Fig.13.7 ).Inadditiontoalveolarloss,thenumberofalveolarcapillariesisdiminished.Terminalandrespiratorybronchiolesmaybedeformedbecauseofthelossofseptathathelptetherthesestructuresintheparenchyma.Withtheloss of elastic tissue inthesurroundingalveolarsepta,radialtractiononthesmallairwaysisreduced.Asaresult,theytendtocollapseduringexpiration—animportantcauseofchronicairflowobstructioninsevereemphysema.Bronchiolarinflammationandsubmucosalfibrosisareconsistentlypresentinadvanceddisease.
Fig. 13.7 Pulmonaryemphysema.Thereismarkedenlargementoftheairspaces,withdestructionofalveolarseptabutwithoutfibrosis.Notethepresenceofblackanthracoticpigment.
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Dyspnea usually is the first symptom; it begins insidiously but is steadily progressive. In patients with underlying chronic bronchitis or chronic asthmatic bronchitis, cough and wheezing may be the initial complaints. Weight loss is common and may be severe enough to suggest an occult malignant tumor. Pulmonary function tests reveal reduced FEV1 with normal or near-normal FVC. Hence, the FEV1 to FVC ratio is reduced.
The classic presentation of emphysema with no “bronchitic” component is one in which the patient is barrel-chested and dyspneic, with obviously prolonged expiration, sitting forward in a hunched-over position. In these patients, air space enlargement is severe and diffusing capacity is low. Dyspnea and hyperventilation are prominent, so that until very late in the disease, gas exchange is adequate and blood gas values are relatively normal. Because of prominent dyspnea and adequate oxygenation of hemoglobin, these patients sometimes are sometimes called “pink puffers.”
At the other end of the clinical spectrum is a patient with emphysema who also has pronounced chronic bronchitis and a history of recurrent infections. Dyspnea usually is less prominent, and in the absence of increased respiratory drive the patient retains carbon dioxide, becoming hypoxic and often cyanotic. For unclear reasons, such patients tend to be obese—hence the designation “blue bloaters.”
In most patients with COPD the symptoms fall in between these two extremes. Hypoxia-induced pulmonary vascular spasm and loss of pulmonary capillary surface area from alveolar destruction causes the gradual development of secondary pulmonary hypertension, which in 20% to 30% of patients leads to right-sided congestive heart failure (cor pulmonale, Chapter 11). Death from emphysema is related to either respiratory failure or right-sided heart failure.
Conditions Related to Emphysema
Several conditions involving abnormal airspaces or accumulations of air within the lungs or other tissues also are recognized:
Compensatory emphysema describes the dilation of residual alveoli in response to loss of lung substance elsewhere, such as occurs after surgical removal of a diseased lung or lobe.
Obstructive overinflation refers to expansion of the lung due to air trapping. A common cause is subtotal obstruction of an airway by a tumor or foreign object. Obstructive overinflation can be life-threatening if expansion of the affected portion produces compression of the remaining normal lung.
Bullous emphysema refers to any form of emphysema that produces large subpleural blebs or bullae (spaces >1 cm
Fig. 13.8 Bullousemphysemawithlargeapicalandsubpleuralbullae.(From the Teaching Collection of the Department of Pathology, University of Texas South-western Medical School, Dallas,Texas.) in diameter in the distended state) (
Fig. 13.8 ). Such blebs represent localized accentuations of one of the four forms of emphysema; most often the blebs are subpleural, and on occasion they may rupture, leading to pneumothorax.