Comparison of Impulse Oscillometry with Spirometry to Assess Lung Function in Children with Sickle Cell Disease (SCD)

BACKGROUND

Spirometry is a validated pulmonary function test (PFT) for assessment of airway function in older children and adults, including children with SCD. However, it is not consistently reliable in children less than 6 years of age. Impulse oscillometry (IOS), a technique to evaluate airway obstruction via assessment of airway resistance, has been validated for use in children as young as 3 years, but has not been used widely in children with SCD.

OBJECTIVE

The primary objective was to examine the correlation between spirometry and oscillometry in assessment of airway obstruction and bronchodilator response in children with SCD > 6 years old, in order to assess its utility in our patient population. The a priori hypothesis is oscillometry correlates well with spirometry in assessment of airway function and bronchodilator responsiveness in children with SCD.

METHODS

After IRB approval, this prospective study was offered to all eligible patients followed in our sickle cell clinic who fulfilled age criteria and were due for a clinical PFT study. Clinical and laboratory data on the participants were collected from medical records. Symptoms of asthma and airway hyper-responsiveness were assessed using the modified ISAAC questionnaire prior to lung function testing. Airway function was concurrently assessed pre-and post-bronchodilator using oscillometry (area of reactance, AX; airway resistance at 5Hz, R5) and spirometry (forced expiratory volume in 1 second, FEV₁; forced mid-expiratory flow, FEF_25-75).

A Wilcoxon Signed-Rank test was run to compare the pre and post predicted percentages for AX, R5, FEV₁ and FEF_25-75. Next, Pearson's test for correlation was run to analyze the correlation between percent change from baseline for all variables (AX, R5, FEV₁ and FEF_25-75). McNemar's exact test was used to compare the proportion of improved patients for AX, R5, and FEV₁, FEF_25-75. All statistical tests were performed at the 5% significance level.

RESULTS

Twenty-three (23) out of 31 consented participants completed oscillometry and spirometry successfully. Of the participants studied, 20/23 were African American and 16/23 were male. The age range was 7.3 - 14.7 years at time of study and the SCD genotypes included HbSS (16/23), HbSC (3/23), HbSβ⁺thalassemia (2/23) and HbSβ°thalassemia (2/23). Of the 22 questionnaire respondents, 10 described a history of asthma symptoms (wheezing, whistling in chest, wheezing with exercise or coughing at night), but only 4/22 reported experiencing symptoms in the preceding 12 months.

We correlated the percent change from baseline between FEV₁ vs. AX (r² = -0.15, p= 0.49) and FEV₁ vs R5 (r² = -0.48, p = 0.02), as well as between FEF_25-75 vs. AX (r² = -0.24, p= 0.28) and FEF_25-75 vs. R5 (r² = -0.54, p= 0.008). We then compared the percentage of patients with improved bronchodilator response in FEV₁ vs. AX (21.74 vs 65.22%; p= 0.0063) and FEV₁ vs. R5 (21.74 vs 56.52%; p= 0.02) as well as FEF_25-75 vs. AX (39.13 vs. 65.22%; p= 0.11) and FEF_25-75 vs. R5 (39.13 vs. 56.52%; p= 0.29)

CONCLUSION

Our findings suggest that airway function as denoted by percent changes in FEV₁ and FEF_25-75 (spirometry) better correlate with R5 (oscillometry) than AX and that percent change in R5 can serve as a good measure of airway obstruction in children with SCD who are unable to perform spirometry. In addition, a higher proportion of SCD patients showed improved bronchodilator response in oscillometry (AX, R5) when compared to spirometry (FEV₁ , FEF_25-75 ), suggesting that impulse oscillometry may be more sensitive in detecting bronchodilator responsiveness in children with SCD when compared to spirometry, even in children without acute symptoms of asthma or airway hyper-responsiveness. Prospective studies of oscillometry in younger children with SCD are necessary to evaluate its role in SCD pulmonary disease.