RT30 PFT Quiz 477 Questions with Correct Answers 2023 Forced Expiration (FEV) - Correct Answer Forced expiration is a simple but extremely useful pulmonary function test. A spirometry tracing is obtained by having a person inhale to total lung capacity and then exhaling as hard and as completely as possible. These tracings are a very effective way of separating normal ventilatory states from obstructive and restrictive states. In a normal forced expiration curve, the volume that the subject can expire in one second (referred to as FEV1) is usually about 80% of the total forced vital capacity (FVC), or something like four liters out of five. In an obstructive condition, however, such as asthma, bronchitis or emphysema, the forced vital capacity is not only reduced, but the rate of expiratory flow is also reduced. Thus, an individual with an obstructive defect might have a forced vital capacity of only 3.0 liters, and in the first second of forced expiration, exhale only 1.5 liters, giving a FEV1/FVC of 50%. With a restrictive disease, such as fibrosis, forced vital capacity is also compromised.However, due to the low compliance of the lung in such conditions, and the high recoil, the FEV1/FVC ratio may be normal or even greater than normal. For example, a patient with a restrictive condition might have a FVC of 3.0 liters, as was seen in the obstructive cases, but the FEV1 might be as high as 2.7 liters, giving a FEV1/FVC ratio of 90%.forced expiration curves - Correct Answer Forced expiration curves are particularly useful because they are so reproducible. At every lung volume there exists a maximal rate of flow which cannot be exceeded. When an individual tries to exceed his maximal flow rate, he forcefully contracts his abdominal muscles to increase his already positive pleural pressure. This increases the driving pressure for air flow from the alveoli to the mouth but also causes the bronchi (whose pressure lies somewhere between that in the alveoli and that at the mouth, but is less than pleural pressure) to collapse. Thus the airways become occluded and flow is slowed until the pressure difference across the airways drops a bit, the airways can reopen, and flow can continue obstructive ventilatory defect - Correct Answer This is a respiratory abnormality characterized by a slow rate of forced expiration (low FEV1/FVC). In those with active asthma or emphysema, a high residual volume and functional residual capacity and a low vital capacity are usually seen as well. In individuals with bronchitis these lung volumes are more likely to be normal.asthma, bronchitis, emphysema - Correct Answer are all considered obstructive conditions, but the way each results in an obstructive defect is quite different. More information about any of these diseases can be found in the appropriate encyclopedia entry.compliance - Correct Answer Change of volume per change in pressure 1 / 4
refers to the distensibility of an elastic structure (such as the lung) and is defined as the change in volume of that structure produced by a change in pressure across the structure. It is important to understand that the lung (or any other elastic structure) will not increase in size if the pressure within it and around it are increased equally at the same time.Distending Pressure curve comparison - Correct Answer In a normal healthy lung at low volume, relatively little negative pressure outside (or positive pressure inside) needs to be applied to blow up the lung quite a bit. However lung compliance decreases with increasing volume. Therefore as the lung increases in size, more pressure must be applied to get the same increase in volume. This can be seen from the following pressure-volume curve of the lung: Lung compliance and the slope are the same: Compliance can also change in various disease states. For example, in fibrosis the lungs become stiff, making a large pressure necessary to maintain a moderate volume. Such lungs would be considered poorly compliant. However, in emphysema, where many alveolar walls are lost, the lungs become so loose and floppy that only a small pressure difference is necessary to maintain a large volume. Thus, the lungs in emphysema would be considered highly compliant.emphysema - Correct Answer Emphysema is a disease characterized by dilation of the alveolar spaces and destruction of the alveolar walls. With their loss, much of the elastic recoil of the lung is also lost.Compliance of the lung in emphysema is significantly above normal; the lung becomes easy to distend but empties slowly. This results in a chronically overinflated lung (high total lung capacity, functional residual capacity, and residual volume), which lessens the curvature of the diaphragm, making it less efficient in generating even the small swings in pleural pressure necessary for breathing. Pulmonary function tests on a patient with emphysema will reveal a compromised expiratory flow (due to their low lung recoil), including a low FEV1, FVC, and FEV1/FVC ratio.Bronchitis - Correct Answer Bronchitis is a condition which is clinically defined as a chronic cough with mucus production most months of the year. The mucus secretions and inflammation in the bronchi tend to narrow the airways and provide an obstacle to airflow, thus increasing the resistance of the airways.In this manner bronchitis may cause obstructive pulmonary symptoms.On pulmonary tests, a bronchitic may present a decreased FEV1 and FEV1/FVC. However, unlike the other common obstructive disorders, asthma and emphysema, bronchitis rarely causes a high residual volume. This is because the air flow obstruction found in bronchitis is due to increased resistance, which does not generally cause the airways to collapse prematurely and trap air in the lungs. 2 / 4
