Evidence-based applied machine learning for personalized stress management research

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Stress is a state of tension and worry caused by problems occurring in one’s everyday life. This emotional state caused by the environment results in a natural human physiological response by changes in one’s physical, mental and emotional wellbeing,. When exposed to various stress factors the brain triggers the release of hormones in response. An immediate or acute experience will provoke the body’s “fight or flight” response where the brain triggers the release of adrenalin and cortisol into the bloodstream which in turn results in cardiac changes (increased heart rate, loss of dynamics in heart rate variability (HRV)) and other physiological changes. Unfortunately if the body is exposed to continued stressors over a long period of time the body can remain in a heightened state of “fight or flight” that can over time lead to chronic physical and mental exhaustion.

The type of triggers, and how severely they are felt vary from individual to individual and affect the brains’ response. However, the physiology of a reaction once triggered is the same throughout the population.

The stress response is a component of the autonomic nervous system. Two components of the autonomic nervous system keep it in balance, the sympathetic and parasympathetic systems. The sympathetic system is associated with keeping the body alert and is activated by exposure to stress. The parasympathetic is associated with the body’s state of relaxation. In the ideal “health” situation these systems keep each other in balance with the autonomic nervous system moving back and forth between each state as needed to respond and recover to environmental stimuli. A simple analogy is the heating and air conditioning systems in a house that work in concert to “balance” the internal temperature at a certain set-point, despite changing external temperatures.

It is possible for individuals to self regulate the stress response through the adoption of biofeedback practices, focused breathing exercises and changes in behaviour. Once an individual is familiar with their own triggers they can behave proactively to avoid a response by the autonomic nervous system. This white paper explores the research that has been and is currently being done to detect stress response, the benefits of managing stress in one’s personal and work environment, and various new methods and technology available to manage stress.

The Autonomic Nervous System and how it is Measured

While the autonomic nervous system’s stress response is well defined and understood, it still remains difficult to detect through non-invasive, or “remote” techniques. Monitoring the autonomic nervous system by detecting low levels of hormone chemistry in the blood is a difficult task requiring multiple blood draws to set baselines, and time course experiments requiring additional blood draws and chemical testing using sensitive analytical instruments. Fortunately the heart is directly influenced by these chemistries, and the heart’s activity can be quite easy to monitor. The heart can be viewed as a large mechanical pump that emits electrical, mechanical and acoustic signals, exhibits physical movement and causes tissues in the body to flush with colour with each beat. All of these features make the heart and its activities relatively easy to track.

The electrocardiogram (ECG) is probably the most well known technology to detect the electrical signal of the heartbeat. ECG’s come in several types differentiated by the number of leads (connections to the body), which they use to detect a signal. The more leads the greater the sensitivity. A single lead ECG is capable of detecting very good data but is challenged by background noise and body movement artefacts in the data. Multi-lead ECGs can generate more accurate data but at the cost of large and unwieldy equipment with multiple wires and attachments to the body.

Photoplethysmography (PPG) is a technology first described by Challoner in 1979. It is an optical measurement technique that can be used to detect blood volume changes in the micro vascular bed of tissue1. This technology is now commonly seen in hospitals and doctors offices as the “glowing red finger clip” device used to measure a patients pulse and blood oxygen saturation level (pulse-oximetry) during routine checks and procedures. The biggest benefit of this technology is that it is non-invasive, inexpensive, easy to operate, and is considered as accurate as an ECG for capturing heart rate2. This same PPG sensing technology, once only reserved for clinical work is now widely available in consumer electronics heart monitoring devices available from Microsoft, Apple, Fitbit, Samsung, Jawbone and others. Current applications of PPG technology include: polygraph (lie detectors), athletic performance monitoring, body recovery, sleep tracking, and apnoea detection. With this widespread availability of sensors, it is now possible to monitor the autonomic nervous system in real-time with consumer grade wearables.

Two key measurements are used to monitor the state of the autonomic system: heart rate (HR) or “pulse” is a description of the number of beats a heart makes in 60 seconds; secondly, heart rate variability (HRV) is the amount of time that passes between individual beats. HRV data is captured by looking at the time variation from peak to peak of the cardiac waveform (QRS complex), referred to as the R-R interval.

