Method and system for heart failure status evaluation based on a disordered breathing index

Abstract

An evaluation of heart failure status is provided based on a disordered breathing index. Patient respiration is sensed and a respiration signal is generated. Disordered breathing episodes are detected based on the respiration signal. A disordered breathing index is determined based on the disordered breathing episodes. The disordered breathing index is trended and used to evaluate heart failure status. The disordered breathing index may be combined with additional information and/or may take into account patient activity, posture, sleep stage, or other patient information.

What is claimed is: 
     
         1 . A method of evaluating a patient's heart failure status, comprising:
 sensing a patient's respiration to ascertain a measure related to respiration rate and a measure related to tidal volume;   determining if the patient is experiencing rapid shallow breathing based, at least in part, on the measure related to respiration rate and the measure related to tidal volume, and if it is determined that the patient is experiencing rapid shallow breathing:
 calculating a ratio of the measure related to respiration rate and the measure related to tidal volume; 
 trending over time the ratio of the measure related to respiration rate and the measure related to tidal volume; 
 determining a measure related to the patient's heart failure status based at least in part on the trending ratio of the measure related to respiration rate and the measure related to tidal volume. 
   
     
     
         2 . The method of  claim 1 , wherein the measure related to respiration rate corresponds to an average respiration rate over a period of time, and the measure related to tidal volume corresponds to an average tidal volume over a period of time. 
     
     
         3 . The method of  claim 2 , wherein determining the measure related to the patient's heart failure status is based on the trending ratio of the measure related to respiration rate and the measure related to tidal volume as well as additional information. 
     
     
         4 . The method of  claim 3 , wherein the additional information comprises an indication of a concurring posture of the patient at a time in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         5 . The method of  claim 3 , wherein the additional information comprises an indication of an activity level of the patient at a time in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         6 . The method of  claim 3 , wherein the additional information comprises an indication of a time of day in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         7 . The method of  claim 3 , wherein the additional information comprises an indication of a particular sleep state of the patient at a time in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         8 . A system for providing an assessment of a patient's heart failure status, the system comprising:
 a respiration sensor configured to generate a respiration signal responsive to patient respiration;   a breathing unit in communication with the respiration sensor, the breathing unit configured to analyze the respiration signal to determine if the patient is undergoing rapid shallow breathing;   an index unit in communication with the breathing unit and configured to determine a disordered breathing index;   a trending unit in communication with the index unit and configured to trend the disordered breathing index over time; and   a diagnostics unit in communication with the trending unit and configured to determine a measure related to the patient's heart failure status based, at least in part, on the trended disordered breathing index.   
     
     
         9 . The system of  claim 8 , wherein the breathing unit is configured to determine a measure related to respiration rate and a measure related to tidal volume, and is further configured to determine if the patient is undergoing rapid shallow breathing based, at least in part, on the measure related to respiration rate and the measure related to tidal volume. 
     
     
         10 . The system of  claim 9 , wherein the index unit is configured to calculate the disordered breathing index based, at least in part, on the measure related to respiration rate and the measure related to tidal volume. 
     
     
         11 . The system of  claim 8 , wherein the diagnostics unit is configured to determine the measure related to the patient's heart failure status based, at least in part, on the trended disordered breathing index as well as additional information. 
     
     
         12 . The system of  claim 11 , wherein the additional information comprises an indication of a concurring posture of the patient at a time in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         13 . The system of  claim 11 , wherein the additional information comprises an indication of an activity level of the patient at a time in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         14 . The system of  claim 11 , wherein the additional information comprises an indication of a time of day in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         15 . The system of  claim 11 , wherein the additional information comprises an indication of a particular sleep state of the patient at a time in which the patient is determined to be experiencing rapid shallow breathing. 
     
     
         16 . The system of  claim 11 , wherein the diagnostics unit is configured to update the measure related to the patient's heart failure status in response to the breathing unit determining that the patient is undergoing rapid shallow breathing. 
     
     
         17 . The system of  claim 11 , wherein the respiration sensor comprises a transthoracic sensor. 
     
     
         18 . A method of ascertaining a patient's heart failure status, comprising:
 sensing a patient's respiration;   determining if the patient is experiencing a disordered breathing episode based, at least in part, on the patient's respiration;   determining a patient tilt angle during the determined disordered breathing episode;   determining an average patient tilt angle over a plurality of determined disordered breathing episodes;   trending the average patient tilt angle over time; and   determining a measure related to the patient's heart failure status based at least in part on the trending average patient tilt angle over time.   
     
     
         19 . The method of  claim 18 , further comprising determining that the patient's heart failure status is worsening if the trended average daily tilt angle is increasing over time, thereby indicating an increase in the number of disordered breathing episodes when the patient is sitting and standing. 
     
     
         20 . The method of  claim 18 , wherein determining if the patient is experiencing a disordered breathing episode is based, at least in part, on a measure related to respiration rate and a measure related to tidal volume.