Method for controlling a bi-level apparatus, and bi-level apparatus

• US 20070089745A1
• Filed: 09/25/2006
• Published: 04/26/2007
• Est. Priority Date: 03/23/2004
• Status: Active Grant

• Current Assignee: Vyaire Medical GmbH
• Original Assignee: Ellis Whitehead, Harald Genger, Stephan Gabriel
• Inventors: Genger, Harald, Whitehead, Ellis, Gabriel, Stephan
• Granted Patent: US 8,402,969 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase

Abstract

This invention relates to a method for controlling a bi-level apparatus. The method includes repeatedly measuring an airflow, choosing an expiration threshold value and choosing an inspiration threshold value. Switching to an inspiration mode takes place if the airflow is greater than the expiration threshold value in a comparison with the expiration threshold value. A switching back to the expiration mode takes place if the airflow is smaller than the inspiration threshold value in a comparison with the inspiration threshold value. Moreover, the invention relates to a bi-level apparatus for performing the method.

Claims

1. A method for controlling a bi-level apparatus, comprising:

repeatedly measuring the airflow thereby obtaining measured airflow values;

choosing an expiration threshold value;

choosing an inspiration threshold value;

repeatedly comparing said airflow values with said expiration threshold value during an expiration mode;

switching to an inspiration mode if an airflow value is greater than said expiration threshold value in a comparison with said expiration threshold value;

repeatedly comparing said airflow values with said inspiration threshold value during said inspiration mode; and

switching to said expiration mode if an airflow value is smaller than said inspiration threshold value in a comparison with said inspiration threshold value.

2. The method according to claim 1, further comprising:

storing a minimum airflow during said expiration mode;

choosing said inspiration threshold value equal to said stored minimum airflow immediately after switching to said inspiration mode;

storing a maximum airflow during said inspiration mode; and

choosing said expiration threshold value equal to said stored maximum airflow immediately after switching to said expiration mode.

3. The method according to claim 1, further comprising:

calculating an airflow derivative by estimating a time derivative of said airflow;

comparing said airflow derivative with an expiration derivative threshold value during an expiration mode;

switching to said inspiration mode only if additionally said airflow derivative is greater than said expiration derivative threshold value;

comparing said airflow derivative with an inspiration derivative threshold value during an inspiration mode;

switching to said expiration mode only if additionally said airflow derivative is greater than said inspiration derivative threshold value.

4. The method according to claim 3, wherein said calculating said airflow derivative includes:

repeatedly calculating the median from a first predetermined number of successive measured airflow values thereby obtaining median values;

calculating an averaged airflow as arithmetic average of a second given number of median values; and

calculating said time derivative of said averaged airflow to obtain said airflow derivative.

5. The method according to claim 3, wherein said airflow derivative is averaged over a first predetermined time span prior to said comparison with said expiration and inspiration derivative threshold value.

6. The method according to claim 1, wherein no switching from said expiration mode to said inspiration mode takes place if an actual pressure is not yet settled on a set pressure and a current actual pressure is above an actual pressure measured before a second given time span prior to the current time.

7. The method according to claim 1, wherein switching from said expiration mode to said inspiration mode takes place if an actual pressure is below a set pressure by a first given value and a current airflow is above an airflow preceding a third given time span prior to the current time by a second given value.

8. The method according to claim 1, further comprising:

calculating a first moving average value by a third predetermined number of measured airflow values;

calculating a second moving average value by a fourth predetermined number of measured airflow values measured exclusively during an inspiration mode.

9. The method according to claim 8, further comprising:

lowering said expiration threshold value during a sixth time span shortly after switching to said expiration mode from a maximum airflow measured during the preceding inspiration phase to a sum of said first moving average value weighted by a first factor plus said second moving average value weighted by a second factor, wherein said first factor is slightly smaller than one and said sum of said first and second factor is equal to one; and

choosing said expiration threshold value equal to said sum following said sixth time span.

