Respiratory Entrainment: Biomarkers and Patterns

Introduction

Previously, we discussed the predictive processing, a valuable tool for comprehending the hierarchy interactions between the brain and body. Within this model, the nervous system constructs predictive models based on past experiences, enabling it to anticipate the impact of environmental or bodily changes on the organism. Continuously, these predictions are compared to incoming sensory information, leading to the identification of prediction errors. Subsequently, the organism takes corrective actions to minimize these errors and update its internal models, ultimately striving for Allostasis – a state of adaptive adjustments in physiological parameters to maintain equilibrium in a dynamic environment.

The respiratory system plays a vital role in the complex processes of interoception, orchestrated by a complex network of brain regions continuously governing breathing patterns and rate in response to the body’s demands. This sophisticated regulatory mechanism entails vigilant monitoring of the respiratory system, influencing a multitude of physiological processes, including heart rate, blood pressure, and emotional states. Remarkably, breath can be easily brought into conscious awareness and controlled deliberately. Employing the concept of active inference, manipulating our breathing rhythm can profoundly impact our interoceptive predictions and shape our perception of bodily states. In this manner, controlled breathing emerges as a readily accessible and expeditious strategy to minimize prediction errors and recalibrate interoceptive predictions, actively engaging both attention and action. [1]

Deliberate control of our breath allows us to regulate our emotions, thoughts, and bodily functions. Through specific breathing patterns, we can send signals to the brain that have the potential to profoundly impact our emotional and cognitive experiences [2]. This study explores the potential of controlled breathing as a flexible and useful technique for improving a range of conditions, and it bases its claim on a variety of experiences. We will explore the role of respiratory biomarkers, investigate the impact of brain oscillations and interoceptive entrainment, and examine how controlled breathing can be harnessed as an intervention for specific health conditions.

Respiratory biomarkers

The respiratory system offers a promising approach for assessing and intervening in interoception. Our conscious control over this domain and its potential to influence other interoceptive variables, such as cardiac arousal is a powerful potential for interoceptive modulations. This ability opens the door to respiratory-brain coupling, which emerges as a unique domain for respiratory training. In this process, individuals actively monitor and regulate their breathing patterns, to optimize hemostasis in response to the inconstant environment [3].

To develop effective assessment methodologies, identifying and utilizing reliable biomarkers is crucial. These biomarkers, including frequency, breathing sound, respiratory exchange ratio (RER), pattern, tidal volume (VT), PO2, and PCO2, provide valuable data that can elucidate interoceptive responses and deepen our understanding of how respiratory health influences overall interoception and internal bodily states. A comprehensive understanding of these biomarkers and new ones can facilitate enhanced interoceptive interventions, resulting in improved respiratory health and overall well-being [4, 5].

Brain oscillations and Interoceptive Entrainment

Brain oscillations, characterized by rhythmic fluctuations in neural activity, provide an interesting insight into the functioning of the human brain and its complex connections with bodily processes. These oscillations are classified into distinct frequency bands, each linked to specific cognitive and physiological functions. These rhythmic oscillations can be modulated through entrainment techniques [6].

Entrainment is a process of stimulation-based synchronization of interoception and the environment through sympathetic and parasympathetic pathways that can be induced by various stimuli such as controlled respiration [3]. Respiratory-modulated brain oscillations (RMBOs) are believed to exert influence on the brain by directly coupling breathing to neural oscillation rhythms. This dynamic interplay between respiration and brain activity holds promising implications for cognitive, emotional, sensory and motor processes [2, 6-8].

During intentional, non-automatic respiration entrainment, such as deep breathing, there is a specific focus on bidirectional cortico-motor pathways that are not active during automatic breathing. This could potentially establish an additional connection between the motor cortex and respiratory motoneurons, effectively creating an extra ‘communication channel’. This circumstance suggests that sensory-motor cortices would simultaneously control respiratory muscles, resulting in separate ‘channels’ of synchronization. This scenario might lead to an overall decrease in beta coherence within motor areas while engaged in deep breathing [9].

Another example of entrainment done by Karavaev, A.S., and their team revealed that Infra-slow rhythms cover a wide range of brain and bodily rhythms, which also include the rhythm of respiration. This gradual oscillatory pattern is postulated to create a connection between visceral and neural rhythms, resulting in the formation of a coherent temporal hierarchy [10].

Respiration as an Intervention for Health Conditions

Respiration has been recognized as a valuable intervention for diverse health conditions due to its profound effects on the body and mind. Numerous studies have demonstrated the significant impact of different respiration patterns on it. Various form of volitional breathing changes,  such as reducing respiratory rate, engaging in deep breathing exercises, employing rest and hold respiration practices, diaphragmatic breathing and emphasizing nostril breathing have been shown to influence and benefit overall health. The evidence underscores the importance of incorporating mindful and controlled breathing practices into healthcare and wellness routines to promote better physical and mental health outcomes. Real-time feedback, including haptic vibrations, visual cues, and sound output, is utilized in different personalized tasks and games that can be applied in virtual reality [11]. These methods provide effective interventions for guiding individuals to achieve desired breathing patterns and further enhance their physiological and emotional well-being. In the following paragraphs, we discuss the evidence supporting the notion that different respiratory rhythms can exert diverse effects and play distinct roles in our health conditions.

