Exhalation

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Diagram showing expiration Expiration diagram.svg
Diagram showing expiration

Exhalation (or expiration) is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles generate abdominal and thoracic pressure, which forces air out of the lungs.

Contents

Exhaled air is 4% carbon dioxide, [1] a waste product of cellular respiration during the production of energy, which is stored as ATP. Exhalation has a complementary relationship to inhalation which together make up the respiratory cycle of a breath.

Exhalation and gas exchange

The main reason for exhalation is to rid the body of carbon dioxide, which is the waste product of gas exchange in humans. Air is brought into the lungs through inhalation. Diffusion in the alveoli allows for the exchange of O2 into the pulmonary capillaries and the removal of CO2 and other gases from the pulmonary capillaries to be exhaled. In order for the lungs to expel air the diaphragm relaxes, which pushes up on the lungs. The air then flows through the trachea then through the larynx and pharynx to the nasal cavity and oral cavity where it is expelled out of the body. [2] Exhalation takes longer than inhalation and it is believed to facilitate better exchange of gases. Parts of the nervous system help to regulate respiration in humans. The exhaled air is not just carbon dioxide; it contains a mixture of other gases. Human breath contains volatile organic compounds (VOCs). These compounds consist of methanol, isoprene, acetone, ethanol and other alcohols. The exhaled mixture also contains ketones, water and other hydrocarbons. [3] [4]

It is during exhalation that the olfaction contribution to flavor occurs in contrast to that of ordinary smell which occurs during the inhalation phase. [5]

Spirometry

Spirometry is the measure of lung function. The total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), and vital capacity (VC) are all values that can be tested using this method. Spirometry is used to help detect, but not diagnose, respiratory issues like COPD, and asthma. It is a simple and cost effective screening method. [6] Further evaluation of a person's respiratory function can be done by assessing the minute ventilation, forced vital capacity (FVC), and forced expiratory volume (FEV). These values differ in men and women because men tend to be larger than women.

TLC is the maximum amount of air in the lungs after maximum inhalation. In men the average TLC is 6000 ml, and in women it is 4200 ml. FRC is the amount of air left in the lungs after normal exhalation. Men leave about 2400 ml on average while women retain around 1800 ml. RV is the amount of air left in the lungs after a forced exhalation. The average RV in men is 1200 ml and women 1100 ml. VC is the maximum amount of air that can be exhaled after a maximum inhalation. Men tend to average 4800 ml and women 3100 ml.[ citation needed ]

Smokers, and those with Asthma and COPD, have reduced airflow ability. People with asthma and COPD show decreases in exhaled air due to inflammation of the airways. This inflammation causes narrowing of the airways which allows less air to be exhaled. Numerous things cause inflammation; some examples are cigarette smoke and environmental interactions such as allergies, weather, and exercise. In smokers the inability to exhale fully is due to the loss of elasticity in the lungs. Smoke in the lungs causes them to harden and become less elastic, which prevents the lungs from expanding or shrinking as they normally would.[ citation needed ]

Dead space can be determined by two types of factors which are anatomical and physiological. Some physiological factors are having non-perfuse but ventilated alveoli, such as a pulmonary embolism or smoking, excessive ventilation of the alveoli, brought on in relation to perfusion, in people with chronic obstructive lung disease, and "shunt dead space," which is a mistake between the left to right lung that moves the higher CO2 concentrations in the venous blood into the arterial side. [7] The anatomical factors are the size of the airway, the valves, and tubing of the respiratory system. [7] Physiological dead space of the lungs can affect the amount of dead space as well with factors including smoking, and diseases. Dead space is a key factor for the lungs to work because of the differences in pressures, but it can also hinder the person.[ citation needed ]

One of the reasons we can breathe is because of the elasticity of the lungs. The internal surface of the lungs on average in a non-emphysemic person is normally 63m2 and can hold about 5lts of air volume. [8] Both lungs together have the same amount of surface area as half of a tennis court. Disease such as, emphysema, tuberculosis, can reduce the amount of surface area and elasticity of the lungs. Another big factor in the elasticity of the lungs is smoking because of the residue left behind in the lungs from the smoking. The elasticity of the lungs can be trained to expand further.[ citation needed ]