10. The method according to claim 9, wherein said expiration threshold value is only lowered to a switching average value during said sixth time span if said switching average value is greater than said sum, and said expiration threshold value is chosen to be equal to said switching average value during a seventh time span following said sixth time span if said switching average value is greater than said sum, wherein said switching average value is equal to said first moving average value at the moment of the preceding switching to said expiration mode.

11. The method according to claim 8, further comprising:

calculating a third moving average value over a fifth predetermined number of measured airflow values;

storing said third moving average value during a seventh time span for an eighth time span being shorter than said seventh time span in a memory if both said airflow and said third moving average value are greater than said first moving average value and said airflow is equal to said third moving average value;

otherwise storing of zero in said memory;

calculating a difference of said second moving average value minus said first moving average value;

multiplying said difference by a third factor to obtain a product; and

adding said product to said value in said memory to obtain said expiration threshold value.

12. The method according to claim 10, wherein during a time span shortly after said switching to said inspiration mode up to the end of said inspiration mode said inspiration threshold value is chosen to be equal to said maximum of said airflow during a current inspiration phase multiplied by a fourth factor minus said switching average value multiplied by a fifth factor, wherein said fourth factor is slightly smaller than one and a sum of said fourth factor plus said fifth factor is equal to one.

13. The method according to claim 1, wherein during a time span shortly after said switching to said inspiration mode up to said end of said inspiration mode said inspiration threshold value is chosen to be equal to a difference of said maximum of said airflow during said current inspiration phase minus a third predetermined value.

14. The method according to claim 1, wherein

said inspiration threshold value is chosen to be equal to said maximum of said airflow during a current inspiration phase multiplied by a fourth factor minus said switching average value multiplied by a fifth factor, wherein said fourth factor is slightly smaller than one and a sum of said fourth factor plus said fifth factor is equal to one, provided that said maximum of said airflow during said current inspiration phase is greater than said switching average value,

while otherwise said inspiration threshold value during this time span is chosen to be equal to a difference of said maximum of said airflow during said current inspiration phase minus a third predetermined value.

15. A Respiratory apparatus, comprising:

a fan;

a pressure sensor for determining an overpressure under which air is provided by said fan;

a flow sensor for measuring an airflow;

a processor connected to said pressure sensor and said flow sensor, to which a pressure signal is fed from said pressure sensor and an airflow signal from said flow sensor, said processor storing a sequence of instructions and being suitable for executing said instructions, said processor performing the following when executing said instructions;

repeatedly obtaining measured airflow values from said airflow signal;

choosing an expiration threshold value;

choosing an inspiration threshold value;

repeatedly comparing said airflow values with said expiration threshold value during an expiration mode;

switching to an inspiration mode if an airflow value is greater than said expiration threshold value in a comparison with said expiration threshold value;

repeatedly comparing said airflow values with said inspiration threshold value during said inspiration mode; and

switching to said expiration mode if an airflow value is smaller than said inspiration threshold value in a comparison with said inspiration threshold value.

16. The respiratory apparatus according to claim 15, said processor further performing the following during operation:

storing a minimum airflow during said expiration mode;

choosing said inspiration threshold value equal to said stored minimum airflow immediately after switching to said inspiration mode;

storing a maximum airflow during said inspiration mode; and

choosing said expiration threshold value equal to said stored maximum airflow immediately after switching to said expiration mode.

17. The respiratory apparatus according to claim 15, said processor further performing the following during operation:

calculating an airflow derivative by estimating a time derivative of said airflow;

comparing said airflow derivative with an expiration derivative threshold value during an expiration mode;

switching to said inspiration mode only if additionally said airflow derivative is greater than said expiration derivative threshold value;

comparing said airflow derivative with an inspiration derivative threshold value during an inspiration mode;

switching to said expiration mode only if additionally said airflow derivative is greater than said inspiration derivative threshold value.

