Laryngeal Function: Supporting the Transition from a Fetus to Spontaneously Breathing Newborn using Phase Contrast X-ray Imaging

Premature newborns commonly receive non-invasive respiratory support, such as continuous positive airway pressure (CPAP), delivered by a face mask in the delivery room. This requires the infant to breathe for itself, but if it does not, positive pressure ventilation (PPV) is applied. However, this approach has a high failure rate, necessitating premature newborns to be invasively intubated and mechanically ventilated. Importantly, CPAP has been implemented into clinical practice without any understanding for how it interacts with the changing physiology at birth. Before birth, the fetus closes its larynx when it is not making breathing movements (is apneic), which blocks anything from entering or leaving the lungs, and only opens the larynx when it makes breathing movements. We hypothesised, if the newborn is not breathing, it will close its larynx and prevent air from entering the lung. Using phase contrast X-ray imaging, we imaged the
larynx of premature newborn rabbits to determine whether the fetal pattern of larynx closure persists after birth. We showed that immediately after birth the larynx is predominantly closed and only opens during a breath, preventing PPV from ventilating the lung. Once the newborn had aerated its lungs and established a stable breathing pattern, the larynx remained predominantly open, allowing PPV to ventilate the lung. These findings provided first understanding for why CPAP can fail in premature newborns in the delivery room.
To understand why the larynx switches from mostly closed into a predominantly open state after birth, we investigated the role of oxygenation. We showed that hypoxia is a potent inhibitor of spontaneous breathing and causes the larynx to close, whereas oxygen stimulates breathing and opens the larynx. Our ongoing work is aimed at generating the evidence required to target interventions that
improve the success of non-invasive respiratory support for premature newborns in the delivery room.