Lung function tests
Techniques
Spirometry
Flow rates
Spirometry
Peak flow
Maximal respiratory pressures
Maximal pressure that can be produced by the patient trying to breath through a blocked mouthpiece
Useful in following the course of patients with neuromuscular disorders.
Diffusing capacity
Single-breath diffusing capacity for carbon monoxide (DLCO)
Oxygen desaturation during exercise
The six-minute walk test is a good index of physical function and therapeutic response
Arterial blood gases
Spirometry
Volume-time curve
Volume (liters) along the Y-axis and time (seconds) along the X-axis
Flow-volume loop
Parameters
There are four lung volumes and four lung capacities
A lung capacity consists of two or more lung volumes
The lung volumes are:
tidal volume (VT)
residual volume (RV)
The four lung capacities are:
total lung capacity (TLC)
inspiratory capacity (IC)
vital capacity (VC)
Obstructive Disease
In obstructive diseases FEV1 is diminished because of increased airway resistance to expiratory flow
The FVC may be decreased as well, due to the premature closure of airway in expiration
Generally not in the same proportion as FEV1
Therefore the FEV1/FVC ratio, also called Tiffeneau index, falls
e.g. asthma, COPD, chronic bronchitis, emphysema
The diagnosis of COPD is made when:
the FEV1/FVC ratio is less than 70% after bronchodilator medication has been given
FEV1% is less than 80% of predicted
Restrictive Disease
The FEV1 and FVC are both reduced proportionally
Thus the FEV1/FVC value may be normal or even increased as a result of decreased lung compliance
e.g. pulmonary fibrosis
Pictures