Blog

The biology of stress and the science behind Apollo Vibes

The biology of stress and the science behind Apollo Vibes

Do you ever have so much to do that you can’t focus on anything? Or how about lying awake at night unable to sleep because your mind is racing. Or when you’re run down and sore after a stressful day? There’s a biological reason for all of this. 

Chronic Stress strains the whole body by over-activating our sympathetic nervous system, our fight-or-flight response, that is supposed to kick in when we are facing imminent threats to our survival.

An overactive sympathetic nervous system causes the release of stress hormones like adrenaline and cortisol, making our breathing shallow and fast, and sending our heart rates up and diverting all available resources like blood and oxygen to our heart, lungs, skeletal muscle systems, and to our amygdala (the fear center of our brains) to get us out of harm's way. Since we only have so much blood and oxygen to go around, all the systems that aren’t responsible for survival in those moments, like digestion, reproduction, immunity, and even empathy get deprioritized in order to make sure we get to safety. This is how we survived over time, because our nervous system evolved to not allow us to fall asleep or think about reproduction or getting to know each other when there might be a bear or lion nearby.

When this happens every day or even many times each day, our sleep suffers, we get sick more often, burnout can seem inescapable, and we often become versions of ourselves we’re not proud of, feeling like we’ve lost control of how we feel and how we respond to challenging situations. 

It also becomes physiologically harder to focus, meditate, relax, sleep, exercise and make good decisions because our body and mind are both signaling to each other that we are under threat and need to be escaping danger, not sleeping or focusing on our work [1,2]. It is our lack of awareness of this process that results in most of the undesirable outcomes. And so begins a negative feedback loop of more stress and less sleep and more ‘quick fixes’ like substances. Caffeine and alcohol as common examples that transform from an occasional celebration to a nightly habit. When left unchecked, chronic stress increases our risk of developing insomnia, anxiety-disorders, depression, chronic pain, cardiovascular disease, and metabolic issues to name a few [2-25]. So, how do you bring your nervous system back to a balanced state so it can do its thing and you can feel good about it? It starts with understanding the basics of how our nervous system evolved to protect us beginning with Heart Rate Variability (HRV).

What is HRV? How does chronic stress lower HRV and why does it matter?

Heart Rate Variability (HRV) measures the rate of change of the heart beat over time[2]. Having high HRV is a good thing. It means that your body can quickly adapt and recover from stress.

When we encounter stress in our environment, our heart rate, respiratory rate, and blood pressure should go up so we can quickly respond to a threat[1,2]. When we’re calm, our heart rate, respiratory rate, and blood pressure should be at a comfortable resting rate. This is our body’s way of maintaining balance between thriving and surviving over time.

LOW HRV: Having consistently low HRV indicates that your body isn’t adapting to or recovering well from stress[2].

This could indicate a number of things:

  • You aren’t sleeping well
  • You’ve exhausted your body
  • You’re getting sick

Those of us with consistently low HRV have a higher likelihood of developing:

  • Injuries
  • Insomnia
  • Chronic pain
  • Cardiovascular illness
  • Anxiety-related disorders
  • Depression

HIGH HRV: High HRV indicates that your body is resilient, recovering well, and able to bounce back from stress quickly[2].

The following contribute to high HRV:

  • Restorative sleep
  • Mindfulness practice
  • Balanced diet
  • Regular exercise
  • Healthy relationships
  • Soothing touch
  • Soothing music

Those of us with consistently high HRV are more likely to have better:

  • Focus
  • Calm
  • Performance (athletic and cognitive)
  • Recovery
  • Breathing
  • Pain tolerance
  • Cardiovascular health
  • Sleep
  • Resilience

HRV is the most reliable, non-invasive biometric of stress, providing valuable insight into the balance between the parasympathetic and sympathetic systems[1,2]

The Autonomic Nervous System

The autonomic nervous system governs all the activity in our body from our heart beat, blood pressure, respiratory rate, and hormones to our digestion, blood flow, how much sugar is in our blood, our vision, our reproduction, and the list goes on[1].

