Chest x-rays often reveal physical changes associated with reduced lung capacity.
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Doctors use measurements of lung capacity to diagnose respiratory system conditions such as asthma and chronic obstructive pulmonary disease. The Centers for Disease Control and Prevention publishes standard values for lung capacities in healthy individuals. Normal lung capacity varies, depending on gender, age and race or ethnicity and other characteristics. Typically, women have smaller lung capacities than men.
Forced Vital Capacity
Lung capacity is typically measured as forced vital capacity, or the maximum amount of air you can breathe out after a full inhalation. To test your forced vital capacity, your doctor will have you blow air into a device called a spirometer, which measures the volume of air you expel in liters. Forced vital capacity is less than total lung volume because some air always remains in the lungs even after a maximal exhalation.
Variation in Vital Capacity
Vital capacity depends on a number of characteristics, including gender, height, age and race or ethnicity. In general, the larger you are, the greater your vital capacity. Men typically have a greater vital capacity than women because of their larger body size. Vital capacity declines with age, so that a young woman will typically have a greater vital capacity than an older woman of the same size. African-American and Mexican-American women typically have smaller lung capacities than Caucasian women.
Reference Values for Caucasian Women
To determine standards for vital capacity for North American women, the American Thoracic Society suggests using reference tables established by the National Health and Nutrition Examination Survey III, or NHANES III. According to reference values from the NHANES III study, a 25-year-old Caucasian woman who is 5 feet, 5 inches tall will typically have a vital capacity of just under 4 liters. The same woman at age 50 would see her vital capacity decline to approximately 3.6 liters. By age 75, her vital capacity would have dropped still further to just under 3 liters.
African-American and Mexican-American Women
The NHANES III survey also includes reference values for African-American and Mexican-American women. An African-American woman who is 5 feet, 5 inches tall would typically have a vital capacity of about 3.4 liters at age 25, just over 3 liters at age 50, and approximately 2.3 liters at age 75. The reference values for a Mexican-American woman of the same height would be roughly 3.9 liters at age 25, 3.6 liters at age 50 and 2.9 liters at age 70.