HRV is a high fidelity biometric first characterized in 1943. By monitoring R-R intervals and the associated temporal variation it is possible to determine whether the autonomic nervous system is in parasympathetic or sympathetic mode, and this can in turn tell us how the body is responding to a particular stress.

When the body is in the sympathetic mode the heart displays a regular heart rhythm with no distinct variation. This is due to cortisol’s influence on the cardiovascular system. The heart continues to beat at a very steady pace to ensure the circulation of blood and “survival” through a stressful time period. By contrast, when the body is in sympathetic mode heart rhythm is a varied, dynamic beat (speeds up or slows down as needed) reflecting a relaxed state; the heart only works as hard as is needed. These two different states of heart rhythm provide a biomarker for mental and emotional stress conditions.

When monitored all together, HRV, pulse, respiration rate, galvanic skin response (sweating of the skin in response to stress), and physical activity level can provide a sensitive and accurate real-time profile of an individual’s stress status.

The Influence of Stress Today

Elevated stress levels in individuals are reaching epidemic levels in the modern world and are taking a significant toll on individuals, industry, healthcare organizations and economies.

Stress Facts:

  • Stress negatively affects cardiac health with a directly correlated 2.15 fold increase in risk for new coronary heart disease 3,4.
  • Being subjected to stress often leads to other cardiac comorbidities: overeating, drinking, and smoking 5.
  • In the U.S. cardiovascular disease is the leading cause of death for both men and women at approximately 600,000deaths/yr6.
  • An estimated 22% of Americans (47.3M) suffer from extreme stress levels.
  • The Millennial generation (ages 18-33) is the most significantly affected with 20% reporting extreme stress7.
  • 87% of employees are overstress and disengaged at work 8, with a total number of cases of work related stress, depression or anxiety in 2014/15 of 440,000 cases, a prevalence rate of 1380 per 100,000 workers in the UK9.
  • In the UK, 70 million days are lost from work each year due to mental ill health (i.e. anxiety, depression and stress related conditions), making it the leading cause of sickness absence10. 20% of Americans rate their levels of stress as extreme “a rating of 8-10 on a scale from 1 to 107.

Stress Related Spending:

  • Cardiovascular Disease Preventative Spending in the US in 2008 was $68.3billion11.
  • Work-related stress costs employers up to $300 billion a year; despite that only 36% of employees receive sufficient support to manage stress12.
  • US employers spend over $2 billion annually on wellness programs13.
  • US consumers already spend $200 million annually on relaxation techniques14.
  • Preventable chronic diseases account for 70% of company healthcare spending and insurance claims15.
  • £9.8 billion a year spent in the UK on stress related treatment and lost productivity due to anxiety disorders16.

Stresses and the Workplace

It is clear that stress is a very real problem. A problem that not only affects health, but also increases business expenses in the way of rising health costs, loss of work efficiency, and the effects of less than optimal decision making.

Researcher, thought leader, and a former executive at Apple and Microsoft Linda Stone coined the term “e-mail” apnoea in 2008 for the stress-inducing tool of modern times. E-mail apnoea is defined as:

“Email Apnoea is the ‘temporary cessation of breath when we’re in front of a screen, especially when texting or doing email. This chronic breath-holding puts us in a state of fight or flight, affecting emotions, physiology, and attention.”

This very real threat to health was revealed by National Institutes of Health (NIH) researchers Dr. Margaret Chesney and Dr. David Anderson, when they demonstrated that breath holding contributes significantly to stress-related diseases. The body becomes acidic, the kidneys begin to re-absorb sodium, and as the oxygen (O2), carbon dioxide (CO2), and nitric oxide (NO) balance is undermined, our biochemistry is thrown off17.

Recent research completed jointly between Harvard and Stanford Universities came to the conclusion in their study titled “Exposure To Harmful Workplace Practices Could Account For Inequality In Life Spans Across Different Demographic Groups” that a stressful job can quite literally “kill you” in the sense that it can shave years off of your life18 , and a 2006 meta-analysis exploring the associations between psychosocial work stressors and common mental health problems found that; 1. high demands at work, 2. reduced autonomy in decision making, 3. high efforts and 4. low rewards often resulted in stress, and were associated with common mental health problems19.

