Determination of leak and respiratory airflow
First Claim
1. A method for determining instantaneous leak flow at a mask having a leak path during mechanical ventilation, the method comprising the steps of:
- (a) determining instantaneous airflow at the mask;
(b) determining instantaneous pressure at the mask;
(c) estimating non-linear conductance of said leak path as the low-pass filtered instantaneous airflow divided by the low-pass filtered square root of the instantaneous pressure; and
(d) determining said instantaneous leak flow to be said conductance multiplied by the square root of the said instantaneous 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.
58 Citations
18 Claims
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1. A method for determining instantaneous leak flow at a mask having a leak path during mechanical ventilation, the method comprising the steps of:
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(a) determining instantaneous airflow at the mask;
(b) determining instantaneous pressure at the mask;
(c) estimating non-linear conductance of said leak path as the low-pass filtered instantaneous airflow divided by the low-pass filtered square root of the instantaneous pressure; and
(d) determining said instantaneous leak flow to be said conductance multiplied by the square root of the said instantaneous pressure.
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2. A method for determining instantaneous respiratory airflow for a subject receiving breathable gas by a mask and in the presence of any mask leak, the method comprising the steps of:
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(a) determining instantaneous airflow at the mask;
(b) determining instantaneous pressure at the mask;
(c) estimating non-linear conductance of said leak path as the low pass filtered instantaneous airflow divided by the low pass filtered square root of the instantaneous pressure;
(d) determining instantaneous leak flow to be said conductance multiplied by the square root of the said instantaneous pressure; and
(e) calculating the respiratory airflow as the instantaneous airflow minus the instantaneous leak flow. - View Dependent Claims (3, 4, 5, 6)
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7. Apparatus for determining respiratory airflow for a subject receiving breathable gas by a mask and in the presence of any mask leak, the apparatus comprising:
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transducer means located at or proximate the mask to determine instantaneous mask airflow and pressure; and
processing means for estimating non-linear conductance of said leak path as the low pass filtered instantaneous airflow divided by the low pass filtered square root of the instantaneous pressure, determining instantaneous leak flow to be said conductance multiplied by the square root of the said instantaneous pressure, and calculating the respiratory airflow as the instantaneous airflow minus the instantaneous leak flow. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. Apparatus for providing continuous positive airway pressure treatment or mechanical ventilation, the apparatus comprising:
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a turbine for the generation of a supply of breathable gas;
a gas delivery tube having connection with the turbine;
a mask having connection to the delivery tube to supply said breathable gas to a subject'"'"'s airway;
transducer means located at or proximate the mask to determine instantaneous mask airflow and pressure;
processor means for estimating non-linear conductance of said leak path as the low pass filtered instantaneous airflow divided by the low pass filtered square root of the instantaneous pressure, determining instantaneous leak flow to be said conductance multiplied by the square root of the said instantaneous pressure, and calculating the respiratory airflow as the instantaneous airflow minus the instantaneous leak flow; and
control means to control the flow generator to, in turn, control the mask pressure and/or mask airflow on the basis of the calculated respiratory airflow. - View Dependent Claims (15, 16, 17)
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18. A computer program for determining instantaneous respiratory airflow for a subject receiving breathable gas by a mask and in the presence of any mask leak, the program receiving input data of instantaneous airflow and pressure at the mask, and comprising the computational steps of:
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(a) determining instantaneous airflow at the mask;
(b) determining instantaneous pressure at the mask;
(c) estimating non-linear conductance of said leak path as the low pass filtered instantaneous airflow divided by the low pass filtered square root of the instantaneous pressure;
(d) determining instantaneous leak flow to be said conductance multiplied by the square root of the said instantaneous pressure; and
(e) calculating the respiratory airflow as the instantaneous airflow minus the instantaneous leak flow.
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Specification