Respiratory Muscle Activity Related to Flow and Lung Volume in Preterm Infants Compared With Term Infants

Abstract

Infants with chronic lung disease (CLD) have a capacity to maintain functional lung volume despite alterations to their lung mechanics. We hypothesize that they achieve this by altering breathing patterns and dynamic elevation of lung volume, leading to differences in the relationship between respiratory muscle activity, flow and lung volume. Lung function and transcutaneous electromyography of the respiratory muscles (rEMG) were measured in 20 infants with CLD and in 39 healthy age-matched controls during quiet sleep. We compared coefficient of variations (CVs) of rEMG and the temporal relationship of rEMG variables, to flow and lung volume [functional residual capacity (FRC)] between these groups. The time between the start of inspiratory muscle activity and the resulting flow (t ria )-in relation to respiratory cycle time-was significantly longer in infants with CLD. Although FRC had similar associations with t ria and postinspiratory activity (corrected for respiratory cycle time), the CV of the diaphragmatic rEMG was lower in CLD infants (22.6 versus 31.0%, p ϭ 0.030). The temporal relationship of rEMG to flow and FRC and the loss of adaptive variability provide additional information on coping mechanisms in infants with CLD. This technique could be used for noninvasive bedside monitoring of CLD. (Pediatr Res 68: 339-343, 2010) C hronic lung disease (CLD) of infancy represents the final common pathway of a heterogeneous group of pulmonary diseases that start in the neonatal period and usually evolve from acute respiratory disorders experienced by newborn infants (1). Tidal breathing parameters, lung volume, and ventilation homogeneity are affected by the morphologic changes in CLD and can be measured by lung function studies. Some studies showed decreased endexpiratory volume [functional residual capacity (FRC)] and lung clearance index (LCI) (2) in sedated infants, whereas other studies in infants during natural sleep could not confirm these observed differences in FRC and LCI between healthy infants and infants with CLD (3). We (4) and other authors (3) indicated that the latter findings are in line with the following clinical observations: infants with CLD in natural sleep may have a high capacity to maintain relatively normal lung volume and relatively normal gas exchange, despite alterations to their lung mechanics, whereas this capacity may be reduced during sedation.Recently, we described the combination of matched tidal breathing measurements and transcutaneous electromyography of the respiratory muscles (rEMG) in healthy infants (5). Our findings suggested that the interaction of the respiratory muscles and lung mechanics are actively controlled breath to breath and that simultaneous measurement of tidal breathing parameters and rEMG parameters potentially provide a more comprehensive picture of pulmonary mechanics in disease. We hypothesize that infants with CLD attempt to maintain a relatively normal lung volume by altering breathing patterns and dynamical elevation of lung volume. Thes...

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