Ventilation, or breathing, is the movement of air through the conducting passages between the atmosphere and the lungs. The air moves through the passages because of pressure gradients that are produced by contraction of the diaphragm and thoracic muscles. Show
Pulmonary ventilationPulmonary ventilation is commonly referred to as breathing. It is the process of air flowing into the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation). Air flows because of pressure differences between the atmosphere and the gases inside the lungs. Air, like other gases, flows from a region with higher pressure to a region with lower pressure. Muscular breathing movements and recoil of elastic tissues create the changes in pressure that result in ventilation. Pulmonary ventilation involves three different pressures:
Atmospheric pressure is the pressure of the air outside the body. Intraalveolar pressure is the pressure inside the alveoli of the lungs. Intrapleural pressure is the pressure within the pleural cavity. These three pressures are responsible for pulmonary ventilation. InspirationInspiration (inhalation) is the process of taking air into the lungs. It is the active phase of ventilation because it is the result of muscle contraction. During inspiration, the diaphragm contracts and the thoracic cavity increases in volume. This decreases the intraalveolar pressure so that air flows into the lungs. Inspiration draws air into the lungs. ExpirationExpiration (exhalation) is the process of letting air out of the lungs during the breathing cycle. During expiration, the relaxation of the diaphragm and elastic recoil of tissue decreases the thoracic volume and increases the intraalveolar pressure. Expiration pushes air out of the lungs. Determination of Functional Residual Capacity, Residual Volume, and Total Lung Capacity—Helium Dilution MethodThe functional residual capacity (FRC), which is the volume of air that remains in the lungs at the end of each normal expiration, is important to lung function. Because its value changes markedly in some types of pulmonary disease, it is often desirable to measure this capacity. The spirometer cannot be used in to measure the FRC directly because the air in the residual volume of the lungs cannot be expired into the spirometer, and this volume constitutes about half of the FRC. To measure FRC, the spirometer must be used in an indirect manner, usually by means of a helium dilution method, as follows. A spirometer of known volume is filled with air mixed with helium at a known concentration. Before breathing from the spirometer, the person expires normally. At the end of this expiration, the remaining volume in the lungs is equal to the FRC. At this point, the subject immediately begins to breathe from the spirometer, and the gases of the spirometer mix with the gases of the lungs. As a result, the helium becomes diluted by the FRC gases, and the volume of the FRC can be calculated from the degree of dilution of the helium, using the following formula: FRC=(CiHeCfHe−1)ViSpir whereFRC is functional residual capacity,CiHe is the initial concentration of helium in the spirometer,CfHe is the final concentration of helium in the spirometer, andViSpir is the initial volume of the spirometer. Once the FRC has been determined, the residual volume (RV) can be determined by subtracting expiratory reserve volume (ERV), as measured by normal spirometry, from the FRC. Also, the total lung capacity (TLC) can be determined by adding the inspiratory capacity (IC) to the FRC. That is: RV=FRC−ERV View chapter on ClinicalKey Neuromuscular and Chest Wall DisordersOscar Henry Mayer, ... Mary Ellen Beck Wohl, in Pediatric Respiratory Medicine (Second Edition), 2008 ALTERATIONS OF LUNG FUNCTION IN NEUROMUSCULAR DISEASETotal lung capacity (TLC) and vital capacity (VC) may be normal in mild neuromuscular disease but are reduced in moderate to severe disease. The reductions in TLC and VC are caused by inspiratory and expiratory muscle weakness, scoliosis, and decreased lung and chest wall compliance due to a progressive decrease in lung and chest wall expansion.169 RV may be normal or elevated as a result of expiratory muscle weakness. Therefore, an elevated RV/TLC ratio in patients with neuromuscular disease is not usually due to air trapping as is the case in obstructive lung disease. Maximal expiratory flow rates in patients with neuromuscular disease are usually diminished as a consequence of both low lung volumes and decreased expiratory muscle strength, because both lung volume and driving force can impact maximal flow. Furthermore, patients with neuromuscular disease often have a characteristic shape of the flow-volume curve at low lung volumes, with a precipitous decrease in flows before reaching RV171 rather than a linear decrease through lower lung volumes. This phenomenon is a result of the diminished ability of the expiratory muscles to overcome the outward recoil of the chest wall. As is the case in most restrictive lung disease, the FEV1/FVC ratio is normal in patients with neuromuscular disease. Lung compliance is reduced in patients with neuromuscular disease,172 whereas specific compliance is usually normal.173 This suggests that the decreased compliance is due to loss of lung units or alveolar number as opposed to an alteration of the tissue properties of the lung. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780323040488500700 The Respiratory System and Neuromuscular DiseasesV. Courtney Broaddus MD, in Murray & Nadel's Textbook of Respiratory Medicine, 2022 Total Lung CapacityRespiratory MusclesThe respiratory muscles are the mechanical effectors of the breathing system. They are often divided into three major groups: (1) the inspiratory muscles, (2) the expiratory muscles, and (3) the accessory muscles of respiration. The muscles that maintain patency of the upper airway during the respiratory cycle are sometimes also considered muscles of respiration because of their close interaction with the other respiratory muscles. The diaphragm is the major muscle of inspiration and accounts for approximately 70% of the inhaled tidal volume in the normal individual (Fig. 130.2). Contraction of the diaphragm results in a downward piston motion of the muscle. The resultant increase in abdominal pressure pushes the lower ribs up and out along thezone of apposition, further expanding the thoracic cage.7 The innervation of the diaphragm is via the phrenic nerve that originates from cervical nerve roots 3 through 5. The intercostal muscles are thin sheets of muscular fibers that run between the ribs in the costal spaces.8 There are two sheets of muscle fibers, the external and internal intercostals. (Fig. 130.3). The external intercostals, which are on the outside (external) of the other muscles, function to expand the rib cage during inspiration. The internal intercostals