Am. J. Respir. Crit. Care Med., Vol 155, No. 2, Feb 1997, 649-653.
Determinants of lung volume in spontaneously breathing preterm infants
CF Poets, GA Rau, K Neuber, M Gappa and J Seidenberg
Department of Pediatric Pulmonology, Hannover Medical School, Germany.
To study the effects of apneic pauses, sighs, and breathing patterns on
functional residual capacity (FRC), we measured FRC repeatedly in 48
healthy preterm infants (weight at study 2,042 +/- 316 g [mean +/- SD],
postconceptional age 36.6 +/- 2.0 wk), during unsedated sleep using a
modified heliox/nitrogen washout technique. Breathing movements and pulse
oximeter saturation (SpO2) were recorded throughout and recordings analyzed
for the presence of regular and nonregular breathing pattern, apneic
pauses, sighs, and desaturations (SpO2 < 90%) during the last 2 min
prior to each FRC measurement. FRC was lower during nonregular than during
regular breathing pattern (23.3 +/- 7.2 ml/kg versus 26.9 +/- 7.8 ml/kg, p
< 0.02); however, this apparent effect of breathing pattern disappeared
after controlling the data for apneic pauses. Apneic pauses resulted in a
significant decrease in FRC: mean FRC was 20.0 +/- 6.8 ml/kg if measured
within 2 min of an apneic pause, 26.0 +/- 6.9 ml/kg if measured after a
sigh (p < 0.001), and 24.0 +/- 7.7 ml/kg if there had been neither a
sigh nor an apneic pause (p < 0.05). The interval between the apneic
pause and the FRC measurement had no effect on FRC. There was an inverse
correlation between FRC and the speed with which SpO2 fell during
desaturation (r = -O.5, p < 0.03). Apneic pauses resulted in a
persistent reduction in FRC in these preterm infants. Sighs appeared to
restore FRC. The significant relationship between FRC and the speed of
desaturation found in this study underscores the importance of endogenous
or exogenous strategies that help to increase FRC, such as sighs or the
application of continuous positive airway pressure, for the stability of
oxygenation in preterm infants who have difficulty maintaining their
oxygenation.
