Lung hyperinflation

Lung hyperinflation is a common condition in patients with chronic obstructive pulmonary disease (COPD). It is also linked to agingageing and other chronic diseases that cause airflow obstruction.

The airflow limitation during expiration is produced by two factors:

• Destructiondestruction of the lung parenchyma. : In

  • ​in healthy subjects, the volume reached by the lungs after exhalation is determined by the balance of forces between the inward elastic recoil pressure of the lung and the outward recoil pressure of the chest wall. Age

  • ageing or pulmonary parenchymal destruction (from other causes emphysema) causeresult in a displacement of this point of equilibrium to a higher volume.

• airway defects: 

  • Airway defects ​such as mucosal edemaoedema, remodeling of airway mucus or impaction. In these cases, the expiratory airflow limitation is increased during exercise

The diseases that limit expiratory airflow produce lung hyperinflation. The most characteristic is chronic obstructive pulmonary disease (COPD).

Other diseases that cause an obstructive airflow pattern are

• asthma,
• cystic fibrosis,
• bronchiectasis,
• bronchiolitis and
• some interstitial diseases such as
  • Langerhan cell histiocytosis X or
  • lymphangioleiomyomatosis (LAM)
  • (in these two diseases in their early stages, in advanced stages show a restrictive pattern).

Radiographic features

Chest X-rayradiograph

• flattened of diaphragmatic contours

  • ​considered one of the most sensitive indicatorindicators of of hyperinflation and interobserver variability is small. It is

  • best seen in the lateral chest radiograph and consists of a loss of height of the convexity of the hemidiaphragm. To

  • to measure, it is possible to draw a line connecting the sternophrenic angle and the posterior costophrenic angle. This

    • this arch height should be greater than or equal to 2.5 centimeterscm. Minor

    • it is considered clearly pathological when measures less than 1.5 cm.

  • minor measures correlate well with the functional importance of airflow obstruction.It is considered clearly pathological when measures less than 1.5 centimeters.

• Retrosternalretrosternal space measurement. A

  • ​a horizontal line is drawn from a point allocated 3 cm below the junction between the manubrium and sternal body, on the posterior cortex of the sternum, and the ascending aorta point. In cases of increased retrosternal space, this distance is equal or greater than 2.5 centimeterscm.

• Airair trapping:. When when comparing two radiographs acquired in maximal inspiration and maximal expiration another in the vertical movement of the diaphragm is less than 3 centimeterscm.

• Ribs.ribs appearances: More

  • more than 6 above or 10 posterior ribs in the mid-clavicular line at the lung and diaphragm level Horizontalization

  • horizontalization of ribs.

• Presencepresence of air below the heart.

• Increasedincreased anteroposterior diameter of the chest, also called barrel chest.

• Hyperlucenthyperlucent lungs (less bronchovascular markings per cm2cm²)

CT

• Airair trapping.: Best best seen in expiration.

• Measuringmeasuring the length of the anterior union line. This

  • ​this is a masurement of retrosternal space more reproducible than in the chest radiograph.

• Saber sheath trachea. It is

  • a pathognomonic finding of chronic obstructive pulmonary disease (COPD). It

  • it refers to decrease in the diameter of the trachea in the coronal plane and increase in the sagittal plane. It can be also seen on the chest radiograph comparing the posteroanterior and lateral projections.

• vascular changes

  • Vascular changes​. This is an indirect sign of destruction of the lung parenchyma. Emphysema

  • emphysema causes destruction of the lung parenchyma and pulmonary arterial hypertension.