Obesity, tidal volume, and pulmonary deposition of fine particulate matter in children with asthma.

BACKGROUND: Obese children with asthma are more vulnerable to air pollution, especially fine particulate matter (PM2.5), but reasons are poorly understood. We hypothesised that differences in breathing patterns (tidal volume, respiratory rate and minute ventilation) due to elevated body mass index (BMI) may contribute to this finding. OBJECTIVE: To investigate the association of BMI with breathing patterns and deposition of inhaled PM2.5. METHODS: Baseline data from a prospective study of children with asthma were analysed (n=174). Tidal breathing was measured by a pitot-tube flowmeter, from which tidal volume, respiratory rate and minute ventilation were obtained. The association of BMI z-score with breathing patterns was estimated in a multivariable model adjusted for age, height, race, sex and asthma severity. A particle dosimetry model simulated PM2.5 lung deposition based on BMI-associated changes in breathing patterns. RESULTS: Higher BMI was associated with higher tidal volume (adjusted mean difference (aMD) between obese and normal-range BMI of 25 mL, 95% CI 5-45 mL) and minute ventilation (aMD 453 mL·min-1, 95% CI 123-784 mL·min-1). Higher tidal volumes caused higher fractional deposition of PM2.5 in the lung, driven by greater alveolar deposition. This translated into obese participants having greater per-breath retention of inhaled PM2.5 (aMD in alveolar deposition fraction of 3.4%, 95% CI 1.3-5.5%), leading to worse PM2.5 deposition rates. CONCLUSIONS: Obese children with asthma breathe at higher tidal volumes that may increase the efficiency of PM2.5 deposition in the lung. This finding may partially explain why obese children with asthma exhibit greater sensitivity to air pollution.

Obstructive sleep apnea screening in children with asthma.

RATIONALE: Obstructive sleep apnea is highly prevalent in children with asthma, particularly in obese children. The sleep-related breathing disorder screening questionnaire has low screening accuracy for obstructive sleep apnea in children with asthma. Our goal was to identify the questions on the sleep-related breathing disorder survey associated with obstructive sleep apnea in children with asthma. METHODS: Participants completed the survey, underwent polysomnography and their body mass index z-score was measured. Participants with survey scores above 0.33 were considered high risk for obstructive sleep apnea and those with an apnea-hypopnea index ≥ 2 events/h classified as having obstructive sleep apnea. Logistic regression was used to examine the association of each survey question and obstructive sleep apnea. Positive and negative predictive values were calculated to estimate screening accuracy. RESULTS: The prevalence of obstructive sleep apnea was 40% in our sample (n = 136). Loud snoring, morning dry mouth, and being overweight were the survey questions associated with obstructive sleep apnea. The composite survey score obtained from all 22 questions had positive and negative predictive values of 51.0% and 65.5%, while the combined model of loud snoring, morning dry mouth, and being overweight had positive and negative predictive values of 60.3% and 77.6%. On the other hand, the body mass index z-score alone had positive and negative predictive values of 76.3% and 72.2%. CONCLUSIONS: The body mass index z-score is useful for obstructive sleep apnea screening in children with asthma and should be applied routinely given its simplicity and concerns that obstructive sleep apnea may contribute to asthma morbidity.