"Pump it up!" About heart rate variability, skin conductance and body temperature. Why biofeedback can ideally complement neurofeedback therapy

Biofeedback describes a method that can offer the way to a better perception and regulation of one's own body. In biofeedback, peripheral physical parameters - also called biosignals - are used. These can be muscle tone, heartbeat or breathing rate, for example. Electrodes, which are attached directly to the skin, for example, or mounted in a chest belt or finger sensor, measure peripheral physiological parameters. These signals are then reported back on a screen - either simply as curves or in animations. 
Biosignals allow conclusions to be drawn about the current stress level - being able to perceive one's own physical reaction can be an enrichment for therapeutic work, or for training relaxation or concentration. Accordingly, biofeedback is used as a therapeutic component for mental and physical illnesses as well as in performance and concentration training - the so-called peak performance - or competitive sports. 

In this blog post, we would like to discuss the central parameters and functionalities of biofeedback and also shed light on the extent to which a combination of biofeedback and neurofeedback can be usefully designed in therapy. 

 

Pump it up - the heart rate and heart rate variability in biofeedback 

 

The pulse is a biological parameter that changes according to external and internal demands. Not only a steady pulse, but also the adaptability of the heart rate to different demands - the so-called heart rate variability (HRV) - is a central parameter in biofeedback. 
Heart rate variability is the variation of the temporal distance between two heartbeats (also: beat to beat interval). This is longer in times of relaxation than in times of physical or emotional stress. A high heart rate variability speaks for a good (peripheral) self-regulation, because it indicates that the organism is able to adjust the heart rate depending on the requirements and finds the optimal frequency for the respective situation. Low heart rate variability is often related to a problem in dealing with stressful situations, memories or stress in general. 

Especially for patients with anxiety disorders, depression or chronic pain, biofeedback with heart rate variability training can be helpful. Often these patients are not aware of the connection between their emotional stress and physical reactions and the perception of their own body does not work well, because they have permanently a very high stress level. Training here to perceive, influence and synchronize central parameters such as heartbeat and breathing and thus lower the general stress level can be a key experience in therapy and make patients aware that they do have control over their physical and mental state.

 

Breathe deeply three times - breathing in biofeedback 

 

You probably know the tip that lay literature and grandmothers like to give whenever someone is stressed: take three deep breaths. Does that really help? Here's a little experiment: put your hand on your stomach. Breathe deeply into your belly, feel how the hand rises, how your belly bulges, when the belly is bulging to the maximum, hold your breath for a moment and then breathe out again slowly and evenly. Feel the air flowing first out of the belly and then out of the tops of the lungs, over both lungs and out the airway. Repeat this three times. What do you notice? How are you conducting yourself? How has your heartbeat changed? 

The HEARTBEAT?! That's right - breathing and heartbeat are closely related physiologically. In a relaxed state, heart rate and breathing rate correlate, this is also what we call "respiratory sinus arrhythmia". When breathing in, the heart rate thereby becomes higher, the sympathetic nervous system is activated, and when breathing out, the heart rate becomes lower, the parasympathetic nervous system is activated. Breathing deeply in and out three times in stressful situations can thus help not only to gain better awareness and control over one's own breathing, but subsequently also to synchronize the correlation of breathing and heartbeat. 

 

Sweat Baby, Sweat - the skin conductance in biofeedback

 

The skin conductance is usually recorded via electrodes on the finger. The texture of the skin on the palm of the hand differs from that on other parts of the body - on the palm of the hand the skin has a particularly large number of sweat glands. These sweat glands, which are innervated by the sympathetic nervous system, react quickly to stress by increasing their glandular activity.  If the palm is dry and the activity of the sweat glands is low, the skin conductance is also low. Since sweat is a salty fluid, skin conductance - measured by 2 electrodes on the fingers - increases as sweat gland activity increases.

If the skin conductance is constant and low at rest, this indicates a relaxed state, but if it fluctuates constantly for no apparent reason, this may indicate that even stimuli that are actually neutral are perceived as stressful. If a stressor is then presented - sometimes the mention or thought of a stressful situation is enough - the skin conductance usually rises quickly. In healthy people it returns to its initial level after 1-2 minutes. However, in patients who have problems in emotional regulation, it also happens that the skin conductance remains at a high level for a long time after the stressor. Since the skin conductance responds quickly to stressful stimuli and is easy to measure, it is particularly well suited as a psychophysiological mirror in therapy - and reflects the change between tension and relaxation. It can also be used as a support in relaxation training or in learning various relaxation techniques.

