Portal:Respiratory physiology
Portal maintenance status: (October 2018)
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Introduction
In physiology, respiration is the movement of oxygen from the outside environment to the cells within tissues, and the transport of carbon dioxide in the opposite direction.
The physiological definition of respiration differs from the biochemical definition, which refers to cellular respiration, a metabolic process by which an organism obtains energy (in the form of ATP) by oxidizing nutrients and releasing waste products. Although physiologic respiration is necessary to sustain cellular respiration and thus life in animals, the processes are distinct: cellular respiration takes place in individual cells of the organism, while physiologic respiration concerns the diffusion and transport of metabolites between the organism and the external environment.
Selected general articles
- Exhalation (or expiration) is the flow of the breath out of an organism. In humans 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. Read more... - Tidal volume (symbol VT or TV) is the lung volume representing the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied. In a healthy, young human adult, tidal volume is approximately 500 mL per inspiration or 7 mL/kg of body mass. Read more...
- The oxygen–hemoglobin dissociation curve, also called the oxyhemoglobin dissociation curve or oxygen dissociation curve (ODC), is a curve that plots the proportion of hemoglobin in its saturated (oxygen-laden) form on the vertical axis against the prevailing oxygen tension on the horizontal axis. This curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (SO2) and partial pressure of oxygen in the blood (PO2), and is determined by what is called "hemoglobin affinity for oxygen"; that is, how readily hemoglobin acquires and releases oxygen molecules into the fluid that surrounds it. Read more...
- Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface in the vicinity of the exit of the 9th and 10th cranial nerves, are sensitive to the pH of their environment.
These act to detect the changes in pH of nearby cerebrospinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues. An increase in carbon dioxide causes tension of the arteries, often resulting from decreased CO2 output (hypercapnia), indirectly causes the blood to become more acidic; the cerebrospinal fluid pH is closely comparable to plasma, as carbon dioxide easily diffuses across the blood–brain barrier. Read more...
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 centre and the apneustic centre.
The respiratory centre is responsible for generating and maintaining the rhythm of respiration, and also of adjusting this in homeostatic response to physiological changes. The respiratory center receives input from chemoreceptors, mechanoreceptors, the cerebral cortex, and the hypothalamus in order to regulate the rate and depth of breathing. Input is stimulated by altered levels of oxygen, carbon dioxide, and pH, by hormonal changes relating to stress, and anxiety from the hypothalamus, and also by signals from the cerebral cortex to give a conscious control of respiration. Read more...
Medulla oblongata purple, part of the brain stem colored
The medulla oblongata (or medulla) is located in the brainstem, anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions ranging from vomiting to sneezing. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and therefore deals with the autonomic functions of breathing, heart rate and blood pressure.
During embryonic development the medulla oblongata develops from the myelencephalon. The myelencephalon is a secondary vesicle which forms during the maturation of the rhombencephalon, also referred to as the hindbrain. Read more...- In respiratory physiology, airway resistance is the resistance of the respiratory tract to airflow during inhalation and expiration. Airway resistance can be measured using body plethysmography. Read more...
- Cyanosis of the hand in an elderly person with low oxygen saturation
Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during hypoventilation training or strenuous physical exercise.
Hypoxia differs from hypoxemia and anoxemia in that hypoxia refers to a state in which oxygen supply is insufficient, whereas hypoxemia and anoxemia refer specifically to states that have low or zero arterial oxygen supply. Hypoxia in which there is complete deprivation of oxygen supply is referred to as anoxia. Read more... - A respirometer is a device used to measure the rate of respiration of a living organism by measuring its rate of exchange of oxygen and/or carbon dioxide. They allow investigation into how factors such as age, or chemicals affect the rate of respiration. Respirometers are designed to measure respiration either on the level of a whole animal or plant or on the cellular level. These fields are covered by whole animal and cellular (or mitochondrial) respirometry, respectively.