Brain involvement

Brain control of exhalation can be broken down into voluntary control and involuntary control. During voluntary exhalation, air is held in the lungs and released at a fixed rate. Examples of voluntary expiration include: singing, speaking, exercising, playing an instrument, and voluntary hyperpnea. Involuntary breathing includes metabolic and behavioral breathing.[ citation needed ]

Voluntary expiration

The neurological pathway of voluntary exhalation is complex and not fully understood. However, a few basics are known. The motor cortex within the cerebral cortex of the brain is known to control voluntary respiration because the motor cortex controls voluntary muscle movement. [9] This is referred to as the corticospinal pathway or ascending respiratory pathway. [9] [10] The pathway of the electrical signal starts in the motor cortex, goes to the spinal cord, and then to the respiratory muscles. The spinal neurons connect directly to the respiratory muscles. Initiation of voluntary contraction and relaxation of the internal and external internal costals has been shown to take place in the superior portion of the primary motor cortex. [9] Posterior to the location of thoracic control (within the superior portion of the primary motor cortex) is the center for diaphragm control. [9] Studies indicate that there are numerous other sites within the brain that may be associated with voluntary expiration. The inferior portion of the primary motor cortex may be involved, specifically, in controlled exhalation. [9] Activity has also been seen within the supplementary motor area and the premotor cortex during voluntary respiration. This is most likely due to the focus and mental preparation of the voluntary muscular movement. [9]

Voluntary expiration is essential for many types of activities. Phonic respiration (speech generation) is a type of controlled expiration that is used every day. Speech generation is completely dependent on expiration, this can be seen by trying to talk while inhaling. [11] Using airflow from the lungs, one can control the duration, amplitude, and pitch. [12] While the air is expelled it flows through the glottis causing vibrations, which produces sound. Depending on the glottis movement the pitch of the voice changes and the intensity of the air through the glottis change the volume of the sound produced by the glottis.[ citation needed ]

Involuntary expiration

Involuntary respiration is controlled by respiratory centers within the medulla oblongata and pons. The medullary respiratory center can be subdivided into anterior and posterior portions. They are called the ventral and dorsal respiratory groups respectively. The pontine respiratory group consists of two parts: the pneumotaxic center and the apneustic center. [10] All four of these centers are located in the brainstem and work together to control involuntary respiration. In our case, the ventral respiratory group (VRG) controls involuntary exhalation.[ citation needed ]

The neurological pathway for involuntary respiration is called the bulbospinal pathway. It is also referred to as the descending respiratory pathway. [10] "The pathway descends along the spinal ventralateral column. The descending tract for autonomic inspiration is located laterally, and the tract for autonomic expiration is located ventrally." [13] Autonomic Inspiration is controlled by the pontine respiratory center and both medullary respiratory centers. In our case, the VRG controls autonomic exhalation. Signals from the VRG are sent along the spinal cord to several nerves. These nerves include the intercostals, phrenic, and abdominals. [10] These nerves lead to the specific muscles they control. The bulbospinal pathway descending from the VRG allows the respiratory centers to control muscle relaxation, which leads to exhalation.[ citation needed ]

Yawning

Yawning is considered a non-respiratory gas movement. A non-respiratory gas movement is another process that moves air in and out of the lungs that do not include breathing. Yawning is a reflex that tends to disrupt the normal breathing rhythm and is believed to be contagious as well. [14] The reason why we yawn is unknown. A common belief is that yawns are a way to regulate the body's levels of O2 and CO2, but studies done in a controlled environment with different levels of O2 and CO2 have disproved that hypothesis. Although there is not a concrete explanation as to why we yawn, others think people exhale as a cooling mechanism for our brains. Studies on animals have supported this idea and it is possible humans could be linked to it as well. [15] What is known is that yawning does ventilate all the alveoli in the lungs.[ citation needed ]

