Deep breathing: Exploring the benefits for health and performance

 

 

Breathing is an essential element of our existence and biological activities. In this review we are looking at the benefits of deep breathing during physical activities and its effect on cardiovascular system (CVS) (1). The rate of respiration and the volume of air inhale can be voluntary as well as involuntary and it is controlled by cranial (CN IX and CN X) and spinal (C3, 4 and 5) nerves 2. CN IX and CN X directly influence the heart and its blood vessels and in turn regulate respiration by gas exchange between haemoglobin of the red blood cells and endothelial cell of the alveoli (2). 

Therefore blood is a contributing factor that influences breathing as it supplies oxygen to the haemoglobin of the red blood cells. This could be the reason for higher value of red blood cells in people living at higher altitude, as there is less oxygen in the air (3). 

It has been shown that high altitude reduces the volume and function of mitochondria 4, indicating that O2 regulates mitochondrial function 5. Thus deep breathing exercise adjusts the partial pressures of O2(PO2) and CO2(PCO2) and regulates conditions such as hypertension and hypotension, and related cardiovascular diseases 6,7. These pathological conditions could be due to the dysfunction of mitochondria and resultant increase in production of Reactive Oxygen Species (ROS) (5).

 

Literature clearly appreciates the influence of the respiratory system in the modifications of cardiovascular system’s performance (8) due to the regular exercise (2). In Early 90’s, scientists exhibited the effect and benefits of meditation on enhancing positive mental power and subsequent reduction in anxiety and illicit drug consumption (9). 

Transcendental Meditation begins with synchronised deep breathing and is the first physiological modification for improving our health. Cardiovascular disease, stress and anxiety are interrelated and mindfulness treatment shows significant positive results (10). 

They are a direct relationship between deep breathing and efficient gas exchange, which is essential for the development of capillary networks in muscle and lungs. These alterations in angiogenesis, which is the development of the capillary network, are synchronised with the cardiovascular system (11). There is an immediate effect of deep breathing exercises on atelectasis and oxygenation of heart, lungs and muscles (12). 

Literature indicated that deep-breathing exercise reduces atelectasis and improves pulmonary function after coronary artery bypass surgery (13).

 

Deep Breathing is a relaxation technique where the focus is on deep inhalation, and holding the breath for a few seconds before exhalation (14). It is uncommonly used by few psychologists for patients suffering from psychological disorders (14). Research exhibits the effect of mindfulness and stress reduction such as for the treatment of anxiety disorder (15).

 

However, there is an interest in developing this technique for rehabilitation therapies 16, which has been used for centuries in Asia under different forms of practice such as Tai Chi, Qi Gong, Yoga and meditation (1, 14, 17-20). In deep breathing the main biological structures are diaphragm, pleural membrane and the alveoli; any modification in the exchange of gases and nutrients in the blood capillaries is conducted by the heart and lungs (21). 

 

Diffusion of the gases are not only directly related to the atmospheric and PO2 and carbon dioxide PCO2 but also to the surface area of the capillaries and alveoli (22). Therefore, deep breathing will not only enhance the efficiency of the lungs for the gas exchange2 but also positively regulate and sustain the function of the cardiovascular system (14, 16, 23). 

Deep breathing becomes a very important factor for physical activities in relation to cardiovascular changes such as increase in cardiac output which in turn increases the blood flow in capillaries and muscles (24). A warm up exercise not only increases the electro-stimuli of cardiovascular and cerebrovascular systems but also results in the flexibility of the joints along with an increase in the breathing rate (25). 

Similarly, deep breathing exercises with positive expiratory pressure at a higher rate improve oxygenation (26) and in conditions such as recovering from a trauma or during rehabilitation, the deep breathing exercises including Qi Gong, Tai Chi, Yoga and meditation improves physical and mental strength (17-20). 

Activities in Qi Gong or Tai Chi are usually combined with regular and synchronised breathing that allows a higher volume of O2 uptake (27) and all muscles in the body including heart muscles learn to contract and relax at a specific body position during these exercises (28). Similarly Yoga and meditation allow breathing improvement and reduce the sensitivity of chemo and cardio reflex due to a reduction of the breathing and heart rate (20). 

Deep breathing techniques increase the efficacy of pre oxygenation and hence rises the tidal volume (29,30). Similarly, a short term training of yoga for the patients of Chronic Obstructive Pulmonary Disease (COPD) induces favourable changes in the respiratory and cardiovascular system (1). 

