The most valuable tool in characterizing disease severity is pulmonary function testing, including examination of lung mechanics, analysis of arterial blood gases, description of ventilatory response patterns, tests of respiratory muscle performance, metabolic assessment, and noninvasive survey of hemodynamic reserve. The ratio of forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC) should be used to diagnose mild COPD. However, once the disease progresses, the percentage of predicted FEV1 is a better measure of disease severity.1,7,89 and 1° Various guidelines characterize COPD severity as mild, moderate, or severe, although agreement on precise FEV1 standards remains arbitrary.189
In the early stages of COPD, arterial blood gas measurements reveal mild-to-moderate hypoxemia without any evidence of hypercapnea. As the disease progresses in severity (especially when the FEV1 falls below 1 L), hypoxemia becomes more severe and the development of hypercapnia becomes more evident. Not only do arterial blood gas measurements worsen during acute exacerbations, they also may worsen during exercise and sleep.1
Radiographic examination is often misleading; mild chronic airflow obstruction is not likely to be radiographically apparent. Dominantly bronchitic disease may be associated with subtle or absent x-ray findings. On the other hand, dominantly emphysematous disease may be associated with remarkable signs of hyperaeration, such as increased anteroposterior diameter, flattened diaphragms, increased parenchymal lucency, and attenuation of pulmonary arterial vascular shadows, despite only mild-to-moderate physiologic alterations. Right or left ventricular enlargement may not produce relative enlargement of the cardiac silhouette. Certainly, radiography is of unquestionable value in diagnosing complications such as pneumothorax, pneumonia, pleural effusion, and pulmonary neoplasia.
Diagnosing heart failure and assessing ventricular function in patients with COPD is difficult. Echocardiography or gated nuclear scans to estimate ejection fractions may prove invaluable. ECGs are useful to identify arrhythmias or ischemic injury but do not accurately assess the severity of pulmonary hypertension or right ventricular dysfunction.
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