Patients with COPD have slowly progressive, irreversible airway obstruction.
The course of the disease is punctuated by periodic exacerbations characterized increased dyspnea, increased sputum production, a change in character of the sputum, and occasionally respiratory failure. Exacerbations may result from bacterial respiratory infection, failure, poor compliance with prescribed therapy, or acute bronchospasm. Pulmonary emboli may be particularly difficult to diagnose in these patients because of their underlying lung disease and abnormal ventilation and perfusion patterns at baseline.
Because it is slowly progressive, COPD usually takes years to become clinically significant, so the diagnosis is usually made first in middle-aged and older persons Dyspnea on exertion is the earliest symptom, but this symptom is often not seen until late in patients gradually reduce their exercise level to match their respiratory capacity to avoid symptoms. Patients with chronic bronchitis have, by definition, a chronic productive cough. As the disease progresses, the physical examination may show increased anteroposterior chest diameter(indicating chronic lung overinflation),use of accessory muscles of respiration, peripheral cyanosis, and, on auscultation of the chest, decreased breath sounds, crackles, rhonchi, and wheezes In the early stages of COPD, pulmonary function testing is the most sensitive means of making the diagnosis. Although cigarette smoking is far and away the most frequent cause of COPD, less than one in five patients who smoke will develop the disease, and signs obstruction on pulmonary function tests, even in asymptomatic smokers, can identify susceptible pa tients. Early pulmonary function test findings re duced flow rates at smaller lung volumes, followed by decreases in forced expiratory volume in second in residual forced vital capacity, with variable increases decreases volume and functional residual capacity and in carbon monoxide diffusing capacity of the lungs. The pulmonary function testing patterns differ depending on whether the predominant disorder is chronic bronchitis or emphysema.
Evidence of gas trap ping and reduced diffusing capacity are hallmarks of emphysema, and these changes are less prominent in patients with chronic bronchitis.
Because most patients , COPD is best viewed as a spectrum with emphysema and chronic bronchitis at either pole,but varying degrees of both disorders as the usual clinical picture.