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DIAGNOSTICS IN PULMONARY MEDICINE
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Used to assess for restrictive lung disease, to show evidence of hyperinflation in obstructive lung disease, and to interpret the diffusing capacity for carbon monoxide (DLCO).
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Common definitions pertinent to the measurement of lung volume are as follows (see also Figure 8.1):
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Residual volume (RV): Air in the lung at maximal expiration.
Expiratory reserve volume (ERV): Air that can be exhaled after normal expiration.
Tidal volume (VT): Air entering and exiting the lungs during normal respirations.
Inspiratory reserve volume (IRV): Air in excess of VT that enters the lungs at full inspiration.
Functional residual capacity (FRC): RV + ERV.
Inspiratory capacity (IC): VT + IRV.
Total lung capacity (TLC): RV + ERV + VT + IRV.
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Pulmonary Function Tests
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Assessing lung function is important in pulmonary disease, and pulmonary function tests (PFTs) may aid significantly in diagnosis. The components of PFTs include spirometry, measurement of lung volume (as discussed above), and quantification of diffusing capacity. PFTs can be used to evaluate several pulmonary diseases or can be used to screen for disease presence in patients with a risk factor, such as smoking (see Tables 8.1 and 8.2). Examples of use include:
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Evaluation of chronic persistent cough, wheezing, dyspnea, or exertional cough/chest pain.
Objective assessment of bronchodilator therapy.
Evaluation of work exposures.
Assessment of risk before major surgery.
Objective assessment of impairment/disability.
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Spirometry is the most useful and readily available of the PFTs. It includes measurement of forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC). It may also include slow vital capacity (SVC), a measure that is useful when FVC is ↓, as slow exhalation causes less airway narrowing, and lung volumes are normal (which can screen for possible restrictive disease).
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