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To interpret ventilatory function tests in any individual, compare the results with reference values obtained from a well-defined population of normal subjects matched for sex, age, height and ethnic origin and using similar test protocols; and carefully calibrated and validated instruments.1
Normal predicted values for ventilatory function generally vary as follows:
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Sex:
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For a given height and age, males have a larger FEV1, FVC, FEF25-75% and PEF, but a slightly lower FEV1/FVC.
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| 2. |
Age:
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FEV1, FVC, FEF25-75% and PEF increase, while FEV1/FVC decreases, with age until about 20 years old in females and 25 years in males.
After this, all indices gradually fall, although the precise rate of decline is probably masked due to the complex interrelationship between age and height. The fall in FEV1/FVC with age in adults is due to the greater decline in FEV1 than FVC.
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| 3. |
Height:
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All indices other than FEV1/FVC increase with standing height.
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| 4. |
Ethnic Origin:
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Caucasians have the largest FEV1 and FVC and, of the various ethnic groups, Polynesians are among the lowest. The values for black Africans are 10-15% lower than for Caucasians of similar age, sex and height because for a given standing height their thorax is shorter; normal values for Indigenous Australians may be even lower. Chinese have been found to have an FVC about 20% lower and Indians about 10% lower than matched Caucasians. There is little difference in PEF between ethnic groups.
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There is a vast literature of normal population studies, many of which have deficiencies in sample size, definition of normality, inclusion of smokers and choice of equipment. Appendix B provides tables of mean predicted values from a well-conducted study on a US Caucasian population2.
Content Updated 28 March, 2008
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Last Updated ( Tuesday, 17 February 2009 )
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