The VC is the largest volume of gas that can be expelled from the lungs after the lungs are first filled to the maximum extent and then slowly emptied to the maximum extent. Measurement of the VC identifies defects of lung or chest wall restriction. Mathematically, it is the sum of the IC and the ERV (see Figure 14.1).
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.
Instruct the patient then to inhale as deeply as possible and then to exhale completely, with no forced or rapid effort.
Record results on graph paper.
Repeat the procedure until the measurements are within about 5% of each other.
A reduced VC is defined as a value <80% (<0.80) of predicted.
The VC can be lower than expected in either a restrictive or an obstructive disorder. Inadequate patient effort causes lower VC values.
A decreased VC can be related to depression of the respiratory center in the brain, neuromuscular diseases, pleural effusion, pneumothorax, pregnancy, ascites, limitations of thoracic movement, scleroderma (autoimmune disease resulting in fibrosis), kyphoscoliosis, or tumors.
The VC increases with physical fitness and greater height.
The VC decreases after age 30 years.
The VC is generally less in women than in men of the same age and height.
The VC is decreased by approximately 15% in Black people and by 20%–25% in Asian people compared with White people of the same age, height, and gender.
Pretest Patient Care
Explain the purpose and procedure of the test and need for patient cooperation. Assess for interfering factors.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Monitor patient signs and symptoms and follow up if necessary.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.