Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
Distribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2led breath is distributed to all the alveoli). For this reason, tests that detect abnormal patterns of ventilation distribution are fairly nonspecific and rarely of diagnostic importance. Their major contribution is that such abnormal patterns almost always are associated with alterations in ventila Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2tion-perfusion relationships (see pages 66 and 55). Abnormal distribution of ventilation also contributes to the frequency dependence of compliance (sEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
ee page 68).There are several tests of ventilation distribution. Some are complex and require sophisticated equipment and complex analysis. This chaptDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2cedure are illustrated in Figure 8-1. The subject exhales to residual volume (RV) and then inhales a full breath of 100% oxygen from the bag on the left. A slow, complete exhalation is directed by the one-way valve through the orifice past the nitrogen meter into the spirometer. The orifice ensures Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2that expiratory flow will be steady and slow (<0.5 L/s), and we recommend its use. The nitrogen meter continuously records the nitrogen concentrationEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
of the expired gas as it enters the spirometer. With simultaneous plotting of the expired nitrogen concentration against expired volume, the normal grDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2 of the normal graph: phases I through IV.To understand this graph, we need to consider how the inhaled oxygen is normally distributed in the lungs of a seated subject. At RV, the alveolar nitrogen concentration can be considered uniform (roughly 80%) throughout the lung and alveolar gas is present Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2in the trachea and upper airway (Fig. 8-3A). At RV» the alveoli (circles in Fig. 8-3A) in the more gravitationally dependent regions of the lung are aEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
t a smaller volume than those in the apical portions. Thus, the apical alveoli contain a larger volume of nitrogen at the same concentration. ThereforDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2of VentilationVolumeFIG. 8-1. Equipment required to perform the single-breath nitrogen washout test. A plot of exhaled nitrogen concentration (N. cone) against exhaled volume is shown at the lower right.cVolume (L)FIG. 8-2. Results of single-breath nitrogen washout tests on a normal subject (A), a s Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2ubject with early chronic obstructive pulmonary disease (COPD; B), and a subject with severe COPD (C). Closing volume (when present) is identified byEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
an arrow. The various phases are identified on (A). The slope of phase III is given below each curve.and the alveolar nitrogen is less diluted than inDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2arther down the lung, and the most diluted alveolar gas is at the base (Fig. 8-3B). At the end of inspiration, the trachea and proximal airways contain only oxygen.8 ■ Distribution or ventilation /bFIG. 8-3. Normal distribution of a breath of oxygen inhaled from residual volume and the resulting gra Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2vity-dependent alveolar nitrogen concentration (N2 cone). A. Lung at residual volume. B. Lung after a maximal inspiration to total lung capacity.MaximEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
al InspirationThe events during expiration in the normal subject (Fig. 8-2A) are as follows. The initial gas passing the nitrogen meter comes from theDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2ing out the dead space oxygen and the nitrogen concentration gradually increases.Phase III consists entirely of alveolar gas. During a slow expiration, initially gas comes predominantly from the dependent alveolar regions, where the nitrogen concentration is lowest. As expiration continues, increasi Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2ng amounts of gas come from the more superior regions, where nitrogen concentrations are higher. This sequence of events produces a gradually increasiEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
ng nitrogen concentration during phase III. The normal slope of phase III is 1.0% to 2.5% nitrogen per liter expired. This value increases in the eldeDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2 lung. Most of the final expiration comes from the apical regions, which have a higher concentration of nitrogen. The onset of phase IV is said to reflect the onset of airway closure in the dependent regions, and it is often called the closing volume. Whether airway closure actually occurs at this v Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2olume is debatable.1 Normally, phase IV occurs with approximately 15% of the vital capacity still remaining. This value increases during normal aging,Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
up to values of 25% vital capacity.8B. Changes in the Single-Breath Nitrogen Test in DiseaseIn obstructive lung disease, the SBN, test is altered in Distribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2because the normal pattern of gas distribution, including the vertical gradient of nitrogen concentration described previously, is gradually abolished. Disease occurs unevenly768 ■ Distribution of Ventilationthroughout the lung. Regions of greater disease with high airway flow resistance empty less Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2completely and hence receive less oxygen, and thus their nitrogen concentration is well above normal levels. Because the diseased areas empty more sloEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
wly than the more normal regions, the slope of phase III is greatly increased.In more advanced obstructive disease (Fig. 8-2C), there is no longer a pDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2n of ventilation, the steeper the slope of phase III. There are associated increases in the nonuniformity of the perfusion of the alveolar capillaries. The impact of these changes on arterial blood gases is noted in Section 6A, page 52.It was thought that the increase in phase IV volume would be a u Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2seful, sensitive indicator of early airway disease. Unfortunately, it was not, and phase IV is rarely measured now. However, for many years phase IIIEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
has been recognized as an excellent index of nonuniform ventilation. As shown in Figure 8-2, with the progress of obstructive airway disease, the slopDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2s of airway obstruction. Increases also occur in pulmonary fibrosis, congestive heart failure, sarcoidosis, and other conditions in which airway disease is not the principal abnormality.In conclusion, consideration of the distribution of ventilation tells much about lung physiology. Disorders of ven Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2tilation distribution are extremely important in the pathophysiology of conditions such as chronic bronchitis, asthma, and emphysema. In clinical pracEbook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2
tice, however, tests of ventilation distribution add very little to a basic battery of spirometry and tests of lung volumes, diffusing capacity, and aDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhal Ebook Interpretation of pulmonary function tests - A practical guide (4/E): Part 2. I Appl Physiol 35:411-419, 1973.aDistribution of VentilationVarious pathologic processes alter the normal pattern of ventilation distribution (i.e., the uniformity with which an inhalGọi ngay
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