Method for calculating the instantaneous inspired volume of a subject during ventilatory assistance

• US 6,575,163 B1
• Filed: 04/13/2000
• Issued: 06/10/2003
• Est. Priority Date: 09/23/1996
• Status: Expired due to Term

• Current Assignee: Resmed Limited (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Berthon-Jones, Michael
• Primary Examiner(s): Lewis, Aaron J.
• Application Number:
  US09/549,221
• Time in Patent Office: 1,153 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23
• US Class Current: 128/204.18
• CPC Class Codes: A61B 5/085 Measuring impedance of respiratory organs or lung elasticity
• CPC Class Codes: A61B 5/087 Measuring breath flow
• 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
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• 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 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/1055 bacterial
• CPC Class Codes: A61M 16/107 in the inspiratory path
• 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
• CPC Class Codes: A61M 2205/15 Detection of leaks
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

The apparatus provides for the determination of the instantaneous phase in the respiratory cycle, subject'"'"'s average respiration rate and the provision of ventilatory assistance. A microprocessor (16) receives an airflow signal from a pressure transducer (18) coupled to a port (17) at a mask (11). The microprocessor (16) controls a servo (19), that in turn controls the fan motor (20) and thus the pressure of air delivered by the blower (10). The blower (10) is coupled to a subject'"'"'s mask (ii) by a conduit (12). The invention seeks to address the following goals: while the subject is awake and making substantial efforts the delivered assistance should be closely matched in phase with the subject'"'"'s efforts; the machine should automatically adjust the degree of assistance to maintain at least a specified minimum ventilation without relying on the integrity of the subject'"'"'s chemoreflexes; and it should continue to work correctly in the presence of large leaks.

Claims

1. A method for calculating the instantaneous inspired volume of a subject during ventilatory assistance, comprising the steps of:

estimating respiratory airflow,

calculating an index equal to the fuzzy extent to which any leak is suddenly changing, and

calculating instantaneous inspired volume as a function of both the estimated respiratory airflow and said index.

2. A method as in claim 1, in which said function is the time integral of the product of said index and said estimated respiratory airflow.

3. The method of claim 1 wherein said fuzzy extent to which any leak is suddenly changing is calculated as the fuzzy extent to which the respiratory airflow is large for longer than expected.

4. The method of claim 1 wherein said fuzzy extent to which any leak is suddenly changing is a function of the fuzzy extent to which the leak has suddenly increased and the fuzzy extent to which the leak has suddenly decreased.

5. The method of claim 4 wherein said function is the fuzzy negation of a peak fuzzy union of said fuzzy extent to which the leak has suddenly increased and said fuzzy extent to which the leak has suddenly decreased.

6. The method of claim 4 wherein said fuzzy extent to which the leak has suddenly increased is the fuzzy intersection of the fuzzy extent to which said respiratory airflow has been positive for longer than expected and the fuzzy extent to which the airflow is large and positive.

7. The method of claim 1 wherein said fuzzy extent to which the leak has suddenly decreased is the fuzzy intersection of the fuzzy extent to which said respiratory airflow has been negative for longer than expected and the fuzzy extent to which the airflow is large and negative.

8. The method for calculating the instantaneous inspired volume of a subject during ventilatory assistance comprising the steps of:

estimating respiratory airflow;

calculating an index equal to the fuzzy extent to which the impedance of any leak is suddenly changing; and

calculating instantaneous inspired volume as a function of both the estimated respiratory airflow and said index.

9. The method of claim 8, in which said function is the time integral of the product of said index and said estimated respiratory airflow.

10. An apparatus for calculating the instantaneous inspired volume of a subject during ventilatory assistance comprising:

a means for delivering ventilatory support to a patient;

a means for determining an estimate of the patient'"'"'s respiratory airflow; and

a means for calculating instantaneous inspired volume from said respiratory airflow;

wherein the means for calculating instantaneous inspired volume from said respiratory airflow includes coded machine control instructions to calculate said instantaneous inspired volume as a function of both the respiratory airflow and an index equal to the fuzzy extent to which any leak is suddenly changing.

11. The apparatus of claim 10 wherein said fuzzy extent to which any leak is suddenly changing is calculated as the fuzzy extent to which the respiratory airflow is large for longer than expected.

12. The apparatus of claim 10 wherein said function is the time integral of the product of said index and said respiratory airflow.

13. An apparatus for calculating the instantaneous inspired volume of a subject during ventilatory assistance comprising:

a mask;

a blower to supply pressurized air to said mask;

a servo-controller coupled to said blower;

a transducer to generate a flow signal representing respiratory airflow; and

a processor, coupled to said transducer and said servo-controller, with programmed instructions;

wherein the instructions calculate instantaneous inspired volume as a function of both a the respiratory airflow and an index equal to the fuzzy extent to which any leak is suddenly changing.

14. The apparatus of claim 13 wherein said fuzzy extent to which any leak is suddenly changing is calculated as the fuzzy extent to which the respiratory airflow is large for longer than expected.

15. The apparatus of claim 13 wherein said function is the time integral of the product of said index and said respiratory airflow.