Plethysmograph pulse recognition processor

• US 6,463,311 B1
• Filed: 12/23/1999
• Issued: 10/08/2002
• Est. Priority Date: 12/30/1998
• Status: Expired due to Term

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Diab, Mohamed K.
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): KREMER, MATTHEW J
• Application Number:
  US09/471,510
• Time in Patent Office: 1,020 Days
• Field of Search: 600/301, 600/309-310, 600/322-324, 600/330, 600/336, 600/363, 600/500-502, 600/516-517, 600/521, 600/515, 356/39-41
• US Class Current: 600/324
• 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 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00

Abstract

An intelligent, rule-based processor provides recognition of individual pulses in a pulse oximeter-derived photo-plethysmograph waveform. Pulse recognition occurs in two stages. The first stage identifies candidate pulses in the plethysmograph waveform. The candidate pulse stage identifies points in the waveform representing peaks and valleys corresponding to an idealized triangular wave model of the waveform pulses. At this stage, waveform features that do not correspond to this model are removed, including the characteristic dicrotic notch. The second stage applies a plethysmograph model to the candidate pulses and decides which pulses satisfies this model. This is done by first calculating certain pulse features and then applying different checks to identify physiologically acceptable features. Various statistics can then be derived from the resulting pulse information, including the period and signal strength of each pulse and pulse density, which is the ratio of the analyzed waveform segment that has been classified as physiologically acceptable.

Claims

1. A processor having a piethysmograph waveform input resulting from light attenuated by body tissue with pulsing blood and a pulse recognition output providing information regarding pulses within said waveform input, said processor comprising:

a candidate pulse portion that determines a plurality of potential pulses within said waveform input;

a physiological model portion that determines the physiologically acceptable ones of said pulses; and

a portion that determines statistics of pulses with said waveform input.

2. The processor of claim 1 wherein one of said statistics is the density of physiologically acceptable pulses within said waveform input.

3. A processor having a plethysmograph waveform input resulting from light attenuated by body tissue with pulsing blood and a pulse recognition output providing information regarding pulses within said waveform input, said processor comprising:

a candidate pulse portion that determines a plurality of potential pulses within said waveform input; and

a physiological model portion that determines the physiologically acceptable ones of said pulses, wherein said physiological model portion comprises a component that disregards ones of said potential pulses that are generally asymmetric.

4. A processor having a plethysmograph waveform input resulting from light attenuated by body tissue with pulsing blood and a pulse recognition output providing information regarding pulses within said waveform input, said processor comprising:

a candidate pulse portion that determines a plurality of potential pulses within said waveform input; and

a physiological model portion that determines the physiologically acceptable ones of said pulses, wherein said physiological model portion comprises a component that disregards ones of said potential pulses that have a descending trend that is generally slower than a subsequent ascending trend.

5. A processor having a plethysmograph waveform input resulting from light attenuated by body tissue with pulsing blood and a pulse recognition output providing information regarding pulses within said waveform input, said processor comprising:

a candidate pulse portion that determines a plurality of potential pulses within said waveform input; and

a physiological model portion that determines the physiologically acceptable ones of said pulses, wherein said physiological model portion comprises a component that disregards ones of said potential pulses having a signal strength that differs from a short-term average signal strength by greater than a predetermined amount.

6. A method of recognizing pulses within a plethysmograph waveform resulting from light attenuated by body tissue with pulsing blood comprising the steps of:

identifying a plurality of potential pulses in said waveform;

comparing said potential pulses to a physiological pulse model to derive at least one physiologically acceptable pulse; and

generating statistics for said at least one acceptable pulse. sufficiently comply with an empirical relationship between pulse rate and pulse signal strength.

7. The method of claim 6 wherein said generating step comprises the steps of:

determining a total period of said at least one acceptable pulse;

calculating the ratio of said total period to a duration of said waveform to derive pulse density.

8. A pulse recognition processor comprising:

a candidate pulse subprocessor means for identifying potential pulses in an input waveform and providing a triangular waveform output;

a plethysmograph model subprocessor means for determining physiologically acceptable pulses in said triangular waveform output and providing as a pulse output the indices of acceptable pulses.

9. The pulse recognition processor of claim 8 further comprising a pulse statistics subprocessor means for determining cumulative pulse characteristics from said pulse output.