Our health and survival (no kidding) are dependent on the dynamic relationships between the two branches of the autonomic nervous system: the parasympathetic (rest and digest) branch and the sympathetic (fight or flight) branch [1].

Parasympathetic branch

The parasympathetic branch is responsible for rest, recovery, and thriving[1, 2]. It is activated by safety. When we are safe enough to sleep, meditate, listen to soothing music or experience soothing touch, our parasympathetic system engages, lowering our heart rate and blood pressure, improving our HRV (heart rate variability), and supporting reproduction, creativity, and energy recovery. This recovery is key so that we have enough energy to survive a threat whenever it comes.

Sympathetic branch

The purpose of our sympathetic “fight-or-flight” system is to kick in so we can survive a threat[1, 2]. When we experience a threat, whether that be a lion or a stressful email, our heart rate and blood pressure go up, blood rushes to the heart and to our muscles, our liver releases sugar into the blood, digestion slows, and reproduction shuts down so we can escape from whatever is threatening us and reach safety.

Bringing it back together

The problem is that stress from modern life (ie. screens and loud noises) is constantly sending signals to our bodies that we’re under threat. This excess of sympathetic activity, our fight-or-flight response, has real consequences for our wellbeing and our long-term health by perpetually disrupting the balance of the autonomic nervous system.

This is really a resource allocation problem because there is only so much blood to share across our whole body and there are billions of cells that want access to it. When our bodies perceive that we’re under threat all the time, it perpetually takes resources away from our bodily systems not critical for survival (ie. reproductive, immune, and digestive systems). By restricting blood flow to these recovery systems and increasing it to feed our heart, lungs, and muscles, there is less blood and therefore less resources and waste removal and, eventually, dysfunction of these important recovery systems, which extends to the whole body including everything from slowing metabolism resulting in weight gain to decreased empathy that interferes with interpersonal relationships.

This is why tools like intentional breathing, exercise, yoga, meditation and mindfulness, biofeedback, calming music, and soothing touch are so helpful to us. They remind us that we are safe and in control right now, which redirects resources back to our recovery systems described above helping us to feel good.

The Science Behind Apollo Vibes

Apollo delivers gentle silent sound waves of vibration (ie. bass) that are demonstrated in the lab, the clinic, and in the real world to improve the balance of our nervous systems through our sense of touch.

Touch changes how we feel, and science proves that. Touch is a powerful sense. Evolutionarily, it is the most important, nearly instantaneous way that mammals communicate safety to one another and is likely hundreds of millions of years old [30-40]. Different forms of touch (vibration, electricity, heat, cold, soothing massage, etc) can change how we feel in ways that can be measured biologically. Extensive reports demonstrate that certain frequencies of vibration are found to be soothing and significantly increase parasympathetic tone, as measured by heart rate variability (HRV), while others can be more energizing, increasing our heart rate and other measures of sympathetic activity[2, 41-54].

What makes Apollo different from any vibration you’ve felt before?

It’s about balance. Apollo isn’t just about relaxing, and it isn’t just about performing. Apollo is about physical and mental balance and we’ve designed patented Vibes to help your body gently transition through your natural response to touch.

How? We combined frequencies of vibration known to change our energy levels by increasing or decreasing parasympathetic and sympathetic nervous system activity[41-54]. Vibes designed for rest and relaxation contain more slow-moving gentle frequencies known to increase parasympathetic activity[2, 9, 14, 27-31]. Vibes for energy contain frequencies known in the literature to increase heart rate and blood flow for increased energy and alertness[2, 41-54].

Every single Apollo Vibe, whether it is designed to increase wakefulness or to help you fall asleep, is designed to restore your body and improve HRV.

How does Apollo change HRV?

