A plethysmographic method for assessment of lung function in mechanically ventilated very low birth weight infants.

We have developed and tested a plethysmographic method for assessment of lung function in mechanically ventilated very low birth weight infants during intensive care. Information about the mechanics of the respiratory system is obtained from the respiratory flow as measured by volume displacement plethysmography and from airway pressure measured in the artificial airway. Data on lung volumes, ventilation, and distribution of ventilation is obtained simultaneously by combining the respiratory flow measurements with nitrogen concentration analyses of the respiratory gas. No significant differences were found when the estimations of mechanical parameters and FRC were compared with reference methods and when determinations of the same parameters were repeated in the same subjects. The plethysmograph was shown to be safe and convenient to use, even in studies lasting several hours.