Lung Function Tests in Neonates and Infants with Chronic Lung Disease of Infancy: Functional Residual Capacity

Abstract

Summary. This is the second paper in a review series that will summarize available data and discuss the potential role of lung function testing in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy. The current paper addresses the expansive subject of measurements of lung volume using plethysmography and gas dilution/ washout techniques. Following orientation of the reader to the subject area, we focus our comments on areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. Measurements of lung volume are important both for assessing growth and development of lungs in health and disease, and for interpreting volume-dependent lung function parameters such as respiratory compliance, resistance, forced expiratory flows, and indices of gas-mixing efficiency. Acute neonatal lung disease is characterized by severely reduced functional residual capacity (FRC), with treatments aimed at securing optimal lung recruitment. While FRC may remain reduced in established chronic lung disease of infancy, more commonly it becomes normalized or even elevated due to hyperinflation, with or without gas-trapping, secondary to airway obstruction. Ideally, accurate and reliable bedside measurements of FRC would be feasible from birth, throughout all phases of postnatal care (including assisted ventilation), and during subsequent long-term follow-up. Although lung volume measurements in extremely preterm infants were described in a research environment, resolution of several issues is required before such investigations can be translated into routine clinical monitoring. Pediatr

New reference equations to improve interpretation of infant lung function

“…2,25 Plethysmographic Functional Residual Capacity (FRC p ) FRC p was measured as described previously. 1,26,27 Up to five technically satisfactory measurements were obtained and the mean of 3-5 valid measurements reported. In exceptional cases, the mean of two good quality, repeatable (within 5% of each other) measurements was used.…”

Lung function in infants and young children with chronic lung disease of infancy: The next steps?

“…[8][9][10][11]13,14 Problems in study design, including failure to recruit sufficient subjects or appropriate controls, ambiguity regarding the definition of CLDI, 3,[19][20][21] or true clinical status at time of testing, 22 use of inappropriate equipment or methods with respect to underlying pathophysiology and lack of data on repeatability with which to interpret what constitutes a clinically significant change, 14,15 have all contributed to contradictory results and difficulties in drawing firm conclusions from many of the published studies in this field. If we are to avoid such problems in the future, there is an urgent need for collaboration between clinicians and physiologists to facilitate optimal use of the exciting technological developments.…”

“…The importance of assessing lung volume in this challenging population has long been recognized, with firm evidence that acute neonatal lung disease is characterized by severely reduced functional residual capacity (FRC). 10 While FRC may remain reduced in established CLDI, more commonly it becomes normalized or even elevated due to hyperinflation, with or without gas trapping, secondary to airway obstruction. Unfortunately, interpretation of these findings and their use in guiding clinical management is still limited by difficulties in 'normalizing data' according to body size and maturation.…”

“…1 During the past year, a series of review articles in Pediatric Pulmonology has responded to this challenge by summarizing the published literature on lung function in infants and young children with acute neonatal respiratory disorders and CLDI. [8][9][10][11][12][13][14] So what have we learnt so far, and what are the next steps?…”

Chest radiograph thoracic areas and lung volumes in infants developing bronchopulmonary dysplasia

“…11 Such a technique, although demonstrating infants with respiratory distress syndrome have low lung volumes and their response to such treatment strategies as addition of positive end expiratory pressure, 12 may under-record lung volumes if there is an elevated respiratory resistance, as suboptimal gas diffusion occurs in lung units with long time constants. Assessment of lung area by calculation of chest radiograph (CXR) thoracic areas avoids such a problem.…”