Overview

An Automated External Defibrillator (AED) is a portable device that checks the heart rhythm automatically and delivers shock when patient requires to restore the rhythm of the heart. More specifically it is used to treat conditions such as Pulseless Ventricular Tachycardia (VT) and Ventricular Fibrillation (VF).

Features of Sosaley’s AED are as follows

ENERGY

Bi-phasic energy delivery in steps starting from 50J (pediatric) & 150J (adults)

MEASUREMENT

Acquisition and classification of shockable ECG rhythms. Accurate transthoracic impedance

DISPLAY

ECG live display |Classification |Impedance |Energy Delivered

DATA

Export ECG, impedance, and energy-delivered data to a USB drive

ASSISTANCE

Optional voice & visual guidance for layman-operators. Guidance for CPR between shocks

Technical description

AED consists of Hardware and Software elements to detect heart rhythm(ECG), the Trans-thoracic impedance of the Patient and high voltage section to deliver shock to the patient and bring back the Patient heart to Normal Condition. The device is fully automated wherein the ECG acquisition, the impedance calculation and the shock delivery based on the impedance doesn’t need any human intervention other than placing the electrodes appropriately and switching on the device.

The hardware circuits consist of the following sections.

High Voltage Charging Section

• The High Voltage Charging circuit consists of Flyback transformer which can charge the DC capacitor with up to 1500 V in 15 seconds using Flyback Power Topology and charge the capacitor to a maximum of 200 Joules.

Discharging Section

• The High Voltage Discharging section is implemented as an H-Bridge Topology to provide Bi-phasic voltage waveform where the current flow in Bidirectional path to the Patient Heart for 10 milli-seconds of maximum of 200 Joules

Electrode Isolation section for Patient Safety

• The Electrode Isolation section provides the isolation between the Patient Heart and the high voltage section of the AED device.

Internal Discharge section

• Internal Discharge is used to bring the capacitor voltage to zero. It is achieved using a solid state relay, which discharges any residual capacitor voltage after the shock delivery.

ECG and Trans-Thoracic Impedance Section

• In the ECG section, the ECG signal is read from the patient with a two-electrode configuration.
•  

• The ECG signal is amplified and filtered using anInstrumentation Amplifier, Low Pass Filter(LPF), High Pass Filter (HPF), Gain Amplifier and Notch Filter and fed to a Micro-controller to be analyzed using a ECG classification Algorithm.

• The algorithm analyzes the ECG signal and classifies it into a normal or abnormal rhythm based on AHA classification. The decision can be a shockable or non-shockable rhythm based on the classification.

• Impedance Measurement Section, measures the trans-thoracic impedance of the patient by passing a Low voltage High Frequency signal of +-3v with 50 KHZ across the patient’sheart through the electrodes.

• The Electrodes sense the differential voltage from the heart and given through an Instrumentation Amplifier, HPF, LPF, and Notch filter for amplification and filtering. The signal is then given to the Microcontroller for measurement calculation of the patient’sTrans- Thoracic Impedance.

• Using this Impedance value, we can calculate and measure how much amount of energy should be delivered to the patient.

Micro-Controller Section

• The Microcontroller section, acts as an interface all the above sections and controls the charging and discharging section. The microcontroller also interfaces and controls the LCD and the touch screen display in the AED.

• Using the ECG classification algorithm and impedance value, the microcontroller will control the capacitor charging voltage and delivers the energy to the patient heart.

• The microcontroller also provides the voice and display prompts to the user by giving instructions like pad placement, ECG sensing, impedance calculation, shock-able or non-shock-able rhythm , indication for high voltage charging, shock delivery and CPR .

• The microcontroller also provides the event storage where the whole process and data of an AED session will be stored and it can copied to USB drive, if the doctor needs any information about the patient in the future.