Cardiac contraction affects respiratory airflow in the term newborn infant

In studies in the newborn infant, it is often assumed that there are similarities in airflow in successive breaths, and, therefore, it is only necessary to measure parameters in a small number of breaths. However, other studies have shown considerable variability in breathing patterns in successive breaths. It was, therefore, decided to examine the variability in the patterns of airflow. By use of the trunk plethysmograph, tidal breathing was measured in 20 term newborn infants during quiet sleep in the first week after delivery; airflow was calculated by differentiating the tidal volume signal. The ECG was also recorded. In all infants, it was found that the shapes of both inspiratory and expiratory airflow showed considerable differences in successive breaths. Spectral analysis of airflow showed the presence of peaks not only in the respiratory rate, as expected, but also in the heart rate. In another five infants studied during episodes of periodic breathing, small fluctuations in airflow were found during the apneic intervals at the same rate as the heart rate. It was concluded that this is not an artifact, but that cardiac contraction modulates respiratory airflow in the term newborn infant, contributing significantly to breath-to-breath variability. These cardiac related changes in airflow amount to approximately one sixth of the tidal airflow.