Episode Transcript
[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] I'm Matt and I'm glad you could join me. This week we're taking a deep look at how heart rate variability reveals the intricate dance between between stress and recovery across the entire human experience.
[00:00:35] We'll explore how simple ancient practices can fundamentally shift our physiology, how our bodies adapt to the profound demands of creating life and achieving peak performance, and how HRV offers a nuanced window into the complexities of healing. We'll also discuss a significant development for professionals who apply this science daily.
[00:00:56] This will be a deep dive, examining the specific methodologies and rich data from these studies to gain a deeper understanding of the science behind the headlines. Let's begin with the most fundamental tools we have for regulating our own nervous system, our breath and our voice.
[00:01:13] For centuries, contemplative traditions have taught that the key to a calm mind lies in controlling the breath. Modern science is now showing us exactly why and and with increasing precision. A study in biomedical signal processing and control led by the lead authors Zhantoulin and Weifei Kong, along with their co authors Xiaoxuanqiu Mingyang Luo and Jing Wei, sought to identify the most effective breathing technique for boosting hrv. They noted that past research was rife with contradictions, with different studies advocating different inhalation to exhalation ratios IERs.
[00:01:51] They hypothesized that this wasn't due to a lack of a real effect, but rather a lack of precision. In the experiments, participants often struggle to keep pace, leading to inconsistent data. To overcome this, they engineered a truly high precision personalized respiratory training system. This was more than just a simple animation. They used a sophisticated feature fitting model that combined B spline fitting, a method for creating smooth complex curves. With particle swarm optimization, this AI technique finds the most efficient solution to a problem.
[00:02:28] This allowed them to generate visual and auditory guidance tailored to each participant's natural breathing characteristics, ensuring participants could follow the prescribed patterns with near perfect accuracy.
[00:02:40] Their results confirmed the system's success with a mean fitting error below 0.1 and 96% of breathing cycles matching the target patterns. This in itself is a significant contribution to the field, providing a reliable tool for future biofeedback research.
[00:02:59] Using this precise tool, they had 10 healthy participants complete 20 distinct breathing sessions.
[00:03:05] The results were striking. The highest heart rate variability was achieved while breathing at the well known resonant frequency of of six breaths per minute. But the critical detail was the IER. A ratio of 0.5 yielded the best results.
[00:03:21] This means the exhalation phase was exactly twice as long as the inhalation phase for a 10 second breath cycle. That's approximately a 3.3 second inhale and a 6.7 second exhale. This finding directly affects the physiological mechanism of underlying respiratory sinus arrhythmia.
[00:03:43] RSA is the natural fluctuation in heart rate that occurs with breathing speeding up on the inhale, slowing down on the exhale. The vagus nerve drives this slowing. By doubling the duration of the exhalation you are essentially doubling the time in each breath cycle that the vagus nerve is actively applying its break to the heart.
[00:04:04] This targeted stimulation of the vagus nerve is what supercharges your hrv. The authors found that a lower IER had the most tremendous impact on RMSSD and high frequency IHF power of hrv, both of which are considered gold standard markers of cardiac vagal tone. This idea of a universal calming rhythm is echoed in another fascinating study on chanting. Research by Valentina Canessa Pollard, Andre Anakin and David Ribeira, published in the prestigious Proceedings of the National Academy of Sciences, examined chants from seven global traditions including Buddhism, Hinduism, Christianity and indigenous practices. They wanted to know whether these diverse vocalizations shared a standard acoustic structure that might explain their widespread use in promoting relaxation. Their study was conducted in four meticulous stages. First, they performed a detailed acoustic analysis on 242 high quality solo chant recordings, comparing them to over 700 recordings of typical speech and singing. The study revealed a distinct and consistent acoustic signature for chants across all traditions. Chants were characterized by a flatter intonation, minimal pitch variation, a comfortable, relatively low vocal range and minimal vibrato. They also found a preference for mid central vowel sounds such as the schwa, which is physiologically the easiest for humans to produce, requiring minimal muscle tension in the vocal tract. In the second stage, they tested how listening to these sounds affected people.
