Lung function tests and common lung conditions Flashcards
What is an obstructive lung disease ?
Obstruction to airflow, especially on expiration
What are some obstructive lung diseases ?
Asthma- over reactive constriction of bronchial smooth muscles, increases resistance
COPD- chronic obstructive pulmonary disease
- chronic bronchitis- inflammation of bronchi
- emphysema- destruction of alveoli, loss of elasticity
What is a restrictive lung disease ?
Restriction of lung expansion
Loss of compliance
What are some restrictive lung diseases ?
Fibrosis- formation of excess fibrous connective tissue that creates a stiff lung
- idiopathic, 50:100,000 new cases per year UK
- asbestosis
Infant respiratory distress syndrome- insufficient surfactant production
oedema-fluid builds up around alveoli creating pressure which requires more force to inflate
pneumothorax- air in the pleural cavity
What is spirometry ?
Technique used to measure lung function
Measurements can be static or dynamic
What does static mean ?
Where the only consideration made is volume exhaled
What does dynamic mean ?
Where the time taken to exhale a certain amount is what is being measured
What can spirometry directly measure ?
Tidal volume IRV ERV Inspiratory capacity Vital capacity
What is the FEV1 in a young healthy male ?
4L
What is the FVC in a young, healthy male ?
5L
What is the normal value of FEV1/FVC ?
80%
What are the FEV and FVC for an obstructive respiratory disorder ?
Rate at which air is expelled is exhaled much slower
Total expired volume (FVC) is also reduced (FRC may be increased)
Major effect is on airways and so FEV1 is reduced to a greater extent than FVC
Ratio also reduced - 42%
What are the FEV and FVC for an restrictive respiratory disorder ?
Absolute rate of airflow is reduced (FEV reduced)
Total volume is reduced due to limitations to lung expansion (FVC)
Ratio remains constant or can increase as a large proportion of volume can be exhaled in the first second
What are the limitations of FEV1/FVC ?
Obstructive: both FEV and FVC fall but FEV more so. So ratio is reduced
Restrictive: both FEV and FVC fall so ratio remains normal, or may even increase, despite severe compromise of function
Therefore normal FEV1/FVC ratio not always indicative of health
What is a forced expiratory flow?
Average expired flow over the middle of a forced vital capacity
