Method and apparatus for removing cardiac artifact in impedance plethysmographic respiration monitoring

• US 4,379,460 A
• Filed: 09/18/1980
• Issued: 04/12/1983
• Est. Priority Date: 09/18/1980
• Status: Expired due to Term

• Current Assignee: E for M Corp. (General Electric Company)
• Original Assignee: Datamedix Incorporated
• Inventors: Judell, Neil H. K.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US06/188,392
• Time in Patent Office: 936 Days
• Field of Search: 128/671, 128/700, 128/716, 128/720, 128/723, 128/734
• US Class Current: 600/484
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval

Abstract

A method of removing cardiac artifact during monitoring of a patient'"'"'s respiration using impedance plethysmography when the patient has a regular, substantially periodic heartbeat. This method comprises generating an impedance signal responsive to both cardiac and respiration activity in the patient'"'"'s chest. The signal is filtered by removing the cardiac activity component due to its substantially periodic character. An output signal is produced from the filter apparatus which is a function of substantially only the patient'"'"'s respiration rate.

An improved impedance plethysmograph carries out the method substantially as described above.

Claims

1. In an impedance plethysmographic apparatus of the type for monitoring respiration of a patient including means for measuring an impedance signal generated by changes occurring in the patient'"'"'s chest, wherein the improvement comprises:

means for removing artifact from the impedance signal caused by cardiac activity in the chest including;

filter means which produces an output signal dependant only upon respiration activity in the patient'"'"'s chest by removing any signals from said output signal caused by cardiac activity which is substantially periodic in character, said filter means receives as input an impedance signal which is a function of both cardiac and respiration activity, said filter means adapted to filter said input impedance signal so that said output signal is a function of only respiration activity,

a first rate means for providing a heart rate signal to said filter means,

said filter means including;

a first analog filter means for receiving said impedance signal as input, and

a second analog filter means for providing said output signal, said second analog filter means arranged in a cascaded, time-delay arrangement with said first filter means,

said output signal being a summation of outputs of said first filter means and said second analog filter means as a function of respiration activity with respect to time.

2. The apparatus of claim 1 wherein:

both said first filter means and said second analog filter means receive said heart rate signal as a function of heart rate information from said patient based on the time interval between peaks of successive heartbeats of a regularly beating, substantially periodic heartbeat.

3. The apparatus of claim 2 wherein the frequency response of said first filter means is represented by the following relationship:

space="preserve" listing-type="equation">H(ω

)=1-e.sup.jω

t 0

wherein j=√

-1, ω

is frequency and t_o is said time interval between peaks of successive heartbeats; and

wherein the frequency response of said second analog filter means is represented by the following relationship;

space="preserve" listing-type="equation">K(ω

)=1/[1-pe.sup.jω

t 0]

wherein p is a constant having a value greater than or equal to zero, but less than 1.

4. A method of removing cardiac artifact during the monitoring of a patient'"'"'s respiration using impedance plethysmography when said patient has a regular, substantially periodic heartbeat comprising:

generating an impedance signal response to both cardiac and respiration activity in the patient'"'"'s chest, a cardiac activity component generated as part of said signal,

filtering said signal by removing said cardiac activity component due to its substantially periodic character to produce a filtered signal; and

producing an output impedance signal from said filtered signal which is a function of substantially only the patient'"'"'s respiration activity,

monitoring the patient'"'"'s heart rate and providing a rate signal which is based upon the time interval between peaks of successive heartbeats of a regularly beating, substantially periodic heartbeat,

said filtering includes passing said signal to a first analog filter whose output is cascaded to a second analog filter, both of said filters also receiving as an input signal the patient'"'"'s heart rate signal, the output from said filters being a function of substantially only the patient'"'"'s respiration activity.