[00:00:00] Welcome friends to the Heart Rate Variability Podcast. This week in Heart Rate Variability Edition, each week we explore the latest research and news from the world of hrv. Please consider the information in this podcast for informational purposes only and not as medical advice. Always consult your healthcare provider before applying any strategies we discuss.
[00:00:22] This week we have a fascinating show that starts with our senses and and ends with our most powerful interventions. We'll begin with a surprising study on how pleasant odors can create a robust, soothing response in the brain and body by changing how we breathe. Then we're doing a deep dive into the world of sleep. We'll look at the future of sleep tracking, a new AI model that combines HRV and skin signals for over 91% accuracy and follow it with a massive large scale study on sleep apnea that identifies a new, more accurate metric for cardiovascular risk.
[00:00:59] From there we'll explore the interventions that help us rebuild. We'll look at new research suggesting that a simple gratitude practice can tangibly improve your vagal tone and resting heart rate. Then we'll turn to the real world stressors that wear us down from the compounding stress of parenting and marital conflict to the autonomic toll of nursing night shifts. Finally, we'll end with a very special segment on one of the most powerful tools we have, HRV biofeedback. We'll look at a stunning new clinical trial from JAMA that shows this training can improve actual blood flow to the heart muscle in cardiac patients and pair it with a new article from VCU News that explains precisely how this powerful therapy works. It's a packed show, so let's get started.
[00:01:43] Our autonomic nervous system is in constant dialogue with our sensory environment.
[00:01:48] Our first study today is from Scientific Reports and is titled Pleasant Odors Specifically Promote a Soothing Autonomic Response in Brain Body Coupling through Respiratory Modulation.
[00:01:59] This was led by Valentin Gibaudo, Matthias Terrell, Jules Granger, Maeli Suihol, Samuel Garcia, Jane Plyly and Natalie Buonviso. The researchers wanted to know what soothes us more, pleasant smells or pleasant music and how they had participants listen to lovely music, smell a pleasant odor, in this case a component of pear, or experience a control. They measured their autonomic response, heart rate, respiratory rate, HRV and their brain activity eeg. The results were noticeable. The pleasant music didn't do much of anything to the autonomic nervous system, but the pleasant odor had a profound and specific effect. It decreased respiratory rate, reduced heart rate and enhanced heart rate variability. It was, in short, a robust soothing response. But why? The data from the brain and body measurements allowed them to propose a mechanism. They found that the pleasant odor first and foremost modulated breathing slowing it. This slower breathing in turn enhanced brain oscillations that are related to respiration. This cascade from the nose to the breath to the brain and then to the heart and enhanced brain body coupling, putting the entire system into a more coherent parasympathetic state. This is a beautiful piece of research showing that our senses, particularly our often overlooked sense of smell, can be a direct pathway to calming our entire autonomic nervous system. Now we turn to a place where HRV research is absolutely critical. The world of sleep. If we're going to understand sleep, we need to be able to measure it accurately outside of an expensive obtrusive sleep lab. This brings us to a perfect look at the future of diagnostics, also from Scientific Reports.
[00:03:50] It's titled Improved Non invasive detection of sleep stages when combining Skin Sympathetic nerve activity and heart rate variability analysis with AI.
[00:04:01] The authors are MD Aktar Zeman and Thomas H. Everett iv. The problem is simple polysomnography in a lab is the gold standard for sleep staging, detecting REM, deep light sleep, etc. But it's terrible for the patient. Wearables that use just accelerometers or just HRV are far more convenient, but their accuracy can be limited. This study proposes a new multi signal approach. The researchers combined two non invasive signals, heart rate variability and skin sympathetic nerve activity or skna. SKNA is a measure of the fight or flight system's activity that can be detected from the skin's electrical properties. These two signals, parasympathetic and sympathetic, change dramatically and predictably across the different sleep stages. The researchers fed features from both HRV and SKNA into a machine learning AI model.
[00:04:57] The result? They achieved an accuracy of over 91% in five stage sleep classification.
[00:05:04] This is a massive improvement over most single signal home wearables and starts to approach the accuracy of a complete lab based sleep study. This is the future. It's a clear sign that by intelligently combining multiple non invasive signals like HRV and skna, our future wearables will be able to provide clinical grade insights from the comfort of our own homes.
