Heated catheter for monitoring cardiac output

• US 5,277,191 A
• Filed: 06/19/1991
• Issued: 01/11/1994
• Est. Priority Date: 06/19/1991
• Status: Expired due to Fees

• Current Assignee: Abbott Laboratories
• Original Assignee: Abbott Laboratories
• Inventors: Hughes, Timothy J.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Gilbert, Samuel
• Application Number:
  US07/717,549
• Time in Patent Office: 937 Days
• Field of Search: 128/713, 128/692, 128/670, 128/671, 128/642, 128/401, 73/204.16, 73/204.17, 73/204.18, 73/204.19
• 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 heated catheter for monitoring cardiac output. Displaced from a distal end of a heated catheter (30) is a resistive heater (32) that heats blood flowing within a heart muscle (10). The resistive heater is mounted on the catheter so that when the catheter is inserted into the heart, the resistive heater is disposed in the right ventricle. A temperature sensor (34) is disposed downstream of the resistive heater, in or proximate the pulmonary artery during use. A differential amplifier (40, 70) provides an electrical current to the resistive heater that varies as a function of the difference between the temperature of the resistive heater, measured by a temperature sensor (35), and a predetermined temperature. In another embodiment of the invention, a resistive heater (90) has a resistance that varies with temperature. The resistive heater comprises one arm of a bridge circuit (85). A differential amplifier (110) provides an electrical current to the bridge circuit in response to the voltage developed across the bridge circuit. In yet another embodiment, a constant power dissipation is maintained in a resistive heater (60 ), so long as its temperature does not exceed a predetermined maximum. Should that occur, a power control block (80) incrementally reduces the power dissipated in the resistive heater, thereby insuring that the temperature of the resistive heater does not damage blood cells, yet is sufficient to provide a good signal-to-noise ratio in respect to a signal indicative of the temperature rise in blood flowing from the heart.

Claims

1. Apparatus for heating blood flowing through a heart in order to determine cardiac output based upon a temperature rise of the blood, comprising:

(a) a resistive heater connectable to a source of electrical current;

(b) a catheter having a distal end that can be inserted intravascularly into the heart the distal end including a temperature sensor for sensing the temperature of blood heated by the resistive heater, the resistive heater being mounted on the catheter and displaced from the distal end thereof so that the temperature sensor is not directly affected by the temperature of the resistive heater;

(c) temperature sensing means, for sensing the temperature of the resistive heater and producing a signal indicative thereof; and

(d) control means, connected to receive the signal indicative of the temperature of the resistive heater, for controlling an electrical current flowing from the source through the resistive heater so that the temperature of the resistive heater does not exceed a predetermined value.

2. The apparatus of claim 1, wherein the temperature sensing means comprise a temperature sensor that is mounted in thermal communication with the resistive heater so as to sense its temperature.

3. The apparatus of claim 1, wherein the resistive heater has a resistance that varies with temperature, and wherein the temperature sensing means includes a plurality of resistors connected in a bridge circuit with the resistive heater, the control means responding to a potential developed across the bridge circuit to control the electrical current flowing through the resistive heater.

4. The apparatus of claim 1, wherein the control means are operative to maintain a nominal fixed power dissipation in the resistive heater, but reduce the electrical current flowing through the resistive heater to establish a different nominal fixed power dissipation if the temperature of the resistive heater otherwise exceeds the predetermined value.

5. The apparatus of claim 1, further comprising means for measuring electrical power dissipated in the resistive heater as a function of the signal indicative of its temperature, producing a signal corresponding thereto for use in determining the cardiac output.

6. Apparatus for use in continuously monitoring cardiac output based upon a temperature rise of blood flowing through a heart due to heat transfer, comprising:

(a) a catheter having a distal end and a temperature sensor disposed proximate the distal end;

(b) means for supplying heat to a heated portion of the catheter, heat transfer from the heated portion of the catheter serving to heat the blood within the heart, the heated portion being displaced from the distal end of the catheter so that the temperature sensor disposed proximate the distal end of the catheter can sense the temperature of blood heated by the means for supplying heat without being directly affected by the temperature of said means;

(c) temperature sensing means for monitoring the temperature of the heated portion of the catheter, producing a signal indicative thereof; and

(d) control means, connected to receive the signal indicative of the temperature of the heated portion of the catheter, for controlling the temperature of the heated portion so that it does not rise to a level likely to damage the blood.

7. The apparatus of claim 6, wherein the temperature sensing means comprise a temperature sensor disposed at the heated portion of the catheter so as to monitor its temperature.

8. The apparatus of claim 6, wherein the means for supplying heat dissipate a nominally fixed power in the heated portion of the catheter and the control means are operative to vary the temperature of the heated portion, thereby causing a different nominally fixed power to be dissipated only if the temperature of the heated portion rises above the level likely to damage the blood.

9. Apparatus for heating blood flowing through a heart in order to determine cardiac output based upon a temperature rise of the blood, comprising:

(a) a resistive heater connectable to a source of electrical current, wherein the resistive heater has a resistance that varies with temperature;

(b) a catheter having a distal end that can be inserted intravascularly into the heart, the resistive heater being mounted on the catheter and displaced from a distal end thereof;

(c) temperature sensing means, for sensing the temperature of the resistive heater and producing a signal indicative thereof, wherein the temperature sensing means comprise means for measuring an electrical current flowing from the source through the resistive heater and a voltage drop across the resistive heater, and

(d) control means, connected to receive the signal indicative of the temperature of the resistive heater, for controlling the electrical current flowing from the source through the resistive heater so that the temperature of the resistive heater does not exceed a predetermined value, wherein the signal indicative of the temperature of the resistive heater is proportional to a ratio of the voltage drop across the resistive heater and the electrical current flowing through the resistive heater.

