The airway occlusion techniques for assessing passive respiratory mechanics have become well established methods in fullterm neonates and older infants. The single breath technique (SBT) is frequently used for assessing lung function in intubated infants on neonatal intensive care units. However, less is known about the reliability of these quick and noninvasive techniques in healthy preterm infants. The aim of this study was to evaluate these methods in healthy unintubated preterm infants to facilitate both establishment of reference values and more meaningful interpretation of lung function assessments in the neonatal unit. Forty-seven studies were attempted in 31 healthy preterm infants (gestational age 29-36 weeks; body weight 1.88 +/- 0.28 kg; mean +/- SD) during the first 2 weeks of life, using both the multiple occlusion technique (MOT) and the SBT. Whereas technically acceptable respiratory system compliance (Crs) data from either the MOT or the SBT were obtained on 37 occasions in 25 infants, satisfactory results from both techniques were achieved only on 22 occasions. In these infants mean +/- SD Crs was 28.1 +/- 5.2 mL kPa-1 when assessed by MOT and 29.1 +/- 6.0 mL kPa-1 when using the SBT. The mean difference between technically satisfactory paired Crs values obtained with MOT and SBT was less than 5% (range, +28 to -18%). By contrast, in infants in whom data were invalidated as a result of expiratory airflow braking, failure to relax or instability of the end-expiratory level, gross discrepancies occurred between the techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Both end-inspiratory (EIO) and end-expiratory (EEO) airway occlusions are used to calculate the strength of the Hering-Breuer inflation reflex (HBIR) in infants. However, the influence of the timing of such occlusions is unknown, as is the extent to which changes in volume within and above the tidal range affect this reflex. The purpose of this study was to compare both techniques and to evaluate the volume dependency of the HBIR in healthy, sleeping infants up to 1 yr of age. The strength of the HBIR was expressed as the ratio of expiratory or inspiratory time during EIO or EEO, respectively, to that recorded during spontaneous breathing, i.e., as the "inhibitory ratio" (IR). Paired measurements of the EIO and EEO in 26 naturally sleeping newborn and 15 lightly sedated infants at approximately 1 yr showed no statistically significant differences in the IR according to technique: mean (95% CI) of the difference (EIO - EEO) being -0.02 (-0.17, 0.13) during the first week of life and 0.04 (-0.14, 0.22) at 1 yr. During tidal breathing, a volume threshold of approximately 4 ml/kg was required to evoke the HBIR. Marked volume and age dependency were observed. In newborn infants, occlusions at approximately 10 ml/kg during sighs always resulted in an IR > 4, whereas a similar response was only evoked at 25 ml/kg in older infants. Age-related changes in the volume threshold may reflect maturational changes in the control of breathing and respiratory mechanics throughout the first year of life.

Chloral hydrate is frequently used to sedate infants for lung function testing. While no effect on respiratory function has been demonstrated, a recent study has reported a fall in oxygen saturation (Sa O 2) following sedation in wheezy infants. This study was designed to assess the effects of the closely related but less gastrically irritant drug triclofos sodium on respiratory rate (RR), heart rate (HR), and Sa O 2 in infants without cardiopulmonary disease. Paired measurements using respiratory inductance plethysmography and pulse oximetry were obtained in 10 infants (4–19 months of age) during natural and sedated sleep. Following sedation with triclofos, mean RR rose by 1.9 breaths min−1 (95% confidence intervals [Cl] of the mean difference: 0.13–3.7 min−1). Mean heart rate rose by 5.5 beats min−1 (95% Cl: −0.9–11.9 min−1). Mean Sa O 2 fell by 0.68% (95% Cl – 1.8–0.45%). None of these changes are considered to be of clinical importance, and only the change in RR reached statistical significance at the 5% level. Pediatr Pulmonol 1991; 10:40–45.