Patient monitoring system

• US 5,765,563 A
• Filed: 08/15/1996
• Issued: 06/16/1998
• Est. Priority Date: 08/15/1996
• Status: Expired due to Term

• Current Assignee: Natus Medical Incorporated
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Vander Schaaf, Larry Allen
• Primary Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US08/698,137
• Time in Patent Office: 670 Days
• Field of Search: 128/633, 128/716, 128/719, 128/725, 128/724, 128/700, 128/666, 128/668, 128/670, 128/671
• US Class Current: 600/538
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/4818 Sleep apnoea

Abstract

A method and apparatus for performing scoring analysis of the pathological sleep events of apnea, hypopnea and desaturation of a patient from a sampled data set of only three sensor signals, namely, airflow, heart rate and oxygen saturation. The data source is either currently sensed data or previously recorded data. A microprocessor provides the display, printing, input and output channels, operator interface and computation capability for the system. Specialized programs direct the analysis and operation thereof.

Claims

1. A system for analyzing patient airflow to determine and score abnormal sleep events, comprising:

at least one sensor for sensing the airflow of a patient;

input means for receiving a time varying analog airflow signal from the at least one sensor wherein the analog airflow signal corresponds to the respiration of the patient and has a number of successive start of inspiration portions, peak of inspiration portions, expiration portions, and end of expiration portions;

said input means digitizing the analog airflow signal thereby providing a digitized airflow signal;

clock means for providing a digital clock signal to correlate the digitized airflow signal with time;

receiving means for receiving the digitized airflow signal and the digital clock signal;

determining means, coupled to said receiving means, for determining a delay in the respiration of the patient; and

wherein said determining means determines the portions of the digitized airflow signal that correspond to the successive peak of inspiration portions and the corresponding successive start of inspiration portions, wherein an apnea interval is defined as the time between a valid peak of inspiration portion and the next succeeding start of inspiration portion;

said determining means determining which of the number of apnea intervals are longer than a predetermined apnea threshold, thereby indicating an apnea event.

2. A system according to claim 1 further comprising storing means for storing the digitized airflow signal and the digital clock signal for later display and analysis.

3. A system according to claim 1 wherein the digitized airflow signal has a number of local maximums and local minimums wherein each of the number of local maximums and local minimums have a corresponding amplitude, each of the number of peak of inspiration portions corresponding to one of the number of local maximums, said determining means determining which of the number of peak of inspiration portions are valid peak of inspiration portions.

4. A system according to claim 3 wherein said determining means determines that a particular peak of inspiration portion is valid if:

i. the amplitude of the local maximum corresponding to the particular peak of inspiration portion exceeds the amplitude of the subsequent local minimum by a predetermined threshold value; and

ii. the amplitude of the local maximum corresponding to the particular peak of inspiration portion drops by a predetermined amount within a predetermined time period.

5. A system according to claim 4 wherein a valid drop distance is defined as the difference in amplitude of the digitized airflow signal from a valid peak of inspiration portion to a next succeeding end of expiration portion, said system further comprising a drop queue for storing in a FIFO manner the "N" most recent valid drop distances.

6. A system according to claim 5 wherein said predetermined threshold value is set at a percentage of a baseline amplitude wherein the baseline amplitude is defined as the average of the second through the sixth highest valid drops in a drop queue of size 10;

the highest valid drop is removed to eliminate breaths which may be atypical of the normal breathing pattern; and

the lowest breaths are removed to eliminate the effect of abnormal breathing patterns on the baseline and thereby being able to continue to detect an abnormal breathing pattern.

7. A system according to claim 5 wherein said valid drop distance must be greater than a predetermined amount before the valid drop distance is stored in the drop queue.

8. A system according to claim 5 wherein said predetermined amount is set to a percentage of the predetermined threshold value.

9. A system according to claim 1, further comprising means for inputting a user defined predetermined apnea threshold.

10. A system according to claim 1 further comprising an oxygen sensor and means for coupling the oxygen sensor to the patient for providing a time varying oxygen saturation signal to said input means thereby resulting in a digitized oxygen saturation signal, said determining means determining if the oxygen saturation level falls below a predetermined oxygen level for a predetermined time period.

