Science & Technology in Action

13th Edition

Implantable Pulse Generators (IPGS) and pain relief

Boston Scientific

This lesson looks at applications of implantable pulse generators (IPGs) in the relief of chronic pain and treatment of tremors. Such ‘neuromodulation’ involves changing or modulating nerve activity through electrical or chemical stimulation in specific areas.
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Lesson excerpt

Early attempts to control pain

The first evidence of active measures to control pain date back to the Stone Age where teeth have been discovered with fillings made of bees wax to reduce the pain of dental cavities. The Ancient Egyptians, Greeks and Romans used electricity to treat pain. How was this possible when the ‘invention’ of electricity was almost 2000 years in the future? The answer is simple; they used electricity produced by animals (fish) to stun their prey or to deter predators. The Egyptians used electricity produced by electric eels from the Nile to treat the pain caused by wounds and also the pains of childbirth, by laying the eels on the site of the pain until it went numb. In the first century AD the personal physician to Emperor Claudius, Scribounius Largus, recommended electrical treatment for the control of the pain of migraine. He placed the electric torpedo ray (right) on the head, in the area of the pain, until the area went numb and the pain disappeared. Benjamin Franklin, who famously and very dangerously flew a kite in a thunderstorm, was one of the first to investigate electricity in a scientific way. He apparently used static electricity to cure his migraine. However it caused retrograde amnesia and as a result of this he went so far as to suggest it could be used to treat the insane. This was probably where the idea of electrotherapy was born.

What is pain?

Pain, according to the International Association for the Study of Pain, ‘is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” You have probably at some time in your life suffered pain from a toothache or a sports injury, and when playing a computer game the pain has disappeared as you became totally involved in the game. The cause of the pain was still there but the feeling had disappeared. The same is true when you are under an anaesthetic. Pain is not simply a physical sensation but also a state of mind. How can this happen?

Sensing pain

There are special sensory neurons called nociceptors that tell the body “this feels bad!” Nociceptors have free nerve endings and the cell body is in the dorsal root ganglion as shown in the diagram to the right. These form three basic groups of nociceptors. Some detect harmful temperature (such as the burning sensation of a hot plate), some detect harmful chemicals (such as capsicum in chillies) and others detect body damage (such as spraining your wrist or ankle in sports.)

True or False?

  1. Myelinated nerves carry impulses faster than non-myelinated nerves. true
  2. Nociceptors respond to potentially harmful situations by sending messages to the brain. true
  3. All pain is the same. false
  4. The stimuli that cause sharp pains travel through the myelinated A fibres. true
  5. Using electrical impulses to control pain is a modern phenomenon. false
  6. Nociceptors are receptors that transmit information about things that may cause damage to the body. true
  7. John Bonica was the first person to establish a multidisciplinary approach to pain relief. true
  8. Pain is felt when impulses bounce between the thalamus and hypothalamus. true
  9. IPG stands for internal pulse generator. false
  10. IPGs can help control Parkinson’s disease. true

Glossary of terms

A-fibre
a type of nociceptor that is myelinated and carries impulses quickly. These are responsible for sharp pains
Alternating current
electric current whose direction is reversed at a fixed frequency known as the mains frequency; the mains frequency in Europe is 50 Hz
C-fibre
a type of nociceptor that is non-myelinated and carries impulses slowly. These are responsible for dull pains
Direct current
an electric current that flows in one direction e.g. produced by a battery
Electric shock therapy
more correctly called electroconvulsive therapy. a procedure, done under general anesthesia, in which small electric currents are passed through the brain, intentionally triggering a brief seizure. ECT seems to cause changes in brain chemistry that can quickly reverse symptoms of certain mental illnesses.
implantable pulse generator (ipg)
an electronic device placed inside the body that produces regular bursts of electric current
Myelinated
a constant pain that is not easily treatable
Neuromodulation
the altering of the cellular or synaptic properties of some neurons so that transmission from one to the other is changed
Nociceptor
a type of receptor on some sensory neurons that responds to potentially damaging
Pain
an unpleasant sensation or emotion associated with actual or potential tissue damage
Parkinson's disease
a disease caused by the lack of dopamine in the body. One of the symptoms is shaking of the lims that can be very painful and debilitating
Phantom pain
pain felt in limbs that are no longer there
Referred pain
a loss of memory-access to events that occurred, or information that was learned, before an injury or the onset of a disease or event
Retrograde amnesia
neurons that carry impulses from receptors to the central nervous system
Sensory neuron
a sensory nerve cell; may detect pressure, temperature, taste, smell, light