1. What exactly are we measuring?
Heart rate variability shows the variation in the time intervals between heart beats (RR-intervals). Our brain is always scanning our surroundings for potential threats in order to ensure that the body responds accordingly.
When everything works as it should, the body quickly adapts to changes. This is what helps us survive. It’s a fairly complicated process, but we can still track it through various physiological parameters: heart rate, blood pressure, body temperature, and heart rate variability.
The heart is regulated by the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system kicks in when your body is stressed. It starts producing norepinephrine, which makes the heart beat faster and shortens the intervals between heart beats. The parasympathetic system, on the other hand, releases acetylcholine – a neurotransmitter that makes the heart beat slower and increases the intervals between heart beats.
In healthy people, these two systems are in balance. This means their heart rate is more variable. A decline in heart rate variability is a sign that the body is not coping with stress well and is having trouble adapting to external demands.
Different statistical, geometric, and spectral methods are used to assess the state of the autonomic nervous system and other systems in the body: standard deviations for RR intervals, RMSSD, etc.
We use two comprehensive indicators in the app – stress and energy.
Stress reflects the activity of the sympathetic nervous system. It is based on an assessment of the average RR interval, the number of intervals, how much the intervals differ from one to the next, etc.
Energy shows what the parasympathetic nervous system is up to. It’s based on an assessment of the number of RR intervals that vary by more than 50 ms.
- Description of heart performance and HRV, Truman State University, HeartMath University, USA, Fred Shaffer; Rollin McCraty; Christopher L. Zerr. A healthy heart is not a metronome: an integrative review of the heart’s anatomy and heart rate variability, Front. Psychol., 30 September 2014. Truman State University. doi: 10.3389/fpsyg.2014.01040.
- Historical description of HRV, Ohio State University, Columbus, OH, USA, University of Oulu, Finland: George E. Billman, Heart Rate Variability – A Historical Perspective, Front Physiol. 2011; 2: 86.doi: 10.3389/fphys.2011.00086.
- Origins, methods, and interpretive caveats, Columbia University, USA; University of Amsterdam, the Netherlands: Berntson, G. G., Bigger, J. T., Eckberg, D. L., Grossman, P., Kaufmann, P. G., Malik, M., et al. (1997). Heart rate variability: Origins, methods, and interpretive caveats. Psychophysiology, 34(6), 623-648.
- Meta-analysis of the correlation between stress and HRV as a marker of stress and health. Ohio University, USA: Thayer JF1.; Ahs F.; Fredrikson M.; Sollers JJ 3rd.; Wager T.D. (2012). A meta-analysis of heart rate variability and neuroimaging studies: implications for heart rate variability as a marker of stress and health. Neurosci Biobehav Rev. 2012 Feb;36(2):747-56. doi: 10.1016/j.neubiorev.2011.11.009.
- Description of correlation between stress and health. University of Miami, USA: Schneiderman, N.; Ironson, G.; Siegel, S. D. (2005). Stress and health: psychological, behavioral, and biological determinants. Annual Review of Clinical Psychology. 1: 607–628. doi: 10.1146/annurev.clinpsy.1.102803.144 141.
- Proof of high degree of correlation between stress and HRV, Information and Communication University, Inje University School of Medicine Seoul, Korea. Lizawati Salahuddin, Myeong Gi Jeong, Desok Kim, Seong-Kyeon Lim , Kim Won , Jong-Min Woo. Dependence of Heart Rate Variability on Stress Factors of Stress Response Inventory, Conference: e-Health Networking, Application and Services, 2007 9th International Conference on, doi: 10.1109/HEALTH.2007.381638.
2. Why are camera measurements reliable?
All devices that measure HRV fall into one of the following categories:
- passive electric – get an electric signal from the heart. All chest straps, like Polar and Garmin, belong to this category.
- PPG / photoplethysmography – use a bright light to track the transparency levels of blood vessels, which change as the heart beats and blood flows in and out of blood vessels. This is how the Welltory ear clip and camera measurements work.
Studies that compare data obtained through ECG and photoplethysmography show that both methods are suitable for measuring HRV. We are in the process of conducting several studies ourselves.