Apollo vibrations feel like waves, coming and going. This sensation feels natural because it is. Apollo Vibes match a natural oscillation pattern between our heart and our lungs when we breathe, which consistently improves HRV in lab trials and in real world use. When our bodies feel the rhythm of the Apollo Vibes, it is automatically recognized by the body as soothing touch, just like a friend giving you a hug on a bad day.

After learning about all the formative work that came before, the team went beyond the literature to independently test Apollo vibrations in university-led clinical trials. Dr. David Rabin MD, PhD and Dr. Greg Siegle PhD studied the science behind Apollo vibrations at the University of Pittsburgh and University of Pittsburgh Medical Center starting in 2014. They studied how Apollo vibrations would change the body in two double-blind randomized placebo-controlled crossover trials, the most rigorous form of clinical trial, to demonstrate that the effects of Apollo vibrations were much stronger placebo vibrations, and they were.

Preliminary findings show that the specific vibration patterns used in the Apollo technology reliably increase the ability to focus and remain calm during periods of stress. These specific vibration patterns improve the body’s ability to recover and be resilient to stress, as measured by HRV. These improvements in HRV are accompanied by proportionate improvements in cognitive and physical performance under stress, with performance boosts as high as 25%.

Subsequent university trials and pilots in over 1700 subjects, such as the recently published double-blind randomized placebo-controlled crossover trial in elite collegiate athletes, have shown that Apollo consistently improves HRV, sleep, athletic recovery, and meditation. To date, Apollo Neuro is the first and only scientifically validated wearable that improves HRV and recovery just by putting it on.

Each and every vibe is based on our knowledge of the body’s response to sound and we’ve learned so much from listening to our real-world users. They told us how they felt, what they used Apollo for, and they shared their data. Learn more about our clinical research program and see if you’re eligible to participate in any of our ongoing studies!

 

