Methods and apparatus with improved ventilatory support cycling
A ventilator that delivers air at different pressures to a patient during inspiratory and expiratory cycles of breathing and that cycles from inspiratory to expiratory operation when the patient's respiratory flow passes a threshold level. The threshold generally increases from the beginning of inspiration to the end of inspiration. The increase can be linear over all or only a portion of the inspiratory cycle, and the threshold can be adjusted so that cycling is prevented during the initial portion of an inspiratory cycle. The minimum and maximum levels may both be functions of peak flow and the threshold may increase as a function of elapsed inspiratory time. The rate at which the threshold increases from a minimum level to a maximum level may be adjustable for individual patient needs and may be determined from previous breaths.
1. A ventilator that delivers air at different pressures during inspiratory and expiratory cycles of a patient's breathing, the ventilator comprising:
a controller or processor coupled to a memory storing programming instructions, the controller or processor configured using the instructions to:
receive data indicative of respiratory flow, the data including inspiratory cycle flow data for an inspiratory cycle, and
determine a computed threshold flow level by computing a threshold flow level that varies as a function of elapsed inspiratory time and that is a predetermined amount above a zero level for at least a portion of a respiratory cycle,
wherein the ventilator cycles from an inspiratory operation to an expiratory operation based on a comparison of the inspiratory cycle flow data to the computed threshold flow level.
2. The ventilator of claim 1 , wherein the controller or processor is further configured using the instructions to compare the inspiratory cycle flow data to the computed threshold flow level and cause the ventilator to cycle from inspiratory to expiratory operation.
3. The ventilator of claim 1 , wherein the computed threshold flow level increases from a minimum level to a maximum level during the inspiratory cycle.
4. The ventilator of claim 3 , wherein the controller computes the minimum and maximum levels as a function of a multiplier and peak inspiratory flow data included in the received respiratory flow data.
5. The ventilator of claim 1 , wherein the computed threshold flow level increases from a minimum level to a maximum level as a function of elapsed inspiratory time and a predetermined maximum inspiratory time.
6. The ventilator of claim 1 , wherein the controller or processor is configured to cause the ventilator to cycle from inspiratory operation to expiratory operation by controlling a motor current associated with a blower.
7. The ventilator of claim 1 , wherein the controller or processor is configured to cause the ventilator to cycle from inspiratory operation to expiratory operation by controlling a motor speed associated with a blower.
8. The ventilator of claim 1 , further comprising a mask and a flow sensor for deriving the data indicative of respiratory flow associated with the mask.
9. The ventilator of claim 8 , further comprising a pressure sensor for deriving pressure data associated with the mask and providing the pressure data to the controller or processor.
10. A method for switching a ventilator between inspiratory operation and expiratory operation, the method comprising:
detecting respiratory flow data for an inspiratory cycle;
determining a computed threshold flow level by computing a threshold flow level that varies as function of elapsed inspiratory time of a respiratory cycle and that is a predetermined amount above a zero level for at least a portion of the respiratory cycle;
comparing the computed threshold flow level to the detected respiratory flow data; and
switching the ventilator from an inspiratory operation to an expiratory operation based on the comparison.
11. The method of claim 10 , wherein the computed threshold flow level varies from a minimum value to a maximum value.
12. The method claim 10 , wherein the computed threshold flow level is set to prevent cycling to expiration during a certain time period.
13. The method claim 10 , wherein the computed threshold flow level increases from a minimum level to a maximum level as a function of the elapsed inspiratory time and a predetermined maximum inspiratory time.
14. An apparatus for providing ventilatory assistance to a patient, the apparatus comprising:
a blower;
a memory containing instructions; and
a controller or processor programmed using the instructions and configured to:
receive respiratory flow data associated with the patient's respiratory flow,
determine a computed threshold flow level by computing a threshold flow level whose value varies between a minimum value and maximum value during an inspiratory cycle associated with the patient's respiratory flow, and
determine whether to cause the apparatus to switch from an inspiratory operation to an expiratory operation based on a comparison of the computed threshold flow level and received respiratory flow data of the inspiratory cycle associated with the patient's respiratory flow.
15. The apparatus of claim 14 , further comprising a mask and an air delivery conduit between the mask and the blower, and a flow sensor for deriving respiratory flow associated with the mask and providing the respiratory flow data to the controller.
16. The apparatus of claim 15 , further comprising a pressure sensor for deriving pressure data associated with the mask and providing the pressure data to the controller or processor.
17. The apparatus of claim 14 , wherein the threshold flow level varies as a function of elapsed inspiratory time during the inspiratory cycle.
18. The apparatus of claim 14 , wherein the minimum and maximum values comprise a predetermined value above a zero based flow measure.
19. The apparatus of claim 14 , wherein the controller is configured to cause the apparatus to switch from inspiratory operation to expiratory operation by controlling a motor current associated with the blower.
20. The apparatus of claim 14 , wherein the controller is configured to cause the apparatus to switch from inspiratory operation to expiratory operation by controlling a motor speed associated with the blower.
21. The apparatus of claim 14 , wherein the controller computes the minimum and maximum values as a function of a multiplier and peak inspiratory flow data included in the received respiratory flow data.