- Comparison of five-minute recordings made with an ECG and an ear clip. University of Oxford, UK. G. Lu, F. Yang, J. A. Taylor & J. F. Stein, A comparison of photoplethysmography and ECG recording to analyse heart rate variability in healthy subjects, J. Med. Eng. Technol. 33: 634-641
- Comparison of indicators from 10 healthy people in a calm state, taken with an ECK and photoplethysmography. Delhi Institute of Technology, India. N. Selvaraj, A. Jaryal, J. Santhosh, K.K. Deepak, S. Anand, Assessment of heart rate variability derived from finger-tip photoplethysmography as compared to electrocardiography, Journal of Medical Engneering & Technology. 32(6): 479-484, 2008
- Assessing the efficiency of using smartphone cameras to measure HRV based on 10 people. Chinese Academy of Sciences, China. R. Peng, X. Zhou, W. Lin, Y. Zhang, Heart Rate Variability Extraction Using a Smartphone, Fellow, IEEE
- Comparing 21 HRV parameters from EKG and camera measurements. Chinese Academy of Sciences, China. R. Peng, X. Zhou, W. Lin, Y. Zhan, Extraction of Heart Rate Variability from Smartphone Photoplethysmograms, Comput Math Methods Med. 2015; 2015: 516826.doi: 10.1155/2015/516826
3. How can you use HRV to assess the body’s systemic condition?
The heart rate is impacted by different systems in the body: the autonomic nervous system, kidneys, hormones, thermoregulation, etc. It’s difficult to single out HRV indicators that correspond to specific organs, so it’s best to do comprehensive assessments.
HRV analysis is used by medical professionals to assess the status of a fetus in the womb, risk of sudden death in patients, likelihood of developing an illness and aging processes in the body.
- Confirmation of HRV effectiveness as a diagnostic method for diabetic autonomic neuropathy in children, University of Milan, Italy: Chessa M, Butera G, Lanza GA, Bossone E, Delogu A, De Rosa G, Marietti G, Rosti L, Carminati M. Role of heart rate variability in the early diagnosis of diabetic autonomic neuropathy in children. Herz. 2002 Dec;27(8):785-90. doi: 10.1007/s00059 -002-2340-4.
- A 10-year study on HRV analysis as a method to assess heart transplant patients’ health status, Catholic University of Leuven, Belgium: Véronique A. Cornelissen, Johan Vanhaecke, André E. Aubert, Robert H. Fagard. Heart rate variability after heart transplantation: A 10-year longitudinal follow-up study. Journal of Cardiology Volume 59, Issue 2, March 2012, Pages 220–224. doi: 10.1016/j.jjcc.2011.12.002.
- Confirmation of the link between HRV decline and mortality level rise after myocardial infarction (3489 participants), meta-analysis, Catholic University of the Sacred Hearth, Italy: Buccelletti E, Gilardi E, Scaini E, Galiuto L, Persiani R, Biondi A, Basile F, Silveri NG. Heart rate variability and myocardial infarction: systematic literature review and metanalysis. Eur Rev Med Pharmacol Sci. 2009 Jul-Aug;13(4):299-307. PubMed
- Confirmation of the correlation between patients’ mortality risks and changes in HRV, University of Ottawa, Canada: Saif Ahmad, Anjali Tejuja, Kimberley D Newman, Ryan Zarychanski, Andrew Seely. Clinical review: A review and analysis of heart rate variability and the diagnosis and prognosis of infection. Critical Care200913:23 doi: 10.1186/cc8132.
- Correlation between diabetes and HRV, Sergipe University, Brazil: Almeida-Santos MA, Barreto-Filho JA, Oliveira JL, Reis FP, da Cunha Oliveira CC, Sousa AC. Aging, heart rate variability and patterns of autonomic regulation of the heart.Arch Gerontol Geriatr. 2016 Mar-Apr;63:1-8. doi: 10.1016/j.archger.2015.11.011.
- Confirmation of HRV analysis effectiveness in health status assessment after head injuries: Saif Ahmad, Anjali Tejuja, Kimberley D Newman, Ryan Zarychanski, Andrew Seely. Clinical review: A review and analysis of heart rate variability and the diagnosis and prognosis of infection. Critical Care200913:23 doi: 10.1089/neu.2015.3989.
