Moment analysis of multibreath lung washout

Abstract

A moment analysis of multibreath nitrogen washout has been developed to provide a sensitive, quantitative measure that characterizes the inhomogeneity of pulmonary ventilation. To test the analysis scheme, we studied 5 normal subjects and 16 subjects with obstructive lung disease who performed each washout test at constant tidal volume and frequency. Subjects executed the wahout test 3-4 times at different tidal volumes (0.5-1.5 liters) and frequencies (10-30/min). Plotting washout data as dimensionless end-tidal nitrogen concentration versus the cumulative expired volume normalized by the functional residual capacity (CEV/FRC) renders the washout curves of each individual almost superposab le despite changes in breathing frequency and tidal volume from test to test. The dimensionless washout curve is treated as a distribution from which the normalized first (M1/Mo) and second (M2/Mo) moments are obtained. These parameters clearly display diagnostic clustering for various disease states. With respect to the normal subjects, the magnitude of M1/Mo was 26% greater for asthmatics, 38% greater for bronchitics, and 52% greater for emphysematics. This moment analysis provides an objective, quantitative assessment of the extent of ventilation inhomogeneities without specification of a lung model.

Multiple-Breath Washout as a Lung Function Test in Cystic Fibrosis. A Cystic Fibrosis Foundation Workshop Report

“…MRs are used to quantify the ventilation inhomogeneity present and are described in detail elsewhere (7)(8)(9). Calculation of MRs is more challenging, but it holds the potential advantage of describing the entire washout curve rather than LCI, which assesses one time point (final cumulative expired volume at 1/40 starting gas concentration).…”

Progressive ventilation inhomogeneity in infants with cystic fibrosis after pulmonary infection

“…MBW testing was performed using 4% sulphur-hexafluoride tracer gas and flow was measured using an ultrasonic flowmeter (Ecomedics AG, Duerton, Switzerland) as previously described [31,32]. A temperature model [33] and deadspace correction were applied to technically acceptable data and the functional residual capacity (FRC), LCI and moment ratios (M 1 /M 0 and M 2 /M 0 ) were derived [34,35]. MBW outcomes from infants with three or more acceptable measurements (FRC within 25% of median and LCI within one lung turnover) or two acceptable measurements (FRC within 10% of the highest value and LCI within one lung turnover) were averaged for inclusion in the analysis.…”

Changes in Ventilation Homogeneity from Preschool through Young Adulthood as Determined by Moment Analysis of Nitrogen Washout

“…Until recently, however, methods used to quantify the level of ventilation inhomogeneity from washout curves have been time consuming and suffered from relatively high degrees of intra and intersubject variability. MANW is a technique that treats the multibreath nitrogen washout curve as a unimodal distribution (1) and that takes all points of the curve into consideration. Since the mathematically derived moments are dimensionless areas under curves, moment ratios referencing the lst, 2nd, .…”

“…Each subject performed three nitrogen washouts during the test session. The subjects first breathed room air until Moment analysis of MANW is a relatively new technique of they were acclimated to the system, and they were then turned quantifying ventilation inhomogeneity (1,2). It has advantages into a circuit consisting of an oxygen supply, a one-way valve, over older indices derived from analysis of the shape of the and a pneumotachygraph in series.…”