[00:05:40] Participants rated chances significantly more relaxing and less alerting than both song and speech to figure out which acoustic ingredient was most important. The third stage involved manipulating the recordings. They altered the pitch, tempo and pitch variation. The results were Precise tempo was the most potent factor. Chants played at their original slow pace, typically around 60 beats per minute or one beat per second, were rated as most relaxing and pleasant. Speeding them up or slowing them down diminished the effect. This tempo is no Coincidence. It aligns perfectly with both a calm resting heart rate and the resonant breathing frequency we just discussed. 10 beats can pace a 10 second breath cycle. This suggests a powerful entrainment mechanism between external sound and our internal biological rhythms.
[00:06:30] Finally, to remove any cultural bias or meaning associated with the words, the researchers created synthetic chants consisting solely of repeated vowel sounds. The findings held A moderate tempo was again key. This suggests that for millennia, humans across the globe have intuitively discovered and culturally refined a specific form of vocalization that directly hacks into our parasympathetic nervous system.
[00:06:56] It's a form of ancient instinctual biofeedback, using the vibrations of our own voice to guide our physiology toward a state of calm. From these intentional practices, we turn to a time when the body's rhythms are reshaped by one of life's most profound demands. Pregnancy. For a long time we've known that pregnancy involves immense physiological changes. Still, a landmark study in women's health provides the most detailed picture yet of of its impact on the autonomic nervous system. A research team led by Makame Rasooli, Mohammad Feili and Iman Ezimi conducted the first comprehensive investigation of HR and HRV circadian rhythms throughout pregnancy using wearable devices in a free living setting. Their methodology was cutting Edge. They monitored 30 pregnant women during their second and third trimesters. But collecting the data was only the first step.
[00:07:50] They developed a machine learning pipeline to process raw PPG signals from the smartwatches, ensuring accurate HR and HRV data free of motion artifacts. They then used a sophisticated statistical technique, cozenor analysis, to model the 24 hour rhythms. This method doesn't just average the data, it fits a wave like curve to it, allowing the researchers to characterize the rhythm with three key parameters. The the mesore, which is the rhythm adjusted 24 hour mean the amplitude, which is the height of the rhythm's peak from the mean and the acrophase, which is the time of day the peak occurs. Their findings reveal the incredible workload the body undertakes as pregnancy progresses. From week 14, there is a clear and statistically significant trend. The mesore for heart rate rises steadily, peaking around week 34 at about 80 beats per minute. While the mesore for HRV, specifically RMSSD, declines hitting its lowest point around the same time, dropping from approximately 46 milliseconds down to 36 milliseconds. This reflects the immense cardiovascular and metabolic load of supporting a growing fetus. The body shifts into a higher gear, a more sympathetically driven state to manage the increased cardiac output. Most strikingly, the study captured objective evidence of elevated stress during the night. The 24 hour rhythm of HRV began to flatten and in some weeks completely invert. In a normal, healthy rhythm, HRV should be highest during the night as the body recovers. However, the researchers found that in week 27 the acrophase, the peak of the rhythm shifted to the afternoon and the minimum point of the entire 24 hour cycle occurred around 3am this provides a stark physiological fingerprint for the sleep disturbances, physical discomfort and anxiety that so many women experience in the third trimester. Their bodies are in a state of autonomic strain even during what should be the most restorative period. This research is vital because it establishes a normative pattern of these circadian changes. By understanding what is normal for a healthy, low risk pregnancy, clinicians may one day be able to use wearable technology to spot deviations from these patterns as early, non invasive warning signs of potential complications like preeclampsia or preterm birth. This theme of the body adapting to intense demands is also seen in the world of elite athletics. A study in Acta Psychologica by Zigging wang examined how 100 professional Chinese tennis players use wearable technology to manage their training over five months.
[00:10:40] The study was a randomized controlled trial with half the athletes forming an intervention group that used smartwatches, biosensors and GPS trackers to inform their training and recovery. The other half served as the control group. The results were not subtle. The group of athletes who used HRV data to guide their work and recovery showed remarkable improvements across the board.