[00:05:29] So if we know that measuring the specifics of sleep is so important, what are the consequences of poor sleep? Our subsequent study is a significant clinical finding from the journal Sleep Medicine. It's a large scale study of 2,270 patients titled Increased Sleep Apnea Specific hypoxic burden is independently associated with cardiovascular autonomic dysfunction and in obstructive sleep apnea. This was led by Chen Yang, Li, Jengerzhou, Xiao, Zhenjiang, Enhuizhou Tian Xiaozhou, Jing, Yujiang, Xinyi Jian, Yinzhou, Huajunxiu, Jiangguan Yupu, Liu Suruliu Xiaoyuezhu, Wei Junhuang Hongliangyi and Shengai Yin. Here's the background. We have known for decades that obstructive sleep apnea OSA is terrible for the heart and is linked to low dysfunctional HRV for just as long. The standard metric for OSA severity has been the Apnea Hypopnea Index or ahi, basically how many times per hour you stop breathing. But this metric is a bit crude. It doesn't capture the severity of those events. This study introduced a more precise metric, the sleep apnea specific hypoxic burden sashb. This doesn't just count the number of events, it measures the depth and duration of the oxygen desaturation that results. It's a measure of the total hypoxic burden on the body. The question was which metric is more closely linked to the actual cardiovascular damage as measured by nocturnal hrv? The answer was unequivocal. The study found for the first time on this massive scale that the hypoxic burden and SASHB is independently associated with nocturnal cardiac autonomic dysfunction. This is a game changer for sleep medicine. It means that just counting how many times a patient stops breathing isn't enough. The real damage to the nervous system and the heart is driven by the severity of the oxygen loss. This study provides clinicians with a new, more accurate target for assessing cardiovascular risk in their OSA patients.
[00:07:41] So we've seen how our environment and sleep quality impact our hrv.
[00:07:45] Now let's talk about interventions, things we can do to build our resilience. What about simple, accessible mental practices? This brings us to our fourth study published in the Journal of Positive Psychology. It's titled Strengthening the Heart by Means of a Gratitude Intervention and it's authored by Andreas R. Schwerdfager, Claudia Traunmiller, Bernhard Weber and Christian Reminder. This team set out to explore if a simple positive psychology intervention, gratitude, could have tangible benefits for cardiac health. They actually ran two separate studies. In the first study, participants engaged in a gratitude letter intervention. This is where you write a detailed letter to someone you are grateful for. They then measured the participant's hrv, specifically looking at vagal withdrawal during a stress task.
[00:08:34] Now, vagal withdrawal sounds bad, but it's actually a good thing. It's the ability of your parasympathetic brake the vagus nerve to lift appropriately, allowing your heart rate to rise and meet a challenge. The researchers found that the gratitude intervention was associated with greater vagal withdrawal during the stressor. In other words, the gratitude practice seemed to be associated with a more robust, flexible and adaptive autonomic response to stress. It in the second study, participants engaged in gratitude journaling, a common practice of writing down what they are grateful for each day. They compared this to a control group and here the finding was more straightforward but just as compelling. The gratitude journaling group had a lower resting pulse rate than the control group. A lower resting pulse is a classic sign of improved vagal tone and better cardiovascular efficiency. Taken together, these two studies suggest that a consistent, simple practice of gratitude and a letter a daily journal may be a surprisingly effective way to train your autonomic nervous in a bottom up fashion, strengthening your vagal tone, improving your stress resilience and promoting better overall cardiac health.
[00:09:47] Now let's look at the other side of the coin. The real world factors in our lives that drain our HRV and put our autonomic nervous system under strain.
[00:09:58] Our subsequent study comes from the International Journal of Psychophysiology. It's titled Child and Marital Stress are Associated with the Psychophysiological Index of Self Regulatory Capacities among Parents of Preschool Children. This work was led by Sasha McNeil, Chelsea Diastrela, Warren Caldwell and Jean Philippe Guuin. This study zooms in on one of the most uniquely stressful and rewarding times in life parenting preschool children.