Receptors

Several receptor groups in the body regulate metabolic breathing. These receptors signal the respiratory center to initiate inhalation or exhalation. Peripheral chemoreceptors are located in the aorta and carotid arteries. They respond to changing blood levels of oxygen, carbon dioxide, and H+ by signaling the pons and medulla. [10] Irritant and stretch receptors in the lungs can directly cause exhalation. Both sense foreign particles and promote spontaneous coughing. They are also known as mechanoreceptors because they recognize physical changes not chemical changes. [10] Central chemoreceptors in the medulla also recognize chemical variations in H+. Specifically, they monitor pH change within the medullary interstitial fluid and cerebral spinal fluid. [10]

Yoga

Yogis such as B. K. S. Iyengar advocate both inhaling and exhaling through the nose in the practice of yoga, rather than inhaling through the nose and exhaling through the mouth. [16] [17] [18] They tell their students that the "nose is for breathing, the mouth is for eating." [17] [19] [20] [16]

See also

Related Research Articles

<span class="mw-page-title-main">Respiratory system</span> Biological system in animals and plants for gas exchange

The respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies greatly, depending on the size of the organism, the environment in which it lives and its evolutionary history. In land animals, the respiratory surface is internalized as linings of the lungs. Gas exchange in the lungs occurs in millions of small air sacs; in mammals and reptiles, these are called alveoli, and in birds, they are known as atria. These microscopic air sacs have a very rich blood supply, thus bringing the air into close contact with the blood. These air sacs communicate with the external environment via a system of airways, or hollow tubes, of which the largest is the trachea, which branches in the middle of the chest into the two main bronchi. These enter the lungs where they branch into progressively narrower secondary and tertiary bronchi that branch into numerous smaller tubes, the bronchioles. In birds, the bronchioles are termed parabronchi. It is the bronchioles, or parabronchi that generally open into the microscopic alveoli in mammals and atria in birds. Air has to be pumped from the environment into the alveoli or atria by the process of breathing which involves the muscles of respiration.

Diffusing capacity of the lung (DL) measures the transfer of gas from air in the lung, to the red blood cells in lung blood vessels. It is part of a comprehensive series of pulmonary function tests to determine the overall ability of the lung to transport gas into and out of the blood. DL, especially DLCO, is reduced in certain diseases of the lung and heart. DLCO measurement has been standardized according to a position paper by a task force of the European Respiratory and American Thoracic Societies.

Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. It means that not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, wasting that part of the inhalation which remains in the conducting airways where no gas exchange can occur.

<span class="mw-page-title-main">Respiratory tract</span> Organs involved in transmission of air to and from the point where gases diffuse into tissue

The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.

<span class="mw-page-title-main">Aquatic respiration</span> Process whereby an aquatic animal obtains oxygen from water

Aquatic respiration is the process whereby an aquatic organism exchanges respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excreting carbon dioxide and some other metabolic waste products into the water.

<span class="mw-page-title-main">Gas exchange</span> Process by which gases diffuse through a biological membrane

Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a biological membrane that forms the boundary between an organism and its extracellular environment.

<span class="mw-page-title-main">Inhalation</span> Flow of the respiratory current into an organism

Inhalation is the process of drawing air or other gases into the respiratory tract, primarily for the purpose of bringing oxygen into the body. It is a fundamental physiological function in humans and many other organisms, essential for sustaining life. Inhalation is the first phase of breathing, allowing the exchange of oxygen and carbon dioxide between the body and the environment, vital for the body's metabolic processes. This article delves into the mechanics of inhalation, its significance in various contexts, and its potential impact on health.

In physiology, respiration is the movement of oxygen from the outside environment to the cells within tissues, and the removal of carbon dioxide in the opposite direction to the surrounding environment.

<span class="mw-page-title-main">Hypercapnia</span> Abnormally high tissue carbon dioxide levels

Hypercapnia (from the Greek hyper = "above" or "too much" and kapnos = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs. Carbon dioxide may accumulate in any condition that causes hypoventilation, a reduction of alveolar ventilation (the clearance of air from the small sacs of the lung where gas exchange takes place) as well as resulting from inhalation of CO2. Inability of the lungs to clear carbon dioxide, or inhalation of elevated levels of CO2, leads to respiratory acidosis. Eventually the body compensates for the raised acidity by retaining alkali in the kidneys, a process known as "metabolic compensation".

