Diagnosing cardiac health using histogram analysis of thoracic impedance

• US 7,778,708 B1
• Filed: 04/14/2005
• Issued: 08/17/2010
• Est. Priority Date: 04/14/2005
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Koh, Steve, Province, Rose
• Primary Examiner(s): Bockelman; Mark W
• Assistant Examiner(s): So; Elizabeth K
• Application Number:
  US11/107,221
• Time in Patent Office: 1,951 Days
• Field of Search: 607/17, 607/37
• US Class Current: 607/17
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/37247 User interfaces, e.g. input or presentation means
• CPC Class Codes: A61N 1/37252 Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

Diagnosing a patient'"'"'s cardiac health through histogram analysis of thoracic impedance is described. Data values indicative of thoracic impedance are measured from a patient over a sample period that includes multiple respiratory cycles. The values are distributed across multiple bins of a histogram. A diagnostic value for use in diagnosing a patient'"'"'s cardiac health is derived from values in one or more of the bins. As one example, a diagnostic value representing minimum thoracic impedance during the sample period can be derived from values in the lowest-valued bins. Diagnostic values can be computed for multiple sample periods in the same fashion. A trend analysis is performed on the diagnostic values to determine whether the patient'"'"'s cardiac condition is improving or worsening. The trend may be presented in a graphical form to provide a visual tool for assessing the patient'"'"'s condition over time.

Claims

1. A system indicating a pulmonary edema condition comprising:

an implantable cardiac device to sense values indicative of thoracic impedance from a patient over multiple respiratory cycles; and

a histogram analysis sub-system to categorize a set of thoracic impedance values using a histogram and to determine a diagnostic value from the set of thoracic impedance values based on the histogram;

wherein the thoracic impedance values are distributed across multiple bins of the histogram, each bin representing a unique impedance value range in the histogram;

wherein only lowest-valued bins of the histogram are selected to determine the diagnostic value; and

wherein the diagnostic value indicates whether a pulmonary edema condition of a patient is improving or worsening.

2. A system as recited in claim 1, wherein the histogram analysis sub-system is configured as part of the implantable cardiac device.

3. A system as recited in claim 1, wherein the histogram analysis sub-system is configured in an external device separate from the implantable cardiac device.

4. A diagnostic system comprising:

a memory to store multiple sets of thoracic impedance values measured from a patient over multiple respiratory cycles; and

a processing unit configured to, for each individual set, distribute the thoracic impedance values in that set in a histogram based upon the impedance value and determine a minimum thoracic impedance value for each individual set by analyzing the distribution of the thoracic impedance values in the corresponding histogram;

wherein the processing unit is further configured to derive a trend of only the minimum thoracic impedance values; and

wherein the processing unit is further configured to interpret the trend of only the minimum impedance values as one of an improving pulmonary edema condition or a worsening pulmonary edema condition.

5. A diagnostic system as recited in claim 4, wherein the processing unit is further configured to interpret the trend as one of an improving cardiac condition or a worsening cardiac condition.

6. A diagnostic system as recited in claim 4, further comprising a user interface to present the trend in a user-perceptible form.

7. A system indicating a pulmonary edema condition comprising:

means for storing thoracic impedance values measured from a patient over multiple respiratory cycles;

means for distributing the thoracic impedance values across multiple bins of a histogram, each bin representing a unique impedance value range in the histogram; and

means for determining only a minimum thoracic impedance from the thoracic impedance values in one or more selected bins of the histogram by selecting only lowest-valued bins of the histogram;

means for deriving a trend of the minimum thoracic impedances determined over time; and

means for presenting the trend and a possible interpretation of the trend as one of an improving pulmonary edema condition or a worsening pulmonary edema condition.

8. A system as recited in claim 7, further comprising means for applying pacing therapy in an event that the minimum thoracic impedance crosses a predetermined threshold.

9. A method indicating a pulmonary edema condition comprising:

sense values indicative of thoracic impedance from a patient over a sample period by calculating voltage drop values of individual HVLIC values;

storing data indicative of the thoracic impedance measured from a patient during the sample period that includes multiple respiratory cycles;

forming a histogram of the data by placing the voltage drop values into histogram bins, each bin representing a unique impedance value range in the histogram; and

deriving a diagnostic value based on selecting only lowest valued bins of the histogram;

wherein the diagnostic value is used to determine whether a pulmonary edema condition of a patient is improving or worsening.