EXPIRATORY TIME CONSTANTS BY ELECTRICAL IMPEDANCE TOMOGRAPHY IN HYPOXEMIC AND HYPERCAPNIC ACUTE LUNG FAILURE - A FEASIBILITY STUDY

Pl Róka,W Windisch,C Karagiannidis,Sh Bohm,F Ender,S Strassmann,Ad Waldmann

doi:10.1186/2197-425x-3-s1-a1000

Abstract

During relaxed breathing expiration can be compared to a RC-circuit with R being the airway resistance, C the respiratory system compliance and τ = R∙C the expiratory time constant. For the adult respiratory system, the normal τ is around 0.8 s. Different lung pathologies have different time