Lung function results 2007 to 2009

Data collected on respondents aged 6 to 79 demonstrate that lung function increases rapidly during childhood and adolescence, in line with normal growth and development, followed by a gradual decline during adulthood caused by the normal deterioration associated with aging.

Lung function measurements, also known as spirometric measurements, are invaluable tools in the study of respiratory health and lung disease. They permit objective diagnosis of lung disease and assess and monitor disease severity by comparing measurements to the expected values for a normal individual of the same age, height, sex and ethnic origin.

The measurements of primary interest are

• the total volume of air that can be forcibly exhaled after a maximal inspiration, known as the forced vital capacity (FVC)
• the volume of air that can be forcibly exhaled in the first second of a FVC manoeuvre, known as the forced expiratory volume in one second (FEV₁)
• the ratio between FEV₁ and FVC.

Chart 1
Mean FVC and mean FEV₁ by age group and sex

Source: Canadian Health Measures Survey (CHMS), 2007 to 2009

Males have larger FVC and FEV₁ volumes in all age groups. This difference between the sexes is not significant in early childhood, however it increases significantly until early adulthood where it remains throughout late adulthood.

FEV₁ to FVC ratio

The ratio of FEV₁ to FVC expresses the fraction of air that was exhaled in the first second of a FVC manoeuvre. This ratio is markedly age dependant, decreasing with age. Females have greater FEV₁/FVC ratios than males at all ages except in the 40 to 59 age group.

Chart 2
Mean FEV₁/FVC ratio by age group and sex

Source: Canadian Health Measures Survey (CHMS), 2007 to 2009

Since normal lung function values do not exist for the Canadian population, one of the CHMS objectives is to provide nationally representative data on lung function to develop normative data for age, gender and racial groups. This information will enable experts to better estimate the prevalence of conditions related to low lung function and interpret lung function testing.

About spirometry

Spirometry is a test that measures the volume of air an individual inhales or exhales and the rate at which the air is moved into or out of the lungs.

Much like blood pressure provides important information about general cardiovascular health, spirometry is invaluable as a screening test of general respiratory health. Used in conjunction with other tests spirometry allows medical practitioners to monitor respiratory health for conditions such as chronic obstructive pulmonary disease (COPD) and cystic fibrosis.

Spirometry results are interpreted by comparing measurements to the expected values for a normal healthy individual with the same anthropometric and ethnic characteristics. In Canada, predominantly American data are used to define these normal and expected values.