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Understanding tVNS: Parameters and Applications – An Overview

 

Transcutaneous Vagus Nerve Stimulation (tVNS) is a non-invasive form of nerve stimulation that has been shown to have a range of potential therapeutic applications. By stimulating the vagus nerve, tVNS can modulate a variety of physiological processes, including inflammation, pain, heart rate, blood pressure, digestion and more. 

In this article, we’ll take a look at the ins and outs of tVNS, including the key parameters that influence its effects on the body. By the end, we hope you will have an appreciation of all the different approaches that are used and the range of possibilities. Look out for future blog posts where we will also take a deeper dive into the specific parameters that are used in selected research studies. 

 

What is tVNS?

At its core, tVNS involves the application of electrical stimulation to the skin overlying the vagus nerve, which runs from the brainstem down through the neck and into the chest and abdomen. Unlike invasive forms of vagus nerve stimulation, such as surgically implanted devices, tVNS uses electrodes placed on the skin to deliver low-level electrical currents to the nerve.

One of the main benefits of tVNS is its non-invasive nature, which allows for repeated use over time without the need for surgery. Additionally, tVNS is generally considered to be safe and well-tolerated, with few significant side effects reported in the literature.

However, like any form of therapy, the effectiveness of tVNS depends on a variety of factors, including the specific condition being treated, the individual characteristics of the patient, and the parameters of the stimulation itself.

 

Key Parameters of tVNS

There are several key parameters of tVNS that can influence its effects on the body, including: session duration (typically measured in minutes), the intensity of the current applied to the skin (measured in milliampere, mA), its pulse width (how long each current pulse lasts, measured in microseconds, μs), its pulse frequency (how frequently pulses are applied, measured in Hertz, Hz), and its duty cycle (on-off stimulation cycles measured in seconds). Time of day the stimulation is applied and how the parameters are combined also make a difference. In the following, we will explain each of these in turn and how they matter.

Duration: The duration refers to the length of time that the electrical pulses are delivered for. Longer durations (such as 30 minutes) may be more effective than shorter durations (such as 5 minutes) for certain conditions. For example, a study that measured the effects of tVNS on heart rate variability found more evidence of changes after 1 h of stimulation than after 10 minutes (De Couck et al., 2017). Similarly, in a study investigating the use of tVNS for insomnia, participants received two sessions of 30 minutes of stimulation per day for 20 days resulted in significant improvements in sleep (Jiao et al., 2020), while in another study 15 minutes for 14 days was only somewhat effective (Bretherton et al., 2019).

Intensity: The intensity of stimulation refers to the strength of the electrical current delivered to the nerve. In general, lower intensities (such as 0.5 mA) are considered safer and more tolerable, while higher intensities (such as 4 mA) may be necessary for certain conditions. Higher intensities will be perceived as stronger when the skin is properly cleaned and prepared. However, varying the intensity of tVNS may not have a strong impact on cardiac vagal activity in healthy adults (Borges et al., 2019). Low-intensity (0-0.6 mA) tVNS applied below the threshold of perception (coupled with low-frequency, 1.5 Hz) was found to still improve symptoms of major depression (Hein et al., 2013). Note that many devices deliver a constant current (<5 mA, typically around 1 mA) and their intensity settings in fact trigger changes in voltage rather than current itself. Vagus.net tVNS device is instead current-controlled and voltage-gated for safety.

Pulse Width: tVNS is typically delivered as a series of pulses. The overall stimulation delivered depends on the frequency (see below) and the width of the pulse. The wider each pulse is, the more stimulation you will obtain from the 25 pulses you receive in one second of 25 Hz stimulation. The width of the pulse is limited by how many such widths you can fit in a second, but within this constraint, differences in pulse width can feel very different. As pulse width increases, perception of the stimulation becomes stronger when the skin is properly cleaned and prepared. It can also have a dramatically different effect on your body’s response. Pulse widths typically range from 100-500 µs, and it is thought that a 500-µs pulse width (together with a 25-Hz stimulation) is the most biologically active (Badran et al., 2018, 2019).

Frequency: The frequency of stimulation refers to the number of electrical pulses delivered per second. It is one of the most important factors in determining the effectiveness of tVNS treatment. Different frequencies have been shown to have varying effects on the body. For example, a clinical study on migraine showed a ≥50% reduction in headache days in far more patients in the group that received 1 Hz stimulation for 4 h per day for 3 months than in the group that received 25 Hz stimulation (Straube et al., 2015), suggesting that lower frequencies may be better for migraine treatment. However, 25-Hz stimulation has been shown to be superior to 1-Hz stimulation for reducing epileptic seizures over 20 weeks (Bauer et al., 2016).