A simple whole plant respirometer designed to measure oxygen uptake or CO2 release consists of a sealed container with the living specimen together with a substance to absorb the carbon dioxide given off during respiration, such as soda lime pellets or cotton wads soaked with potassium hydroxide. The oxygen uptake is detected by manometry. Typically, a U-tube manometer is used, which directly shows the pressure difference between the container and the atmosphere. As an organism takes up O2, it generates a proportionate quantity of CO2 (see respiratory quotient), but all the CO2 is absorbed by the soda lime. Therefore, all of the drop of pressure in the chamber can be attributed to the drop of O2 partial pressure in the container. The rate of change gives a direct and reasonably accurate reading for the organism's rate of respiration. Read more... - Hysteresivity derives from “hysteresis”, meaning “lag”. It is the tendency to react slowly to an outside force, or to not return completely to its original state. Whereas the area within a hysteresis loop represents energy dissipated to heat and is an extensive quantity with units of energy, the hysteresivity represents the fraction of the elastic energy that is lost to heat, and is an intensive property that is dimensionless. Read more...
The Bohr effect is a physiological phenomenon first described in 1904 by the Danish physiologist Christian Bohr: hemoglobin's oxygen binding affinity (see oxygen–haemoglobin dissociation curve) is inversely related both to acidity and to the concentration of carbon dioxide. That is, the Bohr effect refers to the shift in the oxygen dissociation curve caused by changes in the concentration of carbon dioxide or the pH of the environment. Since carbon dioxide reacts with water to form carbonic acid, an increase in CO2 results in a decrease in blood pH, resulting in hemoglobin proteins releasing their load of oxygen. Conversely, a decrease in carbon dioxide provokes an increase in pH, which results in hemoglobin picking up more oxygen. Read more...
Vital capacity (VC) is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.
A person's vital capacity can be measured by a wet or regular spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. Furthermore, the vital capacity is used to determine the severity of respiratory muscle involvement in neuromuscular disease, and can guide treatment decisions in Guillain–Barré syndrome and myasthenic crisis. Read more...
The peak expiratory flow (PEF), also called peak expiratory flow rate (PEFR) is a person's maximum speed of expiration, as measured with a peak flow meter, a small, hand-held device used to monitor a person's ability to breathe out air. It measures the airflow through the bronchi and thus the degree of obstruction in the airways. Peak expiratory flow is typically measured in units of liters per minute (L/min). Read more...
An arterial-blood gas (ABG) test measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe and a thin needle, but sometimes the femoral artery in the groin or another site is used. The blood can also be drawn from an arterial catheter. An ABG test measures the blood-gas tension values of the arterial partial pressure of oxygen, and the arterial partial pressure of carbon dioxide, and the blood's pH. In addition, the arterial oxygen saturation can be determined. Such information is vital when caring for patients with critical illnesses or respiratory disease. Therefore, the ABG test is one of the most common tests performed on patients in intensive-care units. In other levels of care, pulse oximetry plus transcutaneous carbon-dioxide measurement is a less invasive, alternative method of obtaining similar information.
An ABG test can also measure the level of bicarbonate in the blood. Many blood-gas analyzers will also report concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin, and methemoglobin. ABG testing is mainly used in pulmonology and critical-care medicine to determine gas exchange across the alveolar-capillary membrane. ABG testing also has a variety of applications in other areas of medicine. Combinations of disorders can be complex and difficult to interpret, so calculators, nomograms, and rules of thumb are commonly used. Read more...- The closing capacity (CC) is the volume in the lungs at which its smallest airways, the respiratory bronchioles, collapse. It is defined mathematically as the sum of the closing volume and the residual volume. The alveoli lack supporting cartilage and so depend on other factors to keep them open. The closing capacity is greater than the residual volume (RV), the amount of gas that normally remains in the lungs during respiration, and specifically, after forced expiration. This means that there is normally enough air within the lungs to keep these airways open throughout both inhalation and exhalation. As the lungs age, there is a gradual increase in the closing capacity (i.e. The small airways begin to collapse at a higher volume/before expiration is complete). This also occurs with certain disease processes, such as asthma, chronic obstructive pulmonary disease, and pulmonary edema. Any process that increases the CC by increasing the functional residual capacity (FRC) can increase an individual's risk of hypoxemia, as the small airways may collapse during exhalation, leading to air trapping and atelectasis.
