Cardiovascular artifact filter

• US 4,781,201 A
• Filed: 07/22/1986
• Issued: 11/01/1988
• Est. Priority Date: 12/27/1984
• Status: Expired due to Term

• Current Assignee: Corometrics Medical Systems, Inc.
• Original Assignee: American Home Products Corporation (Pfizer Inc.)
• Inventors: Wright, John C., Triebel, Harry M.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): Shay, David
• Application Number:
  US06/887,318
• Time in Patent Office: 833 Days
• Field of Search: 128/696, 128/706, 128/708, 128/716, 128/721, 128/723, 128/670, 128/671, 382/6, 382/54, 333/16 S, 364/415, 364/724
• US Class Current: 600/484
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition

Abstract

For suppressing cardiovascular artifact from a respiration signal derived from a patient'"'"'s transthoracic impedance, an adaptive filtering device determines the patient'"'"'s heart rate, converts the respiration signal from an analog to digital representation at a rate proportional to the heart rate, and then filters the digital respiration signal such that that portion of the respiration signal having a frequency content at or above the heart rate is most greatly attenuated.

Claims

1. For suppressing cardiovascular artifact from a respiration signal derived from a patient, a filtering device comprising:

heat beat detecting means for detecting heart beats of the patient;

processing means for determining the heart rate of the patient in response to the detected heart beats; and

filtering means operable for sampling the respiration signal in proportion to the heart rate and producing a filtered respiration signal as follows;

space="preserve" listing-type="equation">Filtered Respiration Signal=S.sub.(t) +(K.sub.1 +K.sub.2)Z.sup.-1.sub.(t-1) +(K.sub.3 +K.sub.4)Z.sup.-2.sub.(t-1)

where;

S.sub.(t) is the respiration signal currently being sampled;

space="preserve" listing-type="equation">Z.sup.-1.sub.(t) =S.sub.(t) +K.sub.1 Z.sup.-1.sub.(t-1) +K.sub.3 Z.sup.-2.sub.(t-1)

space="preserve" listing-type="equation">Z.sup.-2.sub.(t) =Z.sup.1.sub.(t-1) ;

and

K₁, K₂, K₃, and K₄ are constants.

2. A filtering device as in claim 1;

wherein the heart beat detecting means comprises a QRS detecting means for detecting the QRS complex of each heart beat waveform produced by the patient.

3. A filtering device as in claim 1, wherein the processing means comprises timing means for producing pulses at a predetermined rate and first counting means for counting the number of pulses occurring between detected heart beats.

4. A filtering device as in claim 1;

wherein the device further comprises conversion means for converting from an analog to a digital representation of the respiration signal at a converting rate proportional to the heart rate and wherein the filtering means samples the digital representation of the respiration signal.

5. A filtering device as in claim 4;

wherein the conversion means is a successive approximating analog-to-digital converter.