Determination of leak during CPAP treatment
View Patent ↗In a CPAP or positive pressure ventilation system, leak is determined at each instant by a lookback for a time as long as single breath to establish the start of an averaging window over which low-pass filtered values used in the determination of a parameter of a leak model are averaged. A jamming index indicates whether the leak is rapidly changing. To the extent that jamming is high, the leak estimate used progressively changes from that using sliding breath-window averaging to a more robust and faster responding low-pass filter method, and adjustment of ventilatory support based on measures employing estimated respiratory flow is slowed down or stopped.
1. A method of determining a mask leak conductance in a patient respiratory device, comprising:
determining a first estimate of leak conductance which responds relatively quickly to changes in leak conductance,
determining a second estimate of leak conductance which responds more slowly to changes in leak conductance, and
determining the mask leak conductance as a function of the first and second estimates of leak conductance.
2. A method according to claim 1 , further comprising determining the pressure in the mask.
3. A method according to claim 2 , further comprising determining an estimate of non-deliberate mask leak as a function of the mask leak conductance and the mask pressure.
4. A method according to claim 3 , wherein the non-deliberate mask leak is calculated as:
Q leak =G j √P mask
wherein:
Q leak is non-deliberate mask leak,
G j is mask leak conductance, and
P mask is mask pressure.
5. A method according to claim 1 , further comprising determining an uncompensated leak index representative of an extent to which mask leak is uncompensated.
6. A method according to claim 5 , wherein the mask leak conductance is calculated as a function of the uncompensated leak index and the first and second estimates of leak conductance.
7. A method according to claim 6 , wherein the mask leak conductance is calculated as:
G j =JG 1 +(1− J ) G 2
wherein:
G j is an estimate of mask leak conductance,
G 1 is the first estimate of leak conductance.
G 2 is the second estimate of leak conductance, and
J is a jamming index of the uncompensated mask leak.
8. A method of claim 7 , wherein the jamming index is between zero and one.