Research
Foot Drop
Foot drop is the inability to lift the front part of the foot from the ground. It causes the toes to drag along the ground while walking and can cause fall and injuries. A patient may have Foot drop when there is a loss of communication between the central nervous system and the peroneal nerve. It can be corrected by functional electrical stimulation. Read more..
Team
Bijit Basumatary, Department of Biomedical Engineering, Indian Institute of Technology Ropar
Dr. Ashish Kumar Sahani, Department of Biomedical Engineering, Indian Institute of Technology Ropar
Functional Electrical Stimulation
Functional Electrical Stimulator is used for the correction or treatment of Foot drop. It is used both as an assistive device as well as a therapeutic device. In the FES system, an electrical pulse is applied to the peroneal nerve to cause a muscle contraction to correct the gait pattern of the foot. Read more..
Collaborator
Dr. Rajinder Bansal, Department of Neurology, Dayanand Medical College & Hospital (DMC&H)
Dr. Gagandeep Singh, Department of Neurology, Dayanand Medical College & Hospital (DMC&H)
Funding
Fund supported by Prime Minister's Research Fellowship.
Indian Institute of Technology Ropar.
How functional electrical stimulation works?
Functional Electrical Stimulation (FES) is a technology that uses low-level electrical currents to activate nerves innervating muscles affected by paralysis resulting from spinal cord injury, stroke, or other neurological disorders. This process enables the muscles to contract, thereby improving or restoring function. Here's a detailed explanation of the principles you mentioned:
- Neuron Cells are Electrically Active
Neuron cells, or neurons, have the unique ability to generate and transmit electrical signals. This electrical activity is fundamental to their role in the nervous system, which involves communicating information throughout the body. Neurons maintain a voltage gradient across their cell membrane, primarily through the distribution of ions like sodium (Na+), potassium (K+), chloride (Cl-), and calcium (Ca2+).
- Information Transmission as Electrical Pulses
Neurons transmit information via electrical signals known as action potentials. These are rapid changes in the cell's membrane potential that propagate along the axon to communicate with other neurons, muscles, or glands. An action potential is an all-or-nothing response that travels down the neuron once the membrane potential reaches a critical threshold.
- Nerve Signals are Frequency Modulated
The frequency of action potentials (i.e., how often they occur) encodes information. This is known as frequency modulation. Higher frequency signals can indicate stronger stimuli or more urgent information, while lower frequency signals can represent weaker or less urgent information.
- Number of Action Potentials and Signal Intensity
The intensity of a transmitted signal is proportional to the number of action potentials occurring within a given time period. This means that stronger stimuli produce a higher frequency of action potentials. The brain interprets these frequency-modulated signals to understand the intensity and type of sensory information being received.
- Flow of Electrons in FES and Motor Nerves
In an FES system, an external device generates controlled electrical pulses. These pulses flow through electrodes placed on the skin, creating a current that stimulates the underlying motor nerves. The electrical current from the FES device mimics the natural electrical activity of neurons, converting it into a biological signal that the body can understand.
- Depolarization and Action Potential Generation
When a sufficient electrical charge is applied to a nerve cell via FES, it causes depolarization of the cell membrane. Depolarization occurs when the electrical charge disrupts the balance of ions across the cell membrane, causing an influx of sodium ions (Na+) into the neuron. This influx changes the membrane potential, making it more positive and reaching the threshold needed to trigger an action potential.
- Triggering Action Potentials in Motor Neurons
Once the membrane potential reaches this critical threshold, an action potential is initiated. This action potential propagates along the motor neuron’s axon to the neuromuscular junction, where it triggers the release of neurotransmitters. These neurotransmitters then stimulate muscle fibers to contract. The controlled electrical pulses from the FES device thus cause coordinated muscle contractions, allowing for functional movements in paralyzed muscles.
What happens exactly when electrical pulse is applied to peroneal nerve?
When an electrical pulse is applied to the peroneal nerve of a foot drop patient, it can elicit a muscle contraction and cause the foot to lift during the swing phase of gait. The electrical pulse causes depolarization of the nerve fibers, which triggers the release of neurotransmitters that activate the muscle fibers innervated by the nerve.
At the cellular level, the electrical pulse causes a change in the membrane potential of the nerve fibers, which is a result of the movement of ions across the cell membrane.
The electrical pulse causes an influx of positively charged ions, such as sodium (Na+) and calcium (Ca2+), which depolarizes the cell membrane and triggers the release of neurotransmitters at the nerve terminal.
These neurotransmitters, such as acetylcholine, bind to receptors on the muscle fibers and cause them to contract.
At the muscle level, the electrical pulse causes a series of biochemical events that lead to muscle contraction.
Neurotransmitters are chemical messengers that transmit signals between neurons (nerve cells) or from neurons to other cells such as muscles or glands. They are stored in the nerve terminals of neurons and released when an action potential reaches the terminal.
When the neurotransmitter acetylcholine binds to the receptor on the muscle fiber, it triggers the release of calcium ions from the sarcoplasmic reticulum, which activates the actin-myosin cross-bridge cycling and leads to muscle contraction. This contraction is sustained as long as the electrical pulse is applied, and the muscle relaxes when the pulse is turned off.
In the case of foot drop, the electrical pulse is applied to the peroneal nerve, which innervates the muscles responsible for dorsiflexion of the ankle joint.
By causing these muscles to contract, the electrical pulse can lift the foot during the swing phase of gait, thereby restoring a more normal gait pattern and improving walking function.
The Role of Foot Sensors
To enhance the effectiveness of FES, researchers and engineers have integrated foot sensors into the system. These sensors detect the initial movement of the foot, signaling the FES device to deliver the electrical stimulation precisely when needed.
This real-time feedback loop ensures that the stimulation aligns with the individual's walking pattern, promoting a more natural and efficient gait. Read more....
AI-Powered Foot Lift Detection
Advancements in AI have further propelled the capabilities of FES systems, particularly in the realm of foot lift detection.
In recent years, inertial measurement units (IMUs) have emerged as a valuable tool for capturing movement data. By leveraging AI algorithms trained on vast datasets of IMU recordings, FES devices can accurately predict the onset of foot drop and adjust the stimulation parameters accordingly.
This adaptive approach not only enhances user comfort but also optimizes the therapeutic outcomes over time. Read more...
