Module 4: Physiology of the Respiratory System - Normal Curves and Patterns of Abnormality.

Normal Curves:

These two figures again illustrate the appearance of equivalent, normal flow/volume and volume/time curves. Note that Peak Flow occurs in the first 25% of exhaled volume on the F/V curve.

Patterns of abnormality that can be detected by spirometry:

The two most important patterns of abnormality detected by spirometry are:

1. Obstructive abnormalities related to abnormal airflow limitation caused by airways diseases such as asthma and COPD. Evaluation of the reversibility of obstruction is important.
2. Restrictive abnormalities, caused by a wide range of conditions, including lung or pleural fibrosis, skeletal abnormalities or muscular weakness.

An abnormal spirogram may have a combination of restrictive and obstructive and restrictive abnormalities.

Flow/volume loops, when they measure both a forced expiratory and inspiratory effort are also able to distinguish whether airways obstruction is in the intra- or extra-thoracic airways and whether it is fixed or variable. This is an additional clinical application of flow/volume curves.