Continuous cardiac output monitoring system

• US 5,509,424 A
• Filed: 01/28/1994
• Issued: 04/23/1996
• Est. Priority Date: 01/28/1994
• Status: Expired due to Term

• Current Assignee: Alba Critical Care Limited, Omega Critical Care Limited
• Original Assignee: Aws Salim Nashef
• Inventors: Al-Ali, Ammar
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US08/188,274
• Time in Patent Office: 816 Days
• Field of Search: 128/691-692, 128/713, 128/736, 128/668, 128/687
• US Class Current: 600/505
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: G01F 1/68 by using thermal effects
• CPC Class Codes: G01F 25/13 using a reference counter
• CPC Class Codes: Y10S 128/925 Neural network

Abstract

A cardiac catheter continuously monitors cardiac output within an artery. One temperature sensor measures native blood temperature within the artery, while another temperature sensor measures the temperature of a thermal coil which is in thermal contact with the blood stream. The temperature signals are provided as inputs to a monitoring system which includes isolators, filters, and data processing circuits. A temperature difference signal over time is generated between the native blood temperature and the thermal coil temperature. First and second derivatives are taken of the temperature difference signal and selected features are extracted from the three waveforms. The extracted features are used as to calculate cardiac output. In the present case, a neural network processor is utilized to provide accurate cardiac output measurements based upon the extracted features.

Claims

1. An apparatus for measuring volume flow rate of a liquid having a pulsatile flow within a body lumen, said apparatus comprising:

a heat transfer device in thermal communication with said liquid, said heat device to a first temperature, said first temperature varying with the pulsatile flow of said liquid, wherein said heat transfer device comprises a thermal coil;

a first temperature sensor adapted to be in thermal communication with said heat transfer device to measure the temperature of said heat transfer device, said first temperature sensor having a first output with a first output signal indicative of the temperature of said heat transfer device;

a second temperature sensor adapted to be in thermal contact with said liquid to measure a native temperature of said liquid, said second temperature sensor having a second output with a second output signal indicative of the native temperature of said liquid;

a comparator which responds to said first output signal and said second output signal to provide a temperature difference signal representing the difference in temperature between said native temperature of said liquid and the temperature of said heat transfer device;

a signal processing unit for extracting pre-specified features from said temperature difference signal; and

a neural network responsive to said pre-specified features as input parameters and configured to output volume flow rate of said liquid.

2. An apparatus as defined in claim 1, wherein said heat transfer device further comprises a thermally conductive layer interposed between said thermal coil and said first temperature sensor.

3. An apparatus for measuring volume flow rate of a liquid having a pulsatile flow within a body lumen, said apparatus comprising:

.

a heat transfer device in thermal communication with said liquid, said heat transfer device responsive to a low power electrical signal to heat said heat transfer device to a first temperature, said first temperature varying with the pulsatile flow of said liquid, and wherein said heat transfer device comprise a generally tubular thermally conductive layer and a thermal coil wrapped about said generally tubular thermally conductive layer to form a generally tubular heat transfer device;

a first temperature sensor adapted to be in thermal communication with said heat transfer device to measure the temperature of said heat transfer device, said first temperature sensor having a first output with a first output signal indicative of the temperature of said heat transfer device;

a second temperature sensor adapted to be in thermal contact with said liquid to measure a native temperature of said liquid, said second temperature sensor having a second output with a second output signal indicative of the native temperature of said liquid;

a comparator which responds to said first output signal and said second output signal to provide a temperature difference signal representing the difference in temperature between said native temperature of said liquid and the temperature of said heat transfer device;

a signal processing unit for extracting pre-specified features from said temperature difference signal; and

a neural network responsive to said pre-specified features as input parameters and configured to output volume flow rate of said liquid.

4. An apparatus as defined in claim 3, wherein a cushioning sheet is positioned adjacent said second temperature sensor to apply pressure on said second temperature sensor so as to improve thermal contact between said thermally conductive layer and said second temperature sensor.

5. A method of detecting volume flow rate of a liquid within a body lumen, said method comprising the steps of:

detecting a first temperature of a heat transfer device which is in thermal contact with said liquid, said first temperature varying with the flow of the liquid past the heat transfer device;

detecting a second native temperature of said liquid;

generating a temperature difference signal based upon the first temperature and the second temperature;

extracting pre-specified features from said temperature difference signal, wherein said extracted features include;

frequency, pulse time, average temperature of said difference signal, cooling area, heating area, cooling time and heating time;

providing said pre-specified features to a neural network responsive to said pre-specified features as input parameters and configured to output volume flow rate of said liquid; and

outputting said volume flow rate of said liquid.

6. A method of detecting volume flow rate of a liquid within a body lumen, said method comprising the steps of:

detecting a first temperature of a heat transfer device which is in thermal contact with said liquid, said first temperature varying with the flow of the liquid past the heat transfer device;

detecting a second native temperature of said liquid;

generating a temperature difference signal based upon the first temperature and the second temperature;

extracting pre-specified features from said temperature difference signal, wherein said extracting step further comprises the steps of taking first and second derivatives of said temperature difference signal and extracting additional ones of said pre-specified features from the first and second derivatives of said temperature difference signal and, wherein said additional ones of said pre-specified features include;

positive area in the first derivative of the signal, negative area in the first derivative of the signal, time of the positive area in the first derivative of the signal, time of the negative area in the first derivative of the signal, the value of the maximum point of the first derivative of the signal, the value of the minimum point of the first derivative of the signal, positive area in the second derivative of the signal, negative area in the second derivative of the signal, time of the positive area in the second derivative of the signal, time of the negative area in the second derivative of the signal, the value of the maximum point of the second derivative of the signal, and the value of the minimum point of the second derivative of the signal;

providing said pre-specified features to a neural network responsive to said pre-specified features as input parameters and configured to output volume flow rate of said liquid; and

outputting said volume flow rate of said liquid.

7. A cardiac monitoring system for measuring cardiac output within a blood vessel, said monitoring system comprising:

a catheter having catheter body with a distal end and a proximal end, said catheter comprising;

a proximal temperature sensor positioned along the catheter body, said proximal temperature sensor adapted to measure the temperature of blood within said blood vessel when said catheter is positioned in a body lumen, said proximal temperature sensor having an output indicative of a first blood temperature;

a distal temperature sensor positioned along said catheter body and in thermal contact with a heat transfer device which is adapted to be in thermal contact with blood when said catheter is positioned within a body lumen, said distal temperature sensor having an output of a second temperature signal indicative of the temperature of the heat transfer device;

a central processing unit which communicates with said first and second temperature sensors of said catheter, said central processing unit including;

a comparator which responds to said first temperature signal and said second temperature signal to provide a temperature difference signal;

a differentiator which forms derivatives of said temperature difference signal;

a signal processing unit for extracting pre-specified features from said temperature difference signal and from said derivative signals; and

a processor responsive to said pre-specified features as input parameters and configured to output a value representative of cardiac output of blood within said blood vessel, wherein said processor is further responsive to said temperature difference signal to provide a heart rate.