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Used for the diagnosis of chest diseases and assessment of severity. Lung function tests also provide a measure of the efficiency of the respiratory system (Evans, 1994).

There are 5 main types of test;

  • 1.Peak Flow Rate
  • 2.Dynamic lung volumes
  • 3.Static lung volumes
  • 4.Transfer Fator
  • 5.Postbasic Tests

Peak Flow Rate

Gives a crude estimate of lung function, reflecting larger airway function. It is very effort dependant and the patient is usually given practice runs.

It is measured by the patient giving a short sharp blow into a peak flow meter, which then measures how much air (litres per minute)is being blown out. The average of three attempts is taken, with a rest period of 1 minute between each attempt to avoid bronchoconstriction. The peak flow rate in normal adults will vary depending on age and height (Barnes, 2001).

Dynamic Lung Volumes

These measure the forced vital capacity (FVC) and the forced expiratory volume (FEV). The FVC is the maximum volume of air that can be forcibly exhaled following an inspiration. While the FEV is the maximum volume of air that can be forcibly exhaled in one second following a full inspiration (Evans, 1994).

A spirometer is the instrument used to measure dynamic lung volumes. The patients nose is clipped to ensure that all inspirations/expirations are via the mouth. As with the peak flow rate, the patient is given practice runs (Halpin, 2001).

Static Lung Volumes

Measured in one of two ways;

  • 1.Using a closed circuit helium rebreather. By measuring the dilution of the helium in the circuit the lung volumes can be calculated.
  • 2.Body plethysmograph. The patient sits in an airtight chamber and breathes normally while connected to a volume measuring system (Evans, 1994).

Transfer Factor

This test measures the diffusing capacity of the lungs for carbon monoxide over a one minute period at a pressure gradient of 1 mmHg across the alveolar membrane. Normal values are dependant on age and sex (Evans, 1994).

Postbasic Tests

  • Ear lobe capillary blood pH and gas analysis - used in diagnosis to assess oxygen requirement.
  • Exercise-induced asthma test - involves monitoring spirometery readings before and after exercise.
  • The 6 minute walking test - assesses disablity and effectiveness of rehabilitation programes.
  • Progressive multistage exercise test - monitors pulse rate, oxygen consumption and cardiac output during exercise to exhaustion on a treadmill. Results indicate whether dyspnoea is due to heart or lung disease.
  • Portable oxygen assessment - used in conjunction with the 6 minue walking test to determine whether oxygen therapy is required.
  • Long-term oxygen therapy assessment - measures the oxygen concentration needed to raise the arterial oxygen above a defined level. Used to determine the need for an oxygen concentrator.
  • Airways resistance and conductance - provides additional information about any narrowing of the airways or stiffness of the lungs (Evans, 1994)

References

Halpin, D.M.G (2001)COPD.London. Mosby

Barnes, P.J. (2001) Chronic Obstructive Pulmonary Disease. London. Science Press.

Evans, D.M.D. (1994) Special Tests.London. Mosby.

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