Effect of airway inflation pressure on forced expiratory maneuvers from raised lung volume in infants *

The raised lung volume technique is increasingly used to measure forced expiratory maneuvers in infants. However, there is no consensus regarding the optimal airway inflation pressure (P inf ) required for such maneuvers, or the influence of small changes in P inf within and between infants. The aim of this study was to assess the effect of small differences (0.2–0.3 kPa) in P inf on forced vital capacity (FVC), forced expired volume in 0.5 sec (FEV 0.5 ), and forced expired flow at 75% of vital capacity (FEF 75 ), all derived from the raised volume rapid thoraco‐abdominal compression (RVRTC) technique. Randomized paired forced expiratory maneuvers were obtained in 32 healthy infants ( 3.9–39.3 weeks old, 3.8–9.9 kg) with the safety pressure relief valve for P inf set to 2.7 kPa or 3.0 kPa (27 or 30 cm H 2 0). When mean (SD) P inf was increased by 8.4 (2.8)%, there was a significant ( P  < 0.01) increase in mean (SD) FVC, FEV 0.5 , and FEF 75 by 5.8 (5.7)%, 6.1 (6)%, and 8.3 (16.2)%, respectively. In conclusion, relatively small differences in P inf will result in significant differences in FVC, FEV 0.5 , and FEF 75 by RVRTC technique. Precision in setting and reporting the applied P inf is therefore essential, particularly if data are to be compared between centers. Pediatr Pulmonol. 2002; 33:130–134. © 2002 Wiley‐Liss, Inc.