Fig. 4.2 Obstructive pattern.
sents narrowing of larger to peripheral airways. Spirometry provides the best means for assessing the degree of severity of airflow obstruction and also the response to bronchodilator or corticosteroid treatment.
With increasing levels of obstruction, the initial slope of the volume-time curve becomes progressively less steep and it frequently takes longer to empty the lungs and achieve an FVC plateau. In severe COPD, this may take 15-20 s. The absolute value of FEV1 falls, as does the ratio of FEV1/FVC. The FVC tends to be better maintained until severe levels of obstruction are observed, when it falls. The flow-volume trace continues to show a steep initial rise, but the maximal flow decreases as obstruction becomes worse. The characteristic part of the trace is a concavity of the second part of the curve, the depth of which increases with greater airflow obstruction. Patients with more advanced emphysema may show the diagnostic 'steeple' appearance, with a rapid fall of flow from the maximum levels and then a slow, long tail to residual volume (RV). Illustrative examples are shown in Fig. 4.2.
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