The control of ventilation is the physiological mechanisms involved in the control of breathing, which is the movement of air into and out of the lungs. Ventilation facilitates respiration. Respiration refers to the utilization of oxygen and balancing of carbon dioxide by the body as a whole, or by individual cells in cellular respiration.

<span class="mw-page-title-main">Spirometry</span> Pulmonary function test

Spirometry is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD. It is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time.

The cough reflex occurs when stimulation of cough receptors in the respiratory tract by dust or other foreign particles produces a cough, which causes rapidly moving air which usually remove the foreign material before it reaches the lungs. This typically clears particles from the bronchi and trachea, the tubes that feed air to lung tissue from the nose and mouth. The larynx and carina are especially sensitive. Cough receptors in the surface cells (epithelium) of the respiratory tract are also sensitive to chemicals. Terminal bronchioles and even the alveoli are sensitive to chemicals such as sulfur dioxide gas or chlorine gas.

Ujjayi is a breathing technique employed in a variety of yoga practices. In the context of yoga, it is sometimes called "the ocean breath." Unlike some other forms of pranayama, the ujjayi breath is typically done in association with asana practice in some styles of yoga as exercise, such as Ashtanga Vinyasa Yoga.

<span class="mw-page-title-main">Incentive spirometer</span> Handheld device to improve lung function

An incentive spirometer is a handheld medical device used to help patients improve the functioning of their lungs. By training patients to take slow and deep breaths, this simplified spirometer facilitates lung expansion and strengthening. Patients inhale through a mouthpiece, which causes a piston inside the device to rise. This visual feedback helps them monitor their inspiratory effort. Incentive spirometers are commonly used after surgery or certain illnesses to prevent pulmonary complications.

<span class="mw-page-title-main">Muscles of respiration</span> Muscles involved in breathing

The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. The elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.

<span class="mw-page-title-main">Respiratory system of the horse</span> Biological system by which a horse circulates air for the purpose of gaseous exchange

The respiratory system of the horse is the biological system by which a horse circulates air for the purpose of gaseous exchange.

<span class="mw-page-title-main">Respiratory center</span> Brain region controlling respiration

The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal respiratory group, and the ventral respiratory group. In the pons, the pontine respiratory group includes two areas known as the pneumotaxic center and the apneustic center.

<span class="mw-page-title-main">Breathing</span> Process of moving air in and out of the lungs

Breathing is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.

<span class="mw-page-title-main">Intrapleural pressure</span> Refers to the pressure within the pleural cavity

In physiology, intrapleural pressure refers to the pressure within the pleural cavity. Normally, the pressure within the pleural cavity is slightly less than the atmospheric pressure, which is known as negative pressure. When the pleural cavity is damaged or ruptured and the intrapleural pressure becomes greater than the atmospheric pressure, pneumothorax may ensue.

Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.