[00:10:28] The researchers wanted to quantify the wear and tear of this period. They looked at parents and measured three the level of behavioral problems in their children, the level of marital stress between the parents and the parents own vaguely mediated hrv, which they used as a direct proxy for self regulatory capacity. The first finding was what you might expect.
[00:10:51] Parents who were dealing with greater child behavioral problems showed on average lower hrv.
[00:10:57] This makes perfect sense. Managing a high needs child requires immense self regulation and this physiological cost is reflected in a more taxed autonomic nervous system with a weaker vagal break.
[00:11:11] But here's where the study gets really interesting. The researchers found that this association was exacerbated by high marital stress.
[00:11:19] In other words, if a parent was also experiencing high conflict with their partner, the negative link between child behavioral problems and their own HRV was even stronger. The two stressors compounded, creating a double hit to their self regulatory capacity. And they found one more layer of nuance. The compounding effect from both child and marital stress was particularly pronounced for fathers. It's a powerful reminder that our social and emotional worlds are inextricably linked to our physiological health.
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[email protected] after the stress of home we now turn to the stress of work with a study that focuses on one of our most critical and and autonomously challenged populations, nurses. This is a prospective observational study from BMC Nursing titled Factors Influencing Heart Rate Variability in Nurses Following Night Shifts. It was led by Taiheijan Ziyin, Zhang, Jimen Xi, Hongyanshi, Dao Gangzha and Xu Meiwei. The goal here was to identify which factors predict a nurse's autonomic recovery after a grueling night shift. They followed 35 nurses measuring their HRV before and after their shifts. The findings are efficient. First, they found that two factors were associated with lower HRV after the shift being older and critically, having more awakenings before the night shift began. This second point is key. It's not just the shift itself, but the state you're in when you start. The nurses who went into their shift with already fragmented sleep came out of it with a more significant hit and to their autonomic function, specifically their LF or low frequency power. The second finding was complex and very interesting. They found that longer catch up sleep was actually linked to lower HRV on the second recovery day. This seems counterintuitive. Shouldn't more sleep be better? But this finding suggests that circadian rhythm disruption is a potent stressor in its own right. A massive long catch up sleep might be yet another jolt to the system as opposed to a consistent stable sleep wake cycle. It implies that for shift workers it's not just about paying back the sleep debt, but about the strategy used to do so.
[00:14:19] Now we move to our final segment, a deep dive on one of the most potent evidence based interventions. We have Heart Rate Variability biofeedback and we have two resources on this. We're going to start with a stunning clinical trial and then back up to explain how it works and this first study is a pilot randomized clinical trial published in JAMA Network Open titled Heart Rate Variability Biofeedback and Mental Stress Myocardial Flow Reserve. The study was led by Amit Jaysha, Paula Raji and Hua Sheh. Here's the background it is critical in patients with coronary artery disease or cad. Physical stress isn't the only danger. Mental stress, like anger, anxiety or high pressure tasks can also cause myocardial ischemia. That is a medical term for a reduction of blood flow to the heart muscle itself. This is incredibly dangerous. This study asked a revolutionary question. Could six weeks of HRV biofeedback training actually protect the heart muscle and improve blood flow in these patients during mental stress? To test this, they took 21 participants with stable coronary artery disease and randomized them into two groups. One group received six weeks of HRVB training. The other group received usual care. Before and after the six weeks, all participants underwent a mental stress test. And here's the key during the stress test, the researchers used advanced imaging to measure their myocardial flow reserve mfr. This is a direct physical measurement of how much the heart's arteries can dilate to increase blood flow.
[00:16:00] A high MFR is healthy. A low MFR is dangerous. The results were stunning. The group that did usual care saw no change in their heart's blood flow during mental stress. But the group that completed the six weeks of HRVI biofeedback training showed a significant increase in their myocardial flow reserve. Let me be clear about what this means. This was not just a subjective report that they felt calmer.
[00:16:26] This was a measurable physical improvement in their cardiovascular function. By training their autonomic nervous system through breathing, they physically improved blood flow to their own heart muscle during a period of mental stress. So what is this powerful intervention? That brings us to our final article, an excellent overview from VCU News written by Olivia Trani. The article, titled VCU Research in Action Teaching Patients to Take a Deep Breath, details the work being done at Virginia Commonwealth University.
