Module 4: Physiology of the Respiratory System - Mild obstruction on F/V Curve.

Mild Obstruction on F/V Curve:

The figures show comparable V/T and F/V in a subject with mild airflow obstruction. Note the slow incline of the volume/time curve where the effort has been prolonged for 10 seconds to ensure complete exhalation. This slow incline is reflected as a prolonged period of low flow seen in the magnified terminal portion of the flow/volume loop on the right. This gives the characteristic "scooped" appearance of the flow/volume curve in obstructive airways disease and reflects disease in the smaller conducting airways where resistance to flow has increased.

Airflow obstruction may be the result of inflamation in the airway lumen, constriction of bronchial smooth muscle or due to airways collapse due to a loss of lung elasticity as occurs in COPD/emphysema. This dynamic collapse of the airways occurs during exhalation and is accentuated by forced efforts. The figure on the left illustrates an inspiratory and expiratory flow/volume curve where severe obstruction is present. Note that the inspiratory limb has a normal appearance. The expiratory limb has a low peak flow indicating obstruction or dynamic collapse of some mid-sized conducting airways, there is pronounced scooping of the curve and a prolonged terminal period of low flow as air moves out of the high resistance, diseased smaller conducting airflows.