Protective and defensive airway reflexes in premature infants.

The incidence of respiratory reactions to stimulation of the nasal and propharyngeal mucose was studied in 44 newborn premature infants. The inhalation of menthol fumes or the administration of drops of Mukoseptonex to the nasal mucosa caused transient respiratory arrest or a drop in the respiration rate. The heart rate rose during chemical stimulation of the nasal mucosa, possibly in association with a general arousal reaction. Mechanical stimulation of the nasal mucosal with a nylon fibre elicited an expulsive reaction in 95% of the cases. As distinct from experimental animals, sneezing was not preceded by a deep initial inspiration. Stimulation of the oropharyngeal region produced transient apnoea in 24.5% of the cases, in 18% expiratory reactions reminiscent of the expiration reflex, in 33% independent, intensive inspiratory reactions and in 24.5% cough. Cough from both the oropharyngeal and the laryngeal region had a pronounced inspiratory component. Independent inspiratory reactions may to some extent be co-responsible for the high incidence of aspirations in the neonatal period.

Mechanics of breathing during sneezing and crying in premature newborns.

In 22 premature newborns the oesophageal pressure, airflow and tidal volume were recorded and the values of various parameters of breathing mechanics were calculated during sneezing and crying. The deep initial inspiration during sneezing occurred in only 20% of the newborns. In the expulsive phase of sneezing, the oesophageal pressure reached the mean value 7.0 +/- 0.3 kPa. The peak expiratory airflow was 0.126 +/- 0.005 1Xs-1 on average: 6.6 times higher than the flow during quiet breathing. The dynamic compliance in this phase decreased from 28.9 +/- 0.5 to 19.3 +/- 2.2 ml X kPa-1 (P less than 0.01), and the total pulmonary resistance increased markedly from 7.9 +/- 1.0 to 50.0 +/- 0.7 kPaX1(-1)Xs (P less than 0.001). On crying the respiratory rate decreased and the inspiration/expiration ratio changed from 1:1.46 to 1:5.1 (P less than 0.001). The change in the ratio was due to the shortening of inspiration as well as the prolongation of expiration. The mean values of oesophageal pressure were -2.9 +/- 0.4 kPa in the inspiratory phase of crying, and 3.7 +/- 0.2 kPa in the expiratory phase. The ventilation during crying increased by 255% in comparison to the quiet ventilation. The dynamic compliance decreased to 13.9 +/- 1.8 mlXkPa-1 and the total pulmonary resistance rose to 26.5 +/- 2.4 kPaX1(-1)Xs.

Effect of lung inflation on the respiratory frequency and heart rate of premature neonates.

Changes in the respiratory frequency and heart rate in response to 10 seconds' inflation of the lungs with oxygen by the CPAP method were studied in 32 premature neonates. Elevation of the pressure in the airways and lungs of 0.25, 0.49, 0.73 and 0.98 kPa led to a slower respiration rate or to apnoea. The incidence of apnoea rose in proportion to the pressure. When inflation was started, forced inspiratory efforts (a gasp reflex) occurred. The incidence of the efforts was higher at higher inflation pressures, but their intensity was not correlated to the size of the pressure. They were manifested in a drop in oesophageal pressure to a mean -2.0 +/- 0.2 kPa and their mean duration was 169 +/- 8 ms. The administration of oxygen without an increase in pressure produced neither apnoea nor forced inspiratory reactions. Neither an increase in the pressure in the airways and lungs to the above values, nor the plain administration of oxygen, produced any significant changes in the instantaneous heart rate.

Upper airway reflexes in newborns with respiratory distress syndrome.

In 16 newborns with respiratory distress syndrome (RDS) not artificially ventilated, oesophageal pressure was recorded with an electromanometer and the reactions to mechanical stimulation of the upper airways by means of a nylon fibre were investigated. The results were compared with the values obtained in 16 newborns without cardiorespiratory disturbances. The reactions were evoked by mechanical stimulation of the airways. Mechanical stimulation of the nasal mucosa produced expulsive reactions only in 45% of cases in newborns with RDS as compared with 95% in healthy newborns (p less than 0.001). Stimulation of the oropharyngeal and laryngeal regions elicited expulsive reactions in 48% of cases in newborns with RDS, but 74% in healthy newborns (p less than 0.001). In other cases, inhibition of breathing or apnoea was the most common reaction. The expulsive component of responses such as sneezing, expiratory reaction and crying was weaker in newborns with RDS than in control infants. The inspiratory component of sneezing and coughing, on the contrary, was stronger in newborns with RDS. These results indicate that active elimination of irritants from the airways is reduced in newborns with RDS.