Cardiac output estimation method and apparatus
OwnerArnold St. J. Leeinventor
Life of this patent
Estimating the term…
Abstract
Thermocouple pairs measure the temperatures at a cold-fluid injection point and a downstream point. The reference thermocouple of each pair sees the temperature of a thermally floating heat sink of unknown temperature that has high thermal conductivity and mass, and is well insulated from the environment. Consequently the heat-sink temperature drift is practically constant. To the extent that heat-sink temperature drift is significant, the invention overcomes the effects of drift to a first approximation by providing electronic circuitry that in effect registers the drift in measurement voltage before fluid injection, extrapolates this voltage drift into the measurement time period, and automatically subtracts the extrapolated voltage drift from the measurement voltages.
Claims14
An apparatus for estimating the flow rate of blood in a bloodstream comprising:
- means for injecting into such bloodstream a quantity of fluid whose temperature is distinctly different from that of the blood;
- means, having a reference thermocouple, for measuring changes in the temperature of the blood at a point downstream from the injection point;
- and
- a reference heat sink which is not temperature-controlled, thermally connected to the reference thermocouple of the means for measuring changes;
- the change-measuring means including:
- a sensing thermocouple disposed at the downstream point,
- a reference thermocouple disposed to substantially assume the temperature of the reference heat sink, and
- means for measuring the voltage produced by the sensing and reference thermocouples, operating as an opposed thermocouple pair, while the injected fluid passes the downstream point;
- and
- electronic means responsive to the measured voltage for determining the blood temperature changes sensed by the sensing thermocouple independently of the temperature of the reference thermocouple considered singly wherein said electronic means compensates for changes in the temperature of the heat sink while the injected fluid passes the downstream point.
A method for use in estimating the flow rate of blood in the bloodstream from a living being's heart, comprising:
- injecting into such bloodstream, at a particular point near such heart, a quantity of fluid whose temperature is distinctly different from that of the blood;
- while the injected fluid passes the downstream point, measuring changes in the voltage output of an opposed thermocouple pair whose sensing junction is disposed downstream from the injection point and whose reference junction is disposed to substantially assume the temperature of a reference heat sink which is not temperature-controlled;
- said measuring step being independent of the temperature of the reference heat sink considered singly;
- and
- compensating for changes in the temperature of the heat sink while the injected fluid passes the downstream point.
Dependencies are inferred from the claim text.