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Obligate nasal breathing describes a physiological instinct to breathe through the nose (or other forms of external nasal passages, depending on the species) as opposed to breathing through the mouth.
The term may be misleading, as it implies that the organism has no choice but to breathe through its nose; however, it is also used to describe cases where effective breathing through the mouth is possible but not preferred. [1] Alternatively, the term has been defined by some as the ability to breathe through the nose while swallowing. While this ability is a common trait of obligate nasal breathers, the definition does not require that nasal breathing is necessary for the animal. Even in obligate nasal breathers such as horses, rabbits, and rodents, there is a potential patent path for air to travel from the mouth to the lungs which can be used for endotracheal intubation. It has been suggested that obligate nasal breathing is an adaptation especially useful in prey species, as it allows an animal to feed while preserving their ability to detect predators by scent. [2]
Horses are considered obligate nasal breathers. The respiratory system of the horse prevents horses from breathing orally. The epiglottis rests above the soft palate while the animal is not swallowing, forming an airtight seal. Oral breathing can only occur with significant anatomical abnormalities or pathological conditions. For example, denervation of the pharyngeal branch of the vagus nerve results in the dorsal displacement of the soft palate (DDSP), [3] and it has been suggested that this leads to a clinical syndrome which may include oral breathing. [4] However, significant respiratory dysfunction including airway obstruction is observed with DDSP, and the animal cannot function normally in this state.
Rabbits and rodents are also obligate nasal breathers. Like horses, the normal anatomical position of the epiglottis causes it to be engaged over the caudal rim of the soft palate, sealing the oral pharynx from the lower airways. [5] Air entering the mouth will not fully make it to the lungs. [6] Even so, rabbits with advanced upper airway disease will attempt to breathe through their mouths.
Many other mammals, such as adult dogs and humans, have the ability to breathe indefinitely through either the oral or nasal cavity. Cats are preferential nasal breathers. [7] [8]
According to Jason Turowski, MD of the Cleveland Clinic, "We are designed to breathe through our noses from birth — it’s the way humans have evolved." [9] This is because it is the job of the nose to filter out all of the particles that enter the body, as well as to humidify the air we breathe and warm it to body temperature. [10] [11] In addition, nasal breathing produces nitric oxide within the body while mouth breathing does not. [12] [10] [13] [14] Mouth breathing also leads to dry mouth, throat infections, a reduced sense of taste, [11] and other chronic conditions. [13] [15] [16] [17] Nasal breathing is a research interest in orthodontics (and the related field of myofunctional therapy) [18] and for biological anthropologists. [19]
Human infants are commonly described as obligate nasal breathers as they breathe through their nose rather than the mouth. [20] Most infants, however, are able to breathe through their mouth if their nose is blocked. [20] There are however certain infants with conditions such as choanal atresia in which deaths have resulted from nasal obstruction. [20] In these cases, there are cyclical periods of cyanosis. The infant initially attempts to breathe through the nose, and is unable to; hypercapnia occurs, and many babies instinctively begin to cry. While crying, oral ventilation occurs and cyanosis subsides. There is variation in the length of time until a baby begins oral breathing, and some will never cease attempts at nasal breathing. It has also been suggested that infants may not be able to sustain oral breathing for significant lengths of time, because of the weakness of the muscles required to seal the nasal airway and open the oral airway. [20] One study employing monitored anatomical occlusion concluded that human infants are not obligate nasal breathers: [21] its sample of nineteen infants, ranging in age from 1 day to 7.5 months, reliably transitioned from nose to mouth breathing after nasal occlusion, providing evidence that infants possess the physiological capability to mouth breathe.
Some authors argue that nasal breathing offers a greater advantage over mouth breathing during exercise. [14]
George Catlin was a 19th-century American painter, author, and traveler, who specialized in portraits of Native Americans in the Old West. Travelling to the American West five times during the 1830s, he wrote about the life of the Plains Indians, and painted portraits that depicted them. [22] He was also the author of several books, including The Breath of Life [23] (later retitled as Shut Your Mouth and Save Your Life) in 1862. [24] [25] It was based on his experiences traveling through the West, where he observed a consistent lifestyle habit among the Native American communities he encountered: a preference for nose breathing over mouth breathing. He also observed that they had perfectly straight teeth. [26] He repeatedly heard that this was because they believed that mouth breathing made an individual weak and caused disease, while nasal breathing made the body strong and prevented disease. [26] He also observed that mothers repeatedly closed the mouth of their infants while they were sleeping, to instill nasal breathing as a habit. [27]
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. [28] [29] [30] They tell their students that the "nose is for breathing, the mouth is for eating." [29] [31] [32] [28]
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.
Snoring is the vibration of respiratory structures and the resulting sound due to obstructed air movement during breathing while sleeping. The sound may be soft or loud and unpleasant. Snoring during sleep may be a sign, or first alarm, of obstructive sleep apnea (OSA). Research suggests that snoring is one of the factors of sleep deprivation.
