Closing capacity

The closing capacity (CC) is the volume in the lungs at which its smallest airways, the respiratory bronchioles, 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 (i.e. The small airways begin to collapse at a higher volume/before expiration is complete). This also occurs with certain disease processes, such as asthma, chronic obstructive pulmonary disease, and pulmonary edema. Any process that increases the CC by increasing 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.

Respiratory physiology

Respiration	breath inhalation exhalation respiratory rate respirometer pulmonary surfactant compliance elastic recoil hysteresivity airway resistance bronchial hyperresponsiveness constriction dilatation mechanical ventilation

Control	pons pneumotaxic center apneustic center medulla dorsal respiratory group ventral respiratory group chemoreceptors central peripheral pulmonary stretch receptors Hering–Breuer reflex

Lung volumes	VC FRC Vt dead space CC PEF calculations respiratory minute volume FEV1/FVC ratio Lung function tests spirometry body plethysmography peak flow meter nitrogen washout

Circulation	pulmonary circulation hypoxic pulmonary vasoconstriction pulmonary shunt

Interactions	Perfusion (V) ventilation (Q) ventilation/perfusion scan zones of the lung gas exchange pulmonary gas pressures alveolar gas equation alveolar–arterial gradient hemoglobin oxygen–haemoglobin dissociation curve (Oxygen saturation 2,3-BPG Bohr effect Haldane effect) carbonic anhydrase (chloride shift) oxyhemoglobin respiratory quotient arterial blood gas diffusion capacity (DLCO)

Insufficiency	high altitude oxygen toxicity hypoxia

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Closing capacity

See also

Further reading