In cases of acidosis, feedback will increase ventilation to remove more carbon dioxide to reduce the hydrogen ion concentration. Conversely, vomiting removes hydrogen ions from the body as the stomach contents are acidic , which will cause decreased ventilation to correct alkalosis.
Chemoreceptor feedback also adjusts for oxygen levels to prevent hypoxia, though only the peripheral chemoreceptors sense oxygen levels.
In cases where oxygen intake is too low, feedback increases ventilation to increase oxygen intake. A more detailed example would be that if a person breathes through a long tube such as a snorkeling mask and has increased amounts of dead space, feedback will increase ventilation.
Respiratory feedback : The chemoreceptors are the sensors for blood pH, the medulla and pons form the integrating center, and the respiratory muscles are the effector. Evaluate the effect of proprioception the sense of the relative position of the body and effort being employed in movement on breathing. The lungs are a highly elastic organ capable of expanding to a much larger volume during inflation. While the volume of the lungs is proportional to the pressure of the pleural cavity as it expands and contracts during breathing, there is a risk of over-inflation of the lungs if inspiration becomes too deep for too long.
Physiological mechanisms exist to prevent over-inflation of the lungs. Cardiac and respiratory branches of the vagus nerve : The vagus nerve is the neural pathway for stretch receptor regulation of breathing. The Hering—Breuer reflex also called the inflation reflex is triggered to prevent over-inflation of the lungs. There are many stretch receptors in the lungs, particularly within the pleura and the smooth muscles of the bronchi and bronchioles, that activate when the lungs have inflated to their ideal maximum point.
These stretch receptors are mechanoreceptors, which are a type of sensory receptor that specifically detects mechanical pressure, distortion, and stretch, and are found in many parts of the human body, especially the lungs, stomach, and skin.
They do not detect fine-touch information like most sensory receptors in the human body, but they do create a feeling of tension or fullness when activated, especially in the lungs or stomach. When the lungs are inflated to their maximum volume during inspiration, the pulmonary stretch receptors send an action potential signal to the medulla and pons in the brain through the vagus nerve.
This is called the inflation reflex. As inspiration stops, expiration begins and the lung begins to deflate. As the lungs deflate the stretch receptors are deactivated and compression receptors called proprioreceptors may be activated so the inhibitory signals stop and inhalation can begin again—this is called the deflation reflex.
Early physiologists believed this reflex played a major role in establishing the rate and depth of breathing in humans. While this may be true for most animals, it is not the case for most adult humans at rest. However, the reflex may determine the breathing rate and depth in newborns and in adult humans when tidal volume is more than 1 L, such as when exercising.
Additionally, people with emphysema have an impaired Hering—Bauer reflex due to a loss of pulmonary stretch receptors from the destruction of lung tissue, so their lungs can over-inflate as well as collapse, which contributes to shortness of breath.
As the Hering—Bauer reflex uses the vagus nerve as its neural pathway, it also has a few cardiovascular system effects because the vagus nerve also innervates the heart. During stretch receptor activation, the inhibitory signal that travels through the vagus nerve is also sent to the sinus-atrial node of the heart. Its stimulation causes a short-term increase in resting heart rate, which is called tachycardia.
The heart rate returns to normal during expiration when the stretch receptors are deactivated. When this process is cyclical it is called a sinus arrhythmia, which is a generally normal physiological phenomenon in which there is short-term tachycardia during inspiration. Sinus arryhthmias do not occur in everyone, and are more common in youth. The sensitivity of the sinus-atrial node to the inflation reflex is lost over time, so sinus arryhthmias are less common in older people.
Privacy Policy. Skip to main content. Respiratory System. Search for:. Respiration Control. Neural Mechanisms Respiratory Center The medulla and the pons are involved in the regulation of the ventilatory pattern of respiration. Learning Objectives Describe the neural mechanism of the respiratory center in respiration control. Key Takeaways Key Points The ventral respiratory group controls voluntary forced exhalation and acts to increase the force of inspiration.