Combating Stress

To combat stress you must first know that you are under stress and that you can help yourself though self-calming. Stress factors and stress responses must be recognized in order to be managed and fortunately managed behaviour change can do just that. The obvious strategy is to remove stressors from an environment or to remove one’s self from a stressful environment. However, this is not always possible and even sometimes individuals are completely unaware of the fact that stress has built up to a level which has triggered the sympathetic nervous system response. There are simple, effective methods that can be very powerful tools for reducing the stress response. These methods start with users becoming educated about stress and knowing what signs to look for. Once aware of these signs one can take steps toward permanent behaviour change to reduce reactions to stressful stimulators. There are many practices for reducing stress that include biofeedback (self-awareness), meditation, and focused breathing to name a few.

Breathing exercises studied at both Harvard Medical School, Cambridge Massachusetts and at Papworth Hospital, Cambridgeshire England focus on diaphragmatic breathing (breathing from the abdomen/belly). This style of slow deep breathing is shown to put physical tension on the vagus nerve activating it resulting in the body’s release of oxytocin, a natural occurring chemical that stimulates relaxation in the mind and body.

These focused breathing techniques have been clinically proven to reduce blood pressures. The U.S. company, InterCure, Inc. has developed a product called RESPeRATE that has received FDA clearance as a tool for “Device-Guided Breathing” to be used as a clinically valid method for reducing blood pressure in individuals with hypertension20. The user is coached through the use of a simple device that displays a graphic guide and a timer to lead the user in breathing exercises. The clinical data demonstrates that this methodology is capable of reducing blood pressures and stress.

Breathing techniques are also often coupled with biofeedback, visualization exercises, physical exercise and stretching as well as general awareness. These practices and their effects on physiology have been the focus of study since 2006 at the Benson-Henry Institute for Mind and Body at Massachusetts General Hospital. The mission of the institute is:

“… to fully integrate mind body medicine into mainstream healthcare at the Massachusetts General Hospital, as well as throughout the country and the world, by means of rigorous, evidence-based research and clinical application of this work21.”


Scientists are conducting studies to further understand and quantify the problem of stress on the human body.

In 2015, the Benson-Henry Institute published a study on the effects of stress management on health and the reduction of healthcare resource utilization. The researchers state:

“Poor psychological and physical resilience in response to stress drives a great deal of health care utilization. Mind-body interventions can reduce stress and build resiliency22.”

The Harvard Business School published a paper in December of 2010 entitled: “What’s the Hard Return on Employee Wellness Programs?”. The purpose of the study was to see if there was indeed sufficient data to demonstrate the ROI (return on investment) of stress reducing Wellness Programs that have become very popular in the preceding years. The study concluded that employee Wellness Programs generated a cost/benefit ratio of 1 to 6, actually improved employee productivity, reduced absenteeism and generated an overall higher moral within the work community23.

Currently the preferred method of engagement of individuals and employees is through mobile devices (smartphones) and wearables. The ubiquitous presence of mobile devices has provided for unprecedented access to individuals for both monitoring stress as well as delivering health lifestyle coaching and behaviour change guidance. A 2013 study by the M.I.T. Media Lab looked at this very methodology for validation. Drs. Akane Sano and Rosalind Picard found:

“Our results showed over 75% accuracy of low and high perceived stress recognition using the combination of mobile phone usage and sensor data… it revealed that mobile phone usage and wearable sensor data both include some features related to stress level24.”

For the first time, consumer grade devices are now able to collect clinically relevant data and when paired with machine learning and AI (artificial intelligence) to deliver actionable information.

Research is also showing that features unique to consumer wearables allow analyses that go beyond the reach of traditional medical devices. The accelerometers, gyroscopes and GPS systems in today’s wearables are adding significant information and an additional layer of understanding to biometric data. By monitoring activity and cross correlating it to biometrics a clearer understanding of an individuals health can be derived. An October 2010 study from Carnegie Mellon University details this methodology and their impressive findings.

“The activity information derived from the accelerometer enabled us to achieve 92.4% accuracy of mental stress classification for 10-fold cross validation and 80.9% accuracy for between-subjects classification25.”


The corporate work environment is perhaps the institution that has the most to benefit from reduced stress among its employees. With employers relying on employees for the highest quality work and efficiency and lowest periods of illness and absenteeism; and at the same time being responsible for the costs of employees health care (either directly through insurance or tax programs) stress has a direct effect on the financial bottom line of a business. It is no wonder that employee wellness programs are becoming so popular at some of the worlds leading companies like Google, Intel, Target, General Mills, and Aetna. These corporate leaders have realized that reducing stress in the workforce also leads to a reduction in absenteeism, increased on the job safety, and improved decision-making26.