[00:11:03] Physiologically, their resting heart rate dropped significantly from an average of 61 beats per minute in the control group to just 52 beats per minute. Their heart rate recovery after intense exercise was much faster at every measured interval. Their heart rate variability data showed a clear shift towards a more recovered parasympathetic dominant state.
[00:11:25] For example, their LF HF ratio, a marker of sympathovagal balance, was significantly healthier psychologically. They also thrived on the Perceived Stress Scale PSS 10. The intervention group scored significantly lower on experienced stress 9.82 versus 13.12 and considerably higher on stress coping ability 13.32 versus 10.56. The data allowed their coaches to make precise individualized adjustments.
[00:11:56] If an athlete's HRV dropped by more than 20% from their baseline, the training load was reduced to prevent overtraining.
[00:12:04] Sleep data was used to plan recovery days. GPS data was used to optimize on court movement, making it more efficient.
[00:12:11] This study demonstrates that in a high performance environment, HRV is not just a metric to track, it's a tool for a dynamic, responsive feedback loop between the athlete, the coach and and the training plan. It proves that whether the demand is creating a new life or competing at the highest level, HRV is an essential mirror reflecting our body's capacity and its non negotiable need for recovery. Before we move on, I want to thank our sponsor Optimal hrv. Whether you're tracking your own wellness journey or managing clients health, Optimal HRV provides the clear evidence based insights you need.
[00:12:49] Their latest update offers advanced tagging so you can see precisely how your habits and environment affect your numbers.
[00:12:57] Find it in your app store. Now let's explore the more complex nuances of stress and healing. While we often look for HRV to increase as a sign of recovery, new research shows the story can be more complicated, revealing deeper layers of autonomic regulation. A study in Chronobiology International led by Stefan Weinschink and his team examined patients undergoing therapy with local anesthetics for chronic pain. They monitored 24 hour HRV using a holder ECG and analyzed the data in 15 minute epics. As expected, they found that after the TLA treatment, patients showed classic signs of a parasympathetic shift. Their average heart rate and their stress index decreased while their rmssd, a key marker of vagal tone, increased. These effects were most pronounced the night after treatment, indicating deeper, more restorative sleep. But the most novel finding was a metric they introduced to look at the stability of the rhythm itself. They measured the standard deviation of change between consecutive 15 minute intervals. They found that in the TLA group this variability in change was significantly reduced, in other words, the moment to moment fluctuations of their HRV and became less erratic, less chaotic and more stable over the full 24 hours. They called this a smoothing effect. This suggests that a key component of this therapy's long lasting effect might be its ability not just to boost parasympathetic activity, but to restore a calm, predictable and stable rhythm to the entire autonomic nervous system. Healing in this context is a return to rhythmicity. In contrast, a decrease in HRV can sometimes accompany profoundly positive outcomes, a paradox that teaches us a crucial lesson about context. A groundbreaking study in Behavioral Sciences led by Cheryl A. Kraus Perillo and Erica Friedman looked at a unique intervention where female veterans with PTSD volunteered to train service dogs for other veterans. This randomized controlled trial measured a host of psychological and and biological markers. The program was a resounding success on many levels. Psychologically, the veterans reported significant decreases in PTSD symptoms, perceived stress, and anxiety. Biologically, they observed an impressive improvement in a marker of cellular aging, telomere length. Telomeres are the protective caps at the end of our chromosomes and they naturally shorten as we age or experience chronic stress.
[00:15:34] In the control group, telomeres got shorter over the eight weeks, but during group training the dog's telomeres actually lengthened, suggesting a reversal of stress induced cellular aging at a fundamental biological level. But here's the their heart rate variability, measured as RMSSD during the training sessions, actually decreased.
[00:15:55] This finding, which seems to contradict all the other positive results, is a masterclass in the importance of context.
[00:16:02] The authors provide a brilliant discussion of why this likely happened. The intervention was not a passive, relaxing activity. It was an active, ambulatory and cognitively engaging task. The veterans were learning new skills, problem solving and physically interacting with the dogs. This requires physiological arousal, a eustress or good stress.
