Cardiac/respiratory arrest detector

• US 6,821,254 B2
• Filed: 06/27/2001
• Issued: 11/23/2004
• Est. Priority Date: 07/21/2000
• Status: Active Grant

• Current Assignee: Sunlife Science Inc.
• Original Assignee: Institute of Critical Care Medicine
• Inventors: Tang, Wanchun, Bisera, Joe, Weil, Max Harry
• Primary Examiner(s): Dahbour, Fadi H.
• Application Number:
  US09/894,572
• Publication Number:
  US 20020032383A1
• Time in Patent Office: 1,245 Days
• Field of Search: 600/484, 600/547, 600/529, 600/533, 600/508, 600/509, 600/513
• US Class Current: 600/484
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00

Abstract

The condition of a patient who has signs of cardiopulmonary arrest, is evaluated by applying a pair of electrodes (12, 14) to the chest of the patient and passing a low level of alternating current through the patient to detect changes in transthoracic impedance which represent cardiopulmonary activity of the patient. An analyzing circuit determines the average frequency of those signals (40) representing heartbeat rate impedance and determines the average frequency of signals (42) representing breathing of the patient. When the heart rate is below about 20 beats per minutes, the respiratory rate is below about 4 breaths per minute, and cardiac and respiratory impedances are below 0.01 ohms, this indicates cardiac arrest of the patient and signifies that CPR (cardiopulmonary resuscitation) should start.

Claims

1. Apparatus for evaluating the condition of a patient who has symptoms of cardiopulmonary arrest comprising:

a pair of electrodes for application to the chest of the patient;

an electricity source for applying current between said electrodes to pass through the chest of the patient;

a circuit which is coupled to said electrodes and which has an output that carries signals representing changes in impedance encountered by said current that represent cardiopulmonary activity of the patient;

an analyzing circuit with an input that receives said signal representing the cardiopulmonary activity of the patient, and which determines the average frequency of those signals representing heartbeat rate and those signals representing breathing rate;

wherein

said analyzing circuit indicates cardiac arrest when the average frequency of those signals representing heartbeat rate is below a predetermined rate which is about 20 beats per minutes and the average frequency of those signals representing respiratory rate is below a predetermined rate which is about 4 breaths per minute.

2. Apparatus for evaluating the condition of a patient who has symptoms of cardiopulmonary arrest comprising:

a pair of electrodes for application to the chest of the patient;

an electricity source for applying current between said electrodes to pass through the chest of the patient;

a circuit which is coupled to said electrodes and which has an output that carries signals representing changes in impedance encountered by said current that represent cardiopulmonary activity of the patient;

an analyzing circuit with an input that receives said signal representing the cardiopulmonary activity of the patient, and which determines the average frequency of those signals representing heartbeat rate and those signals representing breathing rate, wherein;

said analyzing circuit is constructed to indicate no cardiac arrest when the heart rate is above about 20 beats per minute and the respiratory rate is above about 4 breaths per minute.

3. Apparatus for evaluating the condition of a patient who has symptoms of cardiopulmonary arrest comprising:

a pair of electrodes for application to the chest of the patient;

an electricity source for applying current between said electrodes to pass through the chest of the patient;

a circuit which is coupled to said electrodes and which has an output that carries signals representing changes in impedance encountered by said current that represent cardiopulmonary activity of the patient;

an analyzing circuit with an input that receives said signal representing the cardiopulmonary activity of the patient, and which determines the average frequency of those signals representing heartbeat rate and those signals representing breathing rate;

wherein

said analyzing circuit is constructed to indicate extreme brady arrhythmia when the respiratory rate is above about 4 breaths per minute but the heart rate is below about 20 beats per minute.

4. Apparatus for evaluating the condition of a patient who has symptoms of cardiopulmonary arrest comprising:

a pair of electrodes for application to the chest of the patient;

an electricity source for applying current between said electrodes to pass through the chest of the patient;

a circuit which is coupled to said electrodes and which has an output that carries signals representing changes in impedance encountered by said current that represent cardiopulmonary activity of the patient;

an analyzing circuit with an input that receives said signal representing the cardiopulmonary activity of the patient, and which determines the average frequency of those signals representing heartbeat rate and those signals representing breathing rate;

wherein

said electricity source is constructed to generate current whose amplitude varies at a frequency that is at least 1000 Hz and less than 90 kHz, whereby to provide a current whose frequency is far above the cardiopulmonary frequency of interest and that has minimal inductive and capacitive reactance.

