Wave form filter pulse detector and method for modulated signal

• US 4,867,571 A
• Filed: 02/28/1989
• Issued: 09/19/1989
• Est. Priority Date: 09/26/1986
• Status: Expired due to Term

• Current Assignee: Sensormedics Corporation (Becton, Dickinson & Co)
• Original Assignee: Sensormedics Corporation (Becton, Dickinson & Co)
• Inventors: McCarthy, Rex, Pawlowski, Michael, Frick, Gene
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Oen, William L.
• Application Number:
  US07/317,097
• Time in Patent Office: 203 Days
• Field of Search: 356/41, 356/432, 356/436, 364/550, 364/551, 364/572, 328/24, 328/117, 307/311, 307/358, 128/633
• US Class Current: 356/436
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: G01N 2021/3159 Special features of multiplexing circuits
• CPC Class Codes: G01N 2021/3181 using LEDs
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence

Abstract

A device and method for determining pulses in a modulated signal is disclosed. The modulated signal is processed and converted into a quantized analog type of digital data stream. The data stream is evaluated over time by considering preceeding and subsequent values in the data stream to generate a filtered wave form. By using extreme values in the filtered wave form pulse detection is accurately determined regardless of whether the modulated signal has complicating features, such as dicrotic notch, or high noise levels, or both.

Claims

1. An apparatus for the determination of a pulse in an amplitude modulated quantized analog signal having a signal amplitude complicating feature, comprising:

means for transmitting light through a specimen,

means for monitoring the transmitted light to produce a data stream comprising values representative of the attenuation of light by the specimen over time,

means for storing the series of values whereby each of the values is a discrete moment in time and the stored values are continually updated over time,

wave form filter for evaluating the stored values over time whereby a series of filtered values are determined the filtered values including a plurality of extreme values representing the pulse, and

means for determining a frequency of the extreme values in the series of filtered values.

6. The apparatus of claim 1 wherein the amplitude complicating feature is a high noise level.

7. The apparatus of claim 1 wherein the amplitude complicating feature is a dicrotic notch.

8. The apparatus of claim 1 wherein the amplitude complicating feature is a baseline drift.

2. A method for determining pulses in an amplitude modulated quantized analog signal having a signal complicating feature, comprising:

transmitting light through a specimen,

monitoring the transmitted light to produce a data stream comprising a series of values representative of the attenuation of light by the specimen over time,

storing the series of values whereby each of the stored values is a discrete moment in time,

filtering the stored values whereby a series of filtered values are determined the filtered values including a plurality of extreme values representing the pulse, and

evaluating the series of filtered values to determine a frequency of the extreme values.

9. The method of claim 2 wherein the amplitude complicating feature is a high noise level.

10. The method of claim 2 wherein the amplitude complicating feature is a dicrotic notch.

11. The method of claim 2 wherein the amplitude complicating feature is a baseline drift.

3. An apparatus for the determination of a pulse in an amplitude modulated quantized analog signal having a signal amplitude complicating feature, comprising:

means for monitoring a data stream comprising a series of time spaced values,

means for storing at least a portion of the series of time spaced values whereby the stored values are continually updated over time,

wave form filter for evaluating the stored values over time whereby a series of wave form filter outputs are determined, the filter outputs including a plurality of extreme values representing the pulse, by solving the expression;

##EQU2## where F_i is a wave form filter output for a given time t_i having a data stream value P_i, P_i,j is the data stream value at time t_i -t_j, and p_i+j is the data stream value at time t_i +t_j, and data stream value at time t_i +t_j, and

means for determining a frequency of the extreme values in the series of wave form filter outputs.

4. A wave form filter for the determination of pulses in an amplitude modulated quantized analog signal having a signal amplitude complicating feature comprising a means for generating the digital signal, the quantized analog signal comprising a series of time spaced values, a means for storing and continually updating at least three of the time spaced values, a filtering means to determine a filtered wave form by using at least two of the time spaced values the filtered wave form including a plurality of extreme values representing the pulses, and a means for determining the extreme values in the filtered wave form.

12. The wave form filter of claim 4 wherein the amplitude complicating feature is a high noise level.

13. The wave form filter of claim 4 wherein the amplitude complicating feature is a dicrotic notch.

14. The wave form filter of claim 4 wherein the amplitude complicating feature is a baseline drift.

5. A method for determining pulses in an amplitude modulated quantized analog signal having a signal amplitude complicating feature comprising generating a modulated signal comprised of a series of time space data values, storing some of the data values which are continually updated over time, filtering the stored data values over time to determine a series of filtered values the filtered values including a plurality of extreme value in the signal representing the pulses, and evaluating the filtered values to determine the extreme values.

15. The method of claim 5 wherein the amplitude complicating feature is a high noise level.

16. The method of claim 5 wherein the amplitude complicating feature is a dicrotic notch.

17. The method of claim 5 wherein the amplitude complicating feature is a baseline drift.