Determination of leak and respiratory airflow
First Claim
1. A method for determining the instantaneous leak flow from a face mask comprising the steps of:
- (a) determining pairs of values for pressure in the mask and airflow through the mask;
(b) calculating the conductance of a leak as a function of pairs of values for pressure and airflow that are determined over a time interval that exceeds a normal breath; and
(c) calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneous determined value of mask pressure.
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Abstract
Methods and apparatus for determining leak and respiratory airflow are disclosed. A pressure sensor (34) and a differential pressure sensor (32) have connection with a pneumotach (24) to derive instantaneous mask pressure and airflow respectively. A microcontroller (38) estimates a non-linear conductance of any leak path occurring at a mask (12) as being the low pass filtered instantaneous airflow divided by the low pass filtered square root of the instantaneous pressure. The instantaneous leak flow is then the conductance multiplied by the square root of the instantaneous pressure, and the respiratory airflow is calculated as being the instantaneous airflow minus the instantaneous leak flow. The time constants for the low pass filtering performed by the microcontroller (38) can be dynamically adjusted dependent upon sudden changes in the instantaneous leak flow.
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Citations
33 Claims
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1. A method for determining the instantaneous leak flow from a face mask comprising the steps of:
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(a) determining pairs of values for pressure in the mask and airflow through the mask;
(b) calculating the conductance of a leak as a function of pairs of values for pressure and airflow that are determined over a time interval that exceeds a normal breath; and
(c) calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneous determined value of mask pressure. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for determining the instantaneous leak flow from a patient mask during mechanical ventilation comprising transducer means located at or approximate to the mask to determine instantaneous values for the pressure in the mask and the airflow through the mask;
- and processor means for calculating the conductance of the leak as a function of said pressure and airflow values determined over a time interval exceeding that of a normal breath, and for calculating the instantaneous leak flow as a function of the calculated leak conductance and the instantaneously determined value of mask pressure.
- View Dependent Claims (7, 8, 9)
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10. Apparatus for providing mechanical ventilation for a patient comprising a flow generator for the supply of pressurized breathable gas;
- a gas delivery system having connection with the flow generator;
a mask having connection with the gas delivery system to supply said gas to the airway of said patient;
transducer means continuously taking measurements from which the pressure in the mask and the airflow through the mask can be determined;
processor means calculating the conductance of any mask leak as a function of said mask pressure and airflow values determined over a time interval exceeding that of a normal breath, and for calculating the instantaneous leak flow as a function of the calculated leak conductance and the determined value of mask pressure; and
control means to adjust said flow generator to control at least one of mask pressure and mask airflow on the basis of the mask airflow and calculated leak flow. - View Dependent Claims (11, 12, 13, 14)
- a gas delivery system having connection with the flow generator;
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15. A method for determining the instantaneous leak flow from a patient mask comprising the steps of determining instantaneous values for pressure in the mask and airflow through the mask;
- calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values wherein said average values are taken over a period exceeding a normal breath; and
calculating the instantaneous leak flow as a function of the calculated leak conductance and the instantaneously determined value of mask pressure. - View Dependent Claims (16, 17)
- calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values wherein said average values are taken over a period exceeding a normal breath; and
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18. A method of providing breathable gas for a patient comprising the steps of supplying pressurized breathable gas via a mask to the airway of said patient;
- continuously taking measurements from which the pressure in the mask and the airflow through the mask can be determined;
calculating the conductance of any mask leak as a function of said mask pressure and airflow values determined over a time interval exceeding that of a normal breath, and calculating the instantaneous leak flow as a function of the calculated leak conductance and the determined value of mask pressure; and
adjusting the supply of said breathable gas in accordance with the mask airflow and calculated leak flow. - View Dependent Claims (19, 20, 21, 22)
- continuously taking measurements from which the pressure in the mask and the airflow through the mask can be determined;
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23. Apparatus for determining the instantaneous leak flow from a patient mask comprising means for determining instantaneous values for the pressure in the mask and the airflow through the mask;
- means for calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values taken over a time period of more than a normal breath; and
means for calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneously determined value of pressure in the mask. - View Dependent Claims (24)
- means for calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values taken over a time period of more than a normal breath; and
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25. Apparatus for determining the instantaneous leak flow from a patient mask comprising means for determining instantaneous values for pressure in the mask and airflow through the mask;
- means for calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values; and
means for calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneously determined value of pressure in the mask, wherein the time interval over which pressure and airflow values are used to determine leak conductance is varied inversely with the rate at which the calculated leak conductance changes.
- means for calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values; and
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26. Apparatus for providing breathable gas to a patient comprising means for supplying pressurized breathable gas via a mask to the airway of said patient;
- means for continuously taking measurements from which the pressure in the mask and the airflow through the mask can be determined;
means for calculating the conductance of any mask leak as a function of said mask pressure and airflow values determined over a time interval exceeding that of a normal breath, and for calculating the instantaneous leak flow as a function of the calculated leak conductance and the determined value of mask pressure; and
means for adjusting the supply of said breathable gas in accordance with the mask airflow and calculated leak flow. - View Dependent Claims (27, 28, 29, 30)
- means for continuously taking measurements from which the pressure in the mask and the airflow through the mask can be determined;
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31. A method for determining an instantaneous leak flow from a patient mask during mechanical ventilation comprising the step of:
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(a) continuously determining values for pressure in the mask and airflow through the mask wherein said values are determined by taking direct measures of pressure and airflow;
(b) calculating conductance of a leak as a function of the values for pressure and airflow determined over a time interval wherein said time interval exceeds that of a normal breath and varies inversely with the rate at which the calculated leak conductance changes; and
(c) calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneous determined value of mask pressure.
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32. A method for determining an instantaneous leak flow from a patient mask during mechanical ventilation from an air delivery system comprising the steps of:
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(a) continuously determining values for pressure in the mask and airflow through the mask wherein said values are determined by taking direct measures of pressure and airflow at a point remote from the mask and calculating said values in accordance with physical characteristics of the air delivery system and the direct measures;
(b) calculating conductance of a leak as a function of the values for pressure and airflow determined over a time interval wherein said time interval exceeds that of a normal breath and varies inversely with the rate at which the calculated leak conductance changes; and
(c) calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneous determined value of mask pressure, wherein said mechanical ventilation is accomplished by forcing air to flow through the air delivery system.
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33. A method for determining the instantaneous leak flow from a patient mask comprising the steps of determining instantaneous values for pressure in the mask and airflow through the mask;
- calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values; and
calculating the instantaneous leak flow as a function of the calculated leak conductance and an instantaneously determined value of mask pressure, wherein the time interval over which pressure and airflow values are used to calculate leak conductance is varied inversely with the rate at which the calculated leak conductance changes.
- calculating the conductance of the leak as a function of the average values of the respective pressure and airflow instantaneous values; and
Specification