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.