Tests of Respiratory Muscle Strength In Neonates

Abstract

After completing this article, readers should be able to: 1. Describe the underlying cause of respiratory failure in about 50% of preterm infants who require intubation and mechanical ventilation. 2. Compare compliance characteristics of the chest wall in infants, older children, and adults. 3. List some of the conditions seen in neonates that can adversely affect respiratory muscle function. 4. List noninvasive tests for assessing respiratory muscle strength in neonates. Chest wall mechanics of neonates and infants play an essential role in ventilation that frequently is underappreciated. Dysfunction of the respiratory muscles can cause both a disease process and an inability of the patient to compensate for it. As an example, respiratory muscle failure may be the underlying cause in about 50% of preterm infants who have ventilatory failure. (1) In this article, we detail the current understanding of the physiology of the respiratory muscles in neonates and discuss a number of tests designed to assess their function. Mechanically, the respiratory system can be thought of as being composed of two components. The first includes the respiratory muscles, the rib cage, and the anterior abdominal wall, which together make up the “pump,” whose function is to move air in and out of the lungs. The second includes the airways and lung parenchyma through which gas exchange occurs and can be referred to as the “load” on which the pump must act. For ventilation to occur, the respiratory pump must overcome both the frictional (eg, airway resistance) and tissue elastic forces (eg, lung and chest wall compliance) that create the load. The balance between the capabilities of the pump and the magnitude of the load can influence whether respiratory “success” or “failure” occurs. The chest wall, which contains muscles and skeletal structures, undergoes dramatic maturational changes over the first several years of life. In addition …