Oronasal Ventilation Partitioning in Adults and Children: Effect on Aerosol Deposition in Airways

An accurate estimate of aerosol deposition in children as well as in adults is of special importance for dosimetry after inhalation of radionuclides. The breathing mode, oral, nasal or oronasal, influences total deposition and relative fractions of the inhaled aerosols that will deposit in the extrathoracic and thoracic airways. Human models of airway deposition rely on standard values based on experimental data. In the absence of specific information, the pattern of airflow partitioning between the two routes is assumed to be similar in adults and in children. In order to better assess breathing modes in healthy subjects of various ages, for who specific data are needed, the oronasal partitioning of ventilation during graded exercise was studied in 10 adults, aged 35 to 56 and 10 children, aged 8 to 16. During the test, oral and nasal flow rates were separately recorded, using a mouthpiece and a nasal mask. For all the subjects, the exercise test was symptom limited while for adults a safety limit was added to either cardiac frequency (CF > 160 min-1) or systolic blood pressure (SBP > 210 mm Hg or 28 kPa). Increments of power output were 25 W for adults and 10 W in children, each minute. It was observed that 6 adults out of 10 had a exclusively nasal ventilation at rest and switched abruptly to oronasal breathing during exercise when total ventilatory rate reached 38 to 65 1.min-1. Nine out of the 10 children already had oronasal ventilation at rest and merely increased their oral fraction from 20 to 84% of the total airflow at rest, up to 32 to 99% for the highest power output during the exercise test. The highest oral fractions were seen in the youngest children. The airflow partition between nose and mouth varied greatly among subjects, and this variability seems partly explained by airway resistances. From these results and from those of the relevant literature, the conclusion is that the ventilatory behaviour, both at rest and during exercise tends to be age-dependent. To assess the possible effects of these observations on the reliability of the radiological doses recommended by ICRP, deposition was calculated for 1 and 5 µm particles in adults and for 1 µm in children according to these data and compared with the model's defaults.