18. The respiratory apparatus according to claim 17, wherein said calculating said airflow derivative includes:

repeatedly calculating the median from a first predetermined number of successive measured airflow values thereby obtaining median values;

calculating an averaged airflow as arithmetic average of a second given number of median values; and

calculating said time derivative of said averaged airflow to obtain said airflow derivative.

19. The respiratory apparatus according to claim 17, wherein said processor further averaging said airflow derivative over a first predetermined time span prior to said comparison with said expiration and inspiration derivative threshold value.

20. The respiratory apparatus according to claim 15, wherein no switching from said expiration mode to said inspiration mode takes place if an actual pressure is not yet settled on a set pressure and a current actual pressure is above an actual pressure measured before a second given time span prior to the current time.

21. The respiratory apparatus according to claim 15, wherein switching from said expiration mode to said inspiration mode takes place if an actual pressure is below a set pressure by a first given value and a current airflow is above an airflow preceding a third given time span prior to the current time by a second given value.

22. The respiratory apparatus according to claim 15, said processor further performing the following when executing said instructions:

calculating a first moving average value by a third predetermined number of measured airflow values;

calculating a second moving average value by a fourth predetermined number of measured airflow values measured exclusively during an inspiration mode.

23. The respiratory apparatus according to claim 22, said processor further performing the following when executing said instructions:

lowering said expiration threshold value during a sixth time span shortly after switching to said expiration mode from a maximum airflow measured during the preceding inspiration phase to a sum of said first moving average value weighted by a first factor plus said second moving average value weighted by a second factor, wherein said first factor is slightly smaller than one and said sum of said first and second factor is equal to one; and

choosing said expiration threshold value equal to said sum following said sixth time span.

24. The respiratory apparatus according to claim 23, wherein the expiration threshold value is only lowered to a switching average value during said sixth time span if said switching average value is greater than said sum, and said expiration threshold value is chosen to be equal to said switching average value during a seventh time span following said sixth time span if said switching average value is greater than said sum, wherein said switching average value is equal to said first moving average value at the moment of the preceding switching to said expiration mode.

25. The respiratory apparatus according to claim 22, said processor further performing the following when executing said instructions:

calculating a third moving average value over a fifth predetermined number of measured airflow values;

storing said third moving average value during a seventh time span for an eighth time span being shorter than said seventh time span in a memory if both said airflow and said third moving average value are greater than said first moving average value and said airflow is equal to said third moving average value;

otherwise storing of zero in said memory;

calculating a difference of said second moving average value minus said first moving average value;

multiplying said difference by a third factor to obtain a product; and

adding said product to said value in said memory to obtain said expiration threshold value.

26. The respiratory apparatus according to claim 15, wherein during a time span shortly after said switching to said inspiration mode up to the end of said inspiration mode said inspiration threshold value is chosen to be equal to said maximum of said airflow during a current inspiration phase multiplied by a fourth factor minus said switching average value multiplied by a fifth factor, wherein said fourth factor is slightly smaller than one and a sum of said fourth factor plus said fifth factor is equal to one.

27. The respiratory apparatus according to claim 15, wherein during a time span shortly after said switching to said inspiration mode up to said end of said inspiration mode said inspiration threshold value is chosen to be equal to a difference of said maximum of said airflow during said current inspiration phase minus a third predetermined value.

28. The respiratory apparatus according to claim 15, wherein

said inspiration threshold value is chosen to be equal to said maximum of said airflow during a current inspiration phase multiplied by a fourth factor minus said switching average value multiplied by a fifth factor, wherein said fourth factor is slightly smaller than one and a sum of said fourth factor plus said fifth factor is equal to one, provided that said maximum of said airflow during said current inspiration phase is greater than said switching average value,

while otherwise said inspiration threshold value during this time span is chosen to be equal to a difference of said maximum of said airflow during said current inspiration phase minus a third predetermined value.