Apparatus and method for initiating cardiac output computations

• US 4,417,588 A
• Filed: 03/22/1982
• Issued: 11/29/1983
• Est. Priority Date: 03/22/1982
• Status: Expired due to Fees

• Current Assignee: Arrow International Incorporated (Teleflex Incorporated)
• Original Assignee: Critikon, Inc.
• Inventors: Lentz, David J., Houghton, Richard B.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US06/360,942
• Time in Patent Office: 617 Days
• Field of Search: 128/713, 128/691-694, 73/209
• US Class Current: 600/526
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence

Abstract

A cardiac output computer which measures cardiac output by the indicator method involving the estimation of the area under either a thermodilution of a luminous transmission curve with automatic bolus detection. Evaluation of the area under the curve is made relative to a true baseline and is independent of, in the case of thermodilution, blood temperature as of the time the bolus is injected into the patient. A series of blood temperature samples are read and stored with the magnitude of each successive signal compared to the one received immediately before. As soon as a plurality of successive comparisons, preferably five, of six successively acquired blood temperatures indicate monotonically decreasing blood temperature values, a test for monotonicity is confirmed, with the highest temperature of the six being designated as the baseline. Once the test is confirmed the computer proceeds to evaluate the area under the curve.

Claims

1. In an apparatus for measuring cardiac output flow rate by introducing a predetermined amount of an indicator at a known temperature into the blood stream of a subject and monitoring the temperature of the blood at a location downstream from the point of introduction, including blood temperature sampling means for generating time dependent signals representative of the varying blood temperature at said location as said indicator travels through the bloodstream relative to said location, said signals defining a thermodilution curve, computing means for estimating the area bounded by said thermodilution curve and a baseline temperature subsequent to a first point in time, the improvement comprising:

(a) comparing means for comparing successive signals;

(b) means responsive to said comparing means for designating as said baseline temperature the temperature that corresponds to the first signal that is followed by a predetermined plurality of signals each representing a successively decreasing blood temperature, said first signal representing blood temperature at said first time; and

(c) means for initiating said computing means in response to designating said baseline temperature.

2. In the apparatus according to claim 1 wherein said comparing means includes:

(a) a first multi-stage shift register for storing a predetermined plurality of digitized blood temperature signals and shifting the contents of each stage in a predetermined sequence as each new signal is received;

(b) a comparator for comparing the magnitude of the signals in two of the stages of said first shift register, said comparator having an output for issuing a first signal when the comparison indicates a rise in temperature and a second signal when the comparison indicates a decline in temperature; and

(c) a second multi-stage register coupled to the output of said comparator for sequentially storing in each of its stages an output signal received from said comparator.

3. In an apparatus according to claim 2 wherein said means for initiating said computing means includes a multiple input NAND gate, wherein each of the inputs to said NAND gate connect to one of the stages of said second multi-stage register.

4. In an apparatus according to either of claims 2 or 3 wherein said first register comprises at least six stages and said second register comprises one stage less than said first register.

5. In an apparatus for measuring cardiac output flow rate by introducing into the bloodstream of a subject a predetermined quantity of an indicator dye having a known detectable absorption characteristic different from that of said blood and monitoring the changes in light absorption of the blood at a location downstream from the point of introduction, including blood light absorption sampling means for generating time dependent signals representative of the varying blood light absorption at said location as said indicator travels through the bloodstream relative to said location, said signals defining a luminous transmission curve, computing means for estimating the area bounded by said luminous transmission curve and a baseline of light absoprtion subsequent to a first point in time, the improvement comprising:

(a) comparing means for comparing successive signals;

(b) means responsive to said comparing means for designating as said baseline, the light absorption corresponding to the first signal that is followed by a predetermined plurality of signals each representing a successively decreasing level of light detection, said first signal representing light absorption at said first time; and

(c) means for initiating said computing means in response to designating said baseline of light absorption.

6. A method of measuring cardiac output comprising:

(a) introducing a known volume of an indicator at a known temperature into the blood stream of a subject;

(b) sensing blood temperature at a specified location within said subject;

(c) sampling said blood temperature at predetermined intervals to form a blood temperature profile;

(d) comparing successive blood temperature values;

(e) designating as a baseline temperature the first temperature sampled subsequent to introducing the indicator which is followed by a predetermined plurality of successively decreasing blood temperatures, wherein said first temperature corresponds to a first time; and

(f) estimating cardiac output by steps including integrating the area between said baseline temperature and said blood temperature profile over a specified period commencing with said first time.

7. A method of measuring cardiac output according to claim 6 wherein at least five successive decreases in blood blood temperature are sampled before a baseline is designated.

8. A method of measuring cardiac output comprising:

(a) introducing into the bloodstream of a subject a known volume of an indicator dye having a detectable light absorption characteristic different from that of the subject'"'"'s blood;

(b) detecting blood light absorption at a specified location within said subject;

(c) sampling said blood light detection at predetermined intervals to form a luminous transmission curve;

(d) designating as a baseline the first blood light absorption value sampled subsequent to introducing the dye which is followed by a predetermined plurality of successively decreasing light absorption detection signals, wherein said first light absorption signal corresponds to a first time; and

(e) estimating cardiac output by steps including estimating the area between said baseline and said luminous transmission curve over a specified period commencing with said first time.

9. A method of measuring cardiac output according to claim 8 wherein at least five successive decreases in blood light absorption are sampled before a baseline is designated.