Apnea detector with artifact rejection

• US 6,537,228 B1
• Filed: 04/24/2001
• Issued: 03/25/2003
• Est. Priority Date: 06/19/1998
• Status: Expired due to Fees

• Current Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Original Assignee: Cas Medical Systems Incorporated (Edwards Lifesciences Corporation)
• Inventors: Lambert, Scott
• Primary Examiner(s): Vo, Hieu T.
• Assistant Examiner(s): Hoang, Johnny H.
• Application Number:
  US09/719,868
• Time in Patent Office: 700 Days
• Field of Search: 600/506, 600/529, 600/532, 600/534, 600/538, 600/547, 128/633, 128/204.23
• US Class Current: 600/506
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61B 5/4818 Sleep apnoea

Abstract

A method and apparatus in an apnea detector monitor impedance pneumographic respiratory signals and heart rate of a patient. Magnitudes of excursions of the respiratory signals are monitored to resolve respiratory events, i.e. breaths, inhalations and exhalations. A counter will reach a threshold count and trigger an alarm if a selected interval lapses without a respiratory event being detected. If a respiratory event is detected, as by detecting successive peaks, a peak or a valley of the respiratory signal, the timer is reset. The method and apparatus reject artifact that would otherwise appear as breathing cycles in order to prevent false negative indications of apnea. Cyclically occurring peaks are rejected as being indicative of a breath if they are in a selected magnitude range compared to that of a normal breath and they approximate the patient'"'"'s heart rate. Successive peaks due to sighs or of a baseline change are measured for average rate of change over the period it takes for the waveform to decrease from the second peak by of a selected level generally corresponding to of a normal inhalation or exhalation. They are rejected as artifact if the change is too slow. Consequently, sighs are not misinterpreted as breaths.

Claims

1. An apnea monitor comprising:

a signal processor which receives an impedance pneumography signal and a heart rate signal from a patient and measures an amplitude excursion between a first inflection point and a second inflection point of said impedance pneumography signal;

a threshold detector which classifies said excursion as a first type if it exceeds a first, lower threshold or as a second type if it exceeds a second, higher threshold and discards said excursion if it is below said first threshold;

a timer which measures a time interval from said first inflection point to said second inflection point;

a comparator which compares said time interval to a period of said heart rate signal; and

a discriminator which rejects said first and second inflection points when the time interval is within a preselected range; and

an identifier which identifies said second inflection point as a respiratory event if said time interval is outside of said preselected range or said excursion is of said second type.

2. The monitor according to claim 1 comprising further a processor which compares a rate of change of said impedance pneumography signal with a preselected rate of change indicative of breathing effort;

and

a reporting device which reports said excursion as an artifact when the rate of change is below the preselected rate of change.

3. A method for evaluating respiration comprising the steps of:

a) providing a heart rate signal and an impedance pneumography signal based on electronic ECG and respiratory outputs from electrodes on a patient;

b) detecting a first and second inflection points in said impedance pneumography signal;

c) determining a time interval between said first inflection point and said second inflection point;

d) rejecting said first and second inflection points if the time interval is less than or substantially equal to a period of the heart rate signal;

e) comparing an excursion between said first and second inflection points with a first lower level and rejecting said first and second inflection points if the excursion is less than said first lower level; and

f) comparing said excursion to a second, higher level indicative of a breath and reporting a respiratory event if the excursion exceeds the second, higher level.

4. The method of claim 3 further comprising the steps of:

determining a rate of change of said impedance pneumography signal for which said respiratory event has been reported; and

determining if said rate of change is indicative of baseline shift or sigh apnea.