are deeper (internal) and function to decrease rib cage size during expiration. The orientation of the muscle fibers with respect to the ribs and the spinal column where the rib rotates up or down at the costovertebral joint results in the increase or decrease in the size of the rib cage; as the muscles contract, the greater torque is applied to the point more distal from costovertebral rotating joint at the spine. In the case of the external (inspiratory) intercostal muscles, the distal attachment is at the outside portion of the lower rib compared to the upper rib, so contraction tends to pull the lower rib upward and outward thereby expanding the chest. Although there is a torque on the upper rib, it is smaller so that the overall effect is to expand the chest wall. For the internal (expiratory) intercostal muscles, the distal attachment is at the inner portion of the upper rib and thus contraction of the muscle tends to pull the upper rib down and in, thereby decreasing the chest. Innervation of the intercostals is via the intercostal nerves originating from the thoracic spinal nerve roots. The abdominal muscles (rectus abdominis, internal oblique, external oblique, and transversus abdominis) serve a number of functions in respiration that mainly assist expiration but can also function in inspiration. The internal and external obliques and the transversus abdominis result in an inward movement of the abdominal wall that displaces the diaphragm upward into the thoracic cavity and assists exhalation. The rectus abdominis as well as the internal and external obliques pull the lower rib cage caudally and thereby increase pleural pressure and exhalation. The abdominal muscles also may play a minor role in inspiration9; if their contraction reduces lung volume below function residual capacity, abdominal muscles can store elastic recoil energy in the chest wall that then assists expansion of the chest wall during the next inspiration. This “inspiratory assist” may be seen during exercise when expiration becomes active. View chapter on ClinicalKey Respiratory monitoringAndrew D Bersten, in Oh's Intensive Care Manual (Seventh Edition), 2014 Vital capacityAt TLC inspiratory muscle forces are counterbalanced by elastic recoil of the lung and chest wall. Both these parameters and the size of the lung, which varies with body size and gender (Box 38.1), determine TLC. Vital capacity, the difference between TLC and FRC, is also reduced by factors that reduce FRC, e.g. increased abdominal chest wall elastance and premature airway closure in COPD. The normal VC is ∼70 mL/kg; although reduction to 12–15 mL/kg has been suggested as an indication for mechanical ventilation, many other factors need to be considered including the patient's general condition, the strength of the expiratory muscles, glottic function, and the response to non-invasive ventilation. Indeed, many chronically weak patients are able to manage at home with extremely low VC with the assistance of non-invasive ventilation. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780702047626000382 CT and MRI Gas Ventilation Imaging of the LungsJ.D. Newell, ... M.J. Couch, in Hyperpolarized and Inert Gas MRI, 2017 CT Assessment of Lung VentilationTLC, full inspiration, supine CT imaging of the lungs has been used to assess airway geometry of large airway diseases and tissue destruction by emphysema, and FRC and RV, or partial and full expiration, supine chest imaging of the lungs has been used to assess small conducting airway disease by the assessment of air trapping. The quantitative assessment of air trapping using chest CT scans obtained at either FRC or RV represent a very effective means of assessing air trapping produced by small airway disease in at risk subjects. The success of expiratory CT scanning in assessing air trapping and the presence of small airway disease is the simplest form of “functional lung imaging” [13,16,94,95]. The question that remains is how might more sophisticated CT measures of imaging normal and abnormal ventilation in the human lung add to our ability to understand, diagnose, and treat patients with airway disease. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780128036754000130 Respiratory DysfunctionDavid Lacomis, in Office Practice of Neurology (Second Edition), 2003 Static Lung VolumesTotal lung capacity is the volume of air present in the chest after full inspiration (Fig. 13-2). During quiet ventilation, the volume of air inspired and expired in one breath is the tidal volume, normally 500 to 750 mL. The vital capacity (VC) is perhaps the most commonly measured bedside volume. It is the amount of air that can be moved into or out of the lungs on a single breath, normally about 65 mg/kg. The forced vital capacity (FVC) is the volume of air that can be exhaled forcefully after a maximal inspiration. The volume of air left in the lungs at the end of quiet expiration is the functional residual capacity (FRC), and the amount remaining at the end of maximal expiration is the residual volume (RV). Unlike the other lungs volumes defined earlier, RV and FRC cannot be measured by spirometry. Gas dilution techniques or body plethysmography are needed. RV, but not FRC, depends on expiratory muscle strength in addition to the elastic recoil of the chest wall and airway closure. It is useful to follow lung volumes, especially the FVC, in patients with neuromuscular diseases that may affect respiration because improvement in the FVC may parallel clinical improvement and reflect successful therapy; a falling FVC can warn the clinician of impending respiratory failure. What is the volume of a breath?Tidal volume (TV) is the amount of air breathed in with each normal breath. The average tidal volume is 0.5 litres (500 ml).
How much air is inspired in during a single inhalation?Tidal volume (TV) measures the amount of air that is inspired and expired during a normal breath. On average, this volume is around one-half liter, which is a little less than the capacity of a 20-ounce drink bottle.
What is a normal alveolar ventilation rate?In a normal healthy person, almost all the alveoli are functioning properly, and the physiological dead space is about equal to the anatomic dead space which is about 150 ml. So the alveolar ventilation comes to about (500 - 150) ml or 350 ml per breath, times 15 breaths per minute or about 5.2 litres per minute.
What is included in one breath?When you inhale (breathe in), air enters your lungs, and oxygen from that air moves to your blood. At the same time, carbon dioxide, a waste gas, moves from your blood to the lungs and is exhaled (breathed out). This process, called gas exchange, is essential to life.
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What is the amount of air that is normally ventilated in one breath?
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