Apparatus and method for initiating cardiac output computations

Claim 2

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.

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 10

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.

Claim 13

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.