Russell M.E., et al. [12] highlight the significance of including rest periods within breathing exercises. The study compared two groups to explore the effects of different breathing cycles on high-frequency heart rate variability (HF-HRV) and other heart rate variability indices. The primary focus was on the importance of the rest period following exhalation. Participants were guided in regulating their breathing rates using visual cues displayed on a computer screen, representing expanding, contracting, or still ovals. One group followed the 4-2-4 breathing cycle (inhale-exhale-rest), while the other adhered to the 5-5 breathing cycle. The findings indicated that the breathing cycle incorporating a rest period yielded more significant enhancements in HF-HRV and RMSSD (root mean square of successive differences). An increase in HF-HRV suggests heightened activity of the parasympathetic nervous system, which promotes relaxation and stress reduction.

Deep and slow breathing (DSB) stands out as an effective intervention for anxiety and stress management, with notable impacts on vagal tone, a crucial regulator of the autonomic nervous system and cognitive-emotional processes. Participants engage in DSB through a guided video, aligning their breath with the movement of a water droplet in circular patterns, inhaling as it ascends and exhaling as it descends. The exercise initiates with equal inhalation and exhalation durations (4 seconds each), gradually extending the exhalation phase to 6 seconds. This technique has a direct influence on the autonomic nervous system, particularly in balancing the sympathetic and parasympathetic branches. Vagal outflow is suppressed during inhalation, indicating that the vagus nerve in our bodies is less active during inhalation. An increase in sympathetic dominance and a raised heart rate are brought on by this decrease in vagal activity. However, as we exhale, our body’s vagus nerve activity rises once more, which means that exhalation restores vagal activity. This increase in vagal activity causes a drop in heart rate during exhale. The heart rate variability (HRV), a dependable indicator of autonomic function, coincides with respiration and mirrors parasympathetic activity, particularly high-frequency (HF) HRV, as shown by Magnon, V., F. Dutheil, and G.T. Vallet [13]. Tavoian, D. and D.H. Craighead have illustrated the importance of deep breathing exercises as interventions that enhance both physiological and psychological health. This approach encompasses diverse non-resisted, paced breathing strategies, such as yogic, diaphragmatic, and abdominal breathing. [14].

Paredes, P.E., et al. revealed in their study [15] that slow breathing is identified as an effective method to regulate autonomic arousal. The study explores haptic and voice-based breathing guidance systems as interventions in cars to reduce stress while driving safely. The Haptic Guidance System uses actuators on the driver’s seat to deliver vibration patterns, guiding inhale, exhale, and hold breath phases. The Voice Guidance System provides spoken instructions for breathing. Both methods aim to promote stress reduction and improve mental health during car journeys.

Maric, V., D. Ramanathan, and J. Mishra [16] have highlighted the substantial role of Nostril breathing, also known as nasal breathing, holds a significant role in controlling our breath and has a profound impact on brain activity and cognitive functions. Breathing in through the nose triggers a synchronization of neural activity in the olfactory system, the part of the brain responsible for processing odors. This synchronization not only affects our perception of scents but also extends its influence to other crucial brain regions like the amygdala and hippocampus. These synchronized neural patterns are termed “phase-locked neural dynamics.” Interestingly, nasal breathing maintains and supports these synchronized patterns, while breathing through the mouth diminishes them.

Breath control strategies that emphasize nostril breathing go beyond simple breathing exercises. It has the ability to improve both our respiratory health and our awareness of interior physiological states (interoceptive awareness). Moreover, because of the close relationship between the mind and body, it might even help with better emotional management. In essence, by concentrating on nostril breathing, people can access a technique that not only facilitates better breathing but also enhances emotional stability and cognitive function by synchronizing neuronal activity across critical brain regions.

Ma, X., et al., [17] present compelling evidence for the positive effects of diaphragmatic breathing on sustained attention, mood, and cortisol levels. In this study, 40 participants were divided into two groups, with the breathing intervention group undergoing 20 sessions over an 8-week period. Guided by a real-time feedback device, they maintained a respiratory rate of 4 breaths per minute. The results demonstrated a noteworthy decrease in negative mood following the intervention, as compared to their initial mood levels. Furthermore, the practice of diaphragmatic breathing led to a significant enhancement in sustained attention among the intervention group, surpassing their baseline performance. Notably, diaphragmatic breathing exerted a significant impact on cortisol levels, resulting in a marked decrease after the training sessions. These findings underscore the potential of diaphragmatic breathing as a valuable mind-body technique for augmenting mental function and well-being. The implications extend to the broader realm of promoting overall health even in individuals without existing health conditions.

