What is the difference between stored and delivered energy?

Stored energy (E = ½CV²) is the total energy held in the capacitor before discharge. Delivered energy is the fraction actually transferred to the patient after accounting for waveform efficiency and lead/electrode losses. Biphasic waveforms typically deliver about 94% of stored energy; monophasic waveforms deliver roughly 60–70%.

What is a typical patient impedance value?

Adult transthoracic impedance ranges from about 40 Ω to 150 Ω, with 70–75 Ω as the commonly cited adult average. Pediatric or thin patients may present lower impedance. Many modern AEDs perform impedance sensing and adapt output accordingly.

Why do biphasic waveforms require less energy than monophasic?

Biphasic waveforms deliver current in two opposing phases, which more efficiently depolarizes myocardial cells. Clinical studies show effective defibrillation at 120–200 J biphasic compared to 360 J monophasic, reducing myocardial damage.

What capacitance is used in real defibrillators?

Most external defibrillators use capacitors in the range of 80–200 µF charged to 1,000–5,000 V. Implantable cardioverter-defibrillators (ICDs) use smaller capacitors (~100–150 µF) charged to higher voltages to deliver 20–40 J.

How is peak current calculated?

Peak current at the moment of discharge is approximated as I_peak = V / Z, where V is the initial capacitor voltage and Z is patient impedance. This is the instantaneous maximum; actual current decays exponentially as the capacitor discharges.

What waveform type should I select for an AED?

Virtually all modern AEDs use a biphasic truncated exponential (BTE) or biphasic rectilinear (BRE) waveform. Select "Biphasic" for AEDs manufactured after the late 1990s. Older manual defibrillators may use monophasic damped sinusoidal (MDS) waveforms.

Defibrillator Energy Calculator

Enter capacitance, voltage, and patient impedance to instantly calculate defibrillation energy, stored charge, and peak current for biphasic or monophasic waveforms.

Engineering & Educational Notice: This calculator models theoretical electrical circuit discharge parameters. It is intended strictly for biomedical engineering and educational modeling and must not be used for clinical decision-making, patient care, or emergency cardiac resuscitation protocols.

Defibrillator Parameters

Waveform Type

Biphasic (BTE) Monophasic (MDS)

Capacitance (µF)

Typical AED / manual defib: 80 – 200 µF

Charging Voltage (V)

Typical external defib: 1,000 – 5,000 V

Patient Impedance (Ω)

Adult average: 70 – 75 Ω (range 40 – 150 Ω)

Stored Energy E = ½ C V²

— J

Total energy held in the capacitor before discharge

Delivered Energy 94% efficiency (biphasic)

— J

Energy actually transferred to the patient

Peak Current I = V / Z

— A

Instantaneous peak current at start of discharge

Stored Charge Q = C × V

— mC

Total charge stored in the capacitor

Formula Reference

E = ½ C V²

Stored energy in joules. C in farads, V in volts.

E_del = η × E

Delivered energy. η ≈ 0.94 biphasic, 0.63 monophasic.

I = V / Z

Peak current. Z is patient impedance in ohms.

Q = C × V

Charge in coulombs. C in farads, V in volts.

Summary

This calculator computes key electrical parameters of a defibrillator pulse: stored energy (E = ½CV²), delivered charge (Q = CV), and peak current (I = V / Z) based on capacitance, voltage, and patient impedance. It supports both biphasic truncated exponential (BTE) and monophasic damped sinusoidal (MDS) waveforms, applying the appropriate delivery efficiency factor for each. Note: This tool is strictly for biomedical engineering and circuit physics modeling, not clinical resuscitation dosing.

How it works

Enter the capacitor capacitance in microfarads (µF).
Enter the charging voltage in volts (V).
Enter the patient transthoracic impedance in ohms (Ω), typically 50–100 Ω.
Select the waveform type: biphasic or monophasic.
The calculator instantly outputs stored energy, delivered energy, peak current, and stored charge.
Adjust any input to recalculate results in real time.

Use cases

Biomedical engineers designing or bench-testing defibrillator circuits.
Clinical engineers verifying defibrillator output specifications.
Medical device students studying cardiac resuscitation technology.
Researchers comparing biphasic versus monophasic waveform efficiency.
Quality assurance teams validating AED or manual defibrillator performance.
Hospital biomedical staff performing preventive maintenance checks.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu