External defibrillator
An external defibrillator includes patient electrodes ( 20 ) for obtaining the patient's electrocardiogram (ECG) and for applying a shock to the patient. A microprocessor ( 24 ) analyses the patient's ECU using a diagnostic algorithm to detect if the patient's heart is in a shockable rhythm, and shock delivery circuitry ( 10 ) is enabled when a shockable rhythm is detected by the diagnostic algorithm. The patient electrodes also allow obtaining a signal (Z) which is a measure of the patient's transthoracic impedance and the microprocessor is responsive to Z to detect conditions likely to cause the diagnostic algorithm to generate a false detection of a shockable rhythm. If such detection is made, the microprocessor prevents detection of a shockable rhythm by the diagnostic algorithm, at least for a period of time.
1. A defibrillator comprising:
electrodes;
a processor; and
a circuit connecting the processor and the electrodes, wherein, when the electrodes are in contact with a patient, the processor performs operations comprising:
receiving a signal from the patient;
determining, from the signal, a measure of transthoracic impedance of the patient;
identifying, based on the measure of transthoracic impedance, that an interference condition is present, wherein the interference condition causes a false detection of a shockable rhythm in the patient; and
performing, based on the interference condition, one of: inhibiting the circuit from delivering a shock to the patient and preventing a diagnostic algorithm from detecting a shockable rhythm.
2. The defibrillator of claim 1 , wherein the interference condition is one of a movement of the patient and a touching of the electrodes by an operator.
3. The defibrillator of claim 1 , wherein when the electrodes are in contact with a patient, the processor performs further operations comprising:
establishing an electrocardiogram of the patient.
4. The defibrillator of claim 3 , wherein inhibiting the circuit from delivering a shock to the patient is independent of the electrocardiogram.
5. The defibrillator of claim 1 , wherein inhibiting the circuit from delivering a shock to the patient is performed for a predefined period of time.
6. The defibrillator of claim 1 , wherein when the electrodes are in contact with a patient, the processor performs further operations comprising:
identifying that the interference condition is present by forming a first derivative of the measure of transthoracic impedance with respect to a period of time to yield a first derivative; and
deriving a quantity of interference related to the first derivative.
7. The defibrillator of claim 6 , wherein when the electrodes are in contact with a patient, the processor performs further operations comprising:
determining if the quantity of interference exceeds a threshold level.
8. The defibrillator of claim 7 , wherein the quantity of interference is a measure of the number of times the amplitude of the first derivative exceeds the threshold level.
9. The defibrillator of claim 1 , wherein when the electrodes are in contact with the patient, the processor performs additional operations comprising:
converting the measure of transthoracic impedance from analog to digital, to yield a digital signal; and
using the digital signal for the identifying that the interference condition is present.
10. A method comprising:
receiving a signal from a patient via electrodes;
determining, from the signal and via a processor, a measure of transthoracic impedance of the patient;
identifying, based on the measure of transthoracic impedance, that an interference condition is present, wherein the interference condition causes a false detection of a shockable rhythm in the patient; and
performing, based on the interference condition, one of: inhibiting the circuit from delivering a shock to the patient and preventing a diagnostic algorithm from detecting a shockable rhythm.
11. The method of claim 10 , wherein the interference condition is one of a movement of the patient and a touching of the electrodes by an operator.
12. The method of claim 11 , further comprising:
establishing an electrocardiogram of the patient.
13. The method of claim 12 , wherein inhibiting the circuit from delivering a shock to the patient is independent of the electrocardiogram.
14. The method of claim 11 , wherein inhibiting the circuit from delivering a shock to the patient is performed for a predefined period of time.
15. The method of claim 11 , further comprising:
determining when the interference condition is present by forming a first derivative of the measure of transthoracic impedance with respect to a period of time to yield a first derivative; and
deriving a quantity of interference related to the first derivative.
16. The method of claim 15 , further comprising:
determining if the quantity of interference exceeds a threshold level.
17. The method of claim 16 , wherein the quantity of interference is a measure of the number of times the amplitude of the first derivative exceeds the threshold level.
18. The method of claim 11 , further comprising:
converting the measure of transthoracic impedance from analog to digital, to yield a digital signal; and
using the digital signal for the identifying that the interference condition is present.