Methods and apparatus for varying back-up breathable gas timing
A ventilator device delivers ventilatory support to a patient in a back up timed mode when patient respiration is not detected or a spontaneous mode when patient respiration is detected. The timing threshold governing the back-up mode is chosen to deviate from normal expected respiration time for the patient to promote patient initiated ventilation in the spontaneous mode but permit back-up ventilation in the event of apnea. Automated adjustments to the timing threshold during the timed mode are made from the less vigilant timing threshold to a more vigilant threshold at or near a timing of normal expected breathing of the patient. Such adjustments may be made from a minimum to a maximum vigilance timing settings or incrementally there between as a function of time in the timed mode which is preferably the number of delivered machine breaths.
1. An apparatus for adjusting back-up delivery of breathable gas to a patient for the patient's respiration comprising:
a breathable gas source configured to deliver the breathable gas to a patient, the delivery of the breathable gas being directed to the patient through a respiratory conduit of the apparatus,
a sensor for detecting patient breathing, and
a controller, including at least one processor, the controller coupled with the sensor and the breathable gas source, the controller configured to:
detect patient inspiration with the sensor;
trigger a delivery of the breathable gas if patient inspiration is detected;
in a back-up mode, control automatic delivery, as a back-up, of the breathable gas if patient inspiration is not detected, wherein the automatic delivery of the breathable gas in the back-up mode is determined as a function of an initial timing and elapsed time;
adjust the initial timing to a modified timing after the automatic delivery in the back-up mode, the modified timing being a decrease of the initial timing; and
in the back-up mode, control automatic delivery, as a subsequent back-up, of the breathable gas if patient inspiration is not detected, wherein the automatic delivery of the subsequent breathable gas in the back-up mode is determined as a function of the modified timing and elapsed time.
2. The apparatus according to claim 1 , further comprising a servo-valve configured to permit delivery of the breathable gas, the servo-valve under control of the controller.
3. The apparatus according to claim 1 , wherein the controller adjusts the initial timing to the modified timing with a predetermined number of automatic deliveries.
4. The apparatus according to claim 3 , wherein the modified timing is implemented with a timing threshold that is set to a value that is closer to a (a) patient average breath rate or (b) patient average breath period, if a spontaneous patient breath is absent.
5. The apparatus according to claim 4 , wherein the timing threshold is adjusted to a value that is further away from the (a) patient average breath rate or (b) patient average breath period, if a spontaneous patient breath is detected.
6. The apparatus according to claim 4 , wherein the timing threshold is adjusted based on a measure of adequacy of patient ventilation.
7. The apparatus according to claim 6 , wherein the controller is configured to control delivery of a target ventilation and the sensor is configured to measure actual ventilation and the adequacy of patient ventilation comprises a relationship between the target ventilation and the actual measured ventilation.
8. The apparatus according to claim 7 , wherein the relationship comprises a ratio of the actual measured ventilation and the target ventilation.
9. The apparatus according to claim 7 , wherein the sensor comprises a flow sensor or a differential pressure transducer and the actual measured ventilation is determined from a signal from the flow sensor or the differential pressure transducer.
10. The apparatus according to claim 7 , wherein the apparatus comprises a servoventilator.
11. The apparatus according to claim 10 , wherein the servoventilator comprises an impeller coupled to a motor of the servoventilator.
12. The apparatus according to claim 1 wherein the breathable gas source is a motor operated pressure source.
13. A method for adjusting back-up delivery of breathable gas for a patient for the patient's respiration using a breathable gas source and a controller, the method comprising:
detecting patient inspiration with a sensor;
triggering a delivery of the breathable gas if patient inspiration is detected;
in a back-up mode, control automatic delivery, as a back-up, of the breathable gas if patient inspiration is not detected, wherein the automatic delivery of the breathable gas in the back-up mode is determined as a function of a first timing and elapsed time;
adjusting, by the controller, the first timing to a second timing after the automatic delivery in the back-up mode, the second timing being a decrease of the first timing; and
in the back-up mode, automatically control delivery, as a subsequent back-up, of the breathable gas if patient inspiration is not detected, wherein the automatic delivery of the subsequent breathable gas in the back-up mode is determined as a function of the second timing and elapsed time.
14. The method according to claim 13 , further comprising controlling operation of a servo-valve with the controller to permit delivery of the breathable gas.
15. The method according to claim 13 , wherein the adjusting comprises adjusting the first timing to the second timing with a predetermined number of automatic deliveries.
16. The method according to claim 15 , further comprising adjusting, by the controller, the first timing so that the second timing is closer to a (a) patient average breath rate or (b) patient average breath period, if a spontaneous patient breath is not detected before lapsing of the first timing.
17. The method according to claim 16 , further comprising adjusting, by the controller, timing of delivery of the breathable gas to a third timing so that the third timing is further away from the (a) patient average breath rate or (b) patient average breath period, if a spontaneous patient breath is not detected.
18. The method according to claim 13 , further comprising adjusting timing in the back-up mode based on a measure of adequacy of patient ventilation.
19. The method according to claim 13 wherein the breathable gas source is a motor operated pressure source.