10. The apparatus of claim 9, wherein the controls means include for producing a reference signal corresponding to the predetermined value and a comparator connected to compare the signal indicative of the temperature of the resistive heater to the reference signal, producing an output signal corresponding to their difference that is used to control the electrical current flowing through the resistive heater.

11. Apparatus for heating blood flowing through a heart in order to determine cardiac output based upon a temperature rise of the blood, comprising:

(a) a resistive heater connectable to a source of electrical current;

(b) a catheter having a distal end that can be inserted intravascularly into the heart, the resistive heater being mounted on the catheter and displaced from distal end thereof;

(c) temperature sensing means, for sensing the temperature of the resistive heater and producing a signal indicative thereof;

(d) control means, connected to receive the signal indicative of the temperature of the resistive heater, for controlling the electrical current flowing from the source through the resistive heater so that the temperature of the resistive heater does not exceed a predetermined value; and

(e) means for measuring electrical power dissipated in the resistive heater as a function of the signal indicative of its temperature, producing a signal corresponding thereto for use in determining the cardiac output.

12. Apparatus for use in continuously monitoring cardiac output based upon a temperature rise of blood flowing through a heart due to heat transfer, comprising:

(a) a catheter;

(b) means for supplying heat to a heated portion of the catheter, heat transfer from the heated portion of the catheter serving to heat the blood within the heart, wherein the means for supplying heat comprise a resistive heater disposed at the heated portion of the catheter, the resistive heater adapted to be connected to a source of an electrical current and having a resistance that varies with temperature;

(c) temperature sensing means for monitoring the temperature of the heated portion of the catheter, producing a signal indicative thereof, wherein the temperature sensing means comprise means for measuring an electrical current flowing through the resistive heater and a voltage drop across it, the signal indicative of the temperature of the heated portion being proportional to a ratio of the voltage drop and the electrical current; and

(d) control means, connected to receive the signal indicative of the temperature of the heated portion of the catheter, for controlling the temperature of the heated portion so that it does not rise to a level likely to damage the blood.

13. Apparatus for heating blood flowing through a heart in order to determine cardiac output based upon a temperature rise of the blood, comprising:

(a) a resistive heater connectable to a source of an electrical current, the resistive heater having a resistance that varies with its temperature;

(b) a catheter having a distal end that can be inserted intravascularly into the heart the distal end including a temperature sensor for sensing a temperature of blood heated by the resistive heater, the resistive heater being mounted on the catheter and displaced from the distal end thereof so that the temperature sensor is not directly affected by the temperature of the resistive heater;

(c) temperature sensing means, for sensing the temperature of the resistive heater and producing a signal indicative thereof, wherein the temperature sensing means comprise means for measuring the electrical current flowing through the resistive heater and a voltage drop across it, and wherein the signal indicative of the temperature of the resistive heater is proportional to a ratio of the voltage drop and the electrical current flowing through the resistive heater; and

(d) control means connected to receive the signal indicative of the temperature of the resistive heater, for controlling the electrical current flowing from the source through the resistive heater so that the temperature of the resistive heater does not exceed a predetermined value.

14. Apparatus for heating blood flowing through a heart in order to determine cardiac output based upon a temperature rise of the blood, comprising:

(a) a resistive heater connectable to a source of an electrical current;

(b) a catheter having a distal end that can be inserted intravascularly into the heart the distal end including a temperature sensor for sensing a temperature of blood heated by the resistive heater, the resistive heater being mounted on the catheter and displaced from the distal end thereof so that the temperature sensor is not directly affected by a temperature of the resistive heater;

(c) temperature sensing means, for sensing the temperature of the resistive heater and producing a signal indicative thereof; and

(d) control means, connected to receive the signal indicative of the temperature of the resistive heater, for controlling the electrical current flowing from the source through the resistive heater so that the temperature of the resistive heater does not exceed a predetermined value, wherein the control means include means for producing a reference signal corresponding to the predetermined value and a comparator connected to compare the signal indicative of the temperature of the resistive heater to the reference signal, producing an output signal corresponding to their difference that is used to control the electrical current flowing through the resistive heater.

15. Apparatus for use in continuously monitoring cardiac output based upon a temperature rise of blood flowing through a heart, comprising:

(a) a catheter having a heater mounted thereon;

(b) means for supplying heat to the heater that is insertable intravascularly into a heart, heat transfer from the heater serving to heat the blood within the heart, wherein the means for supplying heat comprise a source of an electrical current coupled electrically to the heater so that the electrical current flows through the heater, and wherein said heater has a resistance that varies with its temperature;

(b) temperature sensing means for monitoring the temperature of the heater, producing a signal indicative thereof; and

(c) control means, connected to receive the signal indicative of the temperature of the heater, for controlling the temperature of the heater so that it does not rise to a level likely to damage the blood.

16. The apparatus of claim 15, wherein the temperature sensing means comprise means for measuring the electrical current flowing through the heater and a voltage drop across it, the signal indicative of the temperature of the heated portion being proportional to a ratio of the voltage drop and the electrical current.

17. The apparatus of claim 15, wherein the temperature sensing means comprise a resistance network that includes the resistive heater and means for sensing voltage differential across the resistance network to produce the signal indicative of the temperature of the heated portion.

18. The apparatus of claim 17, the electrical heating current flowing through the resistive heater provides the signal indicative of the temperature of the heated portion of the catheter.