ERV is the largest volume of gas that can be exhaled from end-tidal expiration. This measurement identifies lung or chest wall restriction. The ERV can be estimated mathematically by subtracting the inspiratory capacity (IC) from the vital capacity (VC). The ERV accounts for approximately 25% of the VC and can vary greatly in patients of comparable age and height (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. Ask the patient to exhale completely and resume normal breathing. Record results on graph paper.

3. Ask the patient to repeat this maneuver at least twice. The measured volumes should be within ±60 mL of one another. Report the average value.

1. A decreased ERV indicates a chest wall restriction resulting from nonpulmonary causes.

2. Decreased values are associated with an elevated diaphragm (e.g., massive obesity, ascites, pregnancy). Decreased values also occur with massive enlargement of the heart, pleural effusion, kyphoscoliosis (abnormal curvature of the spine), or thoracoplasty (removal of one or more ribs).

3. Decreases in ERV also are seen in obstruction resulting from an increase in the RV impinging on the ERV.

Pretest Patient Care

1. Explain the purpose and procedure of the spirometry test. Inform the patient that the test is noninvasive. Assess the patient’s ability to comply with test procedures.

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

Normal

• Approximately 700 mL in women and 1200 mL (1.20 L) in men

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