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Understanding Electrical Stimulation
When a nerve is stimulated, signals travel both towards the body and the brain. Electrical stimulation can cause responses to these signals, either from the brain or the tissues connected by the nerve.
In the context of lower urinary tract dysfunction, electrical stimulation is applied particularly to the pelvic floor muscles, bladder, and sacral nerve roots.
Electrical stimulation of the pelvic floor aims to stimulate motor fibers of the pudendal nerve, which may cause a direct contraction of the pelvic floor or the muscles around the urethra, helping with urethral closure.
While electrical stimulation can help with weak intrinsic sphincter muscles, it's uncertain if electrical stimulation is the best treatment or adds value to functional training.
Electrical Stimulation Techniques
For patients with overactive bladder or urgency urinary incontinence, electrical stimulation can cause direct contractions of the pelvic floor muscles, which then stimulate the pudendal nerve fibers going to the sacral spinal cord. This reflexively reduces the sensation of urgency and decreases involuntary bladder contractions. Electrical stimulation can be used alone or with pelvic floor muscle training.
There are two main types of ES:
neurostimulation: targets motor efferent fibers of the pudendal nerve for direct responses of the pelvic floor muscles.
neuromodulation: remodels reflex loops to cause indirect responses, such as detrusor muscle inhibition.
Neurostimulation further explained
Efferent nerves are motor nerves. They send signals from the brain to your muscles to make your muscles move.
Neurostimulation focuses on stimulating the motor fibers of the pudendal nerve, which directly controls the pelvic floor muscles.
This means it sends signals straight to the nerves that make these muscles move, causing immediate responses or actions in the pelvic floor muscles.
Neuromodulation further explained
Remodels reflex loops: It changes how certain reflexes in the body work. Reflex loops are the pathways that signals travel through in the nervous system.
Indirect responses: Instead of directly making a muscle move, it changes the way the signals are processed in the body to create a different outcome.
Detrusor muscle inhibition: One specific outcome is that it can stop or reduce the activity of the detrusor muscle. The detrusor muscle is the muscle in the bladder that helps push urine out.
So, in simpler terms, neuromodulation changes how the body's reflexes work to achieve specific effects, like stopping the bladder muscle from pushing out urine.
Even today, it's challenging to clearly understand the benefits of electrical stimulation for urinary incontinence. This is due to inconsistent terminology and the lack of a solid biological basis for using electrical stimulation.
Parameters like current source, pulse width, duration, intensity, amplitude, frequency, pulse shape, and electrode placement vary widely in studies, making it hard to determine the best set of parameters for each type of urinary incontinence. Rapid developments in electrical stimulation technology add to the confusion.
Parameters for Electrical Stimulation
Manufacturers of electrical stimulation devices often program their devices with protocols suitable for different pelvic floor dysfunctions. However, these protocols are not always well-documented, limiting the ability to compare and generalize conclusions. Also, it's important for physical therapists to make adjustments to these protocols to the individual needs of patients, which are also not always documented well.
Electrical stimulation is applied via a probe through either the vaginal walls for women, or through the rectal canal for men, diffusing over the entire pudendal plexus and nearby neuromuscular junctions. This recruits all pelvic floor muscles in the area. Therefore, proper electrode placement and pulse parameters are crucial to avoid risks like electrolysis and to ensure patient safety and comfort.
Electrolysis is the unwanted breakdown of bodily fluids and tissues when exposed to electrical currents. This can potentially cause harm if it occurs during procedures like neurostimulation.
Electrical stimulation aims to restore continence by:
strengthening the urethra and bladder neck
inhibiting reflex bladder contractions
improving vascularity
enhancing muscle activation and coordination.
The choice of parameters depends on the device, type of current, type of urinary incontinence, and the individual patient's needs.
A standard list of parameters:
Current Amplitude or Intensity: The strength or power of the electric current. Think of it like how strong the water flows from a faucet.
Pulse Width: How long each burst of electric current lasts. Imagine it as the duration of each heartbeat.
Pulse Shape: The form of the electric pulse, whether it's smooth, spiky, or something else.
Type of Current: If the electric current is steady, changes direction, or pulses on and off.
Frequency: How often the electric pulses happen in a second, like the beats in a song.
Train: A series of electric pulses grouped together, similar to a train with multiple cars.
Impedance: How much the body resists the electric current, like how some materials resist heat.
Session Time: The total length of time the electrical stimulation treatment lasts.
Ramp-Up and Ramp-Down Times: The times it takes for the current to gradually increase to its maximum or decrease to zero, ensuring it's not too sudden.
Duty Cycle: The pattern of when the current is on and off during a session, like work and rest periods in exercise.
References: Bo, K., Berghmans, B., Mørkved, S., & Van Kampen, M. (Eds.). (2023). Evidence-Based Physical Therapy for the Pelvic Floor (3rd ed.). Elsevier.
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