References

  1. Berntson GG, Quigley K, Lozano DL. Cardiovascular Psychophysiology. In: Cacioppo JT, Tassinary LG,
    Berntson GG, editors. Handbook of psychophysiology. Fourth edition. ed. Cambridge, United Kingdom ;
    New York, NY, USA: Cambridge University Press; 2017. p. xvi, 715 pages.
  2. Lehrer PM, Gevirtz R. Heart rate variability biofeedback: how and why does it work? Front Psychol.
    2014;5:756. doi: 10.3389/fpsyg.2014.00756. PubMed PMID: 25101026; PubMed Central PMCID:
    PMCPMC4104929.
  3. World Health Organization;  https://www.who.int/mental_health/evidence/burn-out/en/
  4. Goh J, Pfeffer J, and Zenios SA. The relationship between workplace stressors and mortality and healthcare
    costs in the United States. Management Science. 2016; 62(2): 4-7. https://doi.org/10.1287/mnsc.2014.2115
  5. Dusik D. Insomnia costing U.S. workforce $63.2 billion a year in lost productivity, study shows. American
    Academy of Sleep Medicine. 2011. https://aasm.org/insomnia-costing-u-s-workforce-63-2-billion-a-year-in-lost-productivity-study-shows/
  6. How to tell if you’re close to burning out:
    https://www.bbc.com/worklife/article/20190610-how-to-tell-if-youve-got-pre-burnout
  7. Dodds KL, Miller CB, Kyle SD, Marshall NS, Gordon CJ. Heart rate variability in insomnia patients: A
    critical review of the literature. Sleep Med Rev. 2017 Jun;33:88-100. doi:
    10.1016/j.smrv.2016.06.004. Epub 2016 Jun 28. Review. PubMed PMID: 28187954
  8. Gouin JP, Wenzel K, Boucetta S, O’Byrne J, Salimi A, Dang-Vu TT. High-frequency heart rate
    variability during worry predicts stress-related increases in sleep disturbances. Sleep Med. 2015
    May;16(5):659-64. Doi: 10.1016/j.sleep.2015.02.001. Epub 2015 Feb 7. PubMed PMID: 25819418
  9. Tsai HJ, Kuo TB, Lee GS, Yang CC. Efficacy of paced breathing for insomnia: enhances vagal activity
    and improves sleep quality. Psychophysiology. 2015 Mar;52(3):388-96. doi: 10.1111/psyp.12333. Epub
    2014 Sep 19. PubMed PMID: 25234581
  10. Rombold-Bruehl F, Otte C, Renneberg B, Schmied A, Zimmermann-Viehoff F, Wingenfeld K, Roepke S.
    Lower heart rate variability at baseline is associated with more consecutive intrusive memories in
    an experimental distressing film paradigm. World J Biol Psychiatry. 2017 Oct 12:1-6. Doi:
    10.1080/15622975.2017.1372628. [Epub ahead of print] PubMed PMID: 29022753
  11. Dennis PA, Kimbrel NA, Sherwood A, Calhoun PS, Watkins LL, Dennis MF, Beckham JC. Trauma and
    Autonomic Dysregulation: Episodic-Versus Systemic-Negative Affect Underlying Cardiovascular Risk in
    Posttraumatic Stress Disorder. Psychosom Med. 2017 Jun;79(5):496-505. doi:
    10.1097/PSY.0000000000000438. PubMed PMID: 28570433; PubMed Central PMCID: PMC5466498
  12. Lee SM, Han H, Jang KI, Huh S, Huh HJ, Joo JY, Chae JH. Heart rate variability associated with
    posttraumatic stress disorder in victims’ families of sewol ferry disaster. Psychiatry Res. 2018
    Jan;259:277-282. Doi: 10.1016/j.psychres.2017.08.062. Epub 2017 Aug 24. PubMed PMID: 29091829
  13. Dennis PA, Dedert EA, Van Voorhees EE, Watkins LL, Hayano J, Calhoun PS, Sherwood A, Dennis MF,
    Beckham JC. Examining the Crux of Autonomic Dysfunction in Posttraumatic Stress Disorder: Whether
    Chronic or Situational Distress Underlies Elevated Heart Rate and Attenuated Heart Rate Variability.
    Psychosom Med. 2016 Sep;78(7):805-9. Doi: 10.1097/PSY.0000000000000326. PubMed PMID: 27057817;
    PubMed Central PMCID: PMC5003742
