Alveolar hypoventilation is a pathological condition characterized by a decrease in pulmonary ventilation, leading to impaired gas exchange. The process is driven by disorders of respiratory biomechanics or failures in its regulatory mechanisms.
Types of disordersObstructive (airway narrowing) and restrictive (decreased compliance).
Main mechanismIncreased work of breathing and higher energy expenditure by the body.
DiagnosticsSpirometry: evaluation of FVC, Tiffeneau index, and residual volume.
Causes of obstructionForeign bodies, bronchospasm, tumors, and expiratory compression.
Obstructive Pattern: Airflow Obstruction
Obstruction impairs airway patency, which sharply increases resistance to airflow. This forces the respiratory muscles to work harder, increasing energy costs.
Main Causes:
Obturation: presence of foreign bodies, aspiration of vomitus, accumulation of mucus or blood.
Spasm: bronchospasm (e.g., in asthma) or laryngospasm.
Compression: tumors, enlarged lymph nodes, or thyroid enlargement.
Dynamic compression: collapse of small bronchi during forced expiration (typical for emphysema).
Restrictive Pattern: Impaired Expansion
Restriction is associated with the loss of the lungs' ability to fully expand. As a result, their ventilatory capacity decreases while the load on the respiratory apparatus increases.
Extrapulmonary: pathologies that limit chest excursion or respiratory muscle function.
Diagnostic Criteria
Spirometry is used for differential diagnosis. Obstructive disorders show the following changes:
Parameter
Change
FVC
Decreased
Tiffeneau Index
Decreased
RV
Increased
TLC
Normal
Mnemonic
Obstruction is like a 'fence' (a blockage in the pipe), restriction is like a 'corset' (inability to expand).
Frequently asked questions
What specific extrapulmonary pathologies lead to restrictive hypoventilation?
Extrapulmonary causes of restrictive disorders limit the range of respiratory excursions of the lung. Specific pathologies and conditions include:
Exudative pleurisy.
Pronounced ossification of costal cartilages.
Decreased mobility of chest joints in osteochondrosis.
Mechanical compression of the chest — e.g., during structural collapses or motor vehicle accidents (crush syndrome).
What disorders of central respiratory regulation can lead to alveolar hypoventilation?
Central respiratory regulation disorders associated with hypoventilation or respiratory depression include:
Suppression of respiratory center neuronal activity by toxins during an infectious process: microbial and endogenous toxins.
High-dose narcotic substances: depression of respiratory center neurons.
Respiratory depression in substance abuse and poisonings, caused by decreased sensitivity of respiratory center neurons to blood pCO₂.
Alkalosis: decreased excitation of inspiratory neurons and reduced alveolar ventilation, leading to hypoventilation.
What is the key difference between obstruction and restriction?
Obstruction is caused by a narrowing of the airway lumen and increased resistance, whereas restriction is due to decreased elasticity and compliance of the lung tissue itself.
Why does residual volume increase in obstruction?
Due to bronchial narrowing, air becomes 'trapped' in the alveoli because expiration is hindered, leading to lung hyperinflation.
What is the Tiffeneau index and how does it change in obstruction?
It is the ratio of forced expiratory volume in 1 second (FEV1) to the forced vital capacity (FVC). In obstruction, it decreases because expiration becomes disproportionately slow.
Go deeper
Neurogenic mechanisms of respiratory regulation.
Afferent and efferent control disorders of breathing.