Concept

The concept of stress and autonomic dysfunction

The term “stress” has several meanings and definitions. However, the theory proposed by McEwen (McEwen, Gianaros 2011) has been generally accepted (see Figure 1): Stress involves a stressor and a stress response. The imminent or perceived stimulus that initiates the stress response is called the stressor. The stress response is controlled by the autonomic nervous system.

The brain works consciously and unconsciously. The unconscious brain, the autonomic nervous system, works 24 hours a day. It organizes all bodily functions as well as all conscious behavior related to these functions, including any physical, mental, emotional, psychological, or social behavior.

The unconscious brain varies in activity between being relaxed and being tense like a mechanical spring: it is relaxed when we sleep and tense when we anticipate or are met with a challenge or a threat.  

When the work of the brain is in balance, the shift between being relaxed and being tense happens within seconds when needed, such as when there is an unexpected event while driving a car. This ability to shift is called brain resilience, and when normal the brain reacts to the challenge with an adaptive and transient stress response that is constructive and increases performance. This is positive stress and is also called transient or acute stress. Afterwards, the relaxed state is re-established by processes of homeostasis aiming at maintaining a constant condition of the internal environment (see Figure 1).  

If a person is under a too high stress load for a too long period and with insufficient restitution in between, the balance is lost, and the unconscious brain loses its resilience. This leads to dysfunction of the adaptive transient stress response, a condition called autonomic dysfunction, which is associated with a variety of physical, mental, emotional, psychological, and/or social dysfunctions. This reduces overall performance and may affect health negatively. In this situation, stress has become negative and destructive and is also called persistent or chronic stress (see Figure 1). If the autonomic dysfunction persists, it may lead to diseases such as depression, anxiety, PTSD, hypertension, chronic pain, reduced fertility, diabetes, heart disease, and/or stroke.

There is a close association between the function of the autonomic nervous system, stress, and the PPS (Pressure Pain Sensitivity) measure as the autonomic nervous system is controlling both the stress response and the PPS measurement, and they change in parallel during transient and persistent stress (see Figure 1 and 2).

Persistent stress affects 1/3 of the working population according to a recent EU report. Persistent stress has a bi-directional association to the non-communicable diseases such as diabetes, obesity, and cardiovascular diseases. Presently, these diseases account for 80 % of national health care budgets in Western countries. According to WHO, the prevalence of these diseases will increase during the coming decade.

Figure 1: The concept of stress. The green area marks the healthy and constructive transient stress. The body mobilizes resources in an adaptive response to a perceived challenge or threat and returns to the resting state (homeostasis) when the challenge is over. The PPS measurement increases and decreases in parallel with the level of stress. The red area marks the unhealthy destructive state of autonomic dysfunction and persistent stress. The adaptive response works inadequately, and the body is in a condition with a persistently elevated level of stress. The PPS measurement is also elevated during rest and thus persistently elevated (after McEwen, Gianaros 2011).

Figure 2: The association between stress, PPS measurement, and autonomic nervous system function.  An external or internal stimulus causes the perception of a challenge or threat by the unconscious control center in the brain, which in response activates an adaptive physiological process with a broad bodily impact mediated by the autonomic nervous system, including an elevation of the pressure pain sensitivity of the chest bone (PPS).

The PPS measurement

Table I: Conversion table between PPS measure, SI units (kPa), and pressure applied per cm2

Conducting the PPS measurement

For research purposes, the following procedure is used:

The subject is placed in a supine position and receives the following verbal instruction: “You will gradually experience an increase in pressure, firstly on the index finger and secondly on the chest bone. As soon as you feel discomfort, you say ‘stop’. Accordingly, it is not a matter of how much pressure you can tolerate, but rather when it feels natural for you to withdraw from the pressure.”

The measurement on the index finger is used to introduce the procedure and as a controlling point. The location for measuring on the sternum is identified by palpation as the most tender point within the area between the third, fourth, and fifth inter-costal space, reflecting the area of segmental innervations of the heart (Figure 4). When the researcher observes a noxious withdrawal reflex or a startle reflex during the procedure, the pressure is determined as the PPS measurement.

The technique used to measure PPS at home exclusively relates to the observation of discomfort by the subject (Animation 1).

Figure 4: The PPS measurement device and measurement site

The PPS and stress reduction intervention

The program is based on the working method of the unconscious brain: measure, reflect, act, and control (see Figure 5).

Figure 5: The Intervention: The intervention is based on the four working steps of the unconscious brain: measure, reflect, act, and control.

In order to ensure a fully evidence-based and clinically relevant reduction of an elevated PPS measurement prior to the public introduction of the PPS measurement, a special intervention program has been developed and subsequently tested in clinical trials. This treatment method (the Ballegaard Stress Care Program®) is a multifaceted self-care program. The aim is to maintain a low PPS measurement or to reduce the PPS measurement if elevated.

The person receives a one-to-one introduction to the use of the instrument, to the interpretation of the results of the measurement, and to the actions one can take accordingly. In addition, the person has a personal web journal for daily recording of the measurements.

The daily mandatory intervention program includes morning and evening home Stressmeter® measurements and finger-induced sensory nerve stimulation on specific points on the body surface (neuromodulation). The Stressmeter® home measurements are used as a cognitive guide for behavioral adjustment in daily life as well as an assessment guide for the effects of the used personal life management efforts. Free of choice elements of the program include diet changes and a broad range of supplementary physical, mental, and cognitive exercises, which may be used according to need and personal preference. At the end of each day, the person will monitor the results of the accumulative stress burden and stress management efforts of that day.

The ongoing self-monitoring, which includes the recording and tracking of personal data shared with a professional adviser, allows ongoing professional guidance according to need.

It should be underlined that theBallegaard Stress Care Program®can be combined with any medical or non-medical intervention and that the results of any significant event, effort, or intervention can be measured.

The practical applicability

In contrast to pharmaceutical treatment, the PPS measurement is not associated with any known risks, side effects, or complications. Furthermore, the PPS measurement and the PPS–guided intervention is found to work well in combination. This suggests potential practical applications.

The PPS measurement may be a practical tool for people interested in measuring their level of physiological stress. This interest may be of particular interest to people having stressful job positions and life situations. People having regular returning stress demands in their job like performing artists, surgeons, flight traffic controllers, and soldiers in combat may also benefit. Active sports participants in competitions may find the PPS measurement useful as demonstrated in the paper on Olympic sailors (Ballegaard et al 2016).

In clinical practice, patients with chronic diseases of any kind may find the PPS measurement useful. In particular, the scientific studies have found the methods highly efficient in persons with stable ischemic heart disease, reducing mortality, and in persons with type 2 diabetes, improving glucose metabolism and reducing an elevated level of glycated hemoglobin (HbA1c).

The ethical aspects of the PPS measurement

The PPS measurement may be a useful tool for research and a number of practical purposes as discussed above. However, for any kind of physiological measurement, a risk of adverse effects is potentially present. Although the PPS measurement is harmless, it may still be used inappropriately.  As an example of such inappropriate use, employers may want to screen and monitor their employees’ PPS values, which might in turn be used for determining the suitability of employees for jobs.  

For some people, knowledge related to their level of stress may induce fear and worry if they have a high PPS value. If no possibility for lowering the value existed, this might be an ethical problem. However, several methods are available for stress reduction. Accordingly, measurement of PPS is not unethical.