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Alveolar–arterial Gradient
The Alveolar–arterial gradient (A-, or A–a gradient), is a measure of the difference between the alveolar concentration (A) of oxygen and the arterial (a) concentration of oxygen. It is a useful parameter for narrowing the differential diagnosis of hypoxemia. The A–a gradient helps to assess the integrity of the alveolar capillary unit. For example, in high altitude, the arterial oxygen is low but only because the alveolar oxygen () is also low. However, in states of ventilation perfusion mismatch, such as pulmonary embolism or right-to-left shunt, oxygen is not effectively transferred from the alveoli to the blood which results in an elevated A-a gradient. In a perfect system, no A-a gradient would exist: oxygen would diffuse and equalize across the capillary membrane, and the pressures in the arterial system and alveoli would be effectively equal (resulting in an A-a gradient of zero). However even though the partial pressure of oxygen is about equilibrated between the p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulmonary Alveolus
A pulmonary alveolus (plural: alveoli, from Latin ''alveolus'', "little cavity"), also known as an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where oxygen is exchanged for carbon dioxide. Alveoli make up the functional tissue of the mammalian lungs known as the lung parenchyma, which takes up 90 percent of the total lung volume. Alveoli are first located in the respiratory bronchioles that mark the beginning of the respiratory zone. They are located sparsely in these bronchioles, line the walls of the alveolar ducts, and are more numerous in the blind-ended alveolar sacs. The acini are the basic units of respiration, with gas exchange taking place in all the alveoli present. The alveolar membrane is the gas exchange surface, surrounded by a network of capillaries. Across the membrane oxygen is diffused into the capillaries and carbon dioxide released from the capillaries into the alveoli to be breathed out. Alveoli are pa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bronchial Artery
In human anatomy, the bronchial arteries supply the lungs with nutrition and oxygenated blood. Although there is much variation, there are usually two bronchial arteries that run to the left lung, and one to the right lung and are a vital part of the respiratory system. Structure There are typically two left and one right bronchial arteries. The ''left bronchial arteries'' (superior and inferior) usually arise directly from the thoracic aorta. The single ''right bronchial artery'' usually arises from one of the following: * 1) the thoracic aorta at a common trunk with the right 3rd posterior intercostal artery * 2) the superior bronchial artery on the left side * 3) any number of the right intercostal arteries mostly the third right posterior. Function The bronchial arteries supply blood to the bronchi and connective tissue of the lungs. They travel with and branch with the bronchi, ending about at the level of the respiratory bronchioles. They anastomose with the branche ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minute Ventilation
Minute ventilation (or respiratory minute volume or minute volume) is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs per minute. It is an important parameter in respiratory medicine due to its relationship with blood carbon dioxide levels. It can be measured with devices such as a Wright respirometer or can be calculated from other known respiratory parameters. Although minute volume can be viewed as a unit of volume, it is usually treated in practice as a flow rate (given that it represents a volume change over time). Typical units involved are (in metric) 0.5 L × 12 breaths/min = 6 L/min. Several symbols can be used to represent minute volume. They include \dot (V̇ or V-dot) or Q (which are general symbols for flow rate), MV, and VE. Determination of minute volume Minute volume can either be measured directly or calculated from other known parameters. Measurement of minute volume Minute volume is the amount ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PCO2
''p''CO2, pCO2, or P_\ceis the partial pressure of carbon dioxide (CO2), often used in reference to blood but also used in meteorology, climate science, oceanography, and limnology to describe the fractional pressure of CO2 as a function of its concentration in gas or dissolved phases. The units of ''p''CO2 are mmHg, atm, torr, Pa, or any other standard unit of atmospheric pressure. The ''p''CO2 of Earth's atmosphere has risen from approximately 280 ppm (parts-per-million) to a mean 2019 value of 409.8 ppm as a result of anthropogenic release of carbon dioxide from fossil fuel burning. This is the highest atmospheric concentration to have existed on Earth for at least the last 800,000 years. Medicine In medicine, the partial pressure of carbon dioxide in arterial blood is called P_ or PaCO2. Measurement of P_ in the systemic circulation indicates the effectiveness of ventilation at the lungs' alveoli, given the diffusing capacity of the gas. It is a good indicator of res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ventilation Perfusion Mismatch
Ventilation perfusion mismatch or V/Q defects are defects in the total lung ventilation/perfusion ratio (V/Q ratio). It is a condition in which one or more areas of the lung receive oxygen but no blood flow, or they receive blood flow but no oxygen. In a healthy lung, the rate of alveolar ventilation to the rate of pulmonary blood flow is roughly equal; more precisely, because normal lungs are not perfectly matched, the V/Q ratio of a healthy lung is approximately 0.8. Pathogenesis Consider some scenarios where there is a defect in ventilation and/ or perfusion of the lungs. In a condition such as pulmonary embolism, the pulmonary blood flow is affected, thus the ventilation of the lung is adequate, however there is a perfusion defect. Gas exchange thus becomes highly inefficient leading to hypoxemia, as measured by arterial oxygenation. A ventilation perfusion scan or lung scintigraphy shows some areas of lungs being ventilated but not adequately perfused. This results in a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential. It is possible to diffuse "uphill" from a region of lower concentration to a region of higher concentration, like in spinodal decomposition. The concept of diffusion is widely used in many fields, including physics (particle diffusion), chemistry, biology, sociology, economics, and finance (diffusion of people, ideas, and price values). The central idea of diffusion, however, is common to all of these: a substance or collection undergoing diffusion spreads out from a point or location at which there is a higher concentration of that substance or collection. A gradient is the change in the value of a quantity, for example, concentration, pressure, or temperature with the change in another variable, usually distance. A change in c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alveolar Gas Equation
