Hyperinflation on a chest X-ray means the lungs contain more air than normal, usually because air is trapped during exhalation. It is commonly seen in COPD, especially emphysema, and sometimes in acute asthma.
Typical X-ray features:
Low, flattened diaphragms
Increased lung volume: often more than 6 anterior ribs or 10 posterior ribs visible above the diaphragm on a good inspiratory film
Hyperlucent lungs: lungs look darker because of increased air
Widened intercostal spaces and more horizontal ribs