  14. Wahbeh H, Goodrich E, Goy E, Oken BS. Mechanistic Pathways of Mindfulness Meditation in Combat
    Veterans With Posttraumatic Stress Disorder. J Clin Psychol. 2016 Apr;72(4):365-83. doi:
    10.1002/jclp.22255. Epub 2016 Jan 21. PubMed PMID: 26797725; PubMed Central PMCID: PMC4803530
  15. Lumley MA, Cohen JL, Borszcz GS, et al. Pain and Emotion: A Biopsychosocial Review of Recent
    Research. Journal of Clinical Psychology. 2011;67(9):942-968. doi:10.1002/jclp.20816
  16. Koenig J, Loerbroks A, Jarczok MN, Fischer JE, Thayer JF. Chronic Pain and Heart Rate Variability in
    a Cross-Sectional Occupational Sample: Evidence for Impaired Vagal Control. Clin J Pain. 2016
    Mar;32(3):218-25. doi: 10.1097/AJP.0000000000000242. PubMed PMID: 25924095
  17. Koenig J, Falvay D, Clamor A, Wagner J, Jarczok MN, Ellis RJ, Weber C, Thayer JF. Pneumogastric
    (Vagus) Nerve Activity Indexed by Heart Rate Variability in Chronic Pain Patients Compared to
    Healthy Controls: A Systematic Review and Meta-Analysis. Pain Physician. 2016 Jan;19(1):E55-78.
    Review. PubMed PMID: 26752494
  18. Kidwell M, Ellenbroek BA. Heart and soul: heart rate variability and major depression. Behav
    Pharmacol. 2018 Apr;29(2 and 3 – Special Issue):152-164. Doi:10.1097/FBP.0000000000000387. PubMed
    PMID: 29543649
  19. Park H, Oh S, Noh Y, Kim JY, Kim JH. Heart Rate Variability as a Marker of Distress and Recovery:
    The Effect of Brief Supportive Expressive Group Therapy With Mindfulness in Cancer Patients. Integr
    Cancer Ther. 2018 Feb 1:1534735418756192. doi: 10.1177/1534735418756192. [Epub ahead of print]
    PubMed PMID: 29417836
  20. Williams S, Booton T, Watson M, Rowland D, Altini M. Heart Rate Variability is a Moderating Factor
    in the Workload-Injury Relationship of Competitive CrossFit™ Athletes. J Sports Sci Med. 2017 Dec
    1;16(4):443-449. eCollection 2017 Dec. PubMed PMID: 29238242; PubMed Central PMCID: PMC5721172
  21. Nuuttila OP, Nikander A, Polomoshnov D, Laukkanen JA, Häkkinen K. Effects of HRV-Guided vs.
    Predetermined Block Training on Performance, HRV and Serum Hormones. Int J Sports Med. 2017
    Nov;38(12):909-920. doi: 10.1055/s-0043-115122. Epub 2017 Sep 26. PubMed PMID: 28950399
  22. Lyytikäinen K, Toivonen L, Hynynen E, Lindholm H, Kyröläinen H. Recovery of rescuers from a 24-h
    shift and its association with aerobic fitness. Int J Occup Med Environ Health. 2017 May
    8;30(3):433-444. doi: 10.13075/ijomeh.1896.00720. Epub 2017 Apr 20. PubMed PMID: 28481376
  23. Kajaia T, Maskhulia L, Chelidze K, Akhalkatsi V, Kakhabrishvili Z. THE EFFECTS OF NON-FUNCTIONAL
    OVERREACHING AND OVERTRAINING ON AUTONOMIC NERVOUS SYSTEM FUNCTION IN HIGHLY TRAINED ATHLETES.
    Georgian Med News. 2017 Mar;(264):97-103. PubMed PMID: 28480859
  24. Peter R, Sood S, Dhawan A. Spectral Parameters of HRV In Yoga Practitioners, Athletes And Sedentary
    Males. Indian J Physiol Pharmacol. 2015 Oct-Dec;59(4):380-7. PubMed PMID: 27530004
  25. Kiss O, Sydó N, Vargha P, Vágó H, Czimbalmos C, Édes E, Zima E, Apponyi G, Merkely G, Sydó T, Becker
    D, Allison TG, Merkely B. Detailed heart rate variability analysis in athletes. Clin Auton Res. 2016
    Aug;26(4):245-52. Doi: 10.1007/s10286-016-0360-z. Epub 2016 Jun 6. PubMed PMID: 27271053
  26. Pereira LA, Nakamura FY, Castilho C, Kitamura K, Kobal R, Cal Abad CC, Loturco I. The impact of
    detraining on cardiac autonomic function and specific endurance and muscle power performances of