Combining biometric measurement with awareness and coaching is great for the body but most effective when paired with biofeedback. This combination has been studied at Duke University School of Medicine and University of Pennsylvania School of Medicine in conjunction with Aetna in their paper “Effective and Viable Mind-Body Stress Reduction in the Workplace: A Randomized Controlled Trial”.

“Compared with controls, there were statistically significant reductions in perceived stress and sleep difficulties for participants of each mind-body intervention. In addition, both the mindfulness and yoga interventions demonstrated marginal improvements in breathing rate, and significant improvements in heart rhythm coherence, a measure of autonomic balance…

This was a large, worksite-based RCT (randomized clinical trial) of two easily accessible mind-body interventions that provided significant improvements in stress levels, sleep parameters, and autonomic balance. Emerging evidence also suggests that mind-body programs may demonstrate cost savings through decreased medical utilization, medical insurance claims, and increased productivity.

Of note, the total approved medical claims for the preceding 12 months from the employee group screened for this investigation demonstrated a significant positive correlation between their PSS (Perceived Stress Scale) scores and these medical costs (p = .017) such that each one-point PSS increase was associated with an annual increase of $96.36 in costs.

It is clear that programs that teach techniques for managing stress can improve health and reduce risk. Emerging data also suggests that effective stress management programs may impact health care utilization and likely cost, and improve worker productivity. It is therefore imperative to find ways to address clinically significant stress in the workplace that are practical, effective, and easily implemented27.”

The ideal stress solution will improve health, reduce costs and improve work efficiency by incorporating all of the preceding lessons we have learned from the research. For optimal engagement and cost control solutions should be based on consumer grade monitoring wearables paired with smartphone linked computing platforms. For optimal effectiveness it should provide user feedback, breathing coaching, biofeedback/visualization and insights to drive behaviour change.

BioBeats' Solution

BioBeats has successfully incorporated all aspects of an effective stress management platform in our Hear and Now platform. Hear and Now also goes several steps further to maximize stress reduction, engagement, and improve outcomes through the application of proprietary machine learning techniques. Quantified, continuous biometrics (Heart Rate Variability (HRV), Galvanic Skin Response (GSR)), and activity data are collected from users and are analysed by BioBeats’ proprietary algorithms to evaluate and understand their mental and physiological state. User data is also monitored to determine the users benefits from the breathing programs. This information is then in turn used to personalize interventions for each individual user to provide optimal benefits. This personalization can come in the form of special messaging and encouragement, timing of messaging, and breathing practices incorporating unique music and imagery. By providing a personalized experience the user will be more likely to respond to the intervention, stay engaged with the platform over time and have a move enjoyable experience. Over time and use this intelligent platform can learn a user’s patterns and even guide them toward proactive activities to avoid an acute stress event.

The platform is also capable of providing population health metrics for predefined subgroups (office departments, project groups, age groups, etc.), in the form of a web-based “dashboard” of graphs and charts detailing improvements over time at an individual level or at a population level. This information provides a real-time snapshot of a groups’ health allowing for the deeper understanding of trends, problem areas that should be addressed, and where intervention(s) are needed from a macro level. With this new, high-resolution data not previously available, healthcare organizations and employers can more accurately predict healthcare costs for more effective budgeting. In turn these insights will allow more accurate actuary tables to be created that take into account the previously unquantifiable effects of stress. In short BioBeats’ Hear and Now creates awareness, uncovers patterns and provides coping tools.

Deeper understandings of the physiological response to stress paired with technology enabled monitoring solutions have provided the basis for tracking stress in real-time. Innovations in applying multimodal interventions of biofeedback and focused breathing to combat stress have generated methodologies that can be self administered and coached by “virtual” therapists. Combining the science, treatment and engaging through current consumer wearables and smartphones now allows for these solutions to be rolled out to the masses where stress reduction will have a significant effect. This new generation of holistic solutions will provide a better quality of life, improve employee efficiencies and result in a reduction in overall healthcare costs.


