified first series of perfusion values based on a difference between a first perfusion value of the modified first series of perfusion values and a second perfusion value of the modified first series of perfusion values and a normalization of the difference with the first perfusion value of the modified first series of perfusion values;

store a second series of perfusion values of the plurality of perfusion values in a second buffer;

sort the second series of perfusion values within the second buffer from a largest perfusion value to a smallest perfusion value;

remove at least one perfusion value from a set of largest perfusion values of the second series of perfusion values and at least one perfusion value from a set of smallest perfusion values of the second series of perfusion values to form a modified second series of perfusion values;

determine a second variability value indicative of variability of the modified second series of perfusion values based on a difference between a first perfusion value of the modified second series of perfusion values and a second perfusion value of the modified second series of perfusion values and a normalization of the difference with the first perfusion value of the modified second series of perfusion values;

determine a plethysmograph variability parameter representative of at least the first variability value and the second variability value; and

cause a display to display the plethysmograph variability parameter.

8. The system of claim 7, wherein to determine the plurality of perfusion values, the processor is further configured to normalize the calculated differences for the pulses.

9. The system of claim 8, wherein to determine the first variability value and the second variability value, the processor is further configured to calculate a plurality of plethysmograph variability indices from a percentage difference between a maximum perfusion value and a minimum perfusion value for each of the modified first series of perfusion values and the modified second series of perfusion values.

10. The system of claim 9, wherein to determine the plethysmograph variability parameter the processor is configured to calculate a median value of the plurality of plethysmograph variability indices.

11. The system of claim 10, wherein the processor is further configured to:

identify physiologically acceptable pulses from the pulses, wherein the pulses comprise physiologically acceptable pulses and physiologically unacceptable pulses; and

determine a minimum amount of time of acceptable data in each of the first buffer and the second buffer.

12. A computerized method for determining a plethysmograph variability parameter using a signal processor, the computerized method comprising:

converting digital control signals into analog drive signals;

causing a sensor emitter to emit a plurality of wavelengths of light by communicating the analog drive signals to the sensor emitter;

receiving a sensor signal from a sensor detector in response to attenuation by pulsatile blood flow within a tissue site;

demodulating the sensor signal to generate a plethysmograph waveform having pulses corresponding to the pulsatile blood flow within the tissue site;

identifying relative minimums and relative maximums of the pulses;

calculating differences for the pulses from the identified relative minimums and relative maximums of the pulses to determine a plurality of perfusion values for the pulses, wherein the plurality of perfusion values comprise at least a first set of perfusion values and a second set of perfusion values;

storing the first set of perfusion values in a first buffer;

sorting the first set of perfusion values within the first buffer from a largest perfusion value to a smallest perfusion value;

removing at least two perfusion values from the first set of perfusion values to form a modified first set of perfusion values, wherein one perfusion value is removed from a set of largest perfusion values of the first series of perfusion values and at least one perfusion value is removed from a set of smallest perfusion values of the first series of perfusion values;

calculating a variability value of the modified first set of perfusion values using at least a normalized difference between a first perfusion value of the modified first set of perfusion values and a second perfusion value of the modified first set of perfusion values, wherein the difference is normalized with respect to the first perfusion value of the modified first set of perfusion values;

storing the second set of perfusion values in a second buffer;

sorting the second set of perfusion values within the second buffer from a largest perfusion value to a smallest perfusion value;

removing at least two perfusion values from the second set of perfusion values to form a modified second set of perfusion values, wherein one perfusion value is removed from a set of largest perfusion values of the second set of perfusion values and at least one perfusion value is from a set of smallest perfusion values of the second set of perfusion values;

calculating a variability value of the modified second set of perfusion values using at least a normalized difference between a first perfusion value of the modified second set of perfusion values and a second perfusion value of the modified second set of perfusion values, wherein the difference is normalized with respect to the first perfusion value of the modified second set of perfusion values;

determining a plethysmograph variability parameter representative of at least the variability value of the modified first set of perfusion values and the variability value of the modified second set of perfusion values; and

causing a display device to display the plethysmograph variability parameter.

13. The computerized method of claim 12, further comprising normalizing the calculated differences to determine the plurality of perfusion values.