Breathing In and Out: Airway Resistance

Abstract

An important complement to understanding lung function by spirometry is measurement of airway resistance. Under laminar flow conditions, airway resistance varies inversely with the fourth power of the radius, making the influence of airway diameter and lung volume key determinants of airway resistance. Airway resistance is commonly measured using the relationship of mouth pressure, box pressure, and airflow obtained during body plethysmography, where it is typically expressed as specific airway resistance (sRaw) or specific airway conductance (sGaw). Airway resistance may also be assessed from measurement of respiratory system resistance (Rrs) using the forced oscillation technique and from the interruption of flow using the interrupter technique (Rint). In all cases, airway resistance is a highly sensitive measure that may be useful in detecting disease abnormality, including bronchodilator and bronchoconstrictive responses, even when spirometry is normal.