Distribution of ventilation in normal children

Abnormal Lung Clearance Index in Cystic Fibrosis Children with Normal FEV1 and Single-Breath Nitrogen Washout Test

Single- and multiple-breath washout tests (SBW and MBW) measure ventilation inhomogeneity, but the relationship between them is unclear. Forty-three subjects with cystic fibrosis (CF) and healthy controls (HC) 8-21 years of age were recruited (CF = 30 and HC = 13) and performed nitrogen MBW, vital capacity SBW, spirometry, and plethysmography. Mean phase III slope from SBW (SIII) and lung clearance index (LCI) were significantly different between CF and HC (p = 0.017 and p < 0.0001, respectively). Based on Pearson correlation, SIII and LCI showed strong correlation (ρ = 0.81, p < 0.0001). Both SIII and LCI significantly correlated with spirometry (all p < 0.05). Among CF subjects with normal FEV₁ (≥ 80%; n = 17), 76% (n = 13) had normal SIII but abnormal LCI. We conclude that LCI can be abnormal despite normal SIII and FEV₁ in CF children. Although LCI and SIII showed strong correlation, our results suggest that LCI is a better test to detect ventilation inhomogeneity in CF children with normal FEV₁.

Structural change of the acinus during growth assessed by single-breath tracer gas washouts

In the present investigation we wanted to study the functional and structural development of the acinus, using a vital capacity (VC) single-breath tracer gas washout test, modified so that the subject inspired helium (He) and sulfurhexafluoride (SF6) in oxygen. We used as indices of ventilation the slopes of N2 (SN2), He (SHe), and SF6 (SSF6) as well as (SSF6-SHe), which may be considered an index of acinar mixing linked to acinar structure. We studied two populations: Population I-49 children and adolescents (8-18 years of age); and Population II-18 non-smoking adults (22-48 years of age). Age and vital capacity (VC) were correlated in Population I, but not in Population II. In both populations there was a significant decrease of SN2, SSF6, and SHe as a function of VC. Growth and VC changes were determinants of these decreases in Population I, while only changes in VC were significant determinants in Population II. For each gas, the regression lines of slope versus VC for Populations I and II were not significantly different; we therefore suggest that the decrease in slope in Population I is mainly due to an increase in lung volume during growth. (SSF6-SHe) was not correlated with VC in Population I and was negatively correlated with VC in Population II (P < 0.01). This discrepancy implies that a child will have a smaller (SSF6-SHe) than an adult at comparable VC. Since the magnitude of (SSF6-SHe) values are related to acinar branching asymmetry, our results suggest that asymmetry of the acinus increases with lung growth and maturation.

Computerized single-breath nitrogen washout in children: variability and reproducibility

The variability, short-term (1 hour) and long-term (2 weeks) reproducibility of the variables derived from the single-breath N2 test were evaluated in a group of 56 healthy children aged 10 to 16 years with a computerized system. The variability was low for vital capacity and total lung capacity (coefficient of variation less than 3%), moderate for residual volume and phase III N2 slope (9 and 13%) and very high for closing volume (more than 50%). A closing volume could not be identified by the computer algorithm in 18.3% of the trials. The reproducibility of the variables was satisfactory both at 1 hour and at 2 weeks, with the exception of the closing volume, whose increase at 2 weeks seemed to be due to methodological factors. We conclude that reliable results of static lung volumes and phase III N2 slope, but not of closing volume, may be obtained in children by a computerized system in epidemiological studies.