The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
The epiglottis is a leaf-shaped flap in the throat that prevents food and water from entering the trachea and the lungs. It stays open during breathing, allowing air into the larynx. During swallowing, it closes to prevent aspiration of food into the lungs, forcing the swallowed liquids or food to go along the esophagus toward the stomach instead. It is thus the valve that diverts passage to either the trachea or the esophagus.
Inhalation happens when air or other gases enter the lungs.
Exhalation 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.
Respiratory arrest is a serious medical condition caused by apnea or respiratory dysfunction severe enough that it will not sustain the body. Prolonged apnea refers to a patient who has stopped breathing for a long period of time. If the heart muscle contraction is intact, the condition is known as respiratory arrest. An abrupt stop of pulmonary gas exchange lasting for more than five minutes may permanently damage vital organs, especially the brain. Lack of oxygen to the brain causes loss of consciousness. Brain injury is likely if respiratory arrest goes untreated for more than three minutes, and death is almost certain if more than five minutes.
Choanal atresia is a congenital disorder where the back of the nasal passage (choana) is blocked, usually by abnormal bony or soft tissue (membranous) due to failed hole development of the nasal fossae during prenatal development. It causes persistent rhinorrhea, and with bilateral choanal atresia, an obstructed airway that can cause cyanosis and hypoxia.
Nasal congestion is the partial or complete blockage of nasal passages, leading to impaired nasal breathing, usually due to membranes lining the nose becoming swollen from inflammation of blood vessels.
Mouth breathing, medically known as chronic oral ventilation, is long-term breathing through the mouth. It often is caused by an obstruction to breathing through the nose, the innate breathing organ in the human body. However, by the early 20th century, the term "mouth-breather" had developed a pejorative slang meaning connoting a stupid person.
Oral myology is the field of study that involves the evaluation and treatment of the oral and facial musculature, including the muscles of the tongue, lips, cheeks, and jaw.
Continuous positive airway pressure (CPAP) is a form of positive airway pressure (PAP) ventilation in which a constant level of pressure greater than atmospheric pressure is continuously applied to the upper respiratory tract of a person. The application of positive pressure may be intended to prevent upper airway collapse, as occurs in obstructive sleep apnea, or to reduce the work of breathing in conditions such as acute decompensated heart failure. CPAP therapy is highly effective for managing obstructive sleep apnea. Compliance and acceptance of use of CPAP therapy can be a limiting factor, with 8% of people stopping use after the first night and 50% within the first year.
A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the nose for respiration. Where the nostrils pass through the nasal cavity they widen, are known as nasal fossae, and contain turbinates and olfactory mucosa. The nasal cavity also connects to the paranasal sinuses. From the nasal cavity, the nostrils continue into the pharynx, a switch track valve connecting the respiratory and digestive systems.
The respiratory system of the horse is the biological system by which a horse circulates air for the purpose of gaseous exchange.
Breathing is the rhythmical process of moving air into (inhalation) and out of (exhalation) the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.
The pharynx is the part of the throat behind the mouth and nasal cavity, and above the esophagus and trachea. It is found in vertebrates and invertebrates, though its structure varies across species. The pharynx carries food to the esophagus and air to the larynx. The flap of cartilage called the epiglottis stops food from entering the larynx.
Orofacial myofunctional disorders (OMD) are muscle disorders of the face, mouth, lips, or jaw due to chronic mouth breathing.
In human anatomy, the mouth is the first portion of the alimentary canal that receives food and produces saliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth.
An elongated soft palate is a congenital hereditary disorder that negatively affect dogs and cats' breathing and eating. A soft palate is considered elongated when it extends past the top of the epiglottis and/or past the middle of the tonsillar crypts. The soft palate is made up of muscle and connective tissue located in the posterior portion on the roof of the mouth. The soft palate creates a barrier between the mouth and nose. This continuation between the cavities makes it possible to chew and breathe at the same time. The soft palate only blocks the nasal cavity while swallowing. At rest the soft palate should only stretch caudally from the hard palate to the tip of the epiglottis leaving an opening between the nasal and oral cavities. When the soft palate is elongated, it partially blocks the throat thereby creating breathing and feeding-related issues. The elongation and other accompanying symptoms occur in breeds characterized with “smooshed faces” such as pugs, bulldogs, and Persian cats. This condition is a congenital, meaning it is present when the animal is born. The “smooshed” characteristics is the result of a genetic mutation. The animal’s genetic code causes the bones in their skull to grow to a smaller size. Because the bones are smaller, muscles and other tissues that surround the bones of the skull are out of proportion. These animals are often referred to as brachycephalic, derived from the Greek words for “short” and “head”. An elongated soft palate is a symptom of Brachycephalic Obstructive Airway Syndrome (BOAS) and is common in brachycephalic dog breeds and has been reported in brachycephalic cat breeds as well. Some of the other BOAS related symptoms include stenotic nares, everted laryngeal saccules, and laryngeal collapse.
Breath: The New Science of a Lost Art is a 2020 popular science book by science journalist James Nestor. The book provides a historical, scientific and personal examination of breathing, with a specific interest in contrasting the differences between mouth breathing and nasal breathing. The book became an international bestseller, selling over two million copies worldwide.
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