A mnemonic for factors increasing closing capacity is ACLS-S: Age, Chronic bronchitis, LV failure, Smoking, Surgery. Of note supine positioning will decrease functional residual capacity (FRC) but has no effect on closing capacity. Read more... - The zones of the lung divide the lung into four vertical regions, based upon the relationship between the pressure in the alveoli (PA), in the arteries (Pa), in the veins (Pv) and the pulmonary interstitial pressure (Pi) :
- Zone 1: PA > Pa > Pv
- Zone 2: Pa > PA > Pv
- Zone 3: Pa > Pv > PA
- Zone 4: Pa > Pi > Pv > PA
Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water interface of alveoli, with hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.
As a medication, pulmonary surfactant is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system. Read more...
The pons (Latin for "bridge") is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.
The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio (1543–75). This region of the brainstem includes neural pathways and tracts that conduct signals from the brain down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus. Read more...- Elastic recoil means the rebound of the lungs after having been stretched by inhalation, or rather, the ease with which the lung rebounds. With inhalation, the intrapleural pressure (the pressure within the pleural cavity) of the lungs decreases. Relaxing the diaphragm during expiration allows the lungs to recoil and regain the intrapleural pressure experienced previously at rest. Elastic recoil is inversely related to lung compliance.
This phenomenon occurs because of the elastin in the elastic fibers in the connective tissue of the lungs, and because of the surface tension of the film of fluid that lines the alveoli. As water molecules pull together, they also pull on the alveolar walls causing the alveoli to recoil and become smaller. But two factors prevent the lungs from collapsing: surfactant and the intrapleural pressure. Surfactant is a surface-active lipoprotein complex formed by type II alveolar cells. The proteins and lipids that comprise surfactant have both a hydrophilic region and a hydrophobic region. By absorbing to the air-water interface of alveoli with the hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine, reduces surface tension. It also means the rate of shrinking is more regular because of the stability of surface area caused by surfactant. Pleural pressure is the pressure in the pleural space. When this pressure is lower than the pressure of alveoli they tend to expand. This prevents the elastic fibers and outside pressure from crushing the lungs. It is a homeostatic mechanism. Read more...
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 centre and the apneustic centre.
The respiratory centre is responsible for generating and maintaining the rhythm of respiration, and also of adjusting this in homeostatic response to physiological changes. The respiratory center receives input from chemoreceptors, mechanoreceptors, the cerebral cortex, and the hypothalamus in order to regulate the rate and depth of breathing. Input is stimulated by altered levels of oxygen, carbon dioxide, and pH, by hormonal changes relating to stress, and anxiety from the hypothalamus, and also by signals from the cerebral cortex to give a conscious control of respiration. Read more...
A ventilation/perfusion lung scan, also called a V/Q lung scan, is a type of medical imaging using scintigraphy and medical isotopes to evaluate the circulation of air and blood within a patient's lungs, in order to determine the ventilation/perfusion ratio. The ventilation part of the test looks at the ability of air to reach all parts of the lungs, while the perfusion part evaluates how well blood circulates within the lungs. As Q in physiology is the letter used to describe bloodflow the term V/Q scan emerged. Read more...
Hemoglobin (American) or haemoglobin (British) (/ˈhiːməˌɡloʊbɪn,ˈhɛ-, -moʊ-/); abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells (erythrocytes) of almost all vertebrates (the exception being the fish family Channichthyidae) as well as the tissues of some invertebrates. Haemoglobin in the blood carries oxygen from the lungs or gills to the rest of the body (i.e. the tissues). There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism. A healthy individual has 12 to 16 grams of haemoglobin in every 100 ml of blood.
