section name header

Introduction ⬇

In a healthy person, the concentration of alveolar nitrogen, after a single breath of 100% O2, rapidly increases near the end of expiration. This rise is caused by closure of the small airways in the bases of the lung. The point at which this closure occurs is called the closing volume (CV). CV is used as an index of pathologic changes occurring within the small airways (those <2 mm in diameter). The conventional PFTs are not sensitive enough to make this determination. This test relies on the fact that the upper lung zones contain a proportionately larger RV of gas than the lower lung zones; there is a gradient of intrapleural pressure from the top to the bottom of the lung. Additionally, the uniformity of gas distribution within the lungs can be measured.

Procedure ⬆ ⬇

  1. Have the patient assume a seated position. 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, to inhale 100% O2, and then to exhale completely at the rate of approximately 0.5 L/sec.

  3. During exhalation, monitor simultaneously both the expired volume and percentage of alveolar nitrogen on an X-Y recorder. Remember that a sudden increase in nitrogen represents the CV.

Clinical Implications ⬆ ⬇

  1. Values are increased for those conditions in which the airways are narrowed (e.g., bronchitis, early airway obstruction, chronic smoking, old age).

  2. A change in the slope of the nitrogen curve of >2% is indicative of maldistribution of inspired air (i.e., uneven alveolar ventilation).

  3. Heart failure, with subsequent edema, may also contribute to decreasing patency of the small airways leading to an increase in the CV.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain the purpose and procedure of the test. Explain that this is a noninvasive test that requires patient cooperation.

  2. Assess the patient’s ability to comply with breathing requirement and instructions. Assess for interfering factors.

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

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed.

  2. Discuss with the patient the possible need for follow-up testing to monitor course of therapy.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. The CV increases with age.

  2. Patients in heart failure may show an increased CV.

Reference Values ⬆

Normal