 

It is getting hot in here - the body temperature in biofeedback 

 

Temperature is usually measured by a sensor on the finger. In a relaxed state, the smooth muscles in the walls of the blood vessels usually also relax, which leads to more blood flowing to the extremities - we often recognize this by the feeling of warmth in the hands. Thus, an onset of relaxation is accompanied by an increase in temperature in the extremities. Under stress or tension, the muscles in the vascular walls contract, the vessels become narrower and less blood reaches the extremities, often resulting in a drop in body temperature. The body temperature usually reacts with some delay, from the beginning of the stress reaction to a drop in body temperature in the extremities may well take 1-2 minutes.
 
The body temperature skin conductance can be used in therapy, for example, to demonstrate the influence of thoughts and ideas on physiology, because some patients succeed in achieving a change in temperature by imagining warmth/cold, and body temperature can also play a role in relaxation training. 

 

The combination of bio- and neurofeedback 

 

In symptom-based infra low frequency (ILF) neurofeedback, the patient's symptoms and state changes are the central components. Many of these symptoms also relate to correlates of stress and relaxation. Accordingly, the addition of biofeedback parameters can be a useful complement to ILF neurofeedback. This makes it possible for patient and therapist to include the physiological correlates of state changes in the therapy. Patients who are not able to perceive or verbalize changes in their stress and relaxation state very well will get another possibility to experience changes through neurofeedback. Even changes that are partially below the threshold of perception can be made visible by measuring peripheral signals and can find their way into the therapy. In the case of skeptical or tense patients, the inclusion of biofeedback parameters in the sense of psychoeducation can also help to make the connection between psyche and physiology visible and tangible, to familiarize the patient with the setting with electrodes and to gradually reduce the possible fear of changes through therapy, in order to gently introduce the patient to neurofeedback. 
The therapist can deduce signs of stress and relaxation in the physiological parameters and optimize the therapy accordingly, for example by changing the frequency.

 

Modern Biofeedback with the AliveⓇ Software 

 

Measuring the four central parameters - heart rate variability, respiration, skin conductance and temperature - separately and reporting them back in curves or animations is no longer necessary with our combined biofeedback solution of Combisensor and AliveⓇ software. The Combisensor - a finger sensor with electrodes - is attached to the index finger, derives biosignals and reports them back to the AliveⓇ software, which uses them to generate graphs and curves that are highly informative for patients and therapists.  The Combisensor can be easily connected to the NeuroAmp and the Cygnet and Alive software packages can be operated in parallel.

The AliveⓇ software contains a variety of animations, workshops and tutorials and offers versatile applications for the four peripheral signals. The Alive feedbacks are displayed on two screens - similar to Cygnet - and the therapist can also see the actual derived biosignal. This also allows the therapist to use the software simultaneously with neurofeedback and Cygnet. However, with AliveⓇ it is also possible to use the popular Cygnet animations such as Innertube, Tropical Health or Dreamscapes for biofeedback. However, Alive also includes specific calm feedback options exclusively for biofeedback, which are particularly suitable for anxious and tense patients. Detailed reports can also be generated through the software. 

With Alive, biofeedback can be used both as a separate therapy component and in combination with neurofeedback. 

 

Biofeedback in theory and courses - Our teaching offer 

 

Since biofeedback addresses peripheral parameters, there is no need for a compulsory beginner's course, unlike neurofeedback, which works with central excitation parameters. Biofeedback can also be a useful component in other therapy or training settings, for example in peak performance or competitive sports. 

To learn how to use the finger sensor and AliveⓇ and to try it out in practice, we are regularly offering an introductory course in biofeedback theory and practice. Please check our courses for more information.
 

 

Literature recommendation

For those interested in more intensive study of parameters in biofeedback, we recommend chapter 2, "Peripheral Biofeedback" in the following Springer textbook: Haus KM. et al. (2020). Praxisbuch Biofeedback und Neurofeedback. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-59720-0_1 (in German)