Bennett WD, Zeman KL. J Appl Physiol. 2004;97:821–826
Purpose of the Study.
The fractional deposition (DF) of fine particles was measured in the lower airways of healthy children during their resting breathing pattern to allow for additional investigation of the epidemiologic link between airborne particulates and respiratory morbidity in children.
The study included 36 children, aged 6 to 13 years, with no acute respiratory infections within the past 4 weeks or previous history of lung disease.
To avoid the higher minute ventilation induced in children by breathing on a mouthpiece, resting breathing pattern was measured by respiratory inductance plethysmography using elastic inductance bands around the chest and abdomen with expansion and contraction calibrated to spirometry. The DF of 2-μm carnauba wax aerosol was then measured by using light-scattering photometry at the mouth, with the child breathing according to their previously determined resting breathing pattern. The numbers of inhaled and expired particles were calculated as a function of the inspiratory and expiratory times, tidal flow, and particle concentrations, and the DF was reported as the proportion of particles not expired. The rate of particle deposition (Drate) was a function of the DF and the minute ventilation.
There was good correlation between resting breathing pattern measured by respiratory inductance plethysmography and the breathing pattern measured during DF ascertainment. The mean DF was 0.22 ± 0.10, similar to resting DF measured in adults in previous studies. Tidal volume was the best predictor of DF (r = 0.79; P < .001), and DF was also correlated with body mass index (BMI) (r = 0.47; P = .004). Children with a BMI in the >95th percentile had nearly twice the DF of those with a BMI in the <25th percentile (0.28 ± 0.13 vs 0.15 ± 0.06; P < .02). Resting minute ventilation was also higher in the overweight children (8.5 ± 2.2 vs 5.9 ± 1.1 L/min; P < .01). Drate was correlated with BMI (r = 0.46; P = .004) and was 2.8 times higher in children with a BMI in the >95th percentile compared with those with a BMI in the <25th percentile (P < .02).
Children with higher BMIs may be at greater risk of respiratory morbidity associated with inhalation of airborne fine-particulate matter.
A focus of this study was the determination of resting particle deposition; however, the higher minute ventilation seen with traditional mouthpiece breathing in children may be a closer approximation of how a child would breathe during activity. Assessment of fine-particle deposition during both types of breathing patterns may provide useful information. The higher resting rate of 2-μm particle deposition in children with elevated BMIs suggests that fine particulates may make a greater contribution to respiratory morbidity in obese children, possibly contributing to the association between obesity and the incidence of asthma symptoms. Additional study of a larger number of children, including those with a BMI of >30, would be helpful to confirm these findings.