The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Feb. 15, 1994
Filed:
Mar. 10, 1993
Timothy J Hughes, Palo Alto, CA (US);
Abbott Laboratories, Abbott Park, IL (US);
Abstract
A method and apparatus for continuously monitoring cardiac output based upon the phase shift between an input signal and a temperature signal indicative of the change in temperature of blood leaving the heart. In a first preferred embodiment of a cardiac output monitoring system (10), a catheter (14) is provided with an electrical resistance heater (22). An electrical current having a sinusoidal wave form with a period of from 30 to 60 seconds is applied to the heater, causing power to be dissipated into the blood within a patient's heart (12). A temperature sensor (24) disposed near a distal end of the catheter produces a signal indicative of the temperature of blood leaving the heart. The temperature signal and the signal corresponding to the electrical power dissipated in the heater (an input signal) are filtered at a frequency .omega. corresponding to the frequency of the applied electrical current, i.e., the frequency of the input signal. The amplitude of the input power, the amplitude of the temperature signal, and their phase difference are used in calculating cardiac output. In another embodiment, a temperature conditioned saline solution (84 ) is circulated through a catheter (14') in a closed loop, so that it flows through a heat exchanger (60) disposed within the heart. The fluid is circulated through the catheter on a periodic basis, providing a periodic input signal. The temperature signal produced by the temperature sensor on the catheter distal end and power dissipated to or absorbed from the blood by the heat exchanger comprise the two signals from which the cardiac output is determined as described above. The determination of cardiac output is also corrected for the time constant of the catheter/heater (or heat exchanger) and of the temperature sensor.