Adjustment of ventilator pressure-time profile to balance comfort and effectiveness
View Patent ↗The invention is a ventilator whose servo-controller adjusts the degree of support by adjusting the profile of the pressure waveform as well as the pressure modulation amplitude. As the servo-controller increases the degree of support by increasing the pressure modulation amplitude, it also generates a progressively more square, and therefore efficient, pressure waveform; when the servo-controller decreases the degree of support by decreasing the pressure modulation amplitude, it also generates a progressively more smooth and therefore comfortable pressure waveform.
1. A method of controlling a pressure support ventilator comprising the steps of:
supplying breathable gas to a patient's airway at a pressure that varies during each respiratory cycle in accordance with an adjustable pressure waveform template having a shape and a variable amplitude,
determining adequacy of ventilation of the patient, and
automatically making a change to the amplitude and shape of said pressure waveform template in accordance with the determined adequacy of ventilation, wherein said change produces a decrease in ventilatory support and an increase in comfort when the ventilatory support exceeds that required by the patient,
and wherein said pressure waveform template is nondecreasing during the inspiratory part of a cycle, is nonincreasing during the expiratory part of a cycle, and has both its inspiratory and expiratory parts defined by a single smoothness parameter whose value is automatically varied in accordance with the adequacy of patient ventilation.
2. A method in accordance with claim 1 wherein over at least a portion of each of successive respiratory cycles the amplitude and shape of the pressure waveform template change in directions that cause a ventilatory support change in the same direction.
3. A method in accordance with claim 2 wherein flow of said breathable gas is servo-controlled to adjust said amplitude so that ventilation equals a target value, and the shape of said pressure waveform template is controlled to be a function of said amplitude.
4. A method in accordance with claim 1 wherein flow of said breathable gas is servo-controlled so that ventilation equals a target value, and the shape of said pressure waveform template is controlled to be a function of flow.
5. A method of controlling a pressure support ventilator comprising the steps of:
supplying air to a patient's airway at a pressure that varies during each respiratory cycle, the pressure being characterized by both a pressure modulation amplitude and a pressure waveform template,
deriving a measure of instantaneous patient ventilation, and
controlling both said pressure modulation amplitude and the shape of said pressure waveform template in accordance with said measure of instantaneous patient ventilation,
wherein the shape of said pressure waveform template is changed to control a decrease in ventilation and a gain in comfort when less ventilation is required and said pressure waveform template is nondecreasing during the inspiratory part of a cycle, is nonincreasing during the expiratory part of a cycle, and has both its inspiratory and expiratory parts defined by a single smoothness parameter whose value is automatically varied in accordance with the adequacy of patient ventilation.
6. A method in accordance with claim 5 wherein over at least a portion of each of successive respiratory cycles the pressure modulation amplitude and the pressure waveform template change in directions that cause a ventilation change in the same direction.
7. A pressure support ventilator comprising:
a supply of breathable gas for a patient's airway delivered at a pressure that varies during each respiratory cycle in accordance with an adjustable pressure waveform template having a shape,
means for determining adequacy of ventilation of the patient, and
means for automatically making a change in the shape of said pressure waveform template in accordance with the determined adequacy of ventilation, wherein said change produces a decrease in patient ventilatory support and an increase in patient comfort when the ventilatory support exceeds that required by the patient,
and wherein said pressure waveform template is nondecreasing during the inspiratory part of a cycle, is nonincreasing during the expiratory part of a cycle, and has both its inspiratory and expiratory parts defined by a single smoothness parameter whose value is automatically varied in accordance with the adequacy of patient ventilation.
8. A pressure support ventilator in accordance with claim 7 wherein the pressure of the breathable gas in the patient's airway is also a function of an amplitude factor that varies in accordance with said determined adequacy of ventilation, and over at least a portion of each of successive respiratory cycles the amplitude factor and the pressure waveform template are changed in directions that cause a ventilatory support change in the same direction.
9. A pressure support ventilator in accordance with claim 8 further including a servo-control for controlling flow of said breathable gas to adjust said amplitude factor so that ventilation equals a target value, and the shape of said pressure waveform template is controlled to be a function of said amplitude factor.
10. A pressure support ventilator in accordance with claim 7 wherein said servo-control controls the ventilation to equal a target value, and the shape of said pressure waveform template is controlled to be a function of flow.
11. A patient ventilator comprising:
an air supply for a patient's airway delivered at a pressure that varies during each respiratory cycle in accordance with an adjustable pressure waveform template,
means repeatedly determining from the supplied airflow adequacy of ventilation of the patient, and
means for repeatedly changing said adjustable pressure waveform template in accordance with the determined adequacy of ventilation of the patient, wherein the changes control a decrease in ventilation and an increase in comfort when less ventilation is required,
and wherein said pressure waveform template is nondecreasing during the inspiratory part of a cycle, is nonincreasing during the expiratory part of a cycle, and has both its inspiratory and expiratory parts defined by a single smoothness parameter whose value is automatically varied in accordance with the adequacy of patient ventilation.
12. A patient ventilator in accordance with claim 11 wherein the pressure of the air supplied to the patient's airway is controlled to also be a function of an amplitude factor that varies in accordance with said determined adequacy of ventilation, and over at least a portion of each of successive respiratory cycles the amplitude factor and the pressure waveform template change in directions that cause a ventilation change in the same direction.
13. A patient ventilator in accordance with claim 12 further including a servo-control to adjust said amplitude factor so that ventilation equals a target value, and the shape of said pressure waveform template is controlled to be a function of said amplitude factor.
14. A patient ventilator in accordance with claim 12 further including a servo-control to control the flow of air so that ventilation equals a target value, and wherein the shape of said pressure waveform template is controlled to be a function of flow.
15. A pressure support ventilator comprising:
an air supply for a patient's airway delivered at a pressure that varies during each respiratory cycle, the pressure being characterized by both a pressure modulation amplitude and a pressure waveform template,
means for deriving a measure of instantaneous patient ventilation, and
means for controlling both said pressure modulation amplitude and the shape of said pressure waveform template in accordance with said measure of instantaneous patient ventilation,
wherein said controlling means changes the shape of said pressure waveform template to effect a decrease in ventilation and a gain in comfort when less ventilation is required, and said pressure waveform template is nondecreasing during the inspiratory part of a cycle, is nonincreasing during the expiratory part of a cycle, and has both its inspiratory and expiratory parts defined by a single smoothness parameter whose value is automatically varied in accordance with the adequacy of patient ventilation.
16. A pressure support ventilator in accordance with claim 15 wherein over at least a portion of each of successive respiratory cycles the pressure modulation amplitude and the pressure waveform template are changed in directions that cause ventilation change in the same direction.