Determination of leak and respiratory airflow

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.

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.

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.

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.

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.

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.

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.