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 Table of Contents  
REVIEW ARTICLE
Year : 2019  |  Volume : 5  |  Issue : 3  |  Page : 102-108

Assessment of psychological stress during sleep using digital devices and its clinical relevance to future occupational health practice


Chief Medical Officer UK, Oxitone Medical Inc Member of the Faculty of Occupational Medicine, Royal College of Physicians, London, UK

Date of Web Publication30-Dec-2019

Correspondence Address:
Werner Stipp
Oxitone Medical, Upward Hartford, 20 Church Street, Mezzanine, Hartford CT 06103
UK
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/digm.digm_19_19

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  Abstract 


Psychophysiological decompensation as a result of occupational stress leads to impairment of occupational performance. Adequate recovery from psychological stress is necessary to maintain occupational performance. It is possible to measure the psychophysiological status and recovery during sleep with health data streamed from biomedical digital devices. Such data, with reference to heart and sleep parameters, could be processed to reflect health status and whether there is a risk of psychophysiological decompensation. This article describes the interpretation of resting heart rate measures, heart rate variability, and actigraphy measures during regular sleep in relation to psychological stress. Interpretation of the health data should be done by informed health-care professionals in combination with clinical history taking. The article does not cover digital measurements while awake and active. The aim of this review article is to provide an evidence-based rationale to health professionals how to interpret digital health data profiles from biomedical devices in appraising psychological stress and recovery. The objective is to prevent the adverse impact of psychological stress on health. Specific lifestyle measures and therapy to manage psychological stress, such as exercise, diet, and cognitive behavioral therapy for insomnia, are not discussed in this article. Applications are especially relevant in the field of occupational health in preventing occupational burnout, achieving a healthy work–life balance, and sustaining a healthy working life. There are future implications with regard to disease prevention as a large proportion of chronic diseases, for example, hypertension, diabetes depression, and ischemic heart disease, are related to chronic psychological stress. Stress monitoring with biomedical devices should occur over periods of work and nonwork days.

Keywords: Actigraphy, digital continuous monitoring, heart rate variability, insomnia, occupational stress, psychological stress, resting heart rate


How to cite this article:
Stipp W. Assessment of psychological stress during sleep using digital devices and its clinical relevance to future occupational health practice. Digit Med 2019;5:102-8

How to cite this URL:
Stipp W. Assessment of psychological stress during sleep using digital devices and its clinical relevance to future occupational health practice. Digit Med [serial online] 2019 [cited 2020 Mar 28];5:102-8. Available from: http://www.digitmedicine.com/text.asp?2019/5/3/102/274382




  Introduction Top


The use of biomedical devices to monitor personal health parameters has become more common; devices include wrist sensor devices, actigraphy sensors in smartphones, ballistocardiography, chest strap sensors, galvanometry, and two-lead electrocardiography devices. It is possible to record and store health data while asleep with wrist sensor devices and ballistography, resulting in individual monitoring and reflecting on health status over time. Regulatory bodies such as the US Food and Drug Administration have certification guidance [1] to certify biomedical devices as medical-grade devices, opposed to consumer-based nonmedical-grade devices that measure health parameters. It is, therefore, possible to base medical decision-making protocols on medical-grade devices rather than on consumer (nonmedical grade) devices.

The personalized medical measures available to the patient, complemented by the ability of the patient and health-care professional to visualize health monitoring results, have dramatically increased patient awareness of the impact of their lifestyle and work on health. Patients are then likely to make informed decisions to change work related factors, lifestyle and health behavior and seek medical help at an early stage in order to achieve better work-life balance and improve long-term health outcomes. Tracking of health data over time, for example, work days and nonwork days, enhances the power of associations, such as the effect of stressful periods and their impact on health status. Digital continuous monitoring has, therefore, far reaching positive consequences on maintaining work–life balance and disease prevention by means of patients making informed lifestyle changes with assistance of medical professionals.


  Stress and Its Effects Top


Stress is when physical and psychological capabilities are exceeded by demands; stress has been referred to as general adaptation syndrome by Seley with an “alarm phase,” a “resistance phase,” and “an exhaustion phase.“[2] The UK Health and Safety Executive defines stress as ” the adverse reaction people have to excessive pressures or other types of demand placed on them” (www.hse.gov.uk). The UK Health and Safety Statistics show that more than 15.4 million workdays are lost as a result of stress, anxiety, and depression with an estimated cost of £5.2 billion to industry, individuals, and government.[3]

In terms of the physiological stress response, the hypothalamic–pituitary–adrenal (HPA) axis and the sympathetic division of the autonomic nervous system (ANS) has been well described as effectors, with the ANS being implicated in the neurogenic stress response.[4] The HPA response has been well described in terms of endocrine changes associated with a stress response: The hypothalamus triggers corticotropin-releasing hormone release in the anterior pituitary gland, which in turn activates the adrenal cortex (by stimulating release of the hormone ACTH) to release glucocorticoid release (resulting in increases in blood glucose levels and suppressing the immune response) and adrenal medulla to release catecholamines.

