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ECT Machines

The main aim of Electroconvulsive Therapy is to cause a massive convulsion in the brain (a massive epileptic fit).  This is achieved by giving the brain an electric shock using an ECT Machine.  ECT machines are, basically, transformers which modify Mains Current so that it is transmitted to the patient's skull in timed pulses. 

Two of the most common fallacies regarding Electroconvulsive Therapy (and ECT machines) are that:
a small electric current is passed through the brain
the voltages used are no higher than 150 volts
Nothing could be further from the truth.  As can be seen from the table below, the smallest current is 0.75 amps. more than enough to kill if applied across the chest.  A voltage as high as 450 volts speaks for itself.

Machine Country Voltage
ECTRON Series 5A UK 225 volts 0.75 Amps 700 mC
MECTA SR2 UK 240 volts 0.8 Amps 1200 mC
MECTA SR2 USA 240 volts 0.8 Amps 576 mC
MECTA SR2 EUROPE 240 volts 0.8 Amps 403.2 mC
THYMATRON DGx UK 450 volts 0.9 Amps 1008 mC
THYMATRON DGx USA 450 volts 0.9 Amps 504 mC
THYMATRON DGx EUROPE 450 volts 0.9 Amps 504 mC

The main parameters associated with Electroconvulsive Therapy and ECT Machines are Voltage, Current,Charge, Time, and Threshold Value.

Electrical Quantity (Charge)
The Electrical Quantity (or Charge) is defined as the amount of electricity passing through a given point in a given time.  The SI symbol for Electrical Quantity is "Q" and it is measured in Coulombs or milliCoulombs (thousandths of a Coulomb) and is usually abreviated to 'mC' as in the Table above.
For example, the UK version of the Somatics Thymatron (see above) will deliver a Charge of 1008 milliCoulombs in 5.3 seconds.  Looked at another way, 1008 milliCoulombs of Electricity will pass through a given point (the patient's brain) in a given time (5.3 seconds).
Threshold Value
The Threshold Value is the Electrical Quantity (Charge) required to produce a convulsion in a particular patient.  Since we are all different, it takes different amounts of electricity to cause a convulsion in each of us (i.e. our Threshold Values are different).  The Threshold Value for one person could be as low as 25 millicoulombs whereas the Threshold Value for the next person could be more than 1000 millicoulombs (i.e. it can take more than 40 times as much electricity to cause a convulsion in one person as the next).
Current is the rate of flow of electricity.  It is the amount of electricity – Electrical Quantity or Charge – which passes a given point in a second.  Since Electrical Quantity is measured in Coulombs (or milliCoulombs) the obvious measurement for Current is Coulombs/second or milliCoulombs/second.  However, Current has been given its own special unit; it is measured in "amps".  One amp is equivalent to 1 Coulomb/second.  The SI symbol for Current is "I".
Resistance is that which opposes the flow of electricity.  Resistance tries to reduce the current.  The higher the resistance, the lower the current.  The SI symbol for Resistance is "R" and it is measured in ohms.
Voltage can be defined as that which causes electricity to flow.  It is an electrical force.  Increasing the Voltage will cause the Quantity of Electricity to increase so that more electricity will be passing through a given point each second which means that the Current is increased (i.e. The higher the voltage, the higher the current).  The SI symbol for voltage is "V" and it is measured in volts.

Voltage, Current and Resistance are connected by the formula:
Voltage(V) = Current(I) x Resistance(R)
It can be seen from the formula that if the current is kept fixed, then increasing the resistance will cause the voltage to increase; decreasing the resistance will cause the voltage to decrease.

Electrical Quantity (Charge), Current and Time are connected by the formula:
Charge(Q) = Current(I) x Time(t)

Time is the time in seconds during which the current is flowing.  It can be seen from this formula that if the current is kept fixed, then the quantity of electricity is completely dependent on the time.  The longer the Shock, the more electricity flows through the brain.


The Thymatron, manufactured by Somatics Inc, is an extremely popular machine (with psychiatrists) and is one of the machines recommended by the Royal College of Psychiatrists in their 1995 ECT Handbook.

The UK version of the Thymatron has the following specifications:

Max Output Voltage (V) 450 volts
Output Current (I) 0.9 amps
Frequency 70 hertz
Pulse Width 1.5ms (0.0015 seconds)
Stimulus Duration 0.26-5.3 seconds
OutPut Charge 50.4-1008 mC
Stimulus Intensity (max) 191 mC/sec

Like most modern ECT machines, the Thymatron is a fixed-current machine which means that it will try and maintain the current (0.9 amps) going through the patient's brain no matter the resistance.  If the patient's head has a high resistance, the machine will increase the voltage in order to overcome the resistance and keep the current at 0.9 amps.  If the patient's head has a low resistance the voltage will drop.  Remember that voltage, current and resistance are connected by a formula (see above).

The Thymatron is also a brief-pulse machine which means that it sends the electricity through the patient's brain in a series of short pulses.  Each of these pulses lasts 1.5 milliseconds (thousandths of a second).
It can be seen from the table that the Thymatron has a frequency of 70 hertz which means that it goes through 70 cycles per second.  It is also a bi-phasic machine which means that it sends two pulses on every cycle, thus it sends 140 pulses of electricity through the patient's brain every second.  Since the shock can last up to 5.3 seconds, the machine will send 742 pulses of electricity through the patient's brain in this time.  This means that – at maximum shock length – a current of 0.9 amps would actually be flowing in the patient's brain for 1113 milliseconds (i.e. 742 pulses x 1.5 milliseconds).   Current would be flowing for more than a second.

Earlier, it was mentioned that Electrical Quantity (Charge), Current and Time were connected by the formula below:
Charge(Q) = Current(I) x Time(t)
The maximum Charge that the Thymatron can deliver is 1008 mC.  From the formula it can be seen that this is the current multiplied by the time for which the current flows  The current flowing through the brain of the patient is the Charge (1008 mC) divided by the Time (1113 milliseconds) during which the current is flowing.  This works out at 0.9056 amps which, if rounded down to one decimal place, works out at 0.9 amps. This is exactly as stated in the specification.

The unit of energy in the SI system of units is the "Joule".   In an electrical system, the Energy(E) in Joules is the product of the voltage(V), the current(I) and the time(t) for which the current flows.

Energy (E) = Voltage (V)  x Current (I)  x Time (seconds)

Assuming maximum voltage (450 volts), the energy delivered to the patient's head by each pulse would be:

450 volts x 0.9 amps x 0.0015 seconds (1.5ms) = 0.6075 Joules

Since the machine delivers 140 pulses per second then the energy delivered to the patient's head every second is:

Energy per second = 0.6075 Joules x 140 pulses = 85.05 Joules

Since Power (watts) is the rate of transfer of energy (joules per second), 85.05 joules per second represents a power output of 85.05 watts.  This machine can deliver enough power to keep a large lightbulb glowing brightly for more than 5 seconds.

Does This Sound Like a Small Amount of Electricity?