Higher-frequency stimulation (20-30 Hz) has been shown to improve sleep (Bretherton et al., 2019; Jiao et al., 2020), reduce anxiety (Burger et al., 2019; Grolaux, 2019) and may have more general anti-inflammatory effects. Higher frequencies may have better effects on the brain: a recent brain imaging study of healthy adults (Sclocco et al., 2020) found that 100 Hz stimulation produced the strongest changes in metabolic activity of the brainstem, which receives information from the vagus nerve. So if you are looking for cognitive or psychological improvements from tVNS, a higher stimulation frequency may offer the best chances of success. However, frequency is not always critical – quite a wide range of frequencies (1.5-120 Hz) has been used across several studies to alleviate depression (Kong et al., 2018). 

Duty cycle:

Duty cycle refers to a period of stimulation (e.g., 60 seconds) followed by a period of rest (e.g., another 60 seconds) that are cyclically repeated during the stimulation session. Periods of rest are sometimes used to avoid habituating to the stimulation.

 

The specific combination of changes in the aforementioned parameters may also be important. For example, a study by Badran and colleagues (Badran et al., 2018) tested the effects of various parameter combinations on heart rate and found that a frequency of 10Hz combined with a pulse width of 500 μs led to the strongest decrease in heart rate compared to other parameter combinations. So it is well worth trying different combinations if you are aiming to achieve a specific outcome.

Additionally, the timing of stimulation (the time of day at which tVNS treatment is administered) may matter. For example, some studies have shown that tVNS may be more effective when administered in the morning, while others have found greater benefits with evening stimulation. A closer look at the circadian variations in the system that is targeted (e.g., variations in heart rate variability over the 24-h cycle) and at other changes that are consistent for an individual (e.g., depressive symptoms are typically stronger in the evening) will be a good guide for choosing an ideal time.

These parameters can be adjusted depending on the specific condition being treated and the individual patient’s needs. It’s very important to get this right. Research suggests that individual variations in autonomic function may influence the optimal stimulation frequency for a given individual. So it’s very much a case of using existing research as a starting point and then adjusting the stimulation to meet the needs of each individual. Your provider may be able to tailor a stimulation protocol (i.e., a given set of parameter settings) for you, but if you cannot do that, or want to try out your own parameters, then there are only very few options available with the devices currently on the market. Most devices (and therefore also most research studies) have adopted a fixed pulse width between 200 and 300 μs, a fixed frequency of 25Hz, and a fixed 30-second on, 30-second off duty cycle. This combination of settings may not be ideal for many applications and individuals, even if intensity can still be adjusted by the user. The Vagus.net Research Edition stimulator is the most advanced device in its price range available for changing parameter settings like all of these individually. This enables people to use their tVNS device for different applications.

 

Scientific and Medical Applications of tVNS

tVNS has been investigated for its potential in treating various health conditions, including migraine, sleep disorders, arthritis and immune system support. Here are 10 applications with an idea of some of the common parameter settings which are commonly reported.

Migraine: tVNS has shown promise in reducing the frequency and intensity of migraine attacks. Auricular tVNS studies have reported a significant reduction in migraine days per month and a decrease in pain intensity (Straube et al., 2015; Zhang et al., 2021). Research suggests that 1 Hz stimulation is more effective than higher frequencies like 25 Hz, with intensities adjusted to a level where non-painful tingling is felt (Straube et al., 2015).

Depression: tVNS has been explored as a potential treatment for depression. Research suggests that tVNS may modulate brain regions associated with mood regulation. Clinical trials have shown improvements in depressive symptoms, with parameters typically including a wide range of frequencies (1.5-120 Hz), durations between 15 minutes on 5 days a week to 1 hour per day, and intensities from as low as 0-0.6 mA and as high as 4-6 mA (Kong et al., 2018).

Anxiety: Preliminary studies suggest that tVNS may have anxiolytic effects. The stimulation is believed to modulate the autonomic nervous system, reduce inflammation and reduce anxiety symptoms. Frequency ranges from 20-25 Hz, duration is typically 30 minutes, intensity ranges from 0.5 mA to 1-2 mA and pulse width from 80 to 250 μs (Burger et al., 2019; Grolaux, 2019).

