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Measurement of Ventilatory Function

A great deal can be learned about the mechanical properties of the lungs from measurements of forced maximal expiration and inspiration. The spirometer (developed in 1846 by Hutchinson) is used to measure ventilatory function (dynamic lung volumes and maximal flow rates).

Spirometry

Conventionally, a spirometer is a device used to measure timed expired and inspired volumes, and from these we can calculate how effectively and how quickly the lungs can be emptied and filled. The measurements that are usually made are as follows:

  • VC (vital capacity) is the maximum volume of air which can be exhaled or inspired during either a forced (FVC) or a slow (VC) manoeuvre
  • FEV1 (forced expired volume in one second) is the volume expired in the first second of maximal expiration after a maximal inspiration and is a useful measure of how quickly full lungs can be emptied
  • FEV1/VC is the FEV1 expressed as a percentage of the VC or FVC (whichever volume is larger) and gives a clinically useful index of airflow limitation
  • FEF25-75% is the average expired flow over the middle half of the FVC manoeuvre and is regarded as a more sensitive measure of small airways narrowing than FEV1. Unfortunately FEF25-75% has a wide range of normality, is less reproducible than FEV1, and is difficult to interpret if the VC (or FVC) is reduced or increased
  • PEF (peak expiratory flow) is the maximal expiratory flow rate achieved and this occurs very early in the forced expiratory manoeuvre.

Miller 1996[1]) shows a normal spirogram showing the measurements of forced vital capacity (FVC), forced expired volume in one second (FEV1) and forced expiratory flow over the middle half of the FVC (FEF25-75%).

Static lung volume and capacity

Static Lung volume tests evaluate air movement within the pulmonary tract with no time limitations. McArdle et al. 2000)[3] shows the various static lung volume measurements that can be made.

  • TV - Tidal Volume - Volume inspired or expired per breath
    • Average values Male 600mL, Female 500mL
  • IRV - Inspiratory Reserve Volume - Maximum inspiration at end of tidal inspiration
    • Average values Male 3L, Female 1.9L
  • ERV - Expiratory Reserve Volume - Maximum expiration at end of tidal expiration
    • Average values Male 1.2L, Female 800mL
  • TLC - Total Lung Capacity - Volume in lungs after maximal inspiration
    • Average values Male 6L, Female 4.2L
  • RLV - Residual Lung Volume - Volume in lungs after maximum expiration
    • Average values Male 1.2L, Female 1L
  • FVC - Forced Vital Capacity - Maximum volume expired after maximum inspiration
    • Average values Male 4.8L, Female 3.2L
  • IC - Inspiratory Capacity - Maximum volume inspired following tidal expiration
    • Average values Male 3.6L, Female 2.4L
  • FRC - Functional Residual Capacity - Volume in lungs after tidal expiration
    • Average values Male 2.4L, Female 1.8L

Breathing volumes

The volume of air breathed in and out can be measured using a spirometer. The subject breathes in and out of a sealed chamber through a mouthpiece. As the chamber inflates and deflates, a pen recorder traces out the breathing movements onto a chart. The machine is calibrated so that breathing volumes can be calculated. The amount of air breathed in and out in a normal cycle is called the tidal volume, usually about 500 cm³.

We are able to breathe in and out to a greater extent, and these extra supplies of air are called the inspiratory reserve volume, and the expiratory reserve volume, respectively. During exercise the tidal volume increases, making use of both the inspiratory and expiratory reserve volumes. All three volumes together add up to the vital capacity - the maximum possible tidal volume - usually about 4 to 5 cm³.

When we breath out as hard as we can, there is still some air in the lungs, this is called the residual volume, add this to the vital capacity and we have the total lung volume, usually between 5 to 7 cm³.

Some of the air we breathe in does not reach the alveoli, but remains in the air passages, occupying the so called dead space. These volumes and the effects of exercise are shown on Wasserman 1999[2] spirometer trace.

Lung Function Predictor

The calculator is based on the work by Miller (1996)[1] and Wasserman (1999)[2]. To obtain a prediction of your lung function please enter your height (cm), age and gender and then select the 'Calculate' button.

Height cm Age Gender
Forced Vital Capacity - FVC L
Forced expiratory volume in 1 second - FEV1 L
% Forced vital capacity in 1 second - FEV1/FVC %
Maximum voluntary ventilation - MVV L min

Predicted Normal Values

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 gender, age, height and ethnic origin and using similar test protocols and calibrated instruments .

Normal predicted values for ventilatory function generally vary as follows (Wasserman 1999)[2]:

  1. Gender: For a given height and age, males have a larger FEV1, FVC, FEF25-75% and PEF but a slightly lower FEV1/FVC%
  2. Age: FEV1, FVC, FEF25-75% and PEF increase and FEV1/FVC% decrease 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
  3. Height: All indices other than FEV1/FVC% increase with standing height
  4. Ethnic Origin: Caucasians have the largest FEV1 and FVC and, of the various ethnic groups, Polynesians are among the lowest. The values for people of African origin are 10 to 15% lower than for Caucasians of similar age, sex and height because for a given standing height their thorax is shorter. 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


References

  1. MILLER, A. (1996) Pulmonary Function Tests in Clinical and occupational disease. Philadelphia: Grune & Stratton
  2. WASSERMAN, K. et al. (1999) Principles of exercise testing. Baltimore Lippincott Williams & Wilkins
  3. McARDLE, W.D. et al. (2000) The Physiology Support System. In: McARDLE, W.D. et al., 2nd ed. Essentials of Exercise Physiology, USA: Lippincott Williams and Wilkins, p. 235

Related References

The following references provide additional information on this topic:

  • QUANJER, P. H. et al. (2012) Multi-ethnic reference values for spirometry for the 3–95-yr age range: the global lung function 2012 equations. European Respiratory Journal, 40 (6), p. 1324-1343.

Page Reference

If you quote information from this page in your work then the reference for this page is:

  • MACKENZIE, B. (2004) Measurement of Ventilatory Function [WWW] Available from: https://www.brianmac.co.uk/spirometer.htm [Accessed

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