Asthma - Correct Answer Asthma is a condition characterized by airway hyperresponsiveness, which results in reversible increases in bronchial smooth muscle tone, and variable amounts of inflammation of the bronchial mucosa. During an acute asthma attack, the already inflamed airways narrow further due to bronchospasm, which leads to increased airway resistance. Because of the increased smooth muscle tone during an asthma attack, the airways also tend to close at abnormally high lung volumes, trapping air behind occluded or narrowed small airways. Thus the acute asthmatic will breathe at high lung volumes, his functional residual capacity will be elevated, and he will inspire close to total lung capacity. The accessory muscles of respiration are often used to maintain the lungs in a hyperinflated state.During episodes of acute asthma, pulmonary function tests reveal an obstructive pattern. This includes a decrease in the rate of maximal expiratory air flow (a decrease in FEV1 and the FEV1/FVC ratio) due to the increased resistance, and a reduction in forced vital capacity (FVC) correlating with the level of hyperinflation of the lungs. Because these patients breathe at such high lung volumes (near the top of the pressure-volume curve, where lung compliance greatly decreases), they must exert significant effort to create an extremely negative pleural pressure, and consequently fatigue easily. Over inflation also reduces the curvature of the diaphragm, making it less efficient in generating further negative pleural pressure.Restrictive Ventilatory Defect - Correct Answer Restrictive disease is a condition marked most obviously by a reduction in total lung capacity. A restrictive ventilatory defect may be caused by a pulmonary deficit, such as pulmonary fibrosis (abnormally stiff, non-compliant lungs), or by non-pulmonary deficits, including respiratory muscle weakness, paralysis, and deformity or rigidity of the chest wall.In pulmonary tests, an individual with a restrictive ventilatory defect demonstrates a low total lung capacity, a low functional residual capacity, and a low residual volume. While his forced vital capacity (FVC) may be quite low, his forced expiratory volume in one second divided by the forced vital capacity (FEV1/FVC) is often normal or greater than normal due to the increased elastic recoil pressure of the lung.Because large drops in pleural pressure are required to inflate the lungs, deep breaths are difficult for individuals with restrictive defects, and they tend to breathe shallowly and rapidly.spirometry - Correct Answer Spirometry is the classic pulmonary function test, which measures the volume of air inspired or expired as a function of time. It can monitor quiet breathing and thereby measure tidal volume, and also trace deep inspirations and expirations to give information about vital capacity. Spirometry may also be used to measure forced expiration rates and volumes and to compute FEV1/FVC ratios.Spirometry cannot, however, access information about absolute lung volumes, because it cannot measure the amount of air in the lung but only the amount entering or leaving. Thus information about 3 / 4
functional residual capacity, and lung volumes computed from FRC, such as total lung capacity and residual volume, must be computed via different means, such as body plethysmography or gas dilution.Body Plethysmography - Correct Answer Spirometry is the standard method for measuring most relative lung volumes; however, it is incapable of providing information about absolute volumes of air in the lung. Thus a different approach is required to measure residual volume, functional residual capacity, and total lung capacity. Two of the most common methods of obtaining information about these volumes are gas dilution tests and body plethysmography.In body plethysmography, the patient sits inside an airtight box, inhales or exhales to a particular volume (usually FRC), and then a shutter drops across their breathing tube. The subject makes respiratory efforts against the closed shutter (this looks, and feels, like panting), causing their chest volume to expand and decompressing the air in their lungs. The increase in their chest volume slightly reduces the box volume (the non-person volume of the box) and thus slightly increases the pressure in the box. Using the data from the plethysmography requires use of Boyles Law. To compute the original volume of air in the lungs, we first compute the change in volume of the chest. Using Boyle's Law (P1V1=P2V2, at constant temperature), we set the initial pressure in the box times the initial volume of the box(both of which we know), equal to the pressure times volume of the box at the end of a chest expansion (of which we know only the pressure).We solve for the volume of the box during the respiratory effort. The difference between this volume and the initial volume of the box is the change in volume of the box, which is the same as the change in volume of the chest. Armed with this piece of information, we use Boyle's Law again, this time on the fixed amount of gas in the chest before and at the end of a respiratory effort. We set the initial volume of the chest (unknown) times the initial pressure at the mouth(known), equal to the inspiratory volume of the chest (the same unknown volume plus the change in the volume of the chest, which we have just computed) times the pressure at the mouth during the inspiratory effort (known). Now we solve for the unknown volume, which will be the original volume of gas present in the lungs when the shutter was closed. As mentioned before, the shutter is usually closed at the end of a normal exhalation, or at FRC.Body plethysmography is particularly appropriate for patients who have air spaces within the lung that do not communicate with the bronchial tree. In these individuals, gas dilution methods of measurement would give an erroneously low volume reading gas dilution - Correct Answer Gas dilution is a method of determining those lung volumes that cannot be determined from simple spirometry. These include functional residual capacity, which is computed directly, and residual volume and total lung capacity, which are computed from FRC. The subject is connected to a spirometer containing a known concentration of helium, or some other inert and insoluble gas.After several minutes of breathing, the helium concentrations in the spirometer and lung become the same. From the law of conservation of matter, we know that the total amount of helium before and
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