Wednesday, December 15, 2010
12:36 AM | Posted by Shams Burki | Edit Post
A. Decreased capacity for pulmonary diffusion
B. Decreased surface area of alveolar capillary membranes
C. Hypoventilation of central origin
D. Hypoventilation of peripheral origin
E. Inequalities of ventilation and perfusion
The correct answer is D. It is conceptually worth subclassifying hypoxemia in terms of the groups of the causes listed in the answers. In this case, the patient has no evidence of primary pulmonary or cardiovascular disease, and is known to be morbidly obese. Morbidly obese individuals are vulnerable to the Pickwickian Syndrome (after a character in a Dickens novel), in which pressure from a fatty neck causes intermittent airway obstruction. The many other causes of hypoventilation of peripheral origin include suffocation, submersion, skeletal abnormalities, trauma, phrenic nerve paralysis, polio, and tetanus.
Causes for decreased capacity for pulmonary diffusion (choice A) of 02 include processes such as respiratory distress syndrome, emphysema, pulmonary fibrosis, and some granulomatous processes such as sarcoidosis.
Causes for decreased surface area of alveolar capillary membranes (choice B) include resection or compression of the lung and emphysema.
The usual cause of hypoventilation of central origin (choice C) is respiratory center depression by morphine or barbiturates.
Causes for inequalities of ventilation and perfusion (choice E) include chronic bronchitis, asthma, emphysema, bronchiectasis, some granulomatous processes, and tumors.