expansion are in equilibrium, and the intrapleural pressure is least negative. During
expiration below FRC, the small airways can collapse and close. The closed airways do
not take part in gas exchange, but are still perfused with pulmonary capillary blood, so
that oxygenation in these regions is impaired. The volume at which this occurs is the
closing capacity. Closing capacity increases with age. In young adults, it is below FRC,
and thus does not normally occur during normal tidal breathing. By 65 years, closure of
basal airways occurs during normal tidal breathing in the erect position. This is one of the
reasons why arterial PO2 decreases with age. The closing capacity is less in the supine
than in the erect position, and by the age of 45 years encroaches on FRC in the supine
position.
or
The closing capacity (CC) is the volume in the lungs at which its smallest airways, the alveoli collapse. The alveoli lack supporting cartilage and so depend on other factors to keep them open. The closing capacity is greater than the residual volume (RV), the amount of gas that normally remains in the lungs during respiration, and specifically, after forced expiration. This is because closing capacity is equal to closing volume plus residual volume. This means that there is normally enough air within the lungs to keep these airways open throughout both inhalation and exhalation.
As the lungs age, there is a gradual increase in the closing capacity. This also occurs with certain disease processes, such as asthma, chronic obstructive pulmonary disease, and pulmonary edema. Any process that increases the CC by lowering the functional residual capacity (FRC) can increase an individual's risk of hypoxemia, as the small airways may collapse during exhalation, leading to air trapping and atelectasis.
expiration below FRC, the small airways can collapse and close. The closed airways do
not take part in gas exchange, but are still perfused with pulmonary capillary blood, so
that oxygenation in these regions is impaired. The volume at which this occurs is the
closing capacity. Closing capacity increases with age. In young adults, it is below FRC,
and thus does not normally occur during normal tidal breathing. By 65 years, closure of
basal airways occurs during normal tidal breathing in the erect position. This is one of the
reasons why arterial PO2 decreases with age. The closing capacity is less in the supine
than in the erect position, and by the age of 45 years encroaches on FRC in the supine
position.
or
The closing capacity (CC) is the volume in the lungs at which its smallest airways, the alveoli collapse. The alveoli lack supporting cartilage and so depend on other factors to keep them open. The closing capacity is greater than the residual volume (RV), the amount of gas that normally remains in the lungs during respiration, and specifically, after forced expiration. This is because closing capacity is equal to closing volume plus residual volume. This means that there is normally enough air within the lungs to keep these airways open throughout both inhalation and exhalation.
As the lungs age, there is a gradual increase in the closing capacity. This also occurs with certain disease processes, such as asthma, chronic obstructive pulmonary disease, and pulmonary edema. Any process that increases the CC by lowering the functional residual capacity (FRC) can increase an individual's risk of hypoxemia, as the small airways may collapse during exhalation, leading to air trapping and atelectasis.
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