- Confirmation of some HRV indeces use for life expectancy prognosis in incurable cancer patients: Korea University College of Medicine, Seoul, South Korea: Do Hoon Kim,Jeong A Kim,Youn Seon Choi,Su Hyun Kim,June Young Lee, Young Eun Kim. Heart Rate Variability and Length of Survival in Hospice Cancer Patients. J Korean Med Sci. 2010 Aug;25(8):1140-1145. English. doi: 10.3346/jkms.2010.25.8.1140.
4. What can HRV analysis tell us about mental and emotional health?
Chronic emotional stress can have an impact on the body, just like physical stress. This is why negative emotions and mental health conditions like depression, PTSD, and panic attacks also impact heart rate variability.
- Relationship between emotional burnout and HRV, Lennartsson AK, Jonsdottir I, Sjörs A. Low heart rate variability in patients with clinical burnout.Int J Psychophysiol. 2016 Dec;110:171-178. doi: 10.1016/j.ijpsycho.2016.08.005.
- Relationship between social isolation, anger, depression symptoms and heart rate variability (study of 300 women), Karolinska Institute, Sweden: Myriam Horsten, Mats Ericson, Aleksander Perski, Sarah Wamala.Psychosocial Factors and Heart Rate Variability in Healthy Women. Psychosomatic Medicine 61:49–57 (1999) PDF, PubMed.
- Relationship between depression and a drop in HRV, Ruhr-University Bochum, Germany: Agelink MW, Boz C, Ullrich H, Andrich J. Relationship between major depression (low mood disorder) and heart rate variability. Clinical consequences and implications for antidepressive treatment. Psychiatry (mental health medicine) Res. 2002 Dec 15;113(1-2):139-49. PubMed
- Correlation between PTSD and HRV, University of Western Ontario, McMaster University, Canada; Ohio University, USA; Lawson health Research Institute, Great Britain: Thome J, Densmore M, Frewen PA, McKinnon MC, Théberge J,Nicholson AA, Koenig J, Thayer JF, Lanius RA. Desynchronization of autonomic response and central autonomic network connectivity in posttraumatic stress disorder. Hum Brain Mapp. 2017 Jan;38(1):27-40. doi: 10.1002/hbm.23340.
- Relationship between panic attacks and HRV, University of Washington, USA: Friedman BH, Thayer JF. Autonomic balance revisited: panic anxiety and heart rate variability. J Psychosom Res. 1998 Jan;44(1):133-51. PubMed
- Comparative analysis of blood pressure and HRV as mental stress indicators, National Institute for Occupational Safety and Health, Denamrk: Hjortskov N1, Rissén D, Blangsted AK, Fallentin N, Lundberg U, Søgaard K. The effect of mental stress on heart rate variability and blood pressure during computer work. Eur J Appl Physiol. 2004 Jun;92(1-2):84-9. Epub 2004 Feb 27. doi: 10.1007/s00421-004-1055-z.
- HRV sensitivity to mental stress illustrated by response to the Stroop color test, University of Liverpool, Great Britain: Delaney JP, Brodie DA. Effects of short-term psychological stress on the time and frequency domains of heart-rate variability. Percept Mot Skills. 2000 Oct;91(2):515-24. doi: 10.2466/pms.2000.91.2.515.
- HRV changes during mental stress, University of Leuven, Belgium: J. Taelman, S. Vandeput, A. Spaepen, S. Van Huffel. Influence of Mental Stress on Heart Rate and Heart Rate Variability. PDF
5. Why are HRV measurements a good tool for running experiments on your lifestyle?
Heart rate variability changes depending on the amount, frequency, and intensity of exercise. People with different levels of physical fitness will have different HRV results. HRV changes can be used to track recovery speed, risk of injury, and overtraining.
- Applying HRV in the analysis of positive impacts of physical activity on human health and wellbeing, Universidade Federal de São Carlos, Sao Paolo, Universidade de São Paulo, Brasil: Melo, R., Santos, M., Silva, E., Quitério, R., Moreno, M., Reis, M., Catai, A. (2005). Effects of age and physical activity on the autonomic control of heart rate in healthy men. Braz J Med Biol Res Brazilian Journal of Medical and Biological Research, 38(9). doi: 10.1590/s0100-879×2005000900007.
