Lung Function Measurement with Multiple-Breath-Helium Washout System

TL;DR

This study introduces a novel multiple-helium-breath-washout system using a quartz tuning fork for lung function testing, revealing differences in ventilation inhomogeneity among various respiratory conditions.

Contribution

The paper develops a new MBHW system with a quartz tuning fork detector and demonstrates its application in detecting ventilation inhomogeneity in different respiratory health states.

Findings

Mild asthmatics show higher ventilation inhomogeneity.

A feature in washout curves may indicate early ventilation issues in smokers.

Helium-based washout can differentiate respiratory conditions.

Abstract

Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique which can reflect the ventilation inhomogeneity of respiratory airways. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multi-breath-nitrogen (MBNW) washout tests. In this work, instead of using nitrogen, helium is used as the tracer gas and a multiple-helium-breath-washout (MBHW) system has been developed for the lung function study. A commercial quartz tuning fork with a resonance frequency of 32768 Hz has been used for detecting the change of the respiratory gas density. The resonance frequency of the tuning fork decreases linearly with increasing density of the surrounding gas. Knowing the CO2 concentration from the infrared carbon dioxide detector, the helium concentration can be determined. Results from 12 volunteers (3 mild asthmatics, 2 smokers, 1 with asthma history, 1 with COPD history, 5 normal) have shown that mild asthmatics have higher ventilation inhomogeneity in either conducting or acinar airways (or both). A feature has been found in single breath washout curve from 4 smokers with different length of smoking history which may indicate the early stage of respiratory ventilation inhomogeneity.