This is any respiratory condition where the patient is unable to take in a full, deep breath. It can be due to lung, chest cage, or nervous system disease. By analogy imagine a steel hoop placed around your chest so that you can breathe in a little, but not take a full, deep breath. Your breathing is then restricted. The closer the steel hoop comes to your resting breathing level at the end of a normal breath, the less you can inspire and the more severe is the restriction.
Any respiratory condition resulting in inability to expand fully the lungs is a restrictive problem.
Once air is inhaled, however, patients with restrictive disorders can exhale without any impediment or obstruction. Asthma, chronic bronchitis, and emphysema are examples of obstructive lung disease. Characteristic of this group is difficulty getting all the air out. As a group obstructive lung diseases are the greatest cause of respiratory morbidity in the United States. As shown in Figure 1, the obstructed patient can take a deep breath but the rate of exhalation is slowed.