Gas supply device for sleep apnea
An apparatus is provided for controlling air supplied under pressure to a patient suffering from sleep disorders such as apnoea. The apparatus measures and/or calculates the inspiratory air flow, volume and pressure to the airway. Controlled pressurized air is supplied to the patient's upper anatomical airway, wherein the apparatus measures the air flow and pressure to the airway. The apparatus determines whether to increase or decrease the pressure to the patient's airway based on a determination of one or more factors, such as the occurrence of hypopnoea, hyperventilation, obstructive or central apnoea, air leakage and acoustical vibrations. Occurrences of events representing a sleep problem may be stored by the apparatus and retrieved by a clinician at a later date.
1. A method for managing gas delivery to a patient, comprising:
delivering gas to a patient;
determining a flow amplitude for each of a first plurality of breath cycles;
determining a mean of the determined flow amplitudes for the first plurality of breath cycles;
determining a flow amplitude for a particular breath cycle occurring subsequent to the first plurality of breath cycles;
identifying the particular breath cycle as a hypoventilated breath cycle if the flow amplitude for the particular breath cycle is less than the product of the determined mean flow amplitude for the first plurality of breath cycles and a first factor; and
determining whether to increase the pressure of gas delivered to the patient based at least on whether the particular breath cycle is identified as a hypoventilated breath cycle.
2. A method according to claim 1 , further comprising identifying the particular breath cycle as a hyperventilated breath cycle if the flow amplitude for the particular breath cycle is greater than the product of the determined mean flow amplitude for the first plurality of breath cycles and a second factor greater than the first factor.
3. A method according to claim 1 , wherein the first factor is substantially equal to 40%.
4. A method according to claim 1 , comprising:
determining a duration of consecutive breath cycles identified as hypoventilated breath cycles; and
determining to increase the pressure of gas delivered to the patient if the duration of consecutive breath cycles identified as hypoventilated breath cycles exceeds a predetermined threshold duration.
5. A method according to claim 1 , further comprising:
determining a mean breath cycle duration of a second plurality of breath cycles by the patient; and
determining whether the duration of the particular breath cycle is greater than the product of the mean breath cycle duration of the second plurality of breath cycles and a second factor.
6. A method according to claim 5 , further comprising:
increasing a hypoventilated breath cycle time counter if the duration of the particular breath cycle is greater than the product of the mean breath cycle duration of the second plurality of breath cycles and the second factor; and
using the hypoventilated breath cycle time counter for determining whether to increase the pressure of gas delivered to the patient based on one or more hypoventilated breath cycles subsequent to the particular breath cycle.
7. A method according to claim 5 , wherein the second plurality of breath cycles at least partially overlaps with the first plurality of breath cycles.
8. A method according to claim 1 , further comprising:
identifying the particular breath cycle as a hyperventilated breath cycle if the flow amplitude for the particular breath cycle is greater than the product of the determined mean flow amplitude for the first plurality of breath cycles and a second factor greater than the first factor; and
identifying the particular breath cycle as a normal breath cycle if the flow amplitude for the particular breath cycle is neither (a) less than the product of the determined mean flow amplitude for the first plurality of breath cycles and the first factor, nor (b) greater than the product of the determined mean flow amplitude for the first plurality of breath cycles and the second factor.
9. A method according to claim 1 , wherein each determined flow amplitude comprises a peak inspiratory flow amplitude.
10. A breathing assistance apparatus, comprising:
a pressure supply module configured to supply pressurized air toward a patient;
at least one sensor configured to monitor air supplied by the pressure supply module; and
a pressure control unit coupled to the pressure supply module, the pressure control unit configured to:
determine a flow amplitude for each of a first plurality of breath cycles;
determine a mean of the determined flow amplitudes for the first plurality of breath cycles;
determine a flow amplitude for a particular breath cycle occurring subsequent to the first plurality of breath cycles;
identify the particular breath cycle as a hypoventilated breath cycle if the flow amplitude for the particular breath cycle is less than the product of the determined mean flow amplitude for the first plurality of breath cycles and a first factor; and
determine whether to increase the pressure of gas delivered to the patient based at least on whether the particular breath cycle is identified as a hypoventilated breath cycle.
11. An apparatus according to claim 10 , wherein the pressure control unit is further configured to identify the particular breath cycle as a hyperventilated breath cycle if the flow amplitude for the particular breath cycle is greater than the product of the determined mean flow amplitude for the first plurality of breath cycles and a second factor greater than the first factor.
12. An apparatus according to claim 10 , wherein the pressure control unit is configured to:
determine a duration of consecutive breath cycles identified as hypoventilated breath cycles; and
determine to increase the pressure of gas delivered to the patient if the duration of consecutive breath cycles identified as hypoventilated breath cycles exceeds a predetermined threshold duration.
13. An apparatus according to claim 10 , wherein the pressure control unit is further configured to:
determine a mean breath cycle duration of a second plurality of breath cycles by the patient; and
determine whether the duration of the particular breath cycle is greater than the product of the mean breath cycle duration of the second plurality of breath cycles and a second factor.
14. An apparatus according to claim 13 , wherein the pressure control unit is further configured to:
increase a hypoventilated breath cycle time counter if the duration of the particular breath cycle is greater than the product of the mean breath cycle duration of the second plurality of breath cycles and the second factor; and
use the hypoventilated breath cycle time counter for determining whether to increase the pressure of gas delivered to the patient based on one or more hypoventilated breath cycles subsequent to the particular breath cycle.
15. An apparatus according to claim 13 , wherein the second plurality of breath cycles at least partially overlaps with the first plurality of breath cycles.
16. An apparatus according to claim 10 , wherein the pressure control unit is further configured to:
identify the particular breath cycle as a hyperventilated breath cycle if the flow amplitude for the particular breath cycle is greater than the product of the determined mean flow amplitude for the first plurality of breath cycles and a second factor greater than the first factor; and
identify the particular breath cycle as a normal breath cycle if the flow amplitude for the particular breath cycle is neither (a) less than the product of the determined mean flow amplitude for the first plurality of breath cycles and the first factor, nor (b) greater than the product of the determined mean flow amplitude for the first plurality of breath cycles and the second factor.
17. An apparatus according to claim 10 , wherein each determined flow amplitude comprises a peak inspiratory flow amplitude.
18. Software for managing gas delivery to a patient, the software embodied in tangible computer-readable media and when executed by a processor, configured to:
determine a flow amplitude for each of a first plurality of breath cycles;
determine a mean of the determined flow amplitudes for the first plurality of breath cycles;
determine a flow amplitude for a particular breath cycle occurring subsequent to the first plurality of breath cycles;
identify the particular breath cycle as a hypoventilated breath cycle if the flow amplitude for the particular breath cycle is less than the product of the determined mean flow amplitude for the first plurality of breath cycles and a first factor; and
determine whether to increase the pressure of gas delivered to the patient based at least on whether the particular breath cycle is identified as a hypoventilated breath cycle.