The dorsal respiratory group nucleus tractus solitarius controls mostly inspiratory movements and their timing. Ventilatory rate minute volume is tightly controlled and determined primarily by blood levels of carbon dioxide as determined by metabolic rate. Chemoreceptors can detect changes in blood pH that require changes in involuntary respiration to correct. The apneustic stimulating and pnuemotaxic limiting centers of the pons work together to control rate of breathing.
The medulla sends signals to the muscles that initiate inspiration and expiration and controls nonrespiratory air movement reflexes, like coughing and sneezing.
Key Terms respiratory control centers : The medulla which sends signals to the muscles involved in breathing, and the pons which controls the rate of breathing. The Medulla The medulla oblongata is the primary respiratory control center. Pranayama is primarily related to yoga practice, but it is also part of several meditative practices Jerath et al.
A growing number of scientific studies in the field of Contemplative Neuroscience Thompson, are reporting accurate descriptions of mental and somatic effects elicited by meditation.
The large number of published studies has led to the need of reviews and meta-analyses with the aim of eliminating possible confounding factors, stemming from the heterogeneity of the investigated meditative techniques, differences among experimental designs across studies, and from the overuse of subjective assessments in meditative effects' evaluation.
The purpose of these scientific efforts is threefold: i building a shared and standardized taxonomy of meditation techniques Lutz et al. Heuristically, it is commonly acknowledged that breathing techniques are profoundly intermingled with cognitive aspects of meditation, and in eastern culture, their role for achieving altered states of consciousness is undisputed.
Nevertheless, western science has paid little attention to the investigation of the effects of pure breathing control on neural correlates of consciousness, and on specific mental functions. Returning on meditative practices, the main issue in unveiling the basic mechanisms underlying their effects is to disentangle those related to breathing control from those associated with non-respiratory cognitive components such as focused attention and mental imagery.
To our best knowledge, only ten dedicated reviews tackle the effects of Pranayama, without succeeding in the identification of a common psychophysiological model Srinivasan, ; Brown and Gerbarg, a ; Singh et al. Some authors have even attempted at modeling the effects of Pranayama Brown and Gerbarg, b ; Jerath et al.
Other authors, focusing their attention on the benefits of Pranayama in different pathological conditions e. In western culture, breathing techniques were developed independently from any religious or spiritual belief or purpose, and nowadays are mainly used for therapeutic aims e.
Paced breathing has been associated with relaxation and well-being Jerath et al. To our best knowledge, both for Pranayama and paced breathing, no systematic review focusing either on their basic mechanisms or on their effects in healthy subjects has ever been published but see Lehrer and Gevirtz, ; Mather and Thayer, Only studies involving healthy humans, avoiding thus possible confounding effects due to pathological conditions, and dealing with the voluntary modulation of breathing Pranayama and paced breathing were included.
It is in fact crucial to distinguish between slow breathing techniques, and other techniques that simply direct attention to the act of breathing e. Studies based on self-reports instruments alone were not included, as their reliability is severely weakened by the absence of objective measures, a major and common problem when dealing with contemplative sciences Schmalzl et al. PRISMA comprises a item checklist that has to be completed in order to improve quality of systematic reviews Moher et al.
The check-list is reported in Supplementary Table 1. The initial search was conducted in March , while the final search was carried out in April We searched both for extended names and their acronyms. The complete list of search keywords is reported in Appendix 1. Studies identified from the literature search were included if:. We considered eligible for the inclusion all studies assessing physiological parameters during slow breathing techniques state effect , immediately after state effect , and after long-term interventions trait effect.
The research of the studies, according to databases, terms and quantity of returned studies, is presented in Table 2. A complete flowchart of the study selection process is presented in Figure 1. Two independent reviewers AZ. Titles and abstracts were screened, and 2, studies were removed either because they were duplicated or of no interest for the systematic review. The remaining full-text papers were checked for the eligibility criteria. At the end of the analysis, 15 articles meeting the eligibility criteria were retained and included in the review.