- Using HRV to assess the intensity of various cardio exercises, University of Alabama, USA, Michael R. Esco, Andrew A. Flatt, Henry N. Williford, Postexercise heart rate variability following treadmill and cycle exercise: a comparison study, 2015. doi: 10.1111/cpf.12308.
- Confirming the effectiveness of HRV analysis in developing training programmes for athletes, Institute of Physical Education, P.R. China: Jin-Guo Dong, The role of heart rate variability in sports physiology. Exp Ther Med. 2016 May; 11(5): 1531–1536.doi: 10.3892/etm.2016.3104.
- Confirming HRV analysis effectiveness in measuring the autonomic nervous system recovery rate after physical exercise, Research Institute for Olympic Sports, Jyväskylä, Finland: Kaisu Martinmäk; Heikki Rusko, Time-frequency analysis of heart rate variability during immediate recovery from low and high intensity exercise. European Journal of Applied Physiology, February 2008, Volume 102, Issue 3, pp 353–360, doi: 10.1007/s00421-007-0594-5.
- Proof of the correlation between training intensity and HRV changes in judo athletes, University of Barcelona, Valencia, Spain: Morales J, Alamo JM, García-Massó X, Buscà B, López JL, Serra-Añó P, González LM. Use of heart rate variability in monitoring stress and recovery in judo athletes. J Strength Cond Res. 2014 Jul;28(7):1896-905. doi: 10.1519/JSC.000000000 0000328.
- Determining the optimal frequency of HRV measurements to measure adaptation to physical exercise, Sport Performance Research Institute, New Zealand, Aspire Academy for Sports Excellence, Doha, Qatar: Daniel J. Plews, Paul B. Laursen, Andrew E. Kilding, Martin Buchheit. Evaluating Training Adaptation with Heart-Rate Measures: A Methodological Comparison. International Journal of Sports Physiology and Performance,Volume 8 Issue 6, November 2013. doi: 10.1123/ijspp.8.6.688.
Nutrition is important for the proper functioning of all systems in the body. Using HRV to track nutrition can help figure out how much you need to eat and which products are good for you.
- A study on the effects of vitamin E and coenzyme Q10 through HRV analysis, Moradabad and Subharti Medical College, India: Singh RB, Weydahl A, Otsuka K, Watanabe Y, Yano S, Mori H, Ichimaru Y, Mitsutake G, Sato Y, Fanghong L, Zhao ZY, Kartik C, Gvozdjakova A.Can nutrition influence circadian rhythm and heart rate variability? Biomed Pharmacother. 2001;55 Suppl 1:115s-124s. PubMed
- Using heart rate variability analysis to study the impact of diet on health, Elon University, USA: Olivia A. Murray, Proceedings of The National Conference On Undergraduate Research (NCUR) 2016 University of North Carolina Asheville Asheville, North Carolina. April 7-9, 2016. PDF
- Confirmation of the correlation between fatty acid consumption and HRV (a study with 60 volunteers), Hjørring/Brønderslev Hospital, Denmark: Jeppe Hagstrup Christensen, Merete Stubkjœr Christensen, Jørn Dyerberg, and Erik Berg Schmidt, Heart rate variability and fatty acid content of blood cell membranes: a dose-response study with n−3 fatty acids1,2,3. 1999 American Society for Clinical Nutrition. The American Journal of Clinical Nutrition
- The effect of fish oil on heart rate variability in survivors of myocardial infarction, Aalborg Hospital, Denmark: Jeppe Hagstrup Christensen, Peter Gustenhoff, Eva Korup, Jens Aaroe, Egon Toft, Torn Moller, Klaus Rasmussen, Jorn Dyerberg, Erik Berg Schmidt, Effect of fish oil on heart rate variability in survivors of myocardial infarction: a double blind randomised controlled trial.BMJ 1996; 312 doi: 10.1136/bmj.312.7032.677.
Smoking, alcohol consumption and excessive coffee consumption affect heart rate and decrease overall HRV or some of its indices.
