Obstructive Lung Disease

1. Asthma
2. Chronic Bronchitis
3. Emphysema
or 4. a combination of these

COPD Chronic obstructive pulmonary disease is a general term which may refer to pure emphysema, pure bronchitis, or a mixture of the two (excludes asthma)

1. Asthma: Characterised by reversible airway constriction resulting from a combination of airway hyperactivity, mucous secretion and airway oedema. Known precipitants of hyperactivity include exercise, cold air, infection, drugs, and occupational exposure. Car exhaust pollution may be another precipitant.
2. Chronic Bronchitis: Characterised by excessive mucous with narrowing of airways.
3. Emphysema: - involves the destruction of alveoli and support structures, leading to loss of normal elastic recoil of lungs and subsequent premature airway closure (collapse) at higher than normal lung volumes during exhalation.

Pattern of Impairment
a. Flow rates. A reduced FEV 1 /FVC ratio (less than 70%) is the indicator of obstructive airway disease. However, the FEV 1 /FVC may be normal even with considerable peripheral airway obstruction.

b. Lung volumes. Changes may be seen in moderate to severe obstructive airway disease.
(1 ) Lung volume measurements are useful in identifying hyperinflation due to premature airway closure.
(i) During a forced expiration, if the terminal airways close before all the air is expelled, hyperinflation results, causing an increase in the FRC, RV, and RV/TLC.
(ii) In small airway disorders, because of air trapping, the RV may increase while the FRC and FEV 1 remain normal.
(2) In emphysema, the alveolar wall destruction and loss of lung elastic recoil cause an increase in the TLC.

c. Compliance is increased in emphysema, because lung elastic recoil is reduced.

Restrictive Disease

examples include
A. Intrinsic (within lung) - low T L co
1. Pulmonary interstitial disease ( e.g. fibrosis asbestosis silicosis)
2. Pulmonary oedema
3. Aspiration pneumonitis
4. Acute respiratory distress syndrome (ARDS)

B. Extrinsic (outside lung) - Normal T L co ( gas exchange normal)
1. Chest wall deformity
2. Pleural fluid
3. Diaphragmatic compression by obesity, ascites, pregnancy
4. Respiratory muscle weakness e.g. myasthenia gravis, polio

Pattern of Impairment
a. Flow rates FEV 1 /FVC may be normal or may be increased due to increased traction on the intrathoracic airway walls.

b. Lung volumes
(1) A reduction in VC and TLC is the most useful indicator of a restrictive ventilatory defect.
(2) Lung stiffness in restrictive diseases increases the lung elastic recoil and lowers the FRC.
(3) Chest wall stiffness lowers lung volumes because it restricts lung expansion.

c. Compliance is reduced because lung elastic recoil is increased.

d. Airway resistance is decreased because the elastic forces maintain wider airways at any given lung volume.