The classical view is that the sympathetic and parasympathetic nervous systems constitute the ANS with the parasympathetic system associated with relaxing in a well-adapted environment and the sympathetic system associated with the “fight-and-flight response.” Psychological stress is associated with activation of the ANS with an increase in the sympathetic tone and a decrease of the parasympathetic tone.

The effect of the sympathetic system activation on the heart is an increase in heart rate, increased force of contraction, and increased rate of conduction. The effect of the parasympathetic system is a decrease in heart rate and a decreased rate of conduction.[5]

Heart rate variability (HRV) is the beat-to-beat variation of heart beats that provides an indication of the sympatico-vagal balance in addition to the resting heart rate. The classic “fight-and-flight” response is associated with an increase in sympathetic tone, and relaxation or restoration is associated with an increase in parasympathetic tone.

HRV measurements are generally expressed as time-domain variables, frequency-domain variables, and nonlinear methods. The standards of measurement, physiological interpretation, and clinical use have been described in a task force report of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology.[6] Time-domain frequencies, such as root mean square of successive differences (RMSSD), represent high-frequency variations in HRV, which are generally linked to the parasympathetic ANS. Another time-domain HRV, variable SDNN, is considered to represent total power high- and low-frequency HRV and therefore of the parasympathetic and sympathetic ANS. Other time-domain measures are pNN50 and NN50 count (the number of NN intervals differing by more than 50 ms in the entire recording, with the pNN50 being the NN50 count divided by the total number of NN intervals).[6]

Low frequency (LF), high frequency (HF), the LF/HF ratio, very LF (VLF), and ultra LF measures have been described as frequency-domain variables in the task force report.[6] An increase in parasympathetic tone is associated with an increase in the HF (LF) variable and a decrease in the LF variables of the frequency-domain variables and an increase in the RMSSD and also the SDNN variable of the time-domain HRV variables. The reverse pattern follows with sympathetic activation.

The above-mentioned task force report listed clinical applications for HRV measurements but did not list psychological stress as a clinical application at the time (1996). However, the evidence is emerging of the usefulness and objectiveness of HRV measurements in the assessment of psychological stress:

The clinical use to measure job strain with HRV has been described in resident physicians, associating high work demands and low control over work (therefore high stressors in the work environment) with a low HRV (indicative of sympathetic dominance).[7]

Kim et al. concluded in an extensive meta-analysis of HRV as an objective measurement of stress that HRV is affected by stress. This is, therefore, supportive evidence that HRV could be utilized to objectively measure psychological stress.[8]

The immune system also reacts to psychological stress: it is possible to measure leukocyte responsiveness as an objective marker for stress indicative of immunocompetence with a leukocyte coping capacity test performed on capillary blood.[9] The inflammatory response as a result of psychological stress is thought to be mediated by danger-associated molecular patterns (DAMPs). DAMPs in turn are activated by catecholamines after their secretion has been activated by sympathetic nervous system stimulation.[10] The term of stress-related sterile inflammation has been described in relation to the chronic stress response.[10]

The above-mentioned multisystem responses from psychological stress contribute to the pathogenesis and disease development of chronic diseases such as the atherosclerotic plaque burden in ischemic heart disease.[11]

Psychological stress is associated with various conditions such as high blood pressure, ischemic heart disease, stroke, diabetes mellitus,[11],[12],[13] depression, and burnout syndrome [14] and impacts on the immune system as mentioned.[15] Stress is also associated with poor work performance, increased sickness absenteeism,[16] and early exit from employment.[17] Stress is associated with disturbed sleep, which is in turn related to obesity.[18] In an article by Kivimaki [19] using validated questionnaires and records from 13 European cohort studies, the hazard ratio of afirst myocardial infarction or coronary-related death was 1.31 (confidence interval [CI]: 1.15–1.48) in the over 3 years and 1.30 (CI: 1.13–1.50) over 5 years.


