Method and apparatus for detecting change in intrathoracic electrical impedance

• US 7,986,994 B2
• Filed: 12/03/2003
• Issued: 07/26/2011
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Wang, Li, Stadler, Robert W.
• Primary Examiner(s): Patel; Niketa I
• Assistant Examiner(s): ALTER, ALYSSA MARGO
• Application Number:
  US10/727,008
• Publication Number:
  US 20040172080A1
• Time in Patent Office: 2,792 Days
• Field of Search: 607/1, 607/2, 607/17, 607/20, 607/28, 600/547, 600/484, 600/506, 600/507
• 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 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• CPC Class Codes: A61B 5/4875 Hydration status, fluid retention of the body
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• 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 1/05 for implantation or insertion into the body, e.g. heart electrode A61N1/06 takes precedence
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/3629 in combination with non-electric therapy
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: G06F 12/0802 Addressing of a memory level in which the access to the desired data or data block requires associative addressing means, e.g. caches
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 12/0877 Cache access modes

Abstract

A method and apparatus for detection of changes in impedance a patient that includes generating measured impedances, generating an adaptive baseline trend of the measured impedances corresponding to a first time period, generating a short term trend of the measured impedances corresponding to a second time period less than the first time period, and generating a metric of impedance change between the adaptive baseline trend and one of a most recent measured impedance and the short term trend of the measured impedances.

Claims

1. An implantable medical device for detection of changes in impedance in a patient, comprising:

means for generating measured impedances;

means for generating an adaptive baseline trend of the measured impedances corresponding to a first time;

means for generating a short term trend of the measured impedances corresponding to a second time period less than the first time;

means for accumulating a difference between the adaptive baseline trend and one of a most recent measured impedance and the short term trend of the measured impedances; and

means for updating the adaptive baseline trend by setting the adaptive baseline trend equal to a previous adaptive baseline trend reduced by a predetermined downdrift in response to the current adaptive baseline trend being greater than the current short term trend, and by setting the adaptive baseline trend equal to the previous adaptive baseline trend increased by a predetermined updrift in response to the current adaptive baseline trend being less than the current short term trend, wherein the updrift is greater than the downdrift.

2. The implantable medical device of claim 1, wherein the downdrift is approximately equal to 0.055 ohms and the updrift is approximately equal to 0.18 ohms.

3. The implantable medical device of claim 1, wherein the means for accumulating a difference sets the accumulated difference equal to zero in response to the short term trend being equal to the adaptive baseline trend.

4. A method for detection of changes in impedance a patient, comprising:

generating measured impedances;

generating an adaptive baseline trend of the measured impedances corresponding to a first time period;

generating a short term trend of the measured impedances corresponding to a second time period less than the first time period; and

generating an accumulated difference between the adaptive baseline trend and one of a most recent measured impedance and the short term trend of the measured impedances; and

updating the adaptive baseline trend by setting the adaptive baseline trend equal to a previous adaptive baseline trend reduced by a predetermined downdrift in response to the current adaptive baseline trend being greater than the current short term trend, and by setting the adaptive baseline trend equal to the previous adaptive baseline trend increased by a predetermined updrift in response to the current adaptive baseline trend being less than the current short term trend, wherein the updrift is greater than the downdrift.

5. The method of claim 4, wherein the downdrift is approximately equal to 0.055 ohms and the updrift is approximately equal to 0.18 ohms.