Determination of leak and respiratory airflow
First Claim
1. A method for determining a delivery pressure at a mask during pressure assistance of a patient from remote measurements of pressure comprising:
- providing a controllable pressure delivery device with a mask and conduit;
delivering pressure treatment to a patient through the conduit to the mask with the pressure delivery device;
measuring a pressure distally from the mask;
continuously determining a pressure characteristic for the conduit;
calculating an instantaneous mask pressure as a function of the measured distal pressure and the determined pressure characteristic;
calculating a conductance associated with a leak from said mask as a function of the average values of said instantaneous mask pressure and air flow to the mask taken over a time period that exceeds a normal breath;
calculating an instantaneous leak flow based on said instantaneous mask pressure and said conductance;
selecting a desired mask pressure for setting a delivery pressure for the patient;
controlling the pressure delivery device to deliver the desired mask pressure as a function of the estimated mask pressure and the instantaneous leak airflow.
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Accused Products
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
25 Claims
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1. A method for determining a delivery pressure at a mask during pressure assistance of a patient from remote measurements of pressure comprising:
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providing a controllable pressure delivery device with a mask and conduit;
delivering pressure treatment to a patient through the conduit to the mask with the pressure delivery device;
measuring a pressure distally from the mask;
continuously determining a pressure characteristic for the conduit;
calculating an instantaneous mask pressure as a function of the measured distal pressure and the determined pressure characteristic;
calculating a conductance associated with a leak from said mask as a function of the average values of said instantaneous mask pressure and air flow to the mask taken over a time period that exceeds a normal breath;
calculating an instantaneous leak flow based on said instantaneous mask pressure and said conductance;
selecting a desired mask pressure for setting a delivery pressure for the patient;
controlling the pressure delivery device to deliver the desired mask pressure as a function of the estimated mask pressure and the instantaneous leak airflow. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for determining a mask airflow at a mask during pressure assistance of a patient from remote measurements of pressure comprising:
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providing an airway pressure treatment apparatus with a mask and conduit;
delivering airway pressure treatment to a patient through the conduit to the mask with the apparatus;
measuring a pressure distally from the mask;
continuously determining a pressure drop to the mask for the conduit;
determining a conductance of a leak from the mask;
determining an instantaneous leak airflow from said conductance calculating the air flow at the mask as a function of the determined pressure drop and the instantaneous leak airflow. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15)
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16. An apparatus for determining respiratory airflow during pressure assistance of a patient from remote measurements of pressure comprising:
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a mask through which a gas is provided to the patient, and through which some gas leaks out at a leak airflow dependent on the current respiratory phase;
a conduit with a proximate end and a distal end, wherein the proximate end is coupled to the mask;
a gas delivery device coupled to the distal portion of the conduit and providing a gas at a pressure above atmospheric to the airway of the patient through the mask and conduit;
a sensor disposed at said distal end to determine the input air flow from said gas delivery device into said conduit; and
a controller with a processor adapted to;
determine a leak conductance at the mask and the corresponding instantaneous leak air flow; and
calculate the mask airflow to the patient based on said input airflow and said leak airflow. - View Dependent Claims (17, 18, 19, 20)
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21. A computer program for determining instantaneous respiratory airflow from a blower to a mask worn by a subject through a conduit, said conduit having a distal end connected to said blower and a proximal end connected to the mask, the program receiving input data of instantaneous airflow from the blower and the pressure at the blower, comprising the steps of:
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determining the pressure drop in the conduit due to the blower airflow;
determining the instantaneous pressure at the mask based on the pressure at the blower and said pressure drop;
determining an instantaneous leak airflow from the mask, said instantaneous leak airflow being related to said instantaneous pressure at the mask; and
determining an airflow from the mask based on blower airflow and the leak airflow. - View Dependent Claims (22, 23, 24)
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25. An apparatus for determining respiratory air flow during pressure assistance of a patient from remote measurements of pressure comprising:
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a mask;
a conduit with a proximate end and a distal end, wherein the proximate end is coupled to the mask;
a gas delivery device coupled to the distal portion of the conduit and providing a gas at a pressure above atmospheric to the airway of the patient through the mask and conduit;
a sensor disposed at said distal end to determine the input air flow from said gas delivery device into said conduit; and
processor means processor adapted to;
determine an instantaneous leak airflow based on a leak conductance from said mask; and
calculate the mask airflow to the patient based on said input airflow, and said leak airflow.
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Specification