Seven studies Stark et al. Edmonds et al. No significant difference between the two conditions was observed when considering LF power. Lin et al. All paced breathing sessions were associated with an increased subjective perception of relaxation as compared to the control condition; at variance, no difference in subjectively perceived anxiety was found between paced breathing and control sessions.
Van Diest et al. Stark et al. However, no difference in emotional scores of the Self-Assessment Manikin Scale Bradley and Lang, and in a single-item mental effort measure was found among these different paced breathing frequencies. Kharya et al. Lehrer et al. It is important to highlight that high HRV total power was maintained during a post-session resting-state period, during which respiratory frequency returned to normal.
Moreover, indicating a cumulative effect of Biofeedback training, HRV was significantly higher at the end of each session the last 5 min than at the beginning the first 5 min. Subjects after the biofeedback session reported significantly lower adverse effects, as measured by the Side Effects of Relaxation Scale Kotsen et al. Gross et al. However, authors found increased habitual use of adaptive, somatic-based, emotional regulation strategies after HRV Biofeedback interventions as measured with the Somatic Strategies and Somatic Suppression scale, Gross et al.
Gruzelier et al. There was no difference in the other psychological variables assessed i. Sakakibara et al. They found that HF power increased during sleep only in the Biofeedback group, whereas it did not change in the autogenic training and in control groups.
Moreover, HF power was higher during both nights in the HRV Biofeedback group, compared to autogenic training and control groups. However, authors found no differences in state anxiety measured before bedtime with the State-Trait Anxiety Inventory, Spielberger et al.
Siepmann et al. Fumoto et al. At a subjective level, participants reported improved vigor-activity in the Profile of Mood States McNair et al. Yu et al. Critchley et al. Activated cortical areas were: 1 motor, 2 supplementary motor, and 3 parietal cortices. Across all participants, a trend for increased alertness measured with a single-item visual analog scale was found during 5. This is the only study included in this review that attempted a correlation between brain activity and HRV: authors found a positive correlation between HRV and activations of the medulla and hippocampus, and a negative one with activity in the anterior insula, dorsomedial prefrontal cortex and left occipital cortex.
A possible explanation of these negative findings could stem from the low statistical power of the study only ten subjects were enrolled. The vast majority of records checked were focused on the contribution of slow breathing techniques on the clinical outcomes of chronic and acute pathologies, and therefore were excluded from the review. Many studies investigated the effects of interventions characterized by a combination of breathing techniques, postures and meditation, while others investigated the effects of emotional stimulation while performing a specific breathing technique.
As paced breathing was either intermingled with other kind of interventions or used during active stimulation of the subjects e.
Finally, several other studies lacked a rigorous description of the experimental set-up and of the applied methodologies, impeding thus the study replicability, and were consequently excluded from the review for reasons for the exclusions of all studies, see Figure 1. As regards the included studies, 10 adopted within-subject designs, and 5 adopted pre-post designs.
No studies adopted longitudinal or randomized controlled designs. Risk of bias and methodological quality of the included studies were assessed independently by the first two authors AZ and AP , using two different tools. Disagreements between the reviewers were resolved by discussion with a third reviewer AG. As regards pre-post designs, a Quality Assessment Tool adapted from several published systematic reviews see Cummings et al.
Both assessment tools revealed that the quality of the included studies ranged from sufficient to good. Regarding within-subjects designs, the main concerns were related to the absence of any blinding condition which intrinsically depends on the slow breathing techniques interventions , lack of description of participants demographic data, and missing access to raw databases and to protocol designs.
Regarding pre-post designs, the main concerns relate to sampling methods, sample sizes non-statistically justified, and lacking of randomization in group assignment.
Check-lists are presented for within-subjects and for pre-post designs in Supplementary Tables 2 , 3 , respectively. We have herein reviewed the literature on the psychophysiological effects of both eastern and western slow breathing techniques with the aim of identifying the physiological mediators at the basis of their demonstrated psychological and behavioral beneficial effects. We must underline that the paucity of collected evidence is mostly ascribable to the heterogeneity of the investigated techniques and of the participants selection criteria.