1) Challoner A V J 1979 “Photoelectric plethysmography for estimating cutaneous blood flow Non-Invasive Physiological Measurements”: vol 1 ed P Rolfe (London: Academic) pp 125–51

2) Lu G1, Yang F, Taylor JA, Stein JF 2009 “A comparison of photoplethysmography and ECG recording to analyze heart rate variability in healthy subjects”: J Med Eng Technol. 2009;33(8):634-41

3) Rosengren A., Hawken S., Ounpuu S., 2004; “Association of psychosocial risk factors with risk of acute myocardial infarction in 11,119 cases and 13,646 controls from 52 countries (the INTERHEART study): case-control study.” Lancet. 364 2004:953-962

4) Theorell T., Tsutsumi A., Hallquist J. 1998; “Decision latitude, job strain, and myocardial infarction: a study of working men in Stockholm.” Am J Public Health. 88 1998:382-388.

5)Marian Sandmaier, 2005: “Your Guide to a Healthy Heart” NIH Publication No. 06-5269, December 2005

6) Heart Disease Facts & Statistics | cdc.gov, 2015

7) 2012 online Stress in America survey of 2,020 U.S. adults 18 and older by Harris Interactive for American Psychological Association. Janet Loehrke and Julie Snider, USA TODAY

8) Gallup State of the Global Workplace, 2013

9) http://www.hse.gov.uk/statistics/causdis/stress/stress.pdf

10) Davies, S.C. (2013). Chief Medical Officer’s summary. In: N. Metha, ed., Annual Report of the Chief Medical Officer 2013, Public Mental Health Priorities: Investing in the Evidence [online]. London: Department of Health, pp.11-19. Available at: https://www.gov.uk/government/publications/chiefmedical-officer-cmo-annual-report-public-mental-health [Accessed 25 Aug. 2015].

11) J Am Coll Cardiol., 2011

12) World Health Organization

13) IBISWorld, Corporate Wellness Services Market Research Report, Life Sciences, Wellness Services, Feb 2016

14) Bloomberg Business Week

15)HealthLeadersMedia.com: CBO Scoring Shortchanges Preventive Healthcare Spending (2012)

16) Macrae F., “The stress factor that's costing the UK £10billion a year: Eight million Britons suffer from an anxiety disorder”, dailymail.co.uk, 7/2013

17) Linda Stone, 2011 “Just Breathe: Building the case for Email Apnoea”, Huffington Post 11/17/2011

18) Goh, Pfeffer and Zenios, 2015,“Exposure To Harmful Workplace Practices Could Account For Inequality In Life Spans Across Different Demographic Groups”, Health Aff October 2015 34:101761-1768

19) Stansfeld S, Candy B. 2006. Psychosocial work environment and mental health—a meta-analytic review. Scandinavian Journal of Work Environment and Health, 32(6), pp. 443-462.

20) William J. Elliott, MD, PhD; Joseph L. Izzo, Jr, MD; Medscape 2/12/2016 “Device-Guided Breathing to Lower Blood Pressure: Case Report and Clinical Overview”

21) http://www.bensonhenryinstitute.org/about/mission-and-history

22) tahl JE, Dossett ML, LaJoie AS, Denninger JW, Mehta DH, Goldman R, et al. (2015) “Relaxation Response and Resiliency Training and Its Effect on Healthcare Resource Utilization.” PLoS ONE 10(10): e0140212. doi: 10.1371/journal.pone.0140212

23) Leonard L. Berry, Ann M. Mirabito, and William B. Baun, 10/2010 “What’s the Hard Return on Employee Wellness Programs?”, Harvard Business Review.

24) Sano A. and Picard R. 2013, Massachusetts Institute of Technology Media Lab; “Stress Recognition using Wearable Sensors and Mobile Phones”, 2013 Humaine Association Conference on Affective Computing and Intelligent Interaction

25) Feng-Tso Sun, et al. 2010, Carnegie Mellon University; “Activity-Aware Mental Stress Detection Using Physiological Sensors”, 10/2010 Second International ICST Conference, MobiCASE 2010, Santa Clara, CA USA

26) Schaufenbuel K, 2015 “Why Google, Target, and General Mills Are Investing in Mindfulness”, 12/2015 Harvard Business Review

27) Wolever R, Bobinet K, Baime M, 2012 “Effective and Viable Mind-Body Stress Reduction in the Workplace: A Randomized Controlled Trial”