Insomnia/Sleep Disorders: tVNS has shown potential for improving sleep quality and reducing insomnia symptoms. It may enhance parasympathetic activity, promoting better conditions for falling asleep. The commonly used parameters are a frequency of 20-30 Hz, duration of 15 minutes to up to 4 hours, and intensity of 1-2 mA (Bretherton et al., 2019; Jackowska et al., 2022; Jiao et al., 2020).

Epilepsy: tVNS has been studied as a complementary approach to epilepsy treatment. Some studies have reported reductions in seizure frequency and improvements in seizure control. Parameters used include a frequency of 20-30 Hz, duration of 30 minutes, intensity of 1 mA and pulse width of <1000 μs (Rong et al., 2014).

Immune System Support: tVNS has been investigated for its potential in modulating the immune system. Studies have shown that tVNS can reduce inflammation and improve immune function. A recent study found that tVNS reduced the levels of inflammatory markers in patients with rheumatoid arthritis.

Rheumatoid Arthritis: tVNS has shown potential for reducing pain and inflammation in rheumatoid arthritis. Studies have reported improvements in pain intensity and inflammatory markers. The reported parameters are a frequency of 20 Hz, duration of 30 minutes, intensity of 1 mA and pulse width of 500 μs (Koopman et al., 2016).

Chronic Pain: tVNS has been investigated for its analgesic effects in chronic pain conditions. Studies have demonstrated reductions in pain frequency and intensity and improvements in quality of life.

Stroke Rehabilitation: tVNS has been investigated for its potential in stroke rehabilitation. Research suggests that it may enhance neural plasticity and motor recovery. 

Post-Traumatic Stress Disorder (PTSD): tVNS has been explored as a potential adjunctive treatment for PTSD. Some studies suggest that tVNS may help regulate emotional responses and reduce PTSD symptoms.

 

It’s important to note that the effectiveness of tVNS can vary among individuals, and further research is needed to establish its efficacy in specific conditions. It is always recommended to consult with healthcare professionals or researchers familiar with tVNS for personalized guidance.

 

It is also important to note that the research described here does not imply the proven effectiveness of the Vagus.net stimulator or any other stimulator that may be available on the market. 

 

Common Everyday Uses of tVNS

All this scientific interest in tVNS has led to a great deal of general everyday usage of tVNS. People have found great benefit in using tVNS regularly. Here are five examples of how transcutaneous Vagus Nerve Stimulation (tVNS) can be used in everyday life by the general public:

  1. Stress Reduction: tVNS can be used to help reduce stress and promote relaxation. By stimulating the vagus nerve, it can activate the parasympathetic nervous system, leading to a calming effect on the body and mind. Individuals can apply tVNS during stressful situations or as part of a daily relaxation routine.
  2. Energy Boost: tVNS has been reported to increase alertness and energy levels. By stimulating the vagus nerve, it may enhance neural activity and promote a state of wakefulness. People may use tVNS to combat fatigue, improve focus, and boost energy levels during work or study sessions.
  3. Mood Enhancement: tVNS may have mood-enhancing effects by influencing neurotransmitters and brain regions involved in mood regulation. Some individuals use tVNS to improve mood, increase feelings of well-being, and alleviate symptoms of mild mood disturbances.
  4. Cognitive Enhancement: Research suggests that tVNS can have positive effects on cognitive function, such as memory, attention, and executive functions. It may improve cognitive performance and mental clarity. Some people may use tVNS to enhance cognitive abilities during tasks that require focus and mental acuity, for example when multitasking.
  5. Performance Optimization: Athletes, musicians, and individuals in high-performance professions may utilize tVNS to enhance their performance. By potentially improving autonomic regulation, tVNS may optimize physiological and psychological states, leading to better performance outcomes.

 

It’s important to note that while tVNS has the potential for these applications, individual experiences may vary, and further research is needed to establish the effectiveness and optimal parameters for such everyday uses. One of the most important things is to get the parameters right. Hopefully by looking at the range of finding in the scientific literature, you have a idea of the things that you can try. We will, over the next series of blog post, look at the range of stimulation parameter options open the everyday user of tVNS and hopefully we can come up with some guidelines. 

 

Conclusion

 

Transcutaneous Vagus Nerve Stimulation (tVNS) is a promising non-invasive neuromodulation technique that has shown potential in treating various health conditions. The optimal stimulation parameters, including frequency, duration and pulse width play a crucial role in the effectiveness of tVNS. Studies have suggested that tVNS can be an effective treatment for migraine, epilepsy insomnia, depression, anxiety, arthritis, and provide immune system support. Find the what’s right for you as an individual is the key to success in using tVNS. Parameters are everything. 

 

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