Alveoli and abnormal surfactant.
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Biomedical subjects
Publications and source records attributed to C J Morley.
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40 preterm, ventilated infants (gestational ages 24-33 weeks) were entered into a double-blind randomised trial to assess the effect of oral theophylline on lung function and ventilator dependence. Theophylline administration was associated with a significant improvement in compliance (P less than 0.05) and hastened weaning from ventilation (P less than 0.01).
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Preterm infants who were making expiratory efforts against ventilator inflation were randomised to be paralysed with pancuronium or to receive no paralysing agent during ventilation. Pneumothoraces developed in all 11 unparalysed babies but in only 1 of 11 (p less than 0.0004) of those managed with pancuronium, which had no serious side-effects. In 34 infants excluded from the trial because they were not breathing against the ventilator, no pneumothoraces developed.
The stimulating and moderating factors of augmented inspirations provoked by artificial ventilation have been studied in 40 preterm babies on 182 different occasions. Provoked augmented inspirations were demonstrated by recording spontaneous respiratory activity during artificial ventilation by means of an oesophageal balloon and a pneumotachograph. Augmented inspirations were only seen during 18% of the study occasions. The frequency of this reflex was inversely related to the lung compliance as was the ventilator pressure necessary to provoke the augmented inspiration. The inflating volume which stimulated the reflex, when related to body weight, was similar in all the babies. Augmented inspirations were always provoked during the rapid rise in ventilator pressure at the onset of each inflation. Neonates who were recovering from paralysis by pancuronium and others being treated with theophylline both showed an increased frequency of augmented inspirations. It is possible that theophylline could be used to harness this advantageous reflex for the benefit of the ventilated preterm neonate.
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The respiratory response to therapeutic lung inflation by artificial ventilation in premature babies has been studied. Both the Hering-Breuer and an augmented inspiratory reflex could be provoked by ventilator inflation in neonates as premature as 25 weeks gestational age. No chemo-receptor control was demonstrated on the presence of these reflexes. Augmented inspirations were only seen in the first five postnatal days regardless of gestational age, but the Hering-Breuer reflex persisted throughout the period of study of 11 days. The frequency of elicitation of augmented inspirations was shown to be inversely related to the dynamic compliance. The relative stimulation of these two respiratory reflexes may explain why some infants are easy to ventilate and others difficult.
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Oesophageal pressure measured with an air-filled, thin latex balloon on a 6 French gauge catheter can accurately measure intraoesophageal pressures in ventilated preterm babies. Intraoesophageal pressures and intrapleural pressures are equivalent. Less than 10% of the applied positive ventilator pressure is transmitted to the oesophageal balloon and the intrapleural catheter (intercostal drain). The oesophageal traces show that ventilated babies breath independently of the ventilator. The largest deflections recorded from the oesophageal trace are from spontaneous inspiratory activity. During paralysis with pancuronium spontaneous respiration is inhibited, peristaltic waves are still recorded, and there is little transmitted pressure from the ventilator to the oesophagus or intercostal drain.
Artificial lung surfactant prepared with pure dipalmitoylphosphatidylcholine and phosphatidylglycerol in a ratio of 7:3 was made as a dry powder and then blown down an endotracheal tube into the lungs of 22 very premature babies at birth. Only one dose was given. The treated babies did better than their 33 controls. Fewer needed ventilation, and those who did required lower pressures in the first six hours of life. None of the treated babies died, compared with 8 of the controls.
It is suggested that the phospholipids at the alveolar/air interface exhibit both thermodynamic (equilibrium) and kinetic forces during the course of a respiratory cycle. The alveolae are kept open at full expiration by a residue of nearly pure dipalmitoyl phosphatidylcholine which is condensed and therefore, incompressible at 37 degrees C.
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