[Respiratory mechanics and respiratory regulation in healthy and respiratory-diseased newborn infants of different gestational ages].

The interaction of lung mechanics, peripheral lung reflexes and chemosensitivity of the respiratory center were studied in over 80 newborns. Healthy newborns (gestational age between 30 and 41 weeks) and newborns with respiratory distress syndrome (RDS) (gestational age between 29 and 40 weeks) were studied on the first day of life. Spontaneously breathing newborns were examined using the airway occlusion technique (AOT), and intubated babies using the injection technique (IT) to measure the compliance of the respiratory system (Crs), the strength of the inspiration inhibiting reflex (IIR) and inspiratory time during airway occlusion (Ti occ), and index of chemosensitivity of the respiratory center. Crs in healthy newborns increased only slightly but statistically significant (p less than 0.001) with gestational age. Crs of newborns with RDS had an overwhelming influence on their prognosis. Newborns with Crs of less than or equal to 1 developed respiratory failure and needed ventilatory support. Newborns with a Crs less than or equal to 0.5 died despite respiratory therapy. The activity of the peripheral vagally mediated reflex system also depended on the Crs. Our results indicate that the decrease in reflex activity with gestational age is not brought about by neurologic maturation but is caused by the increasing Crs. We conclude that the peripheral vagally mediated reflexes remain the same throughout life, just the boundary condition Crs, which is given by the lung mechanics, is different for premature or mature newborns and changes with age. The chemosensitivity of the respiratory center for CO2 was characterized by the inspiratory time after an expiratory occlusion (Ti occ) which is not influenced by lung mechanics. Ti occ correlated significantly with pCO2. The relation between Ti occ and pCO2 was similar for premature and mature, healthy and respiratory ill newborns. Consequently, chemosensitivity, expressed as the ratio of Ti occ and pCO2, is independent of gestational age.