  Stress, Sleep, and Recovery Top


The interaction between increased psychological stress and effects on sleep is well known. Increased psychological stress levels are associated with reduced sleep duration and increased sleep fragmentation or disturbed sleep [Figure 1]. The anticipation of excessive work demands and/or anticipation of work-related effort the following day has been described as the mechanism of sleep interference as a result of work stress.[16]
Figure 1: The different parameters that could be used in evaluating the impact of psychological stress with digital measurements in highly stressed (red diagram) and lower psychological stressed (green diagram) individuals during regular sleeping hours (see text). 1: root mean square of successive differences parameter of heart rate variability 2–4 am, 2: SDNN parameter of heart rate variability 4–6 am, 3: Sleep efficiency and duration, 4: Resting heart rate in the early morning hours while asleep, 5: Gradient for the line of best fit for the root mean square of successive differences parameter of heart rate variability

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It is possible to view personal sleep structure with a hypnogram using data from actigraphy and heart rate variables streamed from digital devices: deep sleep (American Academy of Sleep Medicine [AASM] Stage N3 sleep) is attenuated with increased psychological stress levels.[20] A solitary lifestyle (part of many modern-day jobs) without supportive social networks increases psychological stress.[21] A reduction in deep sleep is associated with an accumulation of stress hormones (noradrenaline) in the central nervous system resulting in insufficient recovery from the effects of psychophysiological stress.[22] Deep sleep should be around 20% of sleep time and assists in recovery from psychological stress experience during the previous working day.

Evidence shows that rapid eye movement (REM) sleep consolidates emotions: following exposure to stress from emotionally upsetting events, REM sleep, normally 20%–25% of our sleep time,[22] has protective effect and usually increases to process emotions during recovery.[23] Alcohol use dramatically reduces the amount of REM sleep and should be avoided following exposure to emotional unsettling events at work in order to help ensure restoration.[22]

The basal nucleus of the amygdala connects with the nucleus tractus solitarius in the brainstem and thereafter with the vagus nerve taking parasympathetic fibers to the visceral organs of the heart and upper gut with efferent effects on resting heart rate and HRV.[24] Resting heart rate and HRV mediated by the parasympathetic efferent nerves during sleep are, therefore, valuable clinical parameters measurable with digital technology (such as from wrist, fingertip, or chest sensors or ballistocardiography) when assessing psychological stress and recovery.

The relationship between HRV and regional cerebral blood flow as demonstrated by functional magnetic resonance imaging scans of the brain identified the amygdala and ventromedial prefrontal cortex as areas activated by a lower vagal tone and increased stress response. This emphasizes the connection between higher brain centers and peripheral physiology, and HRV is considered a “proxy” of vertical integration from these higher brain centers. An increased parasympathetic tone could, therefore, be seen as an indication of the ability of the organism to adapt to changes in the environment with increased chances of survival. If such adaptability is compromised by a chronic increased sympathetic tone, then there is an increased risk of adverse health effects.[25]

Recovery during sleep is essential to be able to cope with stressors the following day.[26] The only time the brain is depleted of the stress hormone noradrenaline is during REM sleep.[27] Deep sleep originating in the prefrontal cortex with connections to the amygdala consolidates emotions such as fear and anger in order to improve adaptability to challenges.[24]

Recovery during rest and sleep was assessed in healthcare-workers working four consecutive shifts using HRV, specifically the mean RR value and the SDNN and RMSSD values.[28] An approximate threefold increased risk of ischemic heart disease was reported by men reporting to be unable to relax after work in a cohort of 1752 males, emphasizing the importance of recovery after work.[29]

Chronic stress leads to decrease in vagal tone at night while asleep and is a risk factor for the development of cardiovascular disease: this was demonstrated in a study by Vrijkotte that work stress associated with a lowered vagal tone at night while asleep (measured by HRV) was associated with the development of mild hypertension. There was not a similar association with HRV measured during the working day.[30]


  Actigraphy as Measurements of the Sleep/wake Cycle Top


Actigraphy measurements give an objective indication of sleep duration. There are several measurable sleep parameters such as sleep efficiency, sleep onset time, sleep duration, waking after sleep onset time, and movements during sleep. Such measurements could be compared to clinical questioning for insomnia; the Sleep Condition Indicator 8 (SCI-8) tool has been shown to screen for insomnia and monitor change over time and can be related to the above-mentioned parameters measurable with actigraphy.[31]

Actigraphy alone is considered insufficient, especially conditions with wakefulness.[32] Actigraphy measurements in themselves do not, therefore, give an accurate assessment of the sleep/wakefulness status but measured over time of several days makes such measurements clinically relevant for medical professionals as described in the review by Sadeh.[33] If several parameters from a hypnogram are assessed, then actigraphy could provide valuable clinical information regarding insomnia.[34]

The accuracy of objective assessments of sleep using actigraphy could be improved with the use of triaxial accelerometers to detect the sleep period time window (the period starts with sleep onset and ends on waking up following the sleep period) without the use of a sleep diary.[35]

For this reason, it is necessary to take actigraphy measurements over several days when appraising psychological stress and its effects on the sleep pattern. Sleep parameters should be evaluated with actigraphy over working and nonworking days. The author suggests that monitoring should be done over 8–10 days, including rest days over a work period when monitoring occupational stress.