[00:16:24] Furthermore, the study was conducted under revised COVID 19 protocols which which included outdoor activities and other potential low level stressors. The decreased HRV likely does not reflect a negative outcome, but rather the acute physiological engagement of a meaningful therapeutic activity. It reminds us that HRV is not a simple good or bad number. It's a dynamic signal that reflects our interaction with the world. And sometimes the path to profound psychological and cellular healing is is an active, engaging one that requires our bodies to be aroused and online.
[00:17:03] Finally, let's turn to the professional side of the field with a piece of news that marks a significant milestone for clinicians who use biofeedback in their practice. In a move that culminates over a decade of persistent advocacy, the American Medical Association's CPT Editorial Panel has officially accepted a new, more specific coding structure for biofeedback services, which will take effect in January 2027. To understand the significance, you have to know the history since 1998, all biofeedback practitioners have been using a single non specific CPT code99901, which was defined as biofeedback by any modality.
[00:17:47] This meant that a sophisticated multi channel session of HRV biofeedback or EEG neurofeedback was coded in the same way as a simple temperature training session. This generic code failed to capture the complexity, clinical sophistication, and diversity of modern biofeedback services.
[00:18:06] As a result, it has been a barrier to professional recognition and crucially, to appropriate reimbursement from insurance providers, and this victory is the result of a tireless multi year collaborative effort by organizations like the International Society for Neuroregulation and Research, the Association for Applied Psychophysiology and Biofeedback, and the Biofeedback Certification International Alliance.
[00:18:36] The provided timeline shows just how long this road has been, with initial applications submitted as far back as 2016, followed by years of meetings, revisions and resubmissions. The acceptance of the new code 90x03 and revised guidelines marks a significant step forward for the field. While the exact wording is still confidential, this new structure will allow for more precise documentation of services provided. This improved accuracy is the first and most critical step toward appropriately valuing and and reimbursing these services.
[00:19:11] It is a monumental win that acknowledges the evolution of biofeedback as a mature evidence based therapeutic discipline and will have a lasting, positive impact on both practitioners and the patients they serve.
[00:19:27] So after this deep dive into the latest science, what are the key takeaways for individuals? This week highlights the profound impact of simple and intentional habits on fundamentally changing your physiology. You have direct access to your nervous system from the breathing study. The actionable insight is specific to maximize your hrv, aim for six breaths per minute with an exhale twice as long as your inhale. From the chanting research, we learned that the simple act of humming or holding a single vowel sound at a slow, steady tempo can be a profound tool for relaxation. These are not just anecdotes, they are scientifically backed methods for shifting your body into a state of recovery and building long term resilience for clinicians. The key takeaway is to appreciate the nuances and context of hrv. It is a rich dynamic signal, not a simple score. The TLA study introduces the concept of autonomic smoothing as a potential new biomarker of restored stone.
[00:20:32] The Veterans study is a powerful reminder that a decrease in HRV during an active therapeutic session can be a sign of positive engagement rather than distress.
[00:20:42] And the new CPT code is a call to action.
[00:20:46] Stay informed through your professional organizations, prepare for this critical change and continue to advocate for the value of the sophisticated evidence based work you do.
[00:20:58] For researchers, these studies lay out a clear path forward.
[00:21:02] The Pregnancy study provides an invaluable baseline of circadian dynamics and maternal health, inviting urgent further work into how these rhythms are altered in high risk pregnancies and diverse populations. The Veterans study champions the need for mixed methods research that combines objective physiological data with subjective experience and rigorous contextual analysis to understand the full complex picture of an intervention's effects. The opportunities to build on this work are immense.
[00:21:33] Finally, for businesses and leaders, the tennis study offers a clear and compelling model for peak performance.
[00:21:39] Investing in your team's well being by providing tools to manage stress and optimize recovery is not a soft perk it is a core business strategy. When people have objective, personalized data about their own physiological capacity, they are empowered to work smarter, prevent burnout, and build the sustainable resilience needed to thrive under pressure. An organization that understands the rhythm of stress and recovery is an organization built for long term success.
[00:22:07] Thank you for joining us for this week's journey through the world of heart rate variability. I'm Matt. Until next time, take care, stay curious and keep listening to what your heart is telling you.
