Numerical simulation of nasal airflows and thermal air modification in newborns.

Warming, filtering, and humidification of inspired air are major functions of the upper airway, which can be negatively altered by local disorders or surgical interventions. These functions have not been described in neonates because of ethical and technical problems difficult to solve. Numerical simulations can get around these limitations. The objective of this study was to analyze physiological nasal airflow and thermal distribution using computational fluid dynamics (CFD) techniques in neonates. CT imaging of neonates was collected from the Pediatric Radiology Department of our center. CFD has been used to simulate nasal airflow numerically, with ambient air set at 19 °C, following the recommendations for a neonate's bedroom. Thermal distribution within the nasal cavity was analyzed and coupled with airflow patterns over complete respiratory cycles. Sixteen patients have been included in the study. During inspiration, important air warming is noticed in the first centimeter of the nasal cavity (+ 8 °C at the anterior end of the inferior turbinate). During the expiration phase, the temperature decreases slightly (- 3 °C) between the pharynx and the nostrils. A model with asymmetric nasal fossae showed that nasal obstruction leads to decreased airflow and abnormally high temperatures in the obstructed side (+ 2 °C at the nasal valve, + 4 °C at the choana). According to our results, the nasal valve area is of crucial importance in air warming in neonates, when ambient air is 19 °C, since about 70% of air warming is performed in this area. When needed, surgical interventions should respect the anatomy of this zone and restore normal airflows and warming. Graphical abstract .