THE INFLUENCE OF SLEEPING POSITION ON FUNCTIONAL RESIDUAL CAPACITY AND EFFECTIVE PULMONARY BLOOD-FLOW IN HEALTHY NEONATES

Variation in body position has been shown to affect respiratory functi on in adults and neonates with and without respiratory illness. At pre sent it remains unclear why respiratory function should be affected by different body positions. Mle hypothesized that the effect of body we ight on the relatively compliant chest wall of the newborn infant in t he prone position would cause a reduction in functional residual capac ity (FRC) and a compensatory improvement in ventilation/perfusion matc hing as measured by effective pulmonary blood flow. To evaluate this, a paired crossover study was performed on 12 normal newborn infants. T he inert gas (argon) rebreathing method adapted for neonates was used to measure FRC. Simultaneously effective pulmonary blood flow (QP(eff) ) was determined using Freon 22 and a mass spectrometer with computeri zed analysis. The babies were studied in three different positions in random order: prone, supine, and right lateral decubitus. The means (9 5% confidence intervals) of the three groups for FRC were 23.8 (19.2 t o 28.4), 23.8 (20.2 to 27.5), and 24.3 (19.5 to 29.2) ml/kg, respectiv ely (P = 0.59), and for QP(eff) were 104 (91 to 116), 108 (95 to 122), 109 (97 to 122) ml/kg-min, respectively (P = 0.11). Thus no significa nt differences were demonstrated. In nine of the babies, a repeat supi ne measurement was taken at the end of the study to assess repeatabili ty of the method. In these nine babies alone the results were 22.7 (19 .1 to 26.3) and 22.1 (18.6 to 25.6) ml/kg for FRC, and 102 (89 to 116) and 98 (90 to 107) ml/kg-min for QP(eff). The coefficients of repeata bility were 4.7 ml/kg for FRC (21%) and 30 ml/kg-min for QP(eff) (30%) . (C) 1996 Wiley-Liss, Inc.