Apparatus and method for reduction in respiration artifact in pulmonary artery pressure measurement

• US 4,667,680 A
• Filed: 11/14/1983
• Issued: 05/26/1987
• Est. Priority Date: 11/14/1983
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Ellis, David M.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/551,221
• Time in Patent Office: 1,289 Days
• Field of Search: 128/670-672, 128/680-683
• US Class Current: 600/485
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence

Abstract

Apparatus is disclosed for deriving weighted values SHD i, DHD i and MHD i to respectively represent the systolic, diastolic and mean blood pressures for each heartbeat of a patient from the values S_i, D_i and M_i that are the maximum, minimum and means blood pressures of the current heartbead; S_i-1, D_i-1 and M_i-1 that were the maximum, minimum and mean blood pressures for the previous heartbeat; SHD i-1, DHD i-1 and MHD i-1 that respectively represented the systolic, diastolic and means blood pressures of the previous heartbeat; and a constant K_i that is a function, F, of the difference between M_i and the mean pressure M_i-1 of the previous heartbeat. The expressions for S_i, D_i, M_i and K_i are as follows: ##EQU1##

Claims

1. Apparatus for deriving signals representing the systolic, diastolic and mean pressures of a patient from a signal corresponding to a measured variation in actual pressure, comprising

means responsive to said signal for providing signals representing successive maximum pressures,

means responsive to said signal for providing signals representing successive minimum pressures, the portion of the signal between successive minimum pressures defining a beat,

means responsive to said signal for providing signals representing the mean pressure of each beat,

means for deriving a weighting factor for each beat that is a function of the absolute difference between the mean pressure of a current beat and the mean pressure of the adjacent previous beat,

recursive means for deriving a weighted value representing the systolic pressure for the current beat equal to the weighted value representing the systolic pressure of the adjacent previous beat plus the difference between the maximum pressures of the current and previous beats divided by the weighting factor,

recursive means for deriving a weighted value representing the diastolic pressure for the current beat equal to the weighted value representing the diastolic pressure of the adjacent previous beat plus the difference between the minimum pressures of the current and previous beats divided by the weighting factor,

recursive means for deriving a weighted value representing the mean pressure for the current beat equal to the weighted value representing the mean pressure of the adjacent previous beat plus the difference between mean pressues of the current and adjacent previous beats divided by the weighting factor, and

means for displaying said weighted values as the systolic, diastolic and mean pressures for the current beat.

2. Apparatus as set forth in claim 1 wherein the mean pressure is derived by means for integrating the pressure of the said signal occurring between adjacent minimum pressures and dividing said integral by the time interval between these pressures.

3. Apparatus as set forth in claim 1 wherein said function is a constant times the absolute difference between the mean pressure of a current beat and the mean pressure of the adjacent previous beat.

4. Apparatus as set forth in claim 3 wherein said constant is between 2 and 10 inclusive.

5. Apparatus as set forth in claim 1 wherein means are provided for limiting the weighting factor to values between 2 and 30 inclusive.

6. Apparatus as set forth in claim 1 wherein means are provided for substituting a constant for the weighting factor whenever arterial pressure is being measured.

7. Apparatus as set forth in claim 6 wherein said constant is eight.

8. A method for determing the systolic, diastolic and mean pressures for each heartbeat, comprising

deriving a first signal that varies in amplitude in accordance with blood pressure at a given point in the patient'"'"'s system,

deriving a second signal that successively represents each maximum value of said first signal,

deriving a third signal that successively represents each minimum value of said first signal,

deriving a fourth signal representing a mean pressures occurring in said first signal between successive values of said third signal,

deriving a weighting factor K_i equal to F|M_i -M_i-1 | wherein F is a function, M_i is the mean pressure of a given heartbeat, and M_i-1 is the mean pressure of the previous heartbeat,

recursively deriving a weighted signal SHD i representing the systolic pressure of the given heartbeat which is equal to ##EQU3## wherein S_i is the maximum value of the first signal occurring during the given heartbeat;

S_i-1 is the maximum value of the first signal occurring during the previous heartbeat; and

SHD i-1 is the systolic pressure derived for the previous heartbeat,

recursively deriving a signal DHD i representing the diastolic pressure of the given heartbeat which is equal to ##EQU4## wherein D_i is the minimum value of the first signal occurring during the given heartbeat;

D_i-1 is the minimum value of the first signal occurring during the previous heartbeat; and

DHD i-1 is the diastolic pressure derived for the previous heartbeat,

recursively deriving a signal MHD i representing the mean pressure of the given heartbeat which is equal to ##EQU5## wherein M_i is the mean pressure of the given heartbeat;

M_i-1 is the mean pressure of the previous heartbeat; and

MHD i-1 is the mean pressure derived for the previous heartbeat, and

displaying the values of SHD i, DHD i and MHD i.

9. A method as set forth in claim 8 wherein F is a constant.

10. A method as set forth in claim 8 wherein F is a constant between 2 and 10 inclusive.

11. A method as set forth in claim 8 wherein the weighting factor K_i is limited to values between 2 and 30 inclusive.

12. A method as set forth in claim 8 wherein the weighting factor K_i is set equal to a given constant.

13. A method as set forth in claim 12 wherein said given constant is 8.

14. A method of deriving a signal representing a selected one of the systolic, diastolic and mean pressures of a patient, comprising

deriving an analog signal that varies with the patient'"'"'s blood pressure at a desired point in his blood circulation system,

deriving first signals respectively representing successive maximum values of said analog signal,

deriving second signals respectively representing successive minimum values of said analog signal,

deriving a third signal respectively representing the mean values of the blood pressure for successive heartbeats,

deriving a weighting factor equal to the absolute value of the difference between the value of said third signal for a current heartbeat and the value of said third signal for the adjacent previous heartbeat times a constant,

deriving the difference between the value of one of said first, second and third signals for the current heartbeat and its value for the adjacent previous heartbeat,

dividing the difference so obtained by the weighting factor, and

adding the result of the division to the weighted value of the adjacent previous heartbeat so as to derive the weighted value of said one signal to be displayed for the current heartbeat.