Characterisation of mask systems

Abstract

A method and a CPAP apparatus for characterizing different mask systems, e.g., masks and hoses, are provided. The apparatus can be calibrated for different mask systems and hoses by including sensors for measuring flow and pressure at a flow generator of the apparatus. When the flow generator is fitted to a new system, or changes are made to an existing system, mask or patient interface, and/or hose, a method of calibrating the flow generator is provided. The method includes determining air flow characteristics of the hose using flow measurements made during a first test period when flow through the system is open, measuring or estimating pressure in the system during a second test period when flow through the system is blocked, and determining air flow characteristics of the diffuser using the air first test period flow characteristics of the air delivery hose and the second test period pressure measurements.

1 . A method of characterizing a mask system or a portion of a mask system, the method comprising:
 providing a PAP apparatus for use with a respiratory mask system comprising an air delivery hose and a patient interface including a diffuser, the PAP apparatus including a housing and a flow generator associated with the housing, the flow generator being configured to generate a supply of breathable gas for a patient;   delivering, via the flow generator, a controllable source of breathable gas to the patient interface through the air delivery hose during a test period;   obtaining a plurality of flow measurements of the controllable source of breathable gas during the test period; and   determining a plurality of air flow characteristics of the respiratory mask system at least based on the plurality of flow measurements obtained during the test period, the air flow characteristics of the respiratory mask system being determined while the patient is not wearing the patient interface.   
     
     
         2 . A method of characterizing a respiratory mask system including an air delivery hose, a patient interface, and a PAP apparatus, the PAP apparatus including a housing and a flow generator associated with the housing, the method comprising:
 delivering, via the flow generator, a controllable source of breathable gas to the patient interface through the air delivery hose during a test period;   obtaining a plurality of flow measurements of the controllable source of breathable gas during the test period; and   deter mining a plurality of air flow characteristics of the respiratory mask system at least based on the plurality of flow measurements obtained during the test period, the air flow characteristics of the respiratory mask system being determined while the patient is not wearing the patient interface.   
     
     
         3 . The method of  claim 1 , further comprising determining the air flow characteristics of the air delivery hose and the air flow characteristics of the diffuser of the respiratory mask system. 
     
     
         4 . The method of  claim 1 , further comprising calculating the air flow characteristics of the air delivery hose of the respiratory mask system as a function of a quadratic expression with two hose constants. 
     
     
         5 . The method of  claim 4 , wherein the two hose constants comprise:
   Hose  A =( yX   2   −xY   2 )/( xX   2   −Xx   2 ) and     Hose  B =( xY−yX )/( xX   2   −x   2   X ),   wherein x is a lower air flow for the air delivery hose, X is an upper air flow for the air delivery hose, y is a pressure drop in the air delivery hose at the lower air flow and Y is a pressure drop in the air delivery hose at the upper air flow.   
     
     
         6 . The method of  claim 5 , wherein the two hose constants are used to calculate a true lower test pressure (TrueDiffTP1) and a true upper test pressure (TrueDiffTP2) for the diffuser,
 wherein the true lower test pressure is defined as TrueDiffTP1=DiffTP1−HoseA*x−HoseB*HoseA(x) 2 , where DiffTP1 is the diffuser flow at a lower pressure for the diffuser, and   wherein the true higher test pressure is defined as TrueDiffTP2=DiffTP2−HoseA*x−HoseB*HoseA(X) 2 , where DiffTP2 is the diffuser flow at a higher pressure for the diffuser.   
     
     
         7 . The method of  claim 1 , further comprising determining the air flow characteristics of the respiratory mask system as a function of a quadratic expression with two diffuser constants (Diff A, Diff B). 
     
     
         8 . The method of  claim 7 , wherein the two diffuser constants comprise:
   Diff  A =( zV   2   −vZ   2 )/( vV   2   −Vv   2 ) and     Diff  B =( vZ−zV )/( vV   2   −v   2   V ),   wherein v is a lower pressure for the diffuser, V is an upper pressure for the diffuser, z is a true lower pressure for the diffuser, and Z is a true upper pressure for the diffuser.   
     
     
         9 . The method of  claim 1 , further comprising obtaining a plurality of pressure measurements of the controllable source of breathable gas during at least a portion of the test period. 
     
     
         10 . The method of  claim 9 , further comprising determining the air flow characteristics of the air delivery hose and the air flow characteristics of the diffuser of the respiratory mask system. 
     
     
         11 . The method of  claim 9 , further comprising calculating the air flow characteristics of the air delivery hose of the respiratory mask system as a function of a quadratic expression with two hose constants. 
     
     
         12 . The method of  claim 11 , wherein the two hose constants comprise:
   Hose  A =( yX   2   −xY   2 )/( xX   2   −Xx   2 ) and     Hose  B =( xY−yX )/( xX   2   −x   2   X ),   wherein x is a lower air flow for the air delivery hose, X is an upper air flow for the air delivery hose, y is a pressure drop in the air delivery hose at the lower air flow and Y is a pressure drop in the air delivery hose at the upper air flow.   
     
     
         13 . The method of  claim 12 , wherein the two hose constants are used to calculate a true lower test pressure (TrueDiffTP1) and a true upper test pressure (TrueDiffTP2) for the diffuser,
 wherein the true lower test pressure is defined as TrueDiffTP1=DiffTP1−HoseA*x−HoseB*HoseA(x) 2 , where DiffTP1 is the diffuser flow at a lower pressure for the diffuser, and   wherein the true higher test pressure is defined as TrueDiffTP2=DiffTP2−HoseA*X−HoseB*HoseA(X) 2 , where DiffTP2 is the diffuser flow at a higher pressure for the diffuser.   
     
     
         14 . The method of  claim 9 , further comprising determining the air flow characteristics of the respiratory mask system as a function of a quadratic expression with two diffuser constants (Diff A, Diff B). 
     
     
         15 . The method of  claim 15 , wherein the two diffuser constants comprise:
   Diff  A =( zV   2   −vZ   2 )/( vV   2   −Vv   2 ) and     Diff  B =( vZ−zV )/( vV   2   −v   2   V ),   wherein v is a lower pressure for the diffuser, V is an upper pressure for the diffuser, z is a true lower pressure for the diffuser, and Z is a true upper pressure for the diffuser.   
     
     
         16 . A method of characterizing a mask system or a portion of a mask system, the method comprising:
 providing a PAP apparatus for use with a respiratory mask system comprising an air delivery hose and a patient interface including a diffuser, the PAP apparatus including a housing and a flow generator associated with the housing, the flow generator being configured to generate a supply of breathable gas for a patient;   delivering, via the flow generator, a controllable source of breathable gas to the patient interface through the air delivery hose during a test period;   obtaining a plurality of flow measurements of the controllable source of breathable gas during the test period; and   determining a plurality of air flow characteristics of the respiratory mask system at least based on the plurality of flow measurements obtained during the test period, the air flow characteristics of the respiratory mask system being determined without sending the respiratory mask system back to a manufacturer of the respiratory mask system.