Methods and apparatus for ventilatory treatment of respiratory disorders
Methods and apparatus treat a respiratory disorder. For example, a pressure generator supplies a flow of air at positive pressure to a patient's airway through a patient interface. A sensor generates a signal representing respiratory flow rate of the patient. A controller controls the pressure generator to provide to the patient interface a ventilation therapy having a base pressure. The controller computes a measure of ventilation of the patient from the signal. The controller computes a measure of flow limitation from an inspiratory portion of the signal. The controller computes a ratio of the measure of ventilation and an expected normal ventilation. The controller adjusts a set point for the base pressure of the ventilation therapy based on the measure of flow limitation. The adjustment may further depend on a comparison between the ratio and a relative ventilation threshold that increases as the measure of flow limitation increases.
1. Apparatus for treating a respiratory disorder in a patient, comprising:
a pressure generator configured to supply a flow of air at positive pressure to an airway of the patient through a patient interface;
a sensor configured to generate a signal representative of respiratory flow rate of the patient; and
a controller configured to:
control the pressure generator to provide to the patient interface a ventilation therapy having a base pressure,
compute a measure of ventilation of the patient from the signal representative of respiratory flow rate,
compute a measure of flow limitation from an inspiratory portion of the respiratory flow rate signal,
compute a ratio of the measure of ventilation and an expected normal ventilation, and
adjust a set point for the base pressure of the ventilation therapy based on the measure of flow limitation,
wherein the adjustment further depends on a comparison between the ratio and a relative ventilation threshold determined such that the relative ventilation threshold increases as the measure of flow limitation increases.
2. Apparatus according to claim 1 , wherein the controller is configured to adjust the set point for the base pressure of the ventilation therapy based on the measure of flow limitation by:
computing a ventilation-related multiplier as a function of the ratio and the relative ventilation threshold, and
computing a prescribed increase to the set point for the base pressure from a product of the multiplier and a difference between the measure of flow limitation and a flow limitation threshold.
3. Apparatus according to claim 2 , wherein the ventilation-related multiplier decreases from one to zero as the ratio increases above the relative ventilation threshold.
4. Apparatus according to claim 2 , wherein the ventilation-related multiplier increases as the ratio falls below the relative ventilation threshold.
5. Apparatus according to claim 2 , wherein the flow limitation threshold increases as current base pressure increases.
6. Apparatus according to claim 2 , wherein the ventilation-related multiplier increases in proportion to a measure of recent persistent flow-limited significant hypoventilation over multiple breaths.
7. Apparatus according to claim 6 , wherein the controller is configured to compute the measure of recent persistent flow-limited significant hypoventilation by filtering a measure of flow-limited significant hypoventilation over multiple breaths.
8. Apparatus according to claim 1 , wherein the base pressure set point adjustment further depends on a current value of the base pressure.
9. Apparatus according to claim 8 , wherein the base pressure set point adjustment comprises:
computing a base pressure-related multiplier that decreases from one to zero as the current value of base pressure increases, and
computing a prescribed increase to the set point for the base pressure from a product of the base pressure-related multiplier and a difference between the measure of flow limitation and a flow limitation threshold.
10. Apparatus according to claim 1 , wherein the controller is further configured to estimate a current value of leak flow rate, and the base pressure set point adjustment further depends on the current value of leak flow rate.
11. Apparatus according to claim 10 , wherein the adjustment comprises:
computing a leak-related multiplier that decreases from one to zero as estimated leak flow rate increases, and
computing a prescribed increase to the set point for the base pressure from a product of the leak-related multiplier and a difference between the measure of flow limitation and a flow limitation threshold.
12. Apparatus according to claim 11 , wherein the flow limitation threshold increases as current base pressure increases.
13. Apparatus according to claim 1 , wherein the ventilation therapy is servo-ventilation therapy, and the expected normal ventilation is a target ventilation of the servo-ventilation therapy.
14. Apparatus according to claim 1 , wherein the measure of ventilation is a breathwise ventilation.
15. Apparatus according to claim 1 , wherein the measure of flow limitation includes a measure of M-shape of the inspiratory portion.
16. A method of treating a respiratory disorder in a patient, the method comprising:
controlling, with a ventilator, a ventilation therapy through a patient interface for the patient, the ventilation therapy having a base pressure,
computing a measure of ventilation of the patient from a sensor producing a signal representative of respiratory flow rate of the patient,
computing a measure of flow limitation from an inspiratory portion of the respiratory flow rate signal;
computing a ratio of the measure of ventilation and an expected normal ventilation; and
in a controller of the ventilator, adjusting a set point for the base pressure of the ventilation therapy based on the measure of flow limitation,
wherein the adjusting further depends on a comparison, in the controller, between the ratio and a relative ventilation threshold that increases as the measure of flow limitation increases.
17. A method according to claim 16 , wherein adjusting the set point for the base pressure of the ventilation therapy based on the measure of flow limitation, in the controller of the ventilator, comprises:
computing a ventilation-related multiplier as a function of the ratio and the relative ventilation threshold, and
computing a prescribed increase to the set point for the base pressure from a product of the multiplier and a difference between the measure of flow limitation and a flow limitation threshold.
18. A method according to claim 17 , wherein the ventilation-related multiplier decreases from one to zero as the ratio increases above the relative ventilation threshold.
19. A method according to claim 17 , wherein the ventilation-related multiplier increases as the ratio falls below the relative ventilation threshold.
20. A method according to claim 17 , wherein the flow limitation threshold increases as current base pressure increases.
21. A method according to claim 17 , wherein the ventilation-related multiplier increases in proportion to a measure of recent persistent flow-limited significant hypoventilation over multiple breaths.
22. A method according to claim 21 , further comprising computing the measure of recent persistent flow-limited significant hypoventilation by filtering a measure of flow-limited significant hypoventilation over multiple breaths.
23. A method according to claim 16 , wherein the base pressure set point adjustment further depends on a current value of the base pressure.
24. A method according to claim 23 , wherein adjusting the base pressure set point comprises:
computing a base pressure-related multiplier that decreases from one to zero as the current value of base pressure increases, and
computing a prescribed increase to the set point for the base pressure from a product of the base pressure-related multiplier and a difference between the measure of flow limitation and a flow limitation threshold.
25. A method according to claim 16 , further comprising estimating a current value of leak flow rate, and adjusting the base pressure set point further depends on the current value of leak flow rate.
26. A method according to claim 25 , wherein adjusting the base pressure set point further comprises:
computing a leak-related multiplier that decreases from one to zero as estimated leak flow rate increases, and
computing a prescribed increase to the set point for the base pressure from a product of the leak-related multiplier and a difference between the measure of flow limitation and a flow limitation threshold.
27. A method according to claim 26 , wherein the flow limitation threshold increases as current base pressure increases.
28. A method according to claim 16 , wherein the ventilation therapy is servo-ventilation therapy, and the expected normal ventilation is a target ventilation of the servo-ventilation therapy.
29. A method according to claim 16 , wherein the measure of ventilation is a breathwise ventilation.
30. A method according to claim 16 , wherein the measure of flow limitation includes a measure of M-shape of the inspiratory portion.