Inductive plethysmography--a facilitated postural calibration technique for rapid and accurate tidal volume determination in low birth weight premature newborns.

Inductive plethysmography is a noninvasive method of measuring lung volumes in infants. This technique, however, has had very limited use in premature newborns because of the difficulty of calibrating the device with regard to the small tidal volumes (VT) in such infants. The present study describes a facilitated calibration of the inductive plethysmograph in low birth weight infants. The technique depends on generating significantly different compartmentalization of VT into rib cage and abdominal components by changing the infant's position from supine to upright. Linear regression analyses were performed to compare VT measurements made in 9 premature infants with the inductive plethysmograph and the pneumotachygraph; an overall Z-transformed correlation of 501 breath-to-breath comparisons yielded an r value of 0.80; the mean VT (pneumotachygraph) was 13.9 +/- 4.7 ml SD; the mean VT (inductive plethysmograph) was 14.3 +/- 5.1 ml SD. It is concluded that inductive plethysmography is an accurate method to measure VT in small premature infants. Moreover, the ease of the two-position technique for calibration of the device gives the inductive plethysmograph greater utility as a clinical and research tool for measuring lung volumes in premature infants.