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Introduction ⬇

RV is the volume of gas remaining in the lungs after a maximal exhalation. This measurement can help distinguish between restrictive and obstructive ventilatory defects. Because the lungs cannot be completely emptied (i.e., a maximal expiratory effort cannot expel all of the gas), RV is the only lung volume that cannot be measured directly from the spirometer. It is calculated mathematically by subtracting the measured ERV from the measured FRC (see Figure 14.1).

Procedure ⬆ ⬇

  1. Fit the patient with nose clips. Instruct the patient to breathe normally through the mouthpiece/filter (bacterial/viral) combination that is attached to the lung volume apparatus. The patient is generally in the seated position.

  2. Three methods may be utilized for measurement, depending on the instrumentation used:

    1. Nitrogen washout or open-circuit technique

    2. Helium dilution or closed-circuit technique

    3. Body plethysmography

  3. Remember that the RV is determined indirectly from other tests; that is, it is mathematically derived by subtracting the measured ERV from the FRC.

  4. See Chapter 1 guidelines for intratest care.

Clinical Implications ⬆ ⬇

  1. An increase in the RV (>125% [>1.25] of predicted) indicates that, despite a maximal expiratory effort, the lungs still contain an abnormally large amount of gas (air trapping). This type of change occurs in young patients with asthma and usually is reversible. In emphysema, the condition is permanent.

  2. Increased RV is characteristic of emphysema, chronic air trapping, and chronic bronchial obstruction.

  3. The RV and the FRC usually increase together but not always.

  4. The RV sometimes decreases in diseases that occlude many alveoli.

  5. An RV <75% (<0.75) of predicted is consistent with restrictive disorders (e.g., interstitial pulmonary fibrosis).

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain the purpose of the test and how the results are calculated.

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

Interfering Factors ⬆ ⬇

RV normally increases with age.

Reference Values ⬆

Normal