Infant Pulmonary Mechanics During Tidal Breathing

Abstract

After completing this article, readers should be able to: 1. Define what compliance and resistance represent when used to describe the respiratory system. 2. Calculate dynamic pulmonary compliance and resistance. 3. Characterize passive mechanics and how they are invoked. 4. Describe the single-compartment series elastic-resistive model of the lung. Tests of infant pulmonary function continue to evolve, broadening our understanding of normal growth and development of infant lungs and airways and providing diagnostic and therapeutic approaches for management of respiratory disease. Traditionally, measurements made during tidal breathing in infants have provided valuable information about lung mechanics, namely, compliance and resistance. In this article, we discuss the physiology on which these measurements are made and briefly describe how several tests are performed in infants to calculate tidal mechanics. Both clinical applications and limitations of the various techniques also are reviewed. Compliance describes the change in volume for a given change in pressure (ΔV/ΔP). When used to describe the respiratory system, compliance represents the elastic properties of the airways, pulmonary parenchyma, and chest wall. Resistance is defined as the amount of pressure required for a given flow rate (ΔP/V) and describes the nonelastic or frictional properties of the respiratory system, including resistance to airflow and tissue resistance. Because pressure change (ΔP=P1-P2), is a common factor in both compliance and resistance measurements, the choice of where P1 and P2 are measured defines the system or structures described by these mechanics. Thus, if pressures are measured at the proximal and distal ends of an airway, compliance and resistance of the airway can be calculated. If pressures are measured at the airway opening and in the pleural space (transpulmonary pressure), the airways, alveoli, and lung parenchyma are included, and lung compliance and resistance can be calculated. If pressures are measured at the airway opening …