References

  1. ↑ Carroll, Gregory T.; Kirschman, David L.; Mammana, Angela (2022). "Increased CO2 levels in the operating room correlate with the number of healthcare workers present: an imperative for intentional crowd control". Patient Safety in Surgery. 16 (1): 35. doi: 10.1186/s13037-022-00343-8 . ISSN   1754-9493. PMC   9672642 . PMID   36397098.
  2. ↑ Sahin-Yilmaz, A.; Naclerio, R. M. (2011). "Anatomy and Physiology of the Upper Airway". Proceedings of the American Thoracic Society. 8 (1): 31–9. doi:10.1513/pats.201007-050RN. PMID   21364219.
  3. ↑ Fenske, Jill D.; Paulson, Suzanne E. (1999). "Human Breath Emissions of VOCs". Journal of the Air & Waste Management Association. 49 (5): 594–8. doi: 10.1080/10473289.1999.10463831 . PMID   10352577.
  4. ↑ Weisel, C. P. (2010). "Benzene exposure: An overview of monitoring methods and their findings". Chemico-Biological Interactions. 184 (1–2): 58–66. doi:10.1016/j.cbi.2009.12.030. PMC   4009073 . PMID   20056112.
  5. ↑ Masaoka, Yuri; Satoh, Hironori; Akai, Lena; Homma, Ikuo (2010). "Expiration: The moment we experience retronasal olfaction in flavor". Neuroscience Letters. 473 (2): 92–6. doi:10.1016/j.neulet.2010.02.024. PMID   20171264. S2CID   2671577.
  6. ↑ Kivastik, Jana; Kingisepp, Peet-Henn (2001). "Spirometric reference values in Estonian schoolchildren". Clinical Physiology. 21 (4): 490–7. doi: 10.1046/j.1365-2281.2001.00352.x . PMID   11442581.
  7. 1 2 Hedenstierna, G; Sandhagen, B (2006). "Assessing dead space. A meaningful variable?". Minerva Anestesiologica. 72 (6): 521–8. PMID   16682925.
  8. ↑ Thurlbeck, W. M. (1967). "Internal surface area and other measurements in emphysema". Thorax. 22 (6): 483–96. doi:10.1136/thx.22.6.483. PMC   471691 . PMID   5624577.
  9. 1 2 3 4 5 6 McKay, L. C.; Evans, K. C.; Frackowiak, R. S. J.; Corfield, D. R. (2003). "Neural correlates of voluntary breathing in humans". Journal of Applied Physiology. 95 (3): 1170–8. doi:10.1152/japplphysiol.00641.2002. PMID   12754178. S2CID   15122094.
  10. 1 2 3 4 5 6 7 Caruana-Montaldo, Brendan (2000). "The Control of Breathing in Clinical Practice". Chest. 117 (1): 205–225. CiteSeerX   10.1.1.491.4605 . doi:10.1378/chest.117.1.205. PMID   10631221.
  11. ↑ Newman, D. "The Physiology of Speech Production" (PDF). Retrieved 31 March 2012.
  12. ↑ Heman-Ackah, Yolanda D. (2005). "Physiology of voice production: considerations for the vocal performer". Journal of Singing. 62 (2): 173–6.
  13. ↑ Homma, Ikuo; Masaoka, Yuri (2008). "Breathing rhythms and emotions". Experimental Physiology. 93 (9): 1011–21. doi: 10.1113/expphysiol.2008.042424 . PMID   18487316. S2CID   2686895.
  14. ↑ Sarnecki, John (2008). "Content and Contagion in Yawning". Philosophical Psychology. 21 (6): 721–37. doi:10.1080/09515080802513292. S2CID   144972289.
  15. ↑ Corey, Timothy P.; Shoup-Knox, Melanie L.; Gordis, Elana B.; Gallup, Gordon G. (2012). "Changes in Physiology before, during, and after Yawning". Frontiers in Evolutionary Neuroscience. 3: 7. doi: 10.3389/fnevo.2011.00007 . PMC   3251816 . PMID   22319494.
  16. 1 2 Yoga Journal Editors (2017-04-12). "Q&A: Is Mouth Breathing OK in Yoga?". Yoga Journal . Retrieved 2020-06-26.{{cite web}}: |last= has generic name (help)
  17. 1 2 Payne, Larry. "Yogic Breathing: Tips for Breathing through Your Nose (Most of the Time)". Yoga For Dummies, 3rd Edition . Retrieved 2020-06-26.
  18. ↑ Himalayan Institute Core Faculty, Himalayan Institute Core Faculty (2017-07-13). "Yogic Breathing: A Study Guide". Himalayan Institute of Yoga Science and Philosophy . Retrieved 2020-06-26.
  19. ↑ Krucoff, Carol (2013). Yoga Sparks. New Harbinger Publications. ISBN   9781608827022 . Retrieved 2020-05-31.
  20. ↑ Jurek, Scott (2012). Eat and Run. Houghton Mifflin. ISBN   978-0547569659 . Retrieved 2020-05-31.

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