Method for monitoring cardiac output and protecting blood and tissue

A method for protecting blood and tissue from damage due to overheating caused by heat transfer from a catheter used to monitor cardiac output, comprising the steps of:

• (a) introducing the catheter for monitoring cardiac output intravascularly into a patient's heart;
• (b) establishing a nominal fixed power distribution for heating the blood;
• (c) monitoring a temperature of a portion of the catheter where heat is transferred to the blood, producing a signal indicative thereof;
• and
• (d) in response to the signal, establishing a decreased nominal fixed power dissipation for heating the blood so that the temperature of the portion of the catheter where heat is transferred to the blood is reduced to at least a predetermined maximum safe value to protect blood and tissue from damage due to overheating caused by heat transfer from the catheter.

A method for protecting blood and tissue from damage due to overheating caused by heat transfer from a catheter used to monitor cardiac output, comprising the steps of:

• introducing the catheter for monitoring cardiac output intravascularly into a patient's heart;
• sensing a temperature of a resistive heater, mounted on a distal end of the catheter, after insertion into a patient's body;
• producing a signal indicative of the temperature of the resistive heater;
• and
• controlling an electrical current flowing through the resistive heater so that the temperature of the resistive heater does not exceed a predetermined value to protect blood and tissue from damage due to overheating caused by heat transfer from the catheter.

A method for determining cardiac output based upon a temperature rise of blood in a patient's heart, comprising the steps of:

• placing a catheter including a resistive heater located adjacent a distal end thereof intravascularly into a patient's heart;
• monitoring a temperature of the resistive heater and producing a signal indicative of the temperature;
• controlling the temperature of the resistive heater in response to the signal, to prevent the temperature from exceeding a predetermined maximum safe level;
• measuring electrical power dissipated in the resistive heater and producing a signal indicative of the power dissipated;
• and
• determining cardiac output as a function of the power dissipated.

A method for protecting blood and tissue from damage due to overheating caused by heat transfer from a catheter used to monitor cardiac output, comprising the steps of:

• introducing the catheter for monitoring cardiac output intravascularly into a patient's heart;
• supplying an electrical current to a resistive heater located at a distal end of the catheter;
• monitoring a temperature of the resistive heater and producing a signal indicative of the temperature;
• and
• controlling the electrical current flowing through the resistive heater in response to the signal to prevent the temperature of the resistive heater from exceeding a predetermined maximum safe level to protect blood and tissue from damage due to overheating caused by heat transfer from the catheter.

A method for monitoring cardiac output based upon a temperature rise of blood flowing through a heart and for protecting the blood and tissue from damage due to overheating, comprising the steps of:

• placing a catheter having a resistive heater located at a distal end intravascularly into a heart;
• providing an electrical current to the resistive heater in order to elevate a temperature of the blood;
• monitoring a temperature of the blood heated by the resistive heater;
• sensing a temperature of the resistive heater and producing a signal indicative thereof;
• controlling the temperature of the resistive heater in response to the signal so that the temperature of the resistive heater does not exceed a predetermined value;
• measuring electrical power dissipated in the resistive heater;
• and
• determining cardiac output as a function of the power dissipated.