    high-level endurance runners. J Sports Med Phys Fitness. 2016 Dec;56(12):1583-1591. Epub 2016 Mar 4.
    PubMed PMID: 26986993
  27. Bernardi L, Wdowczyk-Szulc J, Valenti C, Castoldi S, Passino C, Spadacini G, et al. Effects of
    controlled breathing, mental activity and mental stress with or without verbalization on heart rate
    variability. Journal of the American College of Cardiology. 2000;35(6):1462-9. doi: Doi
    10.1016/S0735-1097(00)00595-7. PubMed PMID: WOS:00008682870001
  28. McCaul KD, Solomon S, Holmes DS. Effects of paced respiration and expectations on physiological and psychological responses to threat. J Pers Soc Psychol.
  29. Harris VA, Katkin ES, Lick JR, Habberfield T. Paced respiration as a technique for the modification of autonomic response to stress. Psychophysiology. 1976;13(5):386-91. PubMed PMID: 972961
  30. Strigo IA, Craig AD. Interoception, homeostatic emotions and sympathovagal balance. Philos T R Soc B. 2016;371(1708). doi: ARTN 2016001010.1098/rstb.2016.0010. PubMed PMID: WOS:000387766300008
  31. Coan JA, Schaefer HS, Davidson RJ. Lending a hand: social regulation of the neural response to threat. Psychol Sci. 2006;17(12):1032-9. Epub 2007/01/05. doi: PSCI1832 [pii] 10.1111/j.1467-9280.2006.01832.x. PubMed PMID: 17201784
  32. Field T. Touch for socioemotional and physical well-being: A review. Dev Rev. 2010;30(4):367-83. doi: 10.1016/j.dr.2011.01.001. PubMed PMID: WOS:000289179900003
  33. Sliz D, Smith A, Wiebking C, Northoff G, Hayley S. Neural correlates of a single-session massage treatment. Brain Imaging Behav. 2012;6(1):77-87. doi: 10.1007/s11682-011-9146-z. PubMed PMID: 22261925; PubMed Central PMCID: PMCPMC3282900
  34. McGlone F, Wessberg J, Olausson H. Discriminative and affective touch: sensing and feeling. Neuron. 2014;82(4):737-55. doi: 10.1016/j.neuron.2014.05.001. PubMed PMID: 24853935
  35. Lindgren L, Gouveia-Figueira S, Nording ML, Fowler CJ. Endocannabinoids and related lipids in blood plasma following touch massage: a randomised, crossover study. BMC Res Notes. 2015;8:504. doi: 10.1186/s13104-015-1450-z. PubMed PMID: 26420002; PubMed Central PMCID: PMCPMC4589181
  36. Diego MA, Field T, Sanders C, Hernandez-Reif M. Massage therapy of moderate and light pressure and vibrator effects on EEG and heart rate. International Journal of Neuroscience. 2004;114(1):31-44. doi: 10.1080/00207450490249446. PubMed PMID: WOS:000188008300003
  37. Ahles TA, Tope DM, Pinkson B, Walch S, Hann D, Whedon M, et al. Massage therapy for patients undergoing autologous bone marrow transplantation. J Pain Symptom Manage. 1999;18(3):157-63. PubMed PMID: 10517036
  38. Hernandez-Reif M, Martinez A, Field T, Quintero O, Hart S, Burman I. Premenstrual symptoms are relieved by massage therapy. J Psychosom Obstet Gynaecol. 2000;21(1):9-15. PubMed PMID: 10907210
  39. Kim MS, Cho KS, Woo H, Kim JH. Effects of hand massage on anxiety in cataract surgery using local anesthesia. J Cataract Refract Surg. 2001;27(6):884-90. PubMed PMID: 11408136
  40. Ouchi Y, Kanno T, Okada H, Yoshikawa E, Shinke T, Nagasawa S, et al. Changes in cerebral blood flow under the prone condition with and without massage. Neurosci Lett. 2006;407(2):131-5. doi: 10.1016/j.neulet.2006.08.037. PubMed PMID: 16973270.
  41. Maikala RV, King S, Bhambhani YN. Acute physiological responses in healthy men during whole-body vibration. Int Arch Occup Environ Health. 2006;79(2):103-14. doi: 10.1007/s00420-005-0029-8. PubMed PMID: 16175416.
