Useful also in assesing acceptability of the manoeuvers: 1. Lack of early peak suggest poor effort. 2. Sudden tailing off of expiration curve suggest that the patient stopped blowing too early 3. Cough
COPD (chronic bronchitis, emphysema and the overlap between them).
-Airflow is reduced because the airways narrow and the FEV1 is reduced -Spirogram may continue to rise for more than 6 seconds because lung take longer to empty - FVC may also be reduced because gas is trapped behind obstructed bronchi due to increase in intrathoracic pressure during maneuver compresses airways causing early airway closure and gas trapping but this reduction to a lesser extent than FEV1
The measurements are related to the following factors:
FVC and flow rates decline with age. The value of FVC increases up to 24 years of age and remain stable to age 35.
All spirometric measurements increase with body weight. It is due to an increase in number and/or size of alveoli relative to airways, the larger lungs are likely to take longer than smaller one.
Most pulmonary function values are lower in female than male .
A spirometric results are positively correlated with weight to the extent that increased weight means growth or muscle mass. Beyond this (in obesity) spirometric values (and lung values specially ERV) decrease with greater weight.
Airways may collapse during forced expiration because of destruction of the supporting lung tissue causing very reduced flow at low lung volume and a characteristic (dog-leg) appearance to the flow volume curve
Full lung expantion is prevented by fibrotic tissue in the lung parenchyma and the FVC is reduced .
Elastic recoil may increased by fibrotic tissue lead to increase the airflow
Both FEV1 and FVC may be reduced because the lungs are small and stiff ,but the peak expiratory flow may be preserved or even higher than predicted leads to tall,narrow and steep flow volume loop in expiratory phase.