In lung True about Hyaline membrane disease is (AIIMS NOV 2010)
|A||FRC is more than closing volume|
|B|| FRC is lesser than closing volume |
|C|| FRC is equal to closing volume |
|D||FRC variation is more important than closing volume|
Williams and Wilkins; 1995.
I. Closing Volume or closing capacity (CC)is the volume in the lungs at which its smallest airways, start closing during expiration due to increased intrathoracic pressure around airways.
II. The closing capacity is usually less than the residual volume (RV). This means that there is normally enough air within the lungs to keep these airways open throughout both inhalation and exhalation.
III. As the lungs age, there is a gradual increase in the closing capacity.
IV. In Hyaline membrane disease FRC is lesser than closing volume. When the FRC drops below the critical closing volume, alveolar collapse occurs .
V. The closing volume of alveoli is larger than the FRC until 6-8 years of age. This causes an increased tendency for airway closure at end expiration.
VI. With exhalation, intrathoracic pressure changes will result in airway closure. This occurs first in dependent areas of the lungs around the level of residual volume.
VII. During disease states, increased transpleural pressures result in increased closing volumes. These closing volumes may occur at the level of FRC, which result in atelectasis, subsequent ventilation/perfusion (V/Q) mismatch, and eventual hypoxemia and heypercapuia.
VIII. Continous positive airway pressure is one of the therapies used to increase FRC, prevent atelectasis and maintain ventilation.