In mammals, the protein makes up about 96% of the red blood cells' dry content (by weight), and around 35% of the total content (including water). Haemoglobin has an oxygen-binding capacity of 1.34 mL O2 per gram, which increases the total blood oxygen capacity seventy-fold compared to dissolved oxygen in blood. The mammalian hemoglobin molecule can bind (carry) up to four oxygen molecules. Read more...- The respiratory quotient (or RQ or respiratory coefficient), is a dimensionless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry. It is measured using a respirometer. The Respiratory Quotient value indicates which macronutrients are being metabolized, as different energy pathways are used for fats, carbohydrates, and proteins. A value of 0.7 indicates that lipids are being metabolized, 0.8 for proteins, and 1.0 for carbohydrates. The approximate respiratory quotient of a mixed diet is 0.8. Some of the other factors that may affect the respiratory quotient are energy balance, circulating insulin, and insulin sensitivity.
It can be used in the alveolar gas equation. Read more... - Bronchial hyperresponsiveness (or other combinations with airway or hyperreactivity) is a state characterised by easily triggered bronchospasm (contraction of the bronchioles or small airways).
Bronchial hyperresponsiveness can be assessed with a bronchial challenge test. This most often uses products like methacholine or histamine. These chemicals trigger bronchospasm in normal individuals as well, but people with bronchial hyperresponsiveness have a lower threshold. Read more...
The dorsal respiratory group (DRG) is one of the respiratory groups in the respiratory centre in the brainstem. It is located in the dorsomedial region of the medulla, and is composed of cells in the solitary nucleus. The other medullar group is the ventral respiratory group. Another group in the respiratory centre is the pontine respiratory group. This is located in the pons, and is made up of the pneumotaxic centre and the apneustic centre. The DRG is found in many types of fish and mammals. Read more...- The Haldane effect is a property of hemoglobin first described by John Scott Haldane. Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of carbon dioxide. This property is the Haldane effect. Conversely, oxygenated blood has a reduced affinity for carbon dioxide. Thus, the Haldane effect describes hemoglobin’s ability to carry increased amounts of CO2 in the deoxygenated state as opposed to the oxygenated state. Read more...
- Diffusing capacity of the lung (DL) (also known as Transfer factor is another expression for the formerly used diffusing capacity.) 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.
In respiratory physiology, the diffusing capacity has a long history of great utility, representing conductance of gas across the alveolar-capillary membrane and also takes into account factors affecting the behaviour of a given gas with hemoglobin. Read more... - The respiratory rate is the rate at which breathing occurs. This is usually measured in breaths per minute and is set, and controlled by the respiratory centre. Read more...
Bronchoconstriction is the constriction of the airways in the lungs due to the tightening of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Read more...- The factors that determine the values for alveolar pO2 and pCO2 are:
- The pressure of outside air
- The partial pressures of inspired oxygen and carbon dioxide
- The rates of total body oxygen consumption and carbon dioxide production
- The rates of alveolar ventilation and perfusion
- 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.
Gases are constantly consumed and produced by cellular and metabolic reactions in most living things, so an efficient system for gas exchange between, ultimately, the interior of the cell(s) and the external environment is required. Small, particularly unicellular organisms, such as bacteria and protozoa, have a high surface-area to volume ratio. In these creatures the gas exchange membrane is typically the cell membrane. Some small multicellular organisms, such as flatworms, are also able to perform sufficient gas exchange across the skin or cuticle that surrounds their bodies. However, in most larger organisms, which have a small surface-area to volume ratios, specialised structures with convoluted surfaces such as gills, pulmonary alveoli and spongy mesophyll provide the large area needed for effective gas exchange. These convoluted surfaces may sometimes be internalised into the body of the organism. This is the case with the alveoli, which form the inner surface of the mammalian lung, the spongy mesophyll, which is found inside the leaves of some kinds of plant, or the gills of those molluscs that have them, which are found in the mantle cavity. Read more... - The Hering–Breuer inflation reflex, named for Josef Breuer and Ewald Hering, is a reflex triggered to prevent over-inflation of the lung. Pulmonary stretch receptors present in the smooth muscle of the airways respond to excessive stretching of the lung during large inspirations.
