Clinical and physiological aspects of preterm lung disease

Abstract

This thesis explores three aspects of preterm lung disease, with a focus on physiological assessment and outcomes. Nasal high flow (HF) is widely used in preterm infants, but the optimal approach to weaning HF is unclear. A longitudinal cohort study involving 40 preterm infants was performed exploring changes in diaphragm electrical activity (Edi), an objective measure of respiratory muscle effort, that occur during weaning. HF was weaned according to a standardized protocol, and Edi measured serially. Edi did not change significantly with flow rate reduction steps, but significantly increased when discontinuing HF. This study provides a safe and effective framework for weaning HF in preterm infants, supported by physiological data, and identified Edi as a useful measure of respiratory muscle effort for future study. Preterm infants requiring ongoing positive pressure support near term are a particularly high-risk subgroup, but little is known about the specific characteristics and outcomes of these infants. A national surveillance study of life-threatening bronchopulmonary dysplasia, defined as need for positive pressure respiratory support or pulmonary vasodilator therapy at ≥38 weeks corrected gestation, was performed via the British Paediatric Surveillance Unit. Significant morbidity and mortality were identified in this group, along with marked variation in practice, particularly in key areas of postnatal steroid use and pulmonary hypertension management. Longer term, children born preterm have lung function abnormalities and an altered ventilatory response to exercise that persist with age. Expiratory flow limitation leading to dynamic hyperinflation during exercise has been proposed as a contributory mechanism, but this is difficult to assess during standard exercise testing. Optoelectronic plethysmography (OEP) is a motion analysis system that non-invasively tracks changes in thoracoabdominal volumes. A feasibility study was performed in a cohort of school-aged children, demonstrating the ability of OEP to measure ventilatory changes during exercise and directly assess for dynamic hyperinflation.