Automated control for detection of flow limitation

Abstract

A respiratory flow limitation detection device, which can include an airway pressure treatment generator, determines a flow limitation measure based one or more shape indices for detecting partial obstruction and a measure of a patient's ventilation or respiratory duty cycle. The shape indices may be based on function(s) that ascertain the likelihood of the presence of M-shaped breathing patterns and/or chair-shaped breathing patterns. The measure of ventilation may be based on analysis of current and prior tidal volumes to detect a less than normal patient ventilation. The duty cycle measure may be a ratio of current and prior measures of inspiratory time to respiratory cycle time to detect an increase in the patient's inspiratory cycle time relative to the respiratory cycle time. A pressure setting based on the flow limitation may then be used to adjust the treatment pressure to ameliorate the patient's detected flow limitation condition.

1 . An apparatus for detection of arousal from sleep, the apparatus comprising at least one sensor and a controller, the controller configured to:
 receive a signal from the at least one sensor to generate a measure of respiratory flow;   calculate a measure indicative of arousal based on the measure of respiratory flow;   
       wherein the calculated measure indicative of arousal is a ventilation ratio representing an increase in ventilation; and
 indicate an occurrence of an arousal event based on the calculated measure. 
 
     
     
         2 . The apparatus of  claim 1 , wherein the calculated measure comprises ventilation change following an indication of flow limitation in a measure of flow limitation. 
     
     
         3 . The apparatus of  claim 2 , wherein the controller is configured to determine the measure of flow limitation and to buffer flow limitation values. 
     
     
         4 . The apparatus of  claim 1 , wherein the controller is configured to buffer values of the ventilation ratio. 
     
     
         5 . The apparatus of  claim 1 , wherein the ventilation ratio comprises a ratio of a mean tidal volume to a current three minute ventilation measure. 
     
     
         6 . The apparatus of  claim 4 , wherein the controller is configured to calculate ventilation ratio differences from the buffered values of the ventilation ratio, and to determine a maximum ventilation ratio difference. 
     
     
         7 . The apparatus of  claim 3 , wherein the controller is configured to sum the flow limitation values and limit the sum to a range. 
     
     
         8 . The apparatus of  claim 1 , wherein the controller is configured to indicate the occurrence of the arousal event based on a limited sum of flow limitation values and a maximum ventilation ratio difference. 
     
     
         9 . The apparatus of  claim 8 , wherein the controller is configured to calculate a respiratory effort-related arousal value by multiplying the limited sum and the maximum ventilation ratio difference. 
     
     
         10 . The apparatus of  claim 9 , wherein the controller is configured to normalize the respiratory effort-related arousal value by calculating a square root of the respiratory effort-related arousal value. 
     
     
         11 . The apparatus of  claim 9 , wherein the controller is configured to indicate the occurrence of the arousal event from a comparison of the respiratory effort-related arousal value and a threshold. 
     
     
         12 . The apparatus of  claim 1 , wherein the controller is configured to calculate another measure indicative of arousal comprising a ratio including a peak expiratory flow. 
     
     
         13 . The apparatus of  claim 12 , wherein the controller is configured to:
 determine a peak measure of an expiratory portion of the measure of respiratory flow; and   determine the calculated another measure as a function of the peak measure, wherein the function of the peak measure is a ratio of the peak measure and mean expiratory flow.   
     
     
         14 . The apparatus of  claim 12 , wherein the controller is configured to compare the calculated measure to a threshold to detect an arousal event. 
     
     
         15 . The apparatus of  claim 1 , wherein the controller is configured to determine another arousal measure comprising an expiratory peak location. 
     
     
         16 . The apparatus of  claim 15 , wherein the controller is configured to:
 determine a peak measure of an expiratory portion of the measure of respiratory flow; and   determine the other arousal measure as a function of the peak measure, wherein the function of the peak measure is a function of location within the expiratory portion.   
     
     
         17 . The apparatus of  claim 16 , wherein the other arousal measure is indicative of arousal if the peak measure occurs in a later time portion of the expiratory portion of the measure of respiratory flow. 
     
     
         18 . The apparatus of  claim 17 , wherein time of the expiratory portion is defined by ranges and occurrence of the peak measure within one of the defined ranges defines an index that is indicative of arousal. 
     
     
         19 . The apparatus of  claim 17 , comprising calculating the other arousal measure by dividing time from beginning of expiration to the peak measure by total expiratory time. 
     
     
         20 . The apparatus of  claim 1 , wherein the controller is configured to determine a count of arousal incidents with the indication of the arousal event for evaluation of a respiratory therapy. 
     
     
         21 . The apparatus of  claim 1  further comprising a flow generator, wherein the controller is configured to control the flow generator to provide a respiratory therapy. 
     
     
         22 . The apparatus of  claim 21  wherein the controller is configured to adjust the respiratory therapy based on the indication of the occurrence of the arousal event. 
     