The alveolar gas equation is the method for calculating partial pressure of alveolar oxygen (PAO2). The equation is used in assessing if the lungs are properly transferring oxygen into the blood. The alveolar air equation is not widely used in clinical medicine, probably because of the complicated appearance of its classic forms. The partial pressure of oxygen (pO2) in the pulmonary alveoli is required to calculate both the alveolar-arterial gradient of oxygen and the amount of right-to-left cardiac shunt, which are both clinically useful quantities. However, it is not practical to take a sample of gas from the alveoli in order to directly measure the partial pressure of oxygen. The alveolar gas equation allows the calculation of the alveolar partial pressure of oxygen from data that is practically measurable. It was first characterized in 1946. Assumptions The equation relies on the following assumptions: * Inspired gas contains no carbon dioxide (CO2) * Nitrogen (and any other g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ventilation/perfusion Ratio
In respiratory physiology, the ventilation/perfusion ratio (V/Q ratio) is a ratio used to assess the efficiency and adequacy of the matching of two variables: * V – Ventilation (physiology), ventilation – the air that reaches the Pulmonary alveolus, alveoli * Q – perfusion – the blood that reaches the alveoli via the capillaries The V/Q ratio can therefore be defined as the ratio of the amount of air reaching the alveoli per minute to the amount of blood reaching the alveoli per minute—a ratio of volumetric flow rates. These two variables, V and Q, constitute the main determinants of the blood oxygen (O2) and carbon dioxide (CO2) concentration. The V/Q ratio can be measured with a ventilation/perfusion scan. A V/Q mismatch can cause Respiratory failure#Type 1, Type 1 respiratory failure. Physiology Ideally, the oxygen provided via ventilation would be just enough to saturate the blood fully. In the typical adult, 1 litre of blood can hold about 200 mL of oxygen; 1 lit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulmonary Veins
The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the left atrium of the heart. The pulmonary veins are part of the pulmonary circulation. Structure There are four main pulmonary veins, two from each lung – an inferior and a superior main vein, emerging from each hilum. The main pulmonary veins receive blood from three or four feeding veins in each lung, and drain into the left atrium. The peripheral feeding veins do not follow the bronchial tree. They run between the pulmonary segments from which they drain the blood. At the root of the lung, the right superior pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the lung hilum. Behind the pulmonary artery is the bronchus. The right main pulmonary veins (contains oxygenated blood) pass behind the right atrium and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zones Of The Lung
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 This concept is generally attributed to an article by West et al. in 1964, but was actually proposed two years earlier by Permutt et al. In this article, Permutt suggests "The pressure in the pulmonary arteries and veins is less at the top than at the bottom of the lung. It is quite likely that there is a portion of the lung toward the top in an upright subject in which the pressure in the pulmonary arteries is less than alveolar pressure." The concept is as follows: Alveolar pressure (PA) at end expiration is equal to atmospheric pressure (0 cm H2O differential pressure, at zero flow), plus or minus 2 cm H2O (1.5 mmHg) throughout the lung. On the othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', ''number concentration'', and ''volume concentration''. The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and solvents in solutions. The molar (amount) concentration has variants, such as normal concentration and osmotic concentration. Etymology The term concentration comes from the word concentrate, from the French , from con– + center, meaning “to put at the center”. Qualitative description Often in informal, non-technical language, concentration is described in a qualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. To concentrate a solution, one must add more solute (for example, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
V/Q Mismatch
In respiratory physiology, the ventilation/perfusion ratio (V/Q ratio) is a ratio used to assess the efficiency and adequacy of the matching of two variables: * V – ventilation – the air that reaches the alveoli * Q – perfusion – the blood that reaches the alveoli via the capillaries The V/Q ratio can therefore be defined as the ratio of the amount of air reaching the alveoli per minute to the amount of blood reaching the alveoli per minute—a ratio of volumetric flow rates. These two variables, V and Q, constitute the main determinants of the blood oxygen (O2) and carbon dioxide (CO2) concentration. The V/Q ratio can be measured with a ventilation/perfusion scan. A V/Q mismatch can cause Type 1 respiratory failure. Physiology Ideally, the oxygen provided via ventilation would be just enough to saturate the blood fully. In the typical adult, 1 litre of blood can hold about 200 mL of oxygen; 1 litre of dry air has about 210 mL of oxygen. Therefore, under these conditio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