Once activated, they send action potentials through large myelinated fibers of the vagus nerve to the inspiratory area in the medulla and apneustic center of the pons. In response, the inspiratory area is inhibited directly and the apneustic center is inhibited from activating the inspiratory area. This inhibits inspiration, allowing expiration to occur. Read more... - In physiology, dead space is the volume of air which is inhaled that does not take part in the gas exchange, either because it (1) remains in the conducting airways, or (2) reaches alveoli that are not perfused or poorly perfused. In other words, 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.
Benefits do accrue to a seemingly wasteful design for ventilation that includes dead space.- Carbon dioxide is retained, making a bicarbonate-buffered blood and interstitium possible.
- Inspired air is brought to body temperature, increasing the affinity of hemoglobin for oxygen, improving O2 uptake.
- Particulate matter is trapped on the mucus that lines the conducting airways, allowing its removal by mucociliary transport.
- Inspired air is humidified, improving the quality of airway mucus.
- Hypoxic pulmonary vasoconstriction (HPV), also known as the Euler-Liljestrand mechanism, is a physiological phenomenon in which small pulmonary arteries constrict in the presence of alveolar hypoxia (low oxygen levels). By redirecting blood flow from poorly-ventilated lung regions to well-ventilated lung regions, HPV is thought to be the primary mechanism underlying ventilation/perfusion matching. The process might initially seem counterintuitive, as low oxygen levels might theoretically stimulate increased blood flow to the lungs to increase gas exchange. However, the purpose of HPV is to distribute bloodflow regionally to increase the overall efficiency of gas exchange between air and blood. While the maintenance of ventilation/perfusion ratio during regional obstruction of airflow is beneficial, HPV can be detrimental during global alveolar hypoxia which occurs with exposure to high altitude, where HPV causes a significant increase in total pulmonary vascular resistance, and pulmonary arterial pressure, potentially leading to pulmonary hypertension and pulmonary edema. Several factors inhibit HPV including increased cardiac output, hypocapnia, hypothermia, acidosis/alkalosis, increased pulmonary vascular resistance, inhaled anesthetics, calcium channel blockers, positive end-expiratory pressure (PEEP), high-frequency ventilation (HFV), isoproterenol, nitric oxide, and vasodilators. Read more...
- A chemoreceptor, also known as chemosensor, is a specialized sensory receptor cell which transduces (responds to) a chemical substance (endogenous or induced) and generates a biological signal. This signal may be in the form of an action potential if the chemoreceptor is a neuron (nerve cell), or in the form of a neurotransmitter that can activate a nearby nerve fiber if the chemosensor is a specialized sensory receptor cell, such as the taste receptor in a taste bud or in an internal peripheral chemoreceptor such as the carotid body (ex, in chemotherapy). In more general terms, a chemosensor detects toxic or hazardous chemicals in the internal or external environment of the human body (e.x. chemotherapy) and transmits that information to the central nervous system, (and rarely the peripheral nervous system), in order to expel the biologically active toxins from the blood, and prevent further consumption of alcohol and/or other acutely toxic recreational intoxicants. Read more...
Functional Residual Capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles.
FRC is the sum of Expiratory Reserve Volume (ERV) and Residual Volume (RV) and measures approximately 2100 mL in an 70 kg, average-sized male (or approximately 30ml/kg) .It cannot be estimated through spirometry, since it includes the residual volume. In order to measure RV precisely, one would need to perform a test such as nitrogen washout, helium dilution or body plethysmography. Read more...
Ribbon diagram of human carbonic anhydrase II, with zinc ion visible in the center
The carbonic anhydrases (or carbonate dehydratases) form a family of enzymes that catalyze the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). This interconversion is a reversible reaction and the enzyme catalyzes both reactions, forward and reverse. The active site of most carbonic anhydrases contains a zinc ion; they are therefore classified as metalloenzymes.
The most important functions of this enzyme in animals is to maintain acid-base balance in blood and other tissues, and to help transport carbon dioxide out of tissues. Read more...- A pulmonary shunt is a pathological condition which results when the alveoli of the lungs are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region. In other words, the ventilation/perfusion ratio (the ratio of air reaching the alveoli to blood perfusing them) is zero.
A pulmonary shunt often occurs when the alveoli fill with fluid, causing parts of the lung to be unventilated although they are still perfused.