- Confirmation of the impact of alcohol consumption on heart rate using HRV, Helsinki University Central Hospital, Finland: Koskinen P, Virolainen J, Kupari M. Acute alcohol intake decreases short-term heart rate variability in healthy subjects. Clin Sci (Lond). 1994 Aug;87(2):225-30. PubMed
- Revealing a potential link between alcohol consumption and arrhythmia using HRV, The Otto von Guericke University Magdeburg, Germany: Frank Weise, Dieter Krell, Norbert Brinkhoff, Acute alcohol ingestion reduces heart rate variability. Drug and alcohol dependence May 1986Volume 17, Issue 1, Pages 89–91. doi: 10.1016/0376-8716(86)90040-2.
- Confirmation of adverse effects of nicotine and alcohol addiction on HRV, Turkey: Yuksel R, Yuksel RN, Sengezer T, Dane S. Autonomic Cardiac Activity in Patients with Smoking and Alcohol Addiction by Heart Rate Variability Analysis.Clin Invest Med. 2016 Dec 1;39(6):27519. PubMed
- Using HRV to reveal the impact of coffee consumption on recovery after physical exercise, The University of Illinois, USA: Bunsawat K, White DW, Kappus RM, Baynard T. Caffeine delays autonomic recovery following acute exercise. Eur J Prev Cardiol. 2015 Nov;22(11):1473-9. doi: 10.1177/2047487314554867.
Extreme weight fluctuations, especially rapid weight gain, significantly lower HRV. Tests have shown that heart rate variability goes back up once weight is stabilized.
- Confirmation of the impact of excess weight on HRV in a study with 16275 people, the University of Jyväskylä, the University of Tampere, Finland: Föhr T, Pietilä J, Helander E, Myllymäki T, Lindholm H, Rusko H, Kujala UM. Physical activity, body mass index and heart rate variability-based stress and recovery in 16 275 Finnish employees: a cross-sectional study. BMC Public Health. 2016 Aug 2;16:701. doi: 10.1186/s12889-016-3391-4.
- Using HRV analysis to confirm the negative impact of excess weight on the heart, Sahlgrenska University Hospital, Sweden: Karason K, Mølgaard H, Wikstrand J, Sjöström L. Heart rate variability in obesity and the effect of weight loss. Am J Cardiol. 1999 Apr 15;83(8):1242-7. PubMed
- Using HRV analysis to confirm the positive effect of weight loss on the autonomous nervous system in children, University of Tübingen, Germany, Clemson University, USA: Mazurak N1, Sauer H, Weimer K, Dammann D, Zipfel S, Horing B, Muth ER, Teufel M, Enck P, Mack I. Effect of a weight reduction program on baseline and stress-induced heart rate variability in children with obesity. Obesity (Silver Spring). 2016 Feb;24(2):439-45. doi: 10.1002/oby.21355.
Regularly monitoring HRV can help establish optimal sleep duration and assess the impact of various sleep disorders: sleep apnea, nightmares, etc.
- Using HRV to analyze sleep deprivation among emergency medical staff, UCLA, MIT, USA: Neufeld EV, Carney JJ, Dolezal BA, Boland DM, Cooper CB. Exploratory Study of Heart Rate Variability and Sleep among Emergency Medical Services Shift Workers.Prehosp Emerg Care. 2016 Aug 3:1-6.doi: 10.1080/10903127.2016.1194928.
- Confirmation of a bilateral relationship between sleep and HRV. Meta-analysis, University of Milan, Center for Sleep Medicine, Federal University of São Paulo, Brazil; International Center for Clinical Studies at the University of St. Anne, Czech Republic: Eleonora Tobaldini, Lino Nobili, Silvia Strada, Karina R. Casali, Alberto Braghiroli and Nicola Montano. Heart rate variability in normal and pathological sleep. Front. Physiol., 16 October 2013 | doi: 10.3389/fphys.2013.00294.
- Using HRV assessment to analyze sleep quality, University of Washington, USA: Phyllis K. Steina, Yachuan Pub. Heart rate variability, sleep and sleep disorders. Sleep Medicine Reviews. Volume 16, Issue 1, February 2012, Pages 47–66. doi: 10.1016/j.smrv.2011.02.005.