Consequently, in some cases, results stemming from different studies lead to contradictory conclusions see Table 4. Slow breathing techniques related both to slow paced breathing and to HRV Biofeedback seem to interact with the cardio-respiratory system by increasing HRV and RSA, suggesting thus a strong involvement of the parasympathetic nervous system Reyes del Paso et al. At variance, when considering HF and LF power, a heterogeneous and contradictory set of outcomes was found, mainly depending on the breathing frequency: Park and Park , and Stark et al.
Moreover, Sakakibara et al. When considering LF power, a group of studies highlighted increases in the slow breathing techniques-control comparison Stark et al. However, it is important to stress the fact that abovementioned studies did not measure HRV features immediately after the session, but during the slow breathing techniques with the notable exception of Lehrer et al.
However, the study from Lehrer et al. When considering the central nervous system, slow breathing techniques were often paralleled by increases of alpha and decreases of theta power Fumoto et al.
Measured with by Near-Infrared Spectroscopy, Yu et al. Moreover, in the only fMRI study Critchley et al. The authors found also that insular activation anti-correlated with HRV power. Starting from the results reported in this systematic review, the construction of a psychophysiological model of slow breathing techniques can be attempted.
In general, slow breathing techniques enhance interactions between autonomic, cerebral and psychological flexibility, linking parasympathetic and CNS activities related to both emotional control and well-being. Slow breathing techniques seem to promote a predominance of the parasympathetic autonomic system with respect to the sympathetic one, mediated by the vagal activity Streeter et al. The vagus nerve in turn, transmits interoceptive information from gastrointestinal, cardiovascular and pulmonary systems to the central nervous system through the Nucleus of the Tractus Solitarius.
The enhancement of vagal tone within the cardiovascular system is reflected by the increase of both HRV power and RSA. It is worth underlining that HRV modulation is highly dependent on the respiration frequency, increasing along with the slowing of breath Song and Lehrer, RSA on its side is consistently considered a robust index of parasympathetic activity Reyes del Paso et al.
There is growing evidence suggesting an active role of RSA in regulating homeostasis and improving oxygen uptake Hayano et al. In this framework, we found consistent proofs linking the slowing of breath rhythm to increases in RSA Van Diest et al. Jerath et al. He hypothesized an involvement of lungs stretch receptors i. The stretching of lung tissue in fact produces inhibitory signals, as the fibroblasts activity fosters a slow adaptation of stretch receptors and hyperpolarization currents Matsumoto et al.
However, as already mentioned, the interpretation of these results is not so straightforward since very low respiratory frequencies overlap the frequency interval of LF power 0. Subsequently, the shift toward a parasympathetic predominance is conveyed to the central nervous system via the Nucleus of the Tractus Solitarius, which sends its projection to the thalamus and limbic system via the parabrachial nucleus Streeter et al.
In this framework, Critchley et al. At the same time, slow breathing techniques are necessarily driven by brain top-down processes stemming from the voluntary shift of attention toward breath monitoring aiming at the active control of breathing rhythm.
The nature of these top-down processes could be inferred from the model developed by Gard et al. Gard's model hypothesizes that yoga may involve top-down components such as attention, working memory, and executive monitoring.
Brain networks associated with these functions are the central executive network, including both the dorsolateral prefrontal and the posterior parietal cortices Goulden et al.
Taylor et al. This network includes the anterior cingulate, the prefrontal and the insular cortices, areas involved in physiological self-awareness and cognitive modulation. This hypothesis is partially supported by Critchley et al. At the EEG level, slow breathing techniques are associated with reductions in theta and increases in alpha activity. The increase of alpha power is in line with the results described in a recent systematic review dealing with the neurophysiology of mindfulness Lomas et al.
We hypothesized that the progressive sensory deafferentation occurring during slow breathing techniques induces an inward directed attentional shift allowing both alpha increase and higher DMN synchronization. The thalamus, strongly engaged in a burst mode activity in the alpha range, impedes the expression of other pacemakers such those underlying theta rhythms. According to this hypothesis, the deepening of meditative state allows the emergence of theta rhythm which owing to its off-periods, plays a fundamental role in altering the state of consciousness.
