Measuring Lung Function
Spirometry Testing
Overview
A spirometer is an instrument used to measure the volume of air exchanged during breathing.37,38
- Spirometry testing is quick, noninvasive, and painless. The record produced from spirometry testing is called a spirogram.
- Generally, spirometry is performed with the patient sitting in an upright position. The patient breathes into a tube attached to a machine that calculates the amount of air the lungs can hold and the rate that air can be inhaled and exhaled. Spirometry tests may be given with the patient at rest, following exercise, or after inhaling a medication that dilates the airways.
- The results of the test are compared with those of healthy individuals of similar height and age, and of the same sex and race.
- Spirometry testing helps distinguish between different lung diseases, but it does not provide a diagnosis. It works best for following disease progression.
Respiratory Volumes
Four respiratory volumes are measured using a spirometer. These include tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.37,38
Inspiratory Reserve Volume
Inspiratory reserve volume is the amount of air above the tidal volume that can be inhaled by taking a very deep breath.
Reaches About:
- 3100 mL in males
- 1900 mL in females
Tidal Volume
Tidal volume measures the amount of air that a healthy adult moves into (and then out of) the lungs with each breath under resting conditions.
Average Adult:
- 500 mL
Expiratory Reserve Volume
The expiratory reserve volume is the amount of air beyond the tidal volume that can be forcefully exhaled after a normal exhalation.
On Average:
- 1200 mL for males
- 700 mL for females
Residual Volume
Residual volume is the amount of air remaining in the lungs after a forced exhalation.
Most Adults:
- 1200 mL in males
- 1100 mL in females
Respiratory Capacities
Respiratory capacities are calculated by adding together different combinations of lung volumes. Respiratory capacities include inspiratory capacity, functional residual capacity, vital capacity, and total lung capacity.37,38
Inspiratory Capacity
Inspiratory capacity is the amount of air that can be inspired after a normal expiration.
Inspiratory capacity = Tidal volume + Inspiratory reserve volume
Normal Values
- 3600 mL in males
- 2400 mL in females
Vital Capacity
Vital capacity measures the maximum amount of air that can be expired after a maximum inspiration.
Normal Values:
- 4800 mL in males
- 3100 in females
Vital capacity = Inspiratory reserve volume + Tidal volume + Expiratory reserve volume
Total Lung Capacity
Total lung capacity is the maximum amount of air contained in the lungs after a maximum inspiratory effort.
Normal Values:
- 6000 mL in males
- 4200 mL in females
Total lung capacity = Vital capacity + Residual volume
Functional Residual Capacity
Functional residual capacity represents the amount of air remaining in the lungs after normal tidal volume expiration.
Normal Values
- 2400 mL in males
- 1800 mL in females
Functional residual capacity = Residual volume + Expiratory reserve volume
References:
37. Tortora GJ, Derrickson B. The Respiratory System. In: tortora GJ, Derrickson B, editors. Principles of Anatomy and Physiolgy. 11th ed. Hoboken: John Wiley & Sons, Inc.; 2006. p. 846-94.
38. Marieb EN. The Respiratory System. In: Marieb EN, editor. Human Anatomy and Physiology. 5th ed. San Francisco: Benjamin Cummings; 1999. p. 834-80.