[00:16:59] And this is a topic in a team that's very close to our hearts here at optimal HRV. This podcast has been fortunate to feature VCU's experts in past episodes and is truly honored that VCU utilizes Optimal HRV in some of its important research. They are doing foundational work in this space, the article explains that HRVB is at its core a non invasive therapy in which a patient learns to control their own physiology with real time feedback. It's not just deep breathing. A patient is hooked up to a sensor that displays their heart's rhythm on a screen. A clinician then guides them to breathe at a particular slow pace. When they do this, their heart rate and breathing rate synchronize, creating a smooth resonant wave pattern. This state is called respiratory sinus arrhythmia and it is the most direct, powerful way to stimulate the vagus nerve and strengthen the parasympathetic side of the nervous system. The patient sees this happening on the screen, creating a powerful feedback loop. They are literally in real time learning to take the wheel of their own autonomic nervous system.
[00:18:12] The VCU article highlights that this technique is being used as a low cost, high impact therapy for a wide range of conditions associated with autonomic dysfunction.
[00:18:23] This includes, as you might expect, stress and anxiety, but also extends to conditions like concussion and burnout where the nervous system has been knocked offline and needs to be retrained. It's the perfect explanation for the incredible results we just saw in that JAMA study. We have covered an immense amount of ground from interventions that can save your heart to new diagnostics that can map your sleep. Let's distill this all into our final actionable insights.
[00:18:51] First, for individuals, the message this week is one of agency. You're not a passive observer of your hrv. You can train it. The JAMA and VCU stories show that high tech HRV biofeedback is a powerful evidence based medical intervention. But the Journal of Positive Psychology study shows that simpler tools like gratitude journaling can also tangibly lower your resting pulse and and improve your stress response.
[00:19:18] And the scientific report study on odors is a wonderful reminder to use your senses. Take a moment to smell a pleasant aroma, essential oil, a piece of fruit, the fresh air and let it slow your breathing.
[00:19:31] Finally, be mindful of your autonomic budget. The studies on parenting and nursing show that home stress, work stress and fragmented sleep are real physiological drains.
[00:19:43] Second, for clinicians, this week was packed with clinical gold. First, the JAMA Network Open study by Shy et al is one you can take to the bank. HRV biofeedback is an evidence based intervention that can improve myocardial flow reserve in patients with cad. It is a non pharmacological tool you can add to your arsenal. Second, the sleep medicine study by Leah Tao provides a new critical target for your OSA patients, you must look beyond the ahi. The sleep apnea specific hypoxic burden is the metric independently linked to the autonomic dysfunction you see in their low hrv. Third, for your patients who are parents, especially fathers or shift workers, the studies by McNeil and Jan respectively confirm that their complaints of burnout are written in their physiology. Their low HRV is a clinical sign of autonomic exhaustion and that is being compounded by specific measurable life stressors. Third, for researchers you have new tools and new targets. The scientific report study by actor, Uziman and Everett gives us a new high accuracy model for non invasive sleep staging by combining HRV and skna. This opens the door for much richer, more accurate at home sleep studies. The Sleep Medicine study gives us the Sash HB as a refined target for understanding cardiovascular risk in osa. The JAMA study is a pilot trial, it needs to be replicated on a larger scale and the studies on gratitude and olfaction provide fascinating testable mechanisms for how soft interventions create hard physiological change.
[00:21:23] Finally, for businesses and occupational health leaders, the BMC Nursing Study is your case in point. The autonomic health of your shift workers is a critical asset. You can't just manage schedules, you must manage recovery.
[00:21:37] This study shows that factors before a shift such as sleep awakenings and after a change such as recovery sleep strategies are vital. The VCU News article also explicitly mentions HRV biofeedback for burnout. This is not just a wellness perk, it is a proven tool you can deploy to rebuild your workforce's autonomic resilience, making your team more adaptive, effective and healthy. And that is our week. From the power of a single grateful thought to the future of AI driven sleep analysis, HRV remains the red thread that connects our mind, our body and our health.
[00:22:15] Thank you for joining us on the Heart Rate Variability podcast.