Unexpectedly, the majority of slow breathing techniques studies did not directly investigate slow breathing techniques effects on the state of consciousness, even if its modification is considered one of the mail goals of Pranayama Iyengar, To our best knowledge, only one study analyzed breath-related alterations of the state of consciousness, but it adopted a fast breathing technique Holotropic Breathwork, Rock et al. We speculate that the subjective experience of an altered state of consciousness depends on the rearrangement of cortical functional connectivity, in particular within the DMN, a set of cortical structures whose activity was found to be associated with altered states of consciousness induced by meditation Brewer et al.
Another neurophysiological framework explaining the link between slow breathing techniques and consciousness is related to the fine-tuning of thalamic and cortical activities exerted by the olfactory bulb.
The neural patterns of this structure are modulated by the mechanical stimulation of the olfactory epithelium during nostril breathing Fontanini and Bower, ; Piarulli et al. Even if not specified in all studies see Table 3 , it is plausible that the majority of slow breathing techniques are performed via nasal respiration Jerath et al. Moreover, as historically noted Ramacharaka, , nostril breathing is a fundamental aspect of every form of meditation.
Studies on the animal model, as well as on specific Pranayama techniques, suggest that nasal breathing is able to modulate both the autonomic system and brain activity through receptors located in the superior nasal meatus, which are sensitive both to mechanical and chemical stimuli Wrobel and Leopold, ; Buonviso et al.
More recently, other studies demonstrated the presence of significant oscillations at the same frequency of the respiratory rate in a number of brain cortical and subcortical areas, which disappeared after tracheotomy, and were restored, independently from thoracic respiration, by the rhythmic delivery of air-puffs into the nasal cavity.
These areas included the olfactory bulb, the piriform cortex, the somatosensory cortex, the prefrontal cortex, and the hippocampus Fontanini et al. The modulating effect of nostril breathing on the activity of the piriform cortex, amygdala and hippocampus has been unambiguously demonstrated in humans Zelano et al.
Based on these evidence, a recently published study from our laboratory Piarulli et al. Future studies should be aimed at verifying this hypothesis, possibly comparing brain activity during slow respiration when performing nasal breathing with that detected during mouth breathing.
A general consideration emerging from this systematic review is the lack in scientific literature of a standardized methodology, both when considering the experimental design and the description of breathing techniques. The initial aim of this work was to conduct a meta-analysis of the existent literature, but due to the heterogeneity of the selected experimental groups, of the interventions, and of the outcomes, a statistical pooling was infeasible.
This issue was already highlighted in Gotink et al. Moreover, in order to increase methodological quality in breathing technique's research, we propose a checklist their precise description in scientific literature.
Nash and Newberg have recently stated the importance of breath in every meditation technique. In their attempt to create a taxonomy for meditation, breath is the eighth point that must be described for a scientific definition of a meditation technique.
I Specifying whether breath is consciously attended or not. II Specify if other techniques are associated with breathing e. III Specify the mean breathing frequency and, if present, any significant breathing frequency variations. IV Specify whether during respiration the air passes through the mouth or through the nostrils both, left, right, alternate , or through both mouth and nostrils.
V Specify the presence and the duration of inspiration if any and expiration pauses if any. VII Specify whether the breath is thoracic or abdominal. VIII Specify if applicable what type of metronome is used. IX Specify if applicable the air pressure during the inspiratory phases.
We found evidence of increased psychophysiological flexibility linking parasympathetic activity, CNS activities related to emotional control and psychological well-being in healthy subjects during slow breathing techniques.
This evidence is unfortunately weakened by the lack of clear methodological descriptions that often characterizes slow breathing techniques literature. Further studies are thus needed to unambiguously assess these links. Only few authors have attempted to systematically describe the psychophysiological effects of slow breathing techniques, and a fewer number have attempted to relate them to meditation practice.
Finally, more research is needed to disentangle the pure contribution of breathing in a variety of meditation techniques. As stated by Nash and Newberg , different methods e. We herein proposed a brief check-list that could help to improve research on this topic.
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