Method and apparatus for optimizing the continuous positive airway pressure for treating obstructive sleep apnea

Abstract

A breathing apparatus is provided for the treatment of obstructive sleep apnea that optimizes the positive pressure to the airway of a patient. The apparatus is configured to detect flow limitations in the patient airway from an analysis of inspiratory flow waveforms. The airway pressure setting is raised, lowered or maintained depending on whether a flow limitation has been detected and on the previous actions taken by the apparatus. The apparatus may include a blower, a flow sensor, a pressure sensor, a microprocessor, a pressure controller and a nasal fitting. The apparatus is configured to increase the airway pressure when a flow limitation is detected in the airway of the patient and to decrease the airway pressure when a flow limitation is not detected.

1 . A breathing device for optimizing the positive airway pressure to a patient, comprising: 
 a source of breathing gas applied at a positive pressure to the airway of a patient;    a sensor configured to generate data values representative of an inspiratory flow of breathing gas to the patient;    a microprocessor configured to process the data values, wherein the microprocessor is further configured to calculate, 
 a sinusoidal index as a correlation coefficient of an actual total inspiratory flow wave to a reference sinusoidal half wave,  
 a flatness index as a representation of a degree of flatness or curvature present in the total inspiratory waveform,  
 a respiratory effort index as a comparison of a peak value of the data values with a peak value of a derivative of the data values, and  
 a relative flow index as a peak flow of an inspiratory flow waveform minus a peak flow of a previous inspiratory flow waveform indicating a flow limitation, divided by a running average of peak flows of non-limited breaths minus an average of peak flows of flow limited breaths; and  
   a controller coupled to the source of breathing gas and associated with the microprocessor, wherein the controller is configured to adjust the positive pressure in response to the microprocessor.    
     
     
         2 . The breathing device of  claim 1 , wherein the controller is further configured to increase the positive pressure to the airway of a patient when one or more of the indices indicates a flow limitation in the patient.  
     
     
         3 . The breathing device of  claim 2 , wherein the controller is further configured to decrease the positive pressure to the airway of a patient when the indices do not indicate a flow limitation in the patient.  
     
     
         4 . The breathing device of  claim 1 , wherein the microprocessor correlates the data values with a pure sine wave to calculate the sinusoidal index.  
     
     
         5 . The breathing device of  claim 1 , wherein the microprocessor compares a regression fit of the data values with a regression fit of a pure sine wave to calculate the flatness index.  
     
     
         6 . The breathing device of  claim 1 , wherein the microprocessor compares a ratio of the peak derivative of the early inspiratory waveform to a peak flow value of the inspiratory waveform to calculate the respiratory effort index.  
     
     
         7 . The breathing device of  claim 1 , wherein the microprocessor determines a plurality of peak flow values for flow limited breaths, determines a plurality of peak flow values for non-flow limited breaths, and compares a peak value of the data values with an average of the plurality of peak flow values for flow limited breaths and with an average of the plurality of peak flow values for non-flow limited breaths to calculate the relative flow index.  
     
     
         8 . The breathing device of  claim 3 , wherein the microprocessor determines a plurality of peak inspiratory flow values for flow limited breaths, determines a plurality of peak inspiratory flow values for non-flow limited breaths, correlates the data values with a pure sine wave to create the sinusoidal index, compares a regression fit of the data values with a regression fit of a pure sine wave to create the flatness index, compares a peak value of the data values with a peak value of a derivative of the data values to create the effort index, and compares a peak value of the data values with an average of the plurality of peak flow values for flow limited breaths and with an average of the plurality of peak flow values for non-flow limited breaths to create the relative flow magnitude index.  
     
     
         9 . The breathing device of  claim 1 , wherein the microprocessor calculates a weighted index as a mathematical function of the sinusoidal index, the flatness index, the effort index and the relative flow magnitude index, wherein each index includes a weighted coefficient having a range including a value of zero.  
     