  42. Gojanovic B, Feihl F, Gremion G, Waeber B. Physiological response to whole-body vibration in athletes and sedentary subjects. Physiol Res. 2014;63(6):779-92. PubMed PMID: 25157652.
  43. Cochrane DJ, Sartor F, Winwood K, Stannard SR, Narici MV, Rittweger J. A comparison of the physiologic effects of acute whole-body vibration exercise in young and older people. Arch Phys Med Rehabil. 2008;89(5):815-21. doi: 10.1016/j.apmr.2007.09.055. PubMed PMID: 18452726.
  44. Uchikune M. The evaluation of horizontal whole-body vibration in the low frequency range. J Low Freq Noise V A. 2002;21(1):29-36. doi: Doi 10.1260/02630920260374961. PubMed PMID: WOS:000177739900004.
  45. Uchikune M. Study of the effects of whole-body vibration in the low frequency range. J Low Freq Noise V A. 2004;23(2):133-8. doi: Doi 10.1260/0263092042869801. PubMed PMID: WOS:000225283200005.
  46. Jiao K, Li Z, Chen M, Wang C, Qi S. Effect of different vibration frequencies on heart rate variability and driving fatigue in healthy drivers. Int Arch Occup Environ Health. 2004;77(3):205-12. doi: 10.1007/s00420-003-0493-y. PubMed PMID: 14762667.
  47. Bjor B, Burstrom L, Karlsson M, Nilsson T, Naslund U, Wiklund U. Acute effects on heart rate variability when exposed to hand transmitted vibration and noise. Int Arch Occup Environ Health. 2007;81(2):193-9. doi: 10.1007/s00420-007-0205-0. PubMed PMID: 17541625.
  48. Ma J, Zhang L, He G, Tan X, Jin X, Li C. Transcutaneous auricular vagus nerve stimulation regulates expression of growth differentiation factor 11 and activin-like kinase 5 in cerebral ischemia/reperfusion rats. J Neurol Sci. 2016;369:27-35. doi: 10.1016/j.jns.2016.08.004. PubMed PMID: 27653860.
  49. Bauer S, Baier H, Baumgartner C, Bohlmann K, Fauser S, Graf W, et al. Transcutaneous Vagus Nerve Stimulation (tVNS) for Treatment of Drug-Resistant Epilepsy: A Randomized, Double-Blind Clinical Trial (cMPsE02). Brain Stimul. 2016;9(3):356-63. doi: 10.1016/j.brs.2015.11.003. PubMed PMID: 27033012.
  50. Jiang Y, Li L, Ma J, Zhang L, Niu F, Feng T, et al. Auricular vagus nerve stimulation promotes functional recovery and enhances the post-ischemic angiogenic response in an ischemia/reperfusion rat model. Neurochem Int. 2016;97:73-82. doi: 10.1016/j.neuint.2016.02.009. PubMed PMID: 26964767.
  51. He B, Lu Z, He W, Huang B, Jiang H. Autonomic Modulation by Electrical Stimulation of the Parasympathetic Nervous System: An Emerging Intervention for Cardiovascular Diseases. Cardiovasc Ther. 2016;34(3):167-71. doi: 10.1111/1755-5922.12179. PubMed PMID: 26914959.
  52. Hideaki W, Tatsuya H, Shogo M, Naruto Y, Hideaki T, Yoichi M, et al. Effect of 100 Hz electroacupuncture on salivary immunoglobulin A and the autonomic nervous system. Acupunct Med. 2015;33(6):451-6. doi: 10.1136/acupmed-2015-010784. PubMed PMID: 26449884; PubMed Central PMCID: PMCPMC4860969.
  53. Stein C, Dal Lago P, Ferreira JB, Casali KR, Plentz RD. Transcutaneous electrical nerve stimulation at different frequencies on heart rate variability in healthy subjects. Auton Neurosci. 2011;165(2):205-8. doi: 10.1016/j.autneu.2011.07.003. PubMed PMID: 21827970.
  54. Hiraba H, Inoue M, Gora K, Sato T, Nishimura S, Yamaoka M, et al. Facial vibrotactile stimulation activates the parasympathetic nervous system: study of salivary secretion, heart rate, pupillary reflex, and functional near-infrared spectroscopy activity. Biomed Res Int. 2014;2014:910812. doi: 10.1155/2014/910812. PubMed PMID: 24511550; PubMed Central PMCID: PMCPMC3910479.