5. Apparatus for evaluating the condition of a patient who has symptoms of cardiopulmonary arrest comprising:

a pair of electrodes for application to the chest of the patient;

an electricity source for applying current between said electrodes to pass through the chest of the patient;

a circuit which is coupled to said electrodes and which has an output that carries signals representing changes in impedance encountered by said current that represent cardiopulmonary activity of the patient;

an analyzing circuit with an input that receives said signal representing the cardiopulmonary activity of the patient, and which determines the average frequency of those signals representing heartbeat rate and those signals representing breathing rate; and

a defibrillator generator circuit which is coupled to said electrodes to apply a defibrillating pulse to the patient through said electrodes.

6. Apparatus for evaluating the condition of a weak patient, comprising:

a pair of electrodes for application to the chest of the patient;

an electricity source for applying a voltage between said electrodes to flow current between them;

a circuit which is coupled to said electrodes and which detects impedance encountered by said current and which has an output that carries signals representing the cardiac activity of the patient, said circuit including a filter that passes only signals of a frequency greater than at least about 0.3 Hz to filter out impedance changes caused by respiration of the patient;

means that indicates blood pressure of the patient based on said impedance.

7. The apparatus described in claim 6 wherein:

said means that indicates blood pressure, indicates both systolic pressure and diastolic pressure.

8. Apparatus for evaluating the condition of a patient who has symptoms of cardiopulmonary arrest comprising:

a pair of electrodes for application to the chest of the patient;

an electricity, source for applying current between said electrodes to pass through the chest of the patient;

a circuit which is coupled to said electrodes and which has an output that carries signals representing changes in impedance encountered by said current that represent cardiopulmonary activity of the patient;

an analyzing circuit with an input that receives said signal representing the cardiopulmonary activity of the patient, and which determines the average frequency of those signals representing heartbeat rate and those signals representing breathing rate;

said circuit is constructed to deliver signals representing the volume of breath of the patient, as a function of said impedance.

9. A method for evaluating the condition of a weak patient who has symptoms indicating cardiac arrest, comprising:

applying a pair of electrodes to the chest of the patient;

applying a voltage between said electrodes to pass a current between them and through the chest of the patient;

detecting variations in said current which represent changes in impedance caused by any cardiac activity of the weak patient;

wherein

said step of detecting variations in said current, includes not detecting variations of a frequency at which the patient would be expected to breathe, said frequency at which the patient would be expected to breath being below one Hertz.

10. A method for evaluating the condition of a weak patient who has symptoms indicating cardiac arrest, comprising:

applying a pair of electrodes to the chest of the patient;

applying a voltage between said electrodes to pass a current between them and through the chest of the patient;

detecting variations in said current which represent changes in impedance caused by any cardiac activity of the weak patient; and

detecting variations in said current which represent changes in impedance caused by any breathing of the patient, including detecting variations of a frequency below about two Hertz.

11. A method for evaluating the condition of a weak patient who has symptoms indicating cardiac arrest, comprising:

applying a pair of electrodes to the chest of the patient;

applying a voltage between said electrodes to pass a current between them and through the chest of the patient;

detecting variations in said current which represent changes in impedance caused by any cardiac activity of the weak patient;

wherein

said step of applying a voltage includes applying a voltage that varies sinusoidally in amplitude and that has a frequency between 1000 Hz and 90 kHz.

12. A method for evaluating the condition of a weak patient who has symptoms indicating cardiac arrest, comprising:

applying a pair of electrodes to the chest of the patient;

applying a voltage between said electrodes to pass a current between them and through the chest of the patient;

detecting variations in said current which represent changes in impedance caused by any cardiac activity of the weak patient;

indicating cardiac arrest of the patient when variations in said current indicate beating of the heart at a frequency less than about 20 beats per minute.

13. A method for evaluating the condition of a patient who has symptoms of cardiac arrest, comprising:

applying a pair of electrodes to the chest of the patient;

applying a voltage between said electrodes to pass a current between them and through the chest of the patient, whose said current is too low to cause a noticeable reaction in any patient;

detecting variations in said current which represent changes in impedance caused by any cardiac activity of the patient, and also detecting changes in impedance caused by any breathing activity of the patient;

wherein

said step of detecting changes in impedance caused by any cardiac activity includes detecting variations in impedance at a frequency which is at a rate of at least 0.3 Hertz; and

said step of detecting changes in impedance caused by any breathing activity includes detecting variations in impedance of a frequency which is below about 0.3 Hertz.