This is a cross-sectional observational study, aiming to validate the accuracy of tidal breathing measurements in infants made by VoluSense Pediatrics, a lung function method based on electromagnetic inductance plethysmography, compared to an ultrasonic flowmeter. VoluSense Pediatrics consists of a flexible vest placed around the torso of the baby, and changes in tidal volume and flow is measured. The study will enable a better understanding of the usefulness of this equipment. The equipment is made by VoluSense Norway AS, and is owned by Haukeland University Hospital.

All infants will be assessed at the pediatric department at Haukeland University Hospital, and all data obtained by the same two investigators (Bentsen and Olsen). The infants will be dressed in the appropriate-sized vest selected according to the length from the armpit to the hip of the child. Care will be taken to ensure that the vest fits snugly around the torso and that the width of the copper wire zig-zag coveres the entire thorax and abdomen including the pubic region. The vest will be applied directly to the skin; neither body nor diaper will be worn underneath. The infants will then be fed before they will be placed supine in a cot and encouraged to sleep. No sedation will be used. Once the infant has fallen asleep, data will be collected with VSP for 2-3 minutes before the Exhalyzer D® neonatal facemask connected in series with the ultrasonic flow sensor will be placed gently, but firmly over the infant's mouth and nose, ensuring a good seal. Once the facemask is in place, a marker will be inserted in the VSP recording. The Exhalyzer D® measurement will be started about thirty seconds after the facemask has been put on, to allow adaptation to the facemask. Simultaneous recording using both devices will then be done for about 1 minute before the mask will be removed. New markers will be inserted in the VSP recording as the Exhalyzer D® measurement is started and stopped facilitating analysis of the same breathing cycles.

Data will be analysed and graphs will be created with SPSS version 22 (IBM SPSS Statistics, New York, US) and MedCalc version 13.1 (MedCalc Software, Mariakerke, Belgium). Bland-Altman plots will be used to visualize agreement between the two measurement techniques. For each pair of measurements, the pairwise mean of the breathing parameters will be plotted on the x-axis, and the pairwise difference expressed as a percentage of their mean value on the y-axis. The mean difference and the 95% limits of agreement and their confidence intervals will be represented by horizontal lines in the graphs.

Inclusion Criteria:

• Healthy term born or preterm born babies ≥ 2000 grams.

Exclusion Criteria:

• Being in an unstable clinical condition.
• Weight < 2000 grams.

Term born and preterm born babies ≥ 2000 grams.