Estimation of intrapleural pressure in the newborn

We examined the changes in esophageal (Pes), proximal airway (Paw), and direct intrapleural (Ppl) pressure measurements following end-expiratory airway occlusion in anesthetized spontaneously breathing newborn piglets. Simultaneous occluded pressure measurements were obtained during resting ventilation, inspiratory resistive loaded (IRL) breathing, and bilateral transvenous phrenic nerve stimulation. During spontaneous resting ventilation, occluded Paw/Ppl averaged 104 +/- 4% and occluded Pes/Ppl averaged 89 +/- 3%. Similar values were found for occluded spontaneous breaths with IRL. During phrenic nerve stimulation at end-expiratory lung volume, occluded Paw/Ppl averaged 104 +/- 6% while occluded Pes/Ppl decreased to 70 +/- 22%. We conclude that proximal airway pressure more accurately reflects intrapleural pressure than esophageal pressure with occlusion in newborn swine. During phrenic nerve stimulation, esophageal pressure measures are grossly inaccurate estimates of intrapleural pressure with occlusion.