     
         23 . The apparatus of  claim 22  wherein an index representing the indication of the occurrence of the arousal event is an input to a therapy algorithm. 
     
     
         24 . The apparatus of  claim 23  wherein the index is applied to set a threshold for evaluating a flow limitation index for raising pressure. 
     
     
         25 . The apparatus of  claim 23  wherein the index representing the indication of the occurrence of the arousal event is applied to set a gain for raising pressure in response to a flow limitation index. 
     
     
         26 . The apparatus of  claim 1  wherein the occurrence of the arousal event is a respiratory effort related arousal event, and wherein the ventilation ratio comprises a value that is a ratio of a current ventilation to a recent medium-term ventilation. 
     
     
         27 . A method in a controller of an apparatus for detection of arousal from sleep, the method comprising:
 receiving a signal from a sensor configured to generate a measure of respiratory flow;   calculating a measure indicative of arousal based on the measure of respiratory flow;   
       wherein the calculated measure indicative of arousal is a ventilation ratio representing an increase in ventilation; and
 indicating an occurrence of an arousal event based on the calculated measure. 
 
     
     
         28 . The method of  claim 27 , wherein the calculated measure comprises ventilation change following an indication of flow limitation in a measure of flow limitation. 
     
     
         29 . The method of  claim 28 , further comprising determining the measure of flow limitation and buffering flow limitation values. 
     
     
         30 . The method of  claim 27 , further comprising buffering values of the ventilation ratio. 
     
     
         31 . The method of  claim 29 , wherein the ventilation ratio comprises a ratio of a mean tidal volume to a current three minute ventilation measure. 
     
     
         32 . The method of  claim 30 , further comprising calculating ventilation ratio differences from the buffered values of the ventilation ratio, and determining a maximum ventilation ratio difference. 
     
     
         33 . The method of  claim 29 , further comprising calculating a sum of the flow limitation values and limiting the sum to a range. 
     
     
         34 . The method of  claim 27 , wherein the indicating the occurrence of the arousal event is based on a limited sum of flow limitation values and a maximum ventilation ratio difference. 
     
     
         35 . The method of  claim 34  further comprising calculating a respiratory effort-related arousal value by multiplying the limited sum and the maximum ventilation ratio difference. 
     
     
         36 . The method of  claim 35  further comprising normalizing the respiratory effort-related arousal value by calculating a square root of the respiratory effort-related arousal value. 
     
     
         37 . The method of  claim 35  wherein the indicating the occurrence of the arousal event is based on a comparison of the respiratory effort-related arousal value and a threshold. 
     
     
         38 . The method of  claim 27  further comprising calculating another measure indicative of arousal comprising a ratio including a peak expiratory flow. 
     
     
         39 . The method of  claim 38 , further comprising:
 determining a peak measure of an expiratory portion of the measure of respiratory flow; and   determining the calculated another measure as a function of the peak measure, wherein the function of the peak measure is a ratio of the peak measure and mean expiratory flow.   
     
     
         40 . The method of  claim 39 , further comprising comparing the calculated another measure to a threshold to detect an arousal event. 
     
     
         41 . The method of  claim 27 , further comprising determining another arousal measure comprising an expiratory peak location. 
     
     
         42 . The method of  claim 41 , further comprising:
 determining a peak measure of an expiratory portion of the measure of respiratory flow; and   determining the other arousal measure as a function of the peak measure, wherein the function of the peak measure is a function of location within the expiratory portion.   
     
     
         43 . The method of  claim 42 , wherein the other measure is indicative of arousal if the peak measure occurs in a later time portion of the expiratory portion of the measure of respiratory flow. 
     
     
         44 . The method of  claim 42 , wherein time of the expiratory portion is defined by ranges and occurrence of the peak measure within one of the defined ranges defines an index that is indicative of arousal. 
     
     
         45 . The method of  claim 42 , further comprising calculating the other arousal measure by dividing time from beginning of expiration to the peak measure by total expiratory time. 
     
     
         46 . The method of  claim 27 , further comprising determining a count of arousal incidents with the indication of the arousal event for evaluation of a respiratory therapy. 
     
     
         47 . The method of  claim 27 , further comprising controlling a flow generator to provide a respiratory therapy. 
     
     
         48 . The method of  claim 47  further comprising adjusting the respiratory therapy based on the indication of the occurrence of the arousal event. 
     
     
         49 . The method of  claim 48  wherein an index representing the indication of the occurrence of the arousal event is input to a therapy algorithm. 
     
     
         50 . The method of  claim 49  wherein the index is applied to set a threshold for evaluating a flow limitation index for raising pressure. 
     
     
         51 . The method of  claim 49  wherein the index representing the indication of the occurrence of the arousal event is applied to set a gain for raising pressure in response to a flow limitation index. 
     
     
         52 . The method of  claim 27 , wherein the occurrence of the arousal event is a respiratory effort related arousal event, and wherein the ventilation ratio comprises a value that is a ratio of a current ventilation to a recent medium-term ventilation.