     
         10 . The breathing device of  claim 9 , wherein the controller is configured to increase the positive pressure to the airway of a patient when the weighted index indicates a flow limitation in the patient, and wherein the controller is configured to decrease the positive pressure to the airway of a patient when the weighted index does not indicate a flow limitation in the patient.  
     
     
         11 . The breathing device of  claim 1 , further including a memory device associated with the microprocessor, a blower driven by a motor, a nasal fitting having a vent in fluid communication with the source of breathing gas, and wherein the sensor is a pressure sensor and the controller is a motor speed controller connected to the motor.  
     
     
         12 . The breathing device of  claim 11 , further comprising a flow sensor connected to the source of breathing gas and associated with the microprocessor.  
     
     
         13 . A breathing device for optimizing the positive airway pressure to a patient, comprising: 
 means for applying an initial level of positive airway pressure of a breathing gas to a patient;    means for storing data values representative of an inspiratory flow of breathing gas to the patient;    means for determining whether the stored data values indicate a flow limitation in the patient, wherein the means for determining includes means for using the stored data values to calculate a sinusoidal index, a flatness index, a effort index and a relative flow magnitude index; and    means for adjusting the positive airway pressure in response to the means for determining.    
     
     
         14 . The breathing device of  claim 13 , wherein the means for adjusting further includes means for increasing the positive airway pressure whenever one or more of the sinusoidal index, flatness index, effort index and relative flow magnitude index indicate a flow limitation in the patient.  
     
     
         15 . The breathing device of  claim 14 , wherein the means for adjusting includes means for decreasing the positive airway pressure whenever the sinusoidal index, flatness index, effort index and relative flow magnitude index do not indicate a flow limitation in the patient.  
     
     
         16 . The breathing device of  claim 13 , wherein the means for determining a flow limitation includes processing means for determining a plurality of peak inspiratory flow values for flow limited breaths, for determining a plurality of peak inspiratory flow values for non-flow limited breaths, for correlating the stored data values with a pure sine wave to create the sinusoidal index, for comparing a regression fit of the stored data values with a regression fit of a pure sine wave to create the flatness index, for comparing a peak value of the stored data values with a peak value of a derivative of the stored data values to create the effort index, and for comparing a peak value of the stored data values with an average of the plurality of peak flow values for flow limited breaths and with an average of the plurality of peak flow values for non-flow limited breaths to create the relative flow magnitude index.  
     
     
         17 . The breathing device of  claim 16 , wherein the processing means further includes means for calculating a weighted index as a mathematical function of the sinusoidal index, the flatness index, the effort index and the relative flow magnitude index, wherein each index includes a weighted coefficient having a range including a value of zero.  
     
     
         18 . The breathing device of  claim 13 , wherein the means for applying an initial level of positive airway pressure includes a positive pressure source of breathing gas and a nasal fitting having a vent in fluid communication with the source of breathing gas, and the means for increasing the positive airway pressure includes a pressure control valve.  
     
     
         19 . A method for optimizing the positive airway pressure to a patient, comprising: 
 applying breathing gas at a positive pressure to the airway of a patient;    generating data values representative of an inspiratory flow of breathing gas to the patient;    configuring a microprocessor to process the data values and to calculate, 
 a sinusoidal index as a correlation coefficient of an actual total inspiratory flow wave to a reference sinusoidal half wave,  
 a flatness index as a representation of a degree of flatness or curvature present in a total inspiratory waveform,  
 a respiratory effort index as a comparison of a peak value of the data values with a peak value of a derivative of the data values, and  
 a relative flow index as a peak flow of an inspiratory flow waveform minus a peak flow of a previous inspiratory flow waveform indicating a flow limitation, divided by a running average of peak flows of non-limited breaths minus an average of peak flows of flow limited breaths; and  
   adjusting the positive pressure to the airway of a patient in response to the microprocessor.    
     
     
         20 . The method of  claim 19 , wherein adjusting the positive pressure includes increasing the positive pressure when one or more of the indices indicates a flow limitation, and includes decreasing the positive pressure when the indices do not indicate a flow limitation.