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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 generate

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.

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1. A method for controlling a pressure support servo 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 an adjustable pressure waveform template w

1. A method for controlling a pressure support servo 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 an adjustable pressure waveform template with a profile, andautomatically controlling both said pressure modulation amplitude and the profile of said adjustable pressure waveform template by an output of a servo-controller operated to servo-control patient ventilation to at least equal a target value. 2. A method as in claim 1 in which said servo-controller increases a degree of support by at least one of increasing the pressure modulation amplitude and generating a pressure waveform that progressively becomes a square pressure waveform. 3. A method as in claim 1 in which said servo-controller decreases a degree of support by at least one of decreasing the pressure modulation amplitude and generating a pressure waveform that progressively becomes a smooth pressure waveform. 4. A method as in claim 1 in which the adjustable pressure waveform template is adjustable to a high degree of distinct waveform profiles between a smooth profile and a square profile. 5. A method as in claim 1 in which the profile of the adjustable pressure waveform template is adjusted to be smoother than a profile of a previous pressure waveform template if said pressure modulation amplitude is less than a threshold, and adjusted to be more square than a profile of a previous pressure waveform template otherwise. 6. A method for 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 of adjustable shape,deriving a measure of instantaneous patient ventilation, andautomatically controlling both said pressure modulation amplitude and the shape of said pressure waveform template in accordance with said measure of instantaneous patient ventilation. 7. A method as in claim 6 in which the degree of ventilatory support is increased by at least one of increasing the pressure modulation amplitude and generating a progressively more square pressure waveform. 8. A method as in claim 6 in which a degree of ventilatory support is decreased by at least one of decreasing the pressure modulation amplitude and progressively generating pressure waveform templates that are smoother than a prior pressure waveform template. 9. A method as in claim 6 in which the pressure waveform template is adjustable to a high degree of different waveform shapes between a smooth shape and a square shape. 10. A method as in claim 6 in which the shape of said pressure waveform template is adjusted to be smoother than a shape of a previous pressure waveform template if said pressure modulation amplitude is less than a threshold, and adjusted to be more square than a shape of a previous pressure waveform template otherwise. 11. A pressure support ventilator comprising a supply of air for a patient's airway where a pressure of the supply of air varies during each respiratory cycle, the pressure being characterized by both a pressure modulation amplitude and an adjustable pressure waveform template with a profile, means for deriving a measure of instantaneous patient ventilation, and means for automatically controlling both said pressure modulation amplitude and said profile of said adjustable pressure waveform template in accordance with said measure of instantaneous patient ventilation. 12. A pressure support ventilator as in claim 11 in which a degree of ventilatory support is increased by at least one of increasing the pressure modulation amplitude and generating a pressure waveform that progressively approaches being a square waveform. 13. A pressure support ventilator as in claim 11 in which a degree of ventilatory support is decre ased by at least one of decreasing the pressure modulation amplitude and progressively generating pressure waveform templates that are smoother than a prior pressure waveform template. 14. A pressure support ventilator as in claim 11 in which the profile of the adjustable pressure waveform template is adjustable to a high degree of waveform profiles between a smooth profile and a square profile. 15. A pressure support ventilator as in claim 11 in which said adjustable pressure waveform is adjusted to be smoother if said pressure modulation amplitude is less than a threshold, and adjusted to be more square otherwise. 16. A method for providing positive pressure ventilation comprising the steps of:supplying a patient with breathable gas at a pressure which is a function of at least a measure of phase in a respiratory cycle, an amplitude, and a smoothness parameter;determining a measure of ventilation of the patient; andautomatically adjusting said smoothness parameter within a preset range to servo-control said measure of ventilation to at least equal a target ventilation. 17. A method as in claim 16, in which said amplitude is adjusted within a preset range to servo-control said measure of ventilation to at least equal a target ventilation. 18. A method as in claim 17, in which said smoothness parameter is calculated from said amplitude. 19. A method as in claim 18, in which said servo-control is performed firstly by increasing or decreasing said amplitude, and secondarily adjusting said smoothness parameter if said amplitude is not within a specified range. 20. A pressure support ventilator comprising a supply of air for a patient's airway wherein a pressure of the supply of air is a function of at least a measure of phase in a respiratory cycle of the patient, an amplitude, and a smoothness parameter, wherein said smoothness parameter is a calculated function of a target ventilation, wherein, said amplitude is adjusted within a preset range to servo-control said ventilation to at least equal a target ventilation. 21. A pressure support ventilator as in claim 20, in which said smoothness parameter is calculated from said amplitude. 22. A pressure support ventilator as in claim 20, in which said servo-control is performed firstly by increasing or decreasing said amplitude, and secondarily adjusting said smoothness parameter if said amplitude is not within a specified range. 23. A method for controlling a degree of ventilatory support supplied to a patient by a pressure support ventilator, the method comprising the steps ofsupplying breathable gas to a patient's airway by a pressure waveform having an adjustable amplitude and an adjustable squareness;continuously determining a minute ventilation of the patient;comparing the minute ventilation to a target ventilation;If the minute ventilation is below the target ventilation, then first changing the adjustable amplitude to increase minute ventilation; andif after increasing the minute ventilation it remains below the target ventilation, then making the waveform progressively more square. 24. The method of claim 23 wherein the adjustable amplitude is limited by a maximum amplitude, and wherein if the minute ventilation is below the target ventilation, then the adjustable amplitude is changed toward the maximum amplitude, and wherein if the minute ventilation is below the target ventilation and the adjustable amplitude exceeds a fraction of the maximum amplitude, then the pressure waveform is changed to become progressively more square. 25. The method of claim of 24 wherein the fraction is about 75%. 26. The method of claim 23 wherein the adjustable squareness of the pressure waveform is changes between a minimum and maximum and wherein at the maximum the pressure waveform is not completely square. 27. A method as claimed in claim 23 wherein the adjustable squareness of the pressure waveform changes between a minimum and maximum and wherein changes in waveform squareness near a squ areness indicative of a completely square waveform take place more slowly than changes when the waveform is rounder. 28. A method of providing ventilatory support to a patient comprising the steps of:supplying breathable gas to a patient's airway with a pressure waveform which has an adjustable squareness;continuously determining minute ventilation;comparing the minute ventilation to a target ventilation;determining the presence of leak;determining whether the leak is large; andIf the minute ventilation is below the target ventilation and the leak is large then gradually making the pressure waveform more square.