What are hyperinflated lungs?

What Hyperinflated Lungs Mean

Hyperinflated lungs refer to an abnormal increase in lung volumes, particularly functional residual capacity (the volume of air remaining in the lungs at the end of normal expiration), resulting from air trapping due to expiratory airflow limitation and loss of lung elastic recoil. 1, 2

Pathophysiological Mechanisms

Lung hyperinflation develops through two primary mechanisms that often coexist:

Static Hyperinflation

• Loss of elastic recoil from destruction of alveolar walls (emphysema) causes the lungs to remain more expanded at rest 1, 3
• The lung parenchyma destruction reduces the natural tendency of lungs to collapse, increasing total lung capacity 1
• This occurs in two major emphysema patterns: panacinar and centriacinar 1

Dynamic Hyperinflation

• Expiratory airflow limitation prevents complete lung emptying before the next breath begins 3, 2
• Small airway collapse during expiration traps air distally 3
• The increased ventilatory demand during exercise worsens air trapping as expiratory time shortens 3
• This creates intrinsic positive end-expiratory pressure (PEEPi) that acts as an inspiratory threshold load 1, 4

Clinical Manifestations

Physical Examination Findings

• Increased anterior-posterior chest diameter (barrel chest) 1
• Loss of cardiac dullness on percussion 1
• Decreased cricosternal distance (less than 3 finger breadths) 1
• Flattened diaphragms on chest radiography 1
• Rhonchi (wheezes), especially on forced expiration 1

Diagnostic Measurements

• Spirometry shows FEV1/FVC ratio <70% with FEV1 <80% predicted 1
• Increased residual volume (RV) and RV/TLC ratio 3, 5
• Decreased inspiratory capacity (IC) serves as an indirect marker of hyperinflation 3
• The IC/TLC ratio is an independent predictor of mortality in COPD 3

Clinical Consequences

Respiratory Mechanics

• Inspiratory muscles operate at mechanical disadvantage due to flattened diaphragm position 3, 2
• Increased elastic load on inspiratory muscles at any given minute ventilation 1
• Increased oxygen cost of breathing 2
• The work of breathing increases substantially as tidal breathing approaches total lung capacity 3

Symptom Generation

• Dyspnea (breathlessness) is the cardinal symptom, more closely related to IC than FEV1 3
• Patients describe sensations of "air hunger" and "inability to get a deep breath" 3
• Exercise intolerance occurs as end-inspiratory lung volume encroaches within approximately 500 mL of total lung capacity 6
• The dyspnea limit is reached when operational lung volumes increase toward total lung capacity during exertion 6

Cardiovascular Effects

• Right ventricular afterload increases, potentially leading to cor pulmonale 1
• Cardiovascular side-effects from increased intrathoracic pressure 3

Gas Exchange Abnormalities

• Ventilation/perfusion (V/Q) inequality is the major mechanism causing arterial hypoxemia 1
• Increased dead space ventilation 3

Common Pitfalls

Do not rely solely on FEV1 to assess disease severity or predict symptoms—hyperinflation correlates better with dyspnea and exercise limitation than FEV1 alone 3, 6. The degree of hyperinflation parallels airway obstruction severity but has independent prognostic significance 3.

Recognize that standard spirometry (FEV1, FVC) does not measure hyperinflation directly—inspiratory capacity or plethysmography measurements are required 3. A common error is assuming normal spirometry excludes significant hyperinflation.

Understand that hyperinflation worsens during exercise (dynamic hyperinflation), even when resting measurements appear only mildly abnormal 3. This explains why patients may have disproportionate exercise limitation relative to resting lung function.

Primary Disease Association

COPD is the most common cause of pathological lung hyperinflation, though it also occurs in acute severe asthma 1, 4. The hyperinflation in COPD results from the combination of emphysematous destruction (static component) and expiratory flow limitation (dynamic component) 7, 8.