11. A system according to claim 10 wherein said predetermined oxygen level is defined as a percentage of a baseline threshold.

12. A system according to claim 11 wherein a baseline time interval is broken into "N" time windows, wherein an average oxygen level is computed for each time window, the baseline threshold is computed by averaging the highest "M" oxygen levels for the "N" time windows, wherein M is less than N.

13. A system according to claim 12 wherein any time window that has an invalid oxygen level therein is not selected as one of the highest M oxygen levels.

14. A system according to claim 1 further comprising a pulse sensor coupled to the patient for providing a time varying heart pulse signal to said input means thereby resulting in a digitized pulse signal, said determining means determining the pulse rate of the patient.

15. A system according to claim 1 wherein said determining means comprises a processor.

16. A system according to claim 15 wherein said processor is a standard programmable personal computer.

17. A method for analyzing patient airflow to determine and score abnormal sleep events, comprising the steps of:

inputing a time varying analog airflow signal from at least one sensor that is sensing the airflow of a patient wherein the analog airflow signal corresponds to the respiration of the patient and has a number of successive start of inspiration portions, peak of inspiration portions, expiration portions, and end of expiration portions;

said inputing step digitizing the analog airflow signal thereby providing a digitized airflow signal;

providing a digital clock signal to correlate the digitized airflow signal with time;

receiving the digitized airflow signal and the digital clock signal;

determining the respiration of the patient from the digitized airflow signal by determining a delay in the respiration of the patient; and

wherein said determining step determines the portions of the digitized airflow signal that correspond to the successive peak of inspiration portions and the corresponding successive start of inspiration portions, wherein an apnea interval is defined as the time between a valid peak of inspiration portion and the next succeeding start of inspiration portion;

said determining step determining which of the number of apnea intervals are longer than a predetermined apnea threshold, thereby indicating an apnea event.

18. A system according to claim 17 wherein the digitized airflow signal has a number of local maximums and local minimums wherein each of the number of local maximums and local minimums have a corresponding amplitude, each of the number of peak of inspiration portions corresponding to one of the number of local maximums, said determining step determining which of the number of peak of inspiration portions are valid peak of inspiration portions.

19. A system according to claim 18 wherein said determining step determines that a particular peak of inspiration portion is valid if:

i. the amplitude of the local maximum corresponding to the particular peak of inspiration portion exceeds the amplitude of the subsequent local minimum by a predetermined threshold value; and

ii. the amplitude of the local maximum corresponding to the particular peak of inspiration portion drops by a predetermined amount within a predetermined time period.

20. A system according to claim 19 wherein said predetermined threshold value is set at a percentage of a baseline amplitude wherein the baseline amplitude is defined as the average of the second through the sixth highest valid drops in a drop queue of size 10;

the highest valid drop is removed to eliminate breaths which may be atypical of the normal breathing pattern; and

the lowest breaths are removed to eliminate the effect of abnormal breathing patterns on the baseline and thereby being able to continue to detect an abnormal breathing pattern.

21. A system according to claim 20 wherein said predetermined amount is set to a percentage of the predetermined threshold value.

22. A method according to claim 17 wherein an oxygen sensor is provided such that said oxygen sensor is coupled to the patient for providing a time varying oxygen saturation signal to said inputing step thereby resulting in a digitized oxygen saturation signal, said determining step determining if the oxygen saturation level falls below a predetermined oxygen level for a predetermined time period.

23. A method according to claim 22 wherein said predetermined oxygen level is defined as a percentage of a baseline threshold.

24. A method according to claim 23 wherein a baseline time interval is broken into "IN" time windows, wherein an average oxygen level is computed for each time window, the baseline threshold is computed by averaging the highest "M" oxygen levels for the "N" time windows, wherein M is less than N.

25. A method according to claim 24 wherein any time window that has an invalid oxygen level therein is not selected as one of the highest M oxygen levels.

26. A method according to claim 17 wherein a pulse sensor is provided wherein said pulse sensor is coupled to the patient for providing a time varying heart pulse signal to said inputing step thereby resulting in a digitized pulse signal, said determining step determining the pulse rate of the patient.