IC measures the largest volume of air that can be inhaled from the end-tidal expiratory level. This measurement is used to identify lung or chest wall restrictions. Mathematically, the IC is the sum of the tidal volume (VT) and the inspiratory reserve volume (IRV) (see Figure 14.1).

1. Have the patient either sit or stand. Place nose clips on the nose and instruct the patient to breathe normally through a mouthpiece/filter (bacterial/viral) combination into the spirometer.

2. After several breaths, ask the patient to inhale maximally, expanding the lungs as much as possible from end-tidal expiration. Have the patient resume normal breathing. Record the results on graph paper.

3. Repeat step 2 two or more times until the two best values are within 5% of each other. Select the largest inspired volume value.

1. Changes in the IC usually parallel increases or decreases in the VC.

2. Decreases in IC can be related to either restrictive or obstructive ventilatory impairments.

Pretest Patient Care

1. Instruct the patient about the purpose and procedure of the test and the need for patient cooperation.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Normal

• Approximately 2400 mL (2.40 L) in women; 3500 mL (3.50 L) in men.

• Predicted values are based on age, height, and gender.