In addition to diverse breathing patterns, techniques like Respiratory Muscle Training (RMT) have been developed to enhance the strength and endurance of respiratory muscles, particularly the inspiratory and expiratory muscles. RMT encompasses two key components: Inspiratory Muscle Training (IMT) and Expiratory Muscle Training (EMT). IMT focuses on improving respiratory pressure generation, addressing muscle weakness, enhancing exercise capacity, and elevating overall quality of life. Achieving optimal outcomes necessitates personalized training protocols that consider variables such as frequency, duration, and specific exercise modalities. IMT’s efficacy spans rehabilitation, sports, and occupational contexts, offering benefits to varied respiratory needs. Conversely, EMT targets expiratory muscles, resulting in enhanced abilities related to coughing, speaking, and swallowing. Notably, EMT’s benefits extend to maximal inspiratory pressure, engaging inspiratory muscles in expiration as well.[18]

Conclusion

The future of respiratory research offers the scientific community an exciting new direction to investigate. Viewing respiration as a form of interoceptive awareness, wherein the relationship between breathing, internal states and cognitive dimension is recognized. The identification of new biomarkers within the realm of respiration opens uncharted territories, offering windows into an individual’s inner physiological landscape. Anchored in the active inference framework, a personalized model emerges, where respiratory patterns and rhythms can be fine-tuned to an individual’s distinct needs. This model harness the power of personalized respiration interventions and propels us towards precision medicine, where each individual’s unique respiratory profile becomes a functional of proactive healthcare. Furthering the exploration, capturing long-term respiratory behavior and comparing it over time offers a dynamic perspective, capable of revealing subtle shifts in health conditions.

References

1. Boyadzhieva, A. and E. Kayhan, Keeping the breath in mind: Respiration, neural oscillations, and the free energy principle. Frontiers in Neuroscience, 2021: p. 742.
2. Heck, D.H., et al., Recent insights into respiratory modulation of brain activity offer new perspectives on cognition and emotion. Biological psychology, 2022. 170: p. 108316.
3. Schoeller, F., et al., Interoceptive technologies for clinical neuroscience. 2022, PsyArXiv.
4. Innocenti, L., et al., How to Investigate the Effect of Music on Breathing during Exercise: Methodology and Tools. Sensors (Basel), 2022. 22(6).
5. Czub, M. and M. Kowal, Respiration Entrainment in Virtual Reality by Using a Breathing Avatar. Cyberpsychol Behav Soc Netw, 2019. 22(7): p. 494-499.
6. Brændholt, M., et al., Breathing in waves: Understanding respiratory-brain coupling as a gradient of predictive oscillations. Neuroscience & Biobehavioral Reviews, 2023. 152: p. 105262.
7. Kluger, D.S. and J. Gross, Respiration modulates oscillatory neural network activity at rest. PLoS biology, 2021. 19(11): p. e3001457.
8. Kluger, D.S., et al., Respiration aligns perception with neural excitability. Elife, 2021. 10.
9. Kluger, D.S. and J. Gross, Depth and phase of respiration modulate cortico-muscular communication. Neuroimage, 2020. 222: p. 117272.
10. Karavaev, A.S., et al., Synchronization of infra-slow oscillations of brain potentials with respiration. Chaos, 2018. 28(8): p. 081102.
11. Mitsea, E., A. Drigas, and C. Skianis, Breathing, attention & consciousness in sync: The role of breathing training, metacognition & virtual reality. Technium Soc. Sci. J., 2022. 29: p. 79.
12. Russell, M.E., et al., Inclusion of a rest period in diaphragmatic breathing increases high frequency heart rate variability: Implications for behavioral therapy. Psychophysiology, 2017. 54(3): p. 358-365.
13. Magnon, V., F. Dutheil, and G.T. Vallet, Benefits from one session of deep and slow breathing on vagal tone and anxiety in young and older adults. Scientific Reports, 2021. 11(1): p. 19267.
14. Tavoian, D. and D.H. Craighead, Deep breathing exercise at work: Potential applications and impact. Frontiers in Physiology, 2023. 14: p. 23.
15. Paredes, P.E., et al., Just breathe: In-car interventions for guided slow breathing. Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies, 2018. 2(1): p. 1-23.
16. Maric, V., D. Ramanathan, and J. Mishra, Respiratory regulation & interactions with neuro-cognitive circuitry. Neuroscience & Biobehavioral Reviews, 2020. 112: p. 95-106.
17. Ma, X., et al., The effect of diaphragmatic breathing on attention, negative affect and stress in healthy adults. Frontiers in psychology, 2017. 8: p. 234806.
18. Shei, R.-J., et al., Time to move beyond a “one-size fits all” approach to inspiratory muscle training. Frontiers in physiology, 2022. 12: p. 2452.