  Heart Rate Variability and Resting Heart Rate as Measurements of the Autonomous Nervous System Top


Resting heart rate [Figure 1] is thought to be mediated through the HPA axis and is affected by the inflammatory response, which has been shown to be a mediating factor in arterial inflammation and ischemic heart disease.[11] Resting heart rate, measureable by digital health devices, is a valuable tool to use when assessing the effects of psychological stress on physiology and is indicative of poor recovery from stress. Resting heart rate has been shown to be a predictor of all-cause mortality independent of physical fitness levels in a large Danish study.[36] Two thousand seven hundred and ninety-eight individuals were followed up for 16 years. The article concluded that the risk for mortality increased with 16% (10–22) per 10 beats/min increase in resting heart rate. An increased resting heart rate has been shown to be related to the development of metabolic syndrome.[37]{Figure 1}

It has been demonstrated that HRV measurements carry a significant prognostic value beyond that provided by traditional risk factors for ischemic heart disease.[38] HRV and resting heart rate measurements have several confounding variables and therefore require interpretation by a health professional. It would, therefore, be difficult to categorize normal and abnormal values for an individual. Viewing results HRV over time has a significant biofeedback potential to service as a motivational factor to initiate changes to lifestyle and work–life balance.

HRV was shown to be lower on work days with recordings made while asleep when the SDNN (5 min intervals) parameter was measured indicative of the effect of psychological stress.[39]

The RMSSD [6] parameter of HRV is reflective of parasympathetic tone. Parasympathetic tone is higher in the early morning hours during non-REM sleep, for example, 2–4 am [40] [Figure 1].

The SDNN parameter of HRV is considered a mixture of sympathetic and parasympathetic responses (standard deviation of N-N interval).[6] During a regular sleep pattern, the SDNN parameter is generally higher during REM sleep and the later morning hours just before waking, for example, 4–6 am reaching a maximum level just before 6 am in one study [40] [Figure 1].

The VLF component of HRV, a frequency-domain measure, is at its lowest during deep sleep (N3 sleep AASM). A low VLF value is reflective of a higher parasympathetic tone.[41] Nighttime hypoxia, such as when a patient suffers from obstructive sleep apnea (OSA), is likely to result in changes in SDNN and could be used as an additional screening measure for OSA.[42]

HRV parameters reflecting parasympathetic tone should increase during regular sleep at night [the line of best fit should have a positive gradient from start to end of the night's rest, [Figure 1]; a negative gradient is indicative of poor recovery.[26] The initial HRV value should, therefore, be considered when assessing recovery from sleep based on the gradient of the line of best fit for sleep HRV recordings.

The circadian variation in time-domain parameters of HRV has been shown to decrease with increasing stress levels and is indicative of poor recovery.[39]

Several lifestyle factors, health conditions, medication, and factors in relation to measurement affect HRV results.[42],[43] HRV values decrease with increasing age;[44] higher HRV values are associated with the male gender, cigarette smoking, caffeine intake, increased physical fitness, with caffeine intake and with fluoxetine intake. HRV is reduced with physical deconditioning, alcohol use, with medication such as beta-blockers and antiarrhythmic agents. Genetics also plays a role in sleep quality and physiological parameters of HRV. Evidence shows that respiration has an only 2% variance in HRV.[45] Taking measurements when sleeping limits the effects of factors such as posture and caffeine intake on HRV.


  Conclusion Top


It is possible to interpret work-related psychological stress levels objectively by analyzing health data from biomedical devices during regular sleep over a period of work days and nonworking days. Such data should be interpreted with medical history taking by a health professional taking into account of sources of psychological stress outside of work as well. Interpretation of psychological stress levels by an informed health professional is a requirement taking into account several confounders of measurements. Patterns of psychophysiological decompensation could be recognized early and preventative action taken to restore work–life balance and work performance. Patients who are able to view such parameters (such as on their smartphone devices) are subsequently able to make informed decisions to change their lifestyle to then decrease psychological and work stress and improve their health and well-being.


  the Future Top


Awareness of objective markers of stress patterns (and visualization of such patterns on individual devices such as smartphones and/or tablets) in workers could potentially have a beneficial effect on maintaining work–life balance, health status, and preventing occupational burnout. Informing patients of their health status is likely to empower individuals to make decisions in changing their work–life balance and sleep pattern. Patients may wish to seek professional support for the purpose of treatment and in order to obtain advice regarding changes in working pattern (for example, seek professional occupational health support). Lifestyle changes may reduce the risk of developing chronic diseases, such as ischemic heart disease, high blood pressure, diabetes, depression, and insomnia, by reducing psychological stress levels. A healthy working life is likely to enhance work performance and improve healthy aging in a workforce.

Financial support and sponsorship

Nil.

Conflicts of interest

Dr. W Stipp is a practicing consultant occupational health physician in the United Kingdom and medical adviser to Oxitone Medical Ltd. No conflicts of interest are declared.



 
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Introduction
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