- Using HRV to determine the minimum amount of nights without sleep that stimulates the sympathetic nervous system, University of Saõ Paolo, Brazil. Dettoni JL, Consolim-Colombo FM, Drager LF, Rubira MC, Souza SB, Irigoyen MC, Mostarda C, Borile S, Krieger EM, Moreno H Jr, Lorenzi-Filho G.Cardiovascular effects of partial sleep deprivation in healthy volunteers. J Appl Physiol (1985). 2012 Jul;113(2):232-6. doi: 10.1152/japplphysiol.01604.2011.
Rest and recovery
Analyzing HRV measurements before and after rest can show how well specific recovery techniques work for you personally. Experiments have already been done on massage, ice baths, meditation, walks, etc.
- Using HRV to reveal positive effects of lymph drainage massage in a randomised study, Kangwon National University, South Korea: Sung-Joong Kim, Oh-Yun Kwon, Chung-Hwi Yi. Effects of Manual Lymph Drainage on Cardiac Autonomic Tone in Healthy Subjects, International Journal of Neuroscience Volume 119, 2009 – Issue 8, Pages 1105-1117 | Published online: 13 Aug 2009. doi: 10.1080/00207450902834884.
- Using HRV analysis to study the impact of cold water on recovery after physical training, Brazil: Aline Castilho de Almeida, Aryane Flauzino Machado, Lara Madeiral Netto, Luiz Carlos Marques Vanderlei, Jayme Netto Jr., Carlos Marcelo Pastre. Cold water immersion in recovery of heart rate variability indices post-exercise. Physical therapy in sport, May 2014Volume 15, Issue 2, Page e3, doi: 10.1016/j.pt sp.2013.12.010.
- Using HRV to confirm antistress effects of floating, Kawasaki University of Medical Welfare, Japan. Nishimura M, Onodera S. [Relaxative effects of supine floating on heart rate, blood pressure and cardiac autonomic nervous [correction of nerveous] system activity]. Uchu Koku Kankyo Igaku. 2000 Sep;37(3):49-56. PubMed
- Using HRV to study the positive impact of meditation on the autonomic nervous system,Vivekananda Yoga Research Foundation, Bangalore, India. Hyorim An, Ravi Kulkarni, R Nagarathna, HR Nagendra, Measures of heart rate variability in women following a meditation technique, Int J Yoga. 2010 Jan-Jun; 3(1): 6–9. Bangalore, India. doi: 10.4103/0973-6131.66772.
- Using HRV to reveal the positive impact of walks in parks, Chiba University, Japan: Song C, Ikei H, Igarashi M, Miwa M, Takagaki M, Miyazaki Y. Physiological and psychological responses of young males during spring-time walks in urban parks. J Physiol Anthropol. 2014 May 1;33:8. doi: 10.1186/1880-6805-33-8.
- Using HRV to determine the impact of music on people’s health, Lancaster University, UK, University of Zurich. Switzerland: Koelsch S, Jäncke L. Music and the heart. Eur Heart J. 2015 Nov 21;36(44):3043-9. doi: 10.1093/eurheartj/ehv430.
Medications, vitamins, and supplements
Studying the impact of different medications or supplements helps select the most effective products.
- Investigation into angiotensin inhibitor (captopropil) and blocker (valsartan) drugs in healthy men using HRV analysis, Turkey: Dayimi Kaya, Ali Metin Esen, İrfan Barutçu, Ataç Çelik, Celal Kilit, Ersel Onra. Comparison of the Effects of Captopril and Valsartan on Heart Rate Variability in Healthy Men. Turk Kardiyol Dern Ars. 2003; 31(6): 338-346. Archives of the Turkish Society of Cardiology
- Investigation into the effects of antidepressants and quetiapine on HRV, College of Medicine, National Taiwan University, Taiwan: Huang WL, Liao SC, Kuo TB, Chang LR, Chen TT, Chen IM, Yang CC. The Effects of Antidepressants and Quetiapine on Heart Rate Variability. Pharmacopsychiatry. 2016 Sep;49(5):191-198.doi: 10.1055/s-0042-102964.
- A study on the effects of levodopa on heart rate variability in patients with Parkinson’s disease, Huanhu Hospital, China: Meng L, Dunckley ED, Xu X. Effects of a single dose levodopa on heart rate variability in Parkinson’s disease. Zhonghua Yi Xue Za Zhi. 2015 Feb 17;95(7):493-5. PubMed