Measurements of respiration were compared in normal, full term and premature infants before and after application of 5 cm H2O continuous negative pressure (CNEG) around the body below the neck. Mean minute ventilation in the full term infants decreased when CNEG was applied, secondary to a decrease in respiratory rate, with tidal volume relatively unchanged. The premature infants showed no consistent ventilatory response to CNEG. There were variable changes in occlusion pressure at increased lung volume. Observation with rib cage and abdomen anterior-posterior (A-P) magnetometers showed that the increase in end-expiratory lung volume was accounted for largely by expansion of the rib cage so that the configuration of the diaphragm and its mechanical advantage were maintained. These results suggest that the diaphragm is the major determinant of mask occlusion pressure in infants.Speculation
The effects of increased lung volume on the configuration of the chest wall may relate to the success of continuous distending pressure in the treatment of respiratory disorders in infants, including apnea of prematurity.