 

 

Both Phrenic (C3 to C5) and Vagus (CN10) nerves not only interact with each other (31) but are associated with the direct control of respiratory and cardiovascular systems (32). Intercostal and diaphragm muscles are regulated via phrenic nerves (C3, C4 and C5), which is responsible for the decrease in partial pressure of the lungs by increasing their volume (2). Similarly, stretch receptors in the lungs allow vagal afferent pathways to moderate inflation (33) and modulate the heart rate, through autonomic nervous system (34). The vagus nerve, which originates from the nucleus ambiguous, is not only associated with the breathing process but also controls cardiac function (35). The pontine respiratory group, also known as pneumotaxic centre has an inhibitory effect on inhalation through the dorsal respiratory group (DRG), whereas, the apneustic center has a stimulating effect on DRG to promote inhalation (36). Similarly, ventral respiratory group (VRG) in conjunction with DRG regulate the respiratory rate (37), also controlled by glossopharyngeal nerve (cranial nerve IX) (38). This nerve is also involved in controlling the heart velocity (39), which is regulated by cardiac baroreflex, blood pressure and O2 concentration (40). The heart rate is regulated by sympathetic and parasympathetic neurons via afferent vagal pathway (41), similarly, the aortic and carotid baroreflexes are associated with breathing (42) and hypotension (43). 

 

 

                                                                                               (Refer to Figure 1 below.)                       

 

Figure 1: Showing the locations of pons and medulla in the brain stem with Pontine Respiratory Group (PRG) or Pneumotaxic centre, the Apneustic centre, Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG). The interaction between the sensory signals of the carotid and aortic baroreflex as well as the stretch receptor in the airways and the motor signals that activate the diaphragm and the intercostal muscle

are shown in this figure. Also the interaction between sympathetic and parasympathetic signals on lungs, heart and blood vessels is depicted. It displays sensory and motor nerves (left) and parasympathetic and sympathetic pathways (right). The Vagus nerve innervates the heart and blood vessels on the right side of the diagram. Phrenic nerve innervates lungs and diaphragm on the left side of the diagram. Tortora Gerard, inspired this diagram from Principles of anatomy and physiology the 12th edition published in 2008 (44).

 

 

All components of the respiratory system including nose, pharynx, larynx, trachea, bronchi, bronchioles and alveoli are not only important for speech, warming, humidifying and filtering the air and gas exchange (45) but are also involved in the regulation of the cardiovascular system during deep breathing exercise (46). During this exercise, the decrease in inhalation/exhalation ratio allows the heart to slow down, the diaphragm to relax and the lungs to inflate and deflate with greater efficiency (47). Consequently, deep breathing increases the pressure and the flow of air from inside to outside of lungs (2). This difference in pressure allows an increase in gas exchange between the lungs and the capillaries, which is detected by the baroreceptors present in the aortic and carotid arteries (40) and lungs (48). 

 

The chemoreceptors present at the medulla and pons detect the O2 / CO2 ratio and pH (49) and regulate the breathing and heart rate through the vagus nerve (50). Inhibition or stimulation of the vagus nerve is directly related with the modification of blood pressure, heart rate and breathing rate50 and deep breathing exercises bring these values back to normal (51). Both inspiratory and expiratory centres are located in medulla and pons (52).

Stimulation of the inspiratory centres that are located at the dorsal part of the medulla (53) and pons, results in the expansion of the intercostal muscles, diaphragm and the lungs, decreasing the internal pressure and allowing the air to go inside the body. On the other hand, the expiratory centres which are present at the ventral side of the medulla (54), and pneumotaxic centres that are located at the upper parts of the pons are responsible for controlling the rate and pattern of breathing, and are regulated by the apneustic centres (55). The apneustic centre enhances inspiration and the stimulation of the pneumotaxic centre and the stretch receptors of the lungs resulting in exhalation and diaphragm relaxation (36). The receptors on the pons and medulla that are sensitive to pH fluctuation activates the locus coeruleus or nucleus ambiguous that increases or decreases heart rate and breathing to bring the pH back to normal (56). The vagus innervation from the enteric nervous system also has a significant role in the regulation of cardiovascular and respiratory systems and is influenced by the receptors on the carotid arteries and brain stem (57). The vagus nerve which contains both motor and sensory inputs spread throughout the brachial and visceral areas (58) inducing parasympathetic control. This mechanism has a direct effect on blood pressure, heart and muscles (Fig 1). On the other hand, the sympathetic response has the opposite effect (59) and arterial pressure can act as a biomarker (60). 

