DILUTION METHOD AND APPARATUS FOR MEASUREMENT OF FLUID FLOW RATE

• US 3,678,922 A
• Filed: 01/14/1971
• Issued: 07/25/1972
• Est. Priority Date: 01/14/1971
• Status: Expired due to Term

• Current Assignee: Charles M. Philips, Miguel E. Sanmarco
• Original Assignee: Charles M. Philips, Miguel E. Sanmarco
• Inventors: Philips, Charles M., Sanmarco, Miguel E.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/106,340
• Time in Patent Office: 558 Days
• Field of Search: 128/2.5F,2.5V,2.5R,2A,2R 73/204,194
• US Class Current: 600/505
• CPC Class Codes: A61B 5/0275 using tracers, e.g. dye dilution
• CPC Class Codes: G01F 1/68 by using thermal effects
• CPC Class Codes: G01F 1/704 using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter G01F1/76, G01F25/00 take precedence

Abstract

A dilution technique for measuring fluid flow rate within a circulating fluid system is disclosed, comprising continuous processing of a response signal following injection of an injectate into the fluid system, the process being terminated at a cut off point which is determined in terms of the peak of the response signal. The cut off point of the response signal is determined to compensate for error normally introduced due to recirculation. Apparatus is disclosed for carrying out the steps of the process, comprising an integrator-divider for processing the response signal, a peak detector and comparator for terminating the signal processing at the cut off point, and a lock in amplifier to hold the computed result during the period of recirculation. The method and apparatus for particularly applicable to thermal dilution and dye dilution measurements of blood flow rate.

Claims

1. A dilution method for determining fluid flow rate of a fluid system by automatic processing of a detected dilution response signal, comprising:

a. injecting a predetermined amount of injectate into the fluid system, which injectate carries a sensible property;

b. generating a response signal representing the variation of said property at a point following injection;

c. detecting the peak of said signal;

d. detecting when said signal drops to a predetermined percentage of said peak, said condition defining the cut off time;

e. integrating said response signal to derive a time varying area signal, and dividing said area signal into a predetermined constant, to derive a time varying output signal; and

f. holding and displaying the value of said output signal as computed at said cut off time, such cut off value representing fluid flow rate with recirculation error reduced to a negligible level.

2. The method of clAim 1 wherein said fluid flow rate represents cardiac output, and said response signal is a temperature response signal, and comprising the steps of injecting a predetermined amount of saline of a know temperature into the bloodstream of a patient and deriving said temperature response signal by detecting the temperature of said patient at a point in the bloodstream, subsequent to such injection.

3. A thermal dilution method for determining cardiac output of a patient by automatic processing of a temperature response signal representing blood temperature variation following injection of saline at a know temperature into such patient'"'"''"'"'s bloodstream, comprising:

a. detecting the peak of said signal;

b. detecting when said signal drops to a predetermined percentage of said peak, said condition defining the cut off time;

c. automatically integrating said temperature response signal from the time of saline injection to said cut off time, to derive an area signal; and

d. automatically dividing said area signal into a first predetermined constant, and multiplying by a second predetermined constant, to derive an output signal representative of the patient'"'"''"'"'s cardiac output with recirculation error reduced to a negligible level.

4. Apparatus for automatically computing the cardiac output of a patient by analysis of blood variation following injection of an injectate carrying a sensible property into the patient'"'"''"'"'s bloodstream, comprising:

a. sensing means, adapted for insertion into a patients'"'"''"'"' bloodstream for deriving a response signal representative of said blood variation;

b. automatic base line means which operates on said response signal, for providing a zero base line response signal;

c. automatic integrator means, for integrating said zero base line response signal, to derive an integrated signal;

d. computing means for dividing said integrated signal into a first predetermined constant to obtain a divided signal, and for multiplying said divided signal by a second predetermined constant, to obtain an output signal;

e. display means, for displaying said computed output signal; and

f. cut off means, for determining a cut off time when said response signal falls to a predetermined percentage of its peak value, and for causing said display means to hold the value of said output signal as computed at the cut off time, which value represents computed cardiac output.

5. The apparatus as described in claim 4 wherein said injectate is saline of a know temperature, and said sensing means comprises temperature sensing means for deriving a temperature response signal representative of blood temperature variation.

6. The apparatus as described in claim 5 wherein said cut off means comprises a peak detector which operates on said zero baseline signal to produce a peak signal, connecting means to provide said percentage of said peak value, a comparator amplifier for comparing said percentage of said peak value with said zero base line signal, and a relay circuit means driven by said comparator amplifier for holding said display means.

7. The apparatus as described in claim 6, comprising a lock in circuit means for locking the displayed cardiac output signal subsequent to said cut off time.

8. The apparatus as described in claim 7, wherein said lock in circuit means comprises a connection coupling said integrated signal to said comparator amplifier, said connection being unilateral so as to transmit only signals of one polarity to said comparator amplifier.

9. A dilution method for determining fluid flow rate at a point in a fluid system, comprising:

a. injecting a predetermined amount of injectate into the fluid system, which injectate carries a sensible property;

b. generating a response signal representing the variation of said property at said point following injection;

c. detecting when said response signal drops to a predetermined level, said condition defining the cut off time;

d. inTegrating said response signal to derive a time varying area signal, and dividing said area signal into a predetermined constant, to derive a time varying output signal; and

e. holding and displaying the value of said output signal as computed at said cut off time, such cut off value representing fluid flow rate with recirculation error reduced to a negligible level.

10. The method of claim 9 comprising controlling said predetermined amount of injectate so that the peak of said response curve is controlled within a predetermined range.