Absence of inspiratory laryngeal constrictor muscle activity during nasal neurally adjusted ventilatory assist in newborn lambs

Abstract

It has been demonstrated that a progressive increase in nasal pressure support ventilation (nPSV) leads to an active inspiratory glottal closure in non-sedated newborn lambs, which limits lung ventilation (24, 33). Unlike nPSV, the pressure delivered during nasal Neurally Adjusted Ventilatory Assist (nNAVA) is synchronized to the diaphragm electrical activity on inspiration (36). Given the tight neural integration of the glottal dilators and constrictors with diaphragm activity on inspiration and expiration respectively, the aim of the present study was to test the hypothesis that inspiratory glottal closure does not develop during nNAVA. Polysomnographic recordings were performed in eight non-sedated, chronically instrumented lambs, which were ventilated with progressively increasing levels of nPSV and nNAVA, in random order. States of alertness, diaphragm and glottal muscle electrical activity, tracheal pressure, SpO2, tracheal PETCO2 and respiratory inductive plethysmography were continuously recorded. While phasic inspiratory glottal constrictor electrical activity appeared with increasing levels of nPSV in 5 out of 8 lambs, it was never observed at any nNAVA level in any lamb, even at maximal achievable nNAVA levels. In addition, a decrease in arterial PCO2 was neither necessary nor sufficient for the development of phasic inspiratory glottal constrictor activity. In conclusion, nNAVA does not induce active glottal closure in non-sedated newborn lambs at high-pressure levels, in contrast to nPSV.