Normal Spirometry Flashcards
Define repeatability
the variation in measurement using repeat measurements under identical conditions
– for example performing spirometry on the same patient on the same piece of equipment by the same operator under the same environmental conditions.
Define reproducibility
the variation in measurement when there are different conditions
– for example performing spirometry on a patient on different days, using a different spirometer and performed by a different operator.
Name some sources of error - spirometry
-equiptment
-environment
-procedures and protocols
-patient
-physiologist
What is the repeatability criteria for spirometry?
-3 technically acceptable results selected from up to 8 efforts
-The chosen values for FVC and FEV1 should not differ from the next best values for FVC and FEV1 by more than 150 mL
-In subjects with a FVC of <1.00 L, this difference should not be greater than 100 mL
-Report the highest FEV1 and FVC - these can come from any one of the 3 efforts meeting repeatability criteria (they don’t have to come from the same blow)
-Some equipment will select the best test calculated from a combination of FEV1 and FVC, but this is not recommended
What is the acceptability criteria for spirometry?
-Aim to achieve the best result possible
-Patients may not achieve all the acceptability criteria, but results may still be used with clinical discretion, as long as these are documented and taken into consideration when interpreting results
-The patient needs to be continually observed to ensure that their test technique is correct, and encouraged throughout in order to exhale both as hard and fast as possible, and until they are completely empty
How do we check the spirometry trace was satisfactory?
1-check there was no leak
2-That the mouthpiece was not obstructed
3-poorly coordinated start to the manoeuvre
4-no cough or clottis closure in the first second of expiration
5-that plateau achieved <0.025L in last second of expiration
6-submaximal inspiration
7-poor effort or compliance
8-back extrapolated volumes of 5% of the FVC or 0.1L if the FVC is less than 2L
What factors affect lung volumes?
-age
-height
-sex
-ethnicity
Describe the ageing of the lungs
-lung development starts at day 26 of gestation
-alveoli begin to develop from week 24
-surfactant develop from week 22-24 onwards
-alveoli continue to increase in number during early childhood
-subsequent development is in size of lungs
-lungs fully developed by early 20s
What are the effects of ageing on the lungs?
-reduction in collagen and elastin
-loss of elasticity
-decrease in muscle tone
-exposure to pollution
-impaired nutrient supply
-reduction in cell membrane permeability
-increased rigidity of chest wall
How does sex affect lung volume?
children-similar lung volumes until puberty
males-broader shoulders, increase in thrunk and chest dimensions
for a given height, male lung volumes will be greater than female
How does ethnicity affect lung volumes?
for a given height, caucasians have greater lung volumes than any other ethnicity
How do you create predicted or reference values?
-representative sample of healthy subjects (non smokers)
-drawn from the general population
-exclude those with respiratory disease
-past and present medical history
-paediatric and adult reference equations available
-physical examination
-chest x-ray findings
What is the recommended reference values for adults?
Age-18-70
Males- 1.55- 1.95
Femaales- 1.45-1.80
Ethnicity- caucasians
What are the limitations of reference equations?
-step in transition from paediatric to adult reference values
-reference values for caucasians only- need to readjust results for non-caucasian patients
-extrapolate values for patients > 70 years old
What is the equation for the derivation of reference?
-for each value develop a linear regression equation based on age, height and sex
4.30 x h - 0.029 x a - 2.49