Intrapulmonary shunting is the main cause of hypoxemia (inadequate blood oxygen) in pulmonary edema and conditions such as pneumonia in which the lungs become consolidated. The shunt fraction is the percentage of blood put out by the heart that is not completely oxygenated. Read more...
Climbing Mount Rainier.
The effects of high altitude on humans are considerable. The percentage oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around 2,100 m (7,000 feet) above sea level, the saturation of oxyhemoglobin begins to decrease rapidly. However, the human body has both short-term and long-term adaptations to altitude that allow it to partially compensate for the lack of oxygen. There is a limit to the level of adaptation; mountaineers refer to the altitudes above 8,000 metres (26,000 ft) as the "death zone", where it is generally believed that no human body can acclimatize. Read more...- Lung compliance, or pulmonary compliance, is a measure of the lung's ability to stretch and expand (distensibility of elastic tissue). In clinical practice it is separated into two different measurements, static compliance and dynamic compliance. Static lung compliance is the change in volume for any given applied pressure. Dynamic lung compliance is the compliance of the lung at any given time during actual movement of air.
Low compliance indicates a stiff lung (one with high elastic recoil) and can be thought of as a thick balloon – this is the case often seen in fibrosis. High compliance indicates a pliable lung (one with low elastic recoil) and can be thought of as a grocery bag – this is the case often seen in emphysema. Compliance is highest at moderate lung volumes, and much lower at volumes which are very low or very high. The compliance of the lungs demonstrate lung hysteresis; that is, the compliance is different on inspiration and expiration for identical volumes. Read more...
Inhalation (also known as inspiration) happens when air or other gases enter the lungs. Read more...
Hemoglobin (American) or haemoglobin (British) (/ˈhiːməˌɡloʊbɪn,ˈhɛ-, -moʊ-/); abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells (erythrocytes) of almost all vertebrates (the exception being the fish family Channichthyidae) as well as the tissues of some invertebrates. Haemoglobin in the blood carries oxygen from the lungs or gills to the rest of the body (i.e. the tissues). There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism. A healthy individual has 12 to 16 grams of haemoglobin in every 100 ml of blood.
In mammals, the protein makes up about 96% of the red blood cells' dry content (by weight), and around 35% of the total content (including water). Haemoglobin has an oxygen-binding capacity of 1.34 mL O2 per gram, which increases the total blood oxygen capacity seventy-fold compared to dissolved oxygen in blood. The mammalian hemoglobin molecule can bind (carry) up to four oxygen molecules. Read more...
The pulmonary circulation is the portion of the circulatory system which carries deoxygenated blood away from the right ventricle of the heart, to the lungs, and returns oxygenated blood to the left atrium and ventricle of the heart. The term pulmonary circulation is readily paired and contrasted with the systemic circulation. The vessels of the pulmonary circulation are the pulmonary arteries and the pulmonary veins.
A separate system known as the bronchial circulation supplies oxygenated blood to the tissue of the larger airways of the lung. Read more...- In respiratory physiology, the ventilation/perfusion ratio (V̇/Q̇ ratio or V/Q ratio) is a ratio used to assess the efficiency and adequacy of the matching of two variables:
- V̇ or V – ventilation – the air that reaches the alveoli
- Q̇ or Q – perfusion – the blood that reaches the alveoli via the capillaries
Diagram of an endotracheal tube used in mechanical ventilation. The tube is inserted into the trachea in order to provide air to the lungs.
Mechanical ventilation or assisted ventilation is the medical term for artificial ventilation where mechanical means is used to assist or replace spontaneous breathing. This may involve a machine called a ventilator, or the breathing may be assisted manually by a suitably qualified professional (such as an anesthesiologist or paramedic) compressing a breathing system, bag valve mask device or set of bellows.
Mechanical ventilation is termed "invasive" if it involves any instrument inside the trachea through the mouth, such as an endotracheal tube or the skin, such as a tracheostomy tube.
Face or nasal masks are used for non-invasive ventilation in appropriately selected conscious patients. Read more...
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