CO2-sensitivity in newborn and young infants tested by the rebreathing method. Methodological aspects.

The rebreathing method in newborn and young infants was tested with regard to the effects of increasing levels of CO2 on the behavioral state and to the influence of facial stimulation caused by the use of a face mask and pneumotachograph on the breathing pattern. Successive increases in inspired CO2 levels from 3 to 8.5% did not change the behavioral state. The application or removal of a face mask, with or without an attached pneumotachograph, caused an immediate disruption in the breathing pattern which lasted 10-40 s. Thereafter, breathing stabilized. When only the face mask was used, the increases in minute ventilation, tidal volume and cycle duration of 7, 13 and 5%, respectively, were transient and lasted for 40-50 breaths. The breathing then returned to control levels. In contrast, breathing through the face mask connected to the pneumotachograph caused a long-lasting increase in ventilation (12%) due to the retention of CO2 in the spirometric circuit. We conclude that the inhalation of a continuously increasing mixture of 3-8.5% CO2 in O2 did not influence the behavioral state and that the effect of face mask on breathing pattern was transient.