Area under the inspiratory flow-volume curve (AIN): Proposed normative values

Area of Science:

• Respiratory physiology
• Pulmonary function testing

Background:

• The area under the expiratory flow-volume curve (AEX) is a recognized functional measurement in respiratory physiology.
• The area under the inspiratory flow-volume loop (AIN) shows potential for characterizing both upper and lower airway obstruction.

Purpose of the Study:

• To develop normative reference values for AIN.
• To enable the identification of deviations from normal AIN measurements.

Main Methods:

• Analysis of 4,980 spirometry tests from non-smoking, healthy individuals.
• Calculation of AIN and derived indices, including the square root of AIN (Sqrt AIN).

Main Results:

• Normative data for AIN and Sqrt AIN were established, with values stratified by gender.
• The mean Sqrt AIN/Sqrt AEX (%) was 101.3, with a lower limit of normal (LLN) of 71.8%.
• Some AIN measurements demonstrated independence from age, race, height, and weight.

Conclusions:

• The area under the inspiratory flow-volume curve (AIN) and its derived indices provide a valuable tool for assessing upper airway diseases.
• AIN measurements can help identify conditions affecting the larynx, trachea, or major bronchi.
• The potential independence of AIN from certain demographic factors enhances its utility in clinical practice.