 

In addition, different positions of the body can affect the flow of blood and therefore modify the gas exchange (2). The positions during standing or sitting changes the respiratory parameters, for example in the sitting position the vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in the first second (FEV1) and the peak expiratory flow (PEF) are reduced (61).

 

 

 

Though all the cell organelles are affected by the gas exchange, the mitochondria plays an essential role in the conversion of oxygen into Adenosine Triphosphate (ATP) (62). Mitochondrial dysfunction is directly related to hypertension, cardiovascular and circulatory disorders such as stroke, diabetes, Alzheimer’s disease and Parkinson disease (63-65). It is well known that physical exercise has a positive effect on the cardiovascular system and on cognition (66) and deep breathing alleviate stress anxiety and depression (67).

Similarly, social threats such as public speech and participating in sports events can alter the cardiovascular system (68) and deep breathing can result in improved performance (47). In a study, it was shown that exercise 3 to 5 times per week at moderate intensity reduces the blood pressure (69). The study showed significant decrease in systolic blood pressure of both hypertensive and normotensive subjects; whereas, only diastolic blood pressure was found to decrease in hypertensive subjects (7, 69). 

 

Literature shows that during exercise the increased blood pressure delivers more nutrients and oxygen to the body and removes waste from the tissues through the circulatory system (2, 70). On the other hand, it was revealed that the risk of stroke increases during intense exercise when systolic blood pressure rises more than 19.7 mmHg per minute (70). For that reason, it is fundamental to learn breathing techniques, such as Pranayama, when practising sport activities any form of mindfulness (71). The principle of pranayama breathing is based on a longer exhalation than inhalation (14) which decreases the rate of gas exchange. The literature indicates that pranayama breathing also decreases heart rate, O2 consumption, and blood pressure (14,34,72). It has also been revealed that the pranayama breathing technique allows parasympathetic dominance (14,73), hence enhancing a relaxation state. Therefore the electro activity diminished allowing muscle fibers to relax longer before the next action potential (72). This electrical shift was measured using Respiratory Sinus Arrhythmia (RSA), Electrocardiogram (ECG) and Electroencephalogram (EEG) (74). 

 

One of the major benefits of deep breathing techniques is to increase the gas exchange process, due to the development of the capillary network by the release of cytokines for angiogenesis (75). Angiogenesis takes place by different processes such as intussusception, which is the blood vessel that splits and grows, or the sprouting of blood vessels which is more for proliferation and development (11). During muscle contraction more blood vessels are required for appropriate gas exchange (76). In a study, it was reported that nitric oxide is the leading compound to generate vessel growth during exercise (76). The intussusceptive angiogenesis results in the enlargement of vessels, which in turn increases blood volume and gas exchange (76,77). There is no evidence to date that angiogenesis is occurring in the lungs during exercise. However, in lungs angiogenesis may occur due to the friction caused by the constant blood flow in vessels, releasing nitric oxide from their endothelium (5). 

 

To conclude, The vagus nerves, originating from the nucleus ambiguous, have both sympathetic and parasympathetic effect on the circulatory system (78,79). A sympathetic response increases the heart rate, cardiac output; contractility and arterial blood pressure; whereas the parasympathetic response has the opposite effect (2, 44). Deep breathing increases the amount of gas exchange (80) and allows nutrients and O2 to increase the amount of ATP production in the mitochondria and rebalance the pH of the body due to the change in cardiac output (81). 

 

This mechanism gives energy to the cell and produces waste material (2). Evidence is required to confirm the process of angiogenesis in the lungs. Breathing affects multiple metabolic processes such as the conversion of inactive angiotensin I from the liver into angiotensin II which affect the cardiovascular system (82, 83). Respiration also plays an important role in the breakdown of substances such as noradrenaline, serotonin and acetylcholine (45, 84, 85) which are regulators of moods and behaviours. This review develops possible research and theoretical knowledge on the effect of activities such as Tai Chi, Qi Gong, Yoga and meditation on respiratory and cardiovascular systems (1,17,18,46). And more importantly, it opens the discussion on possible non-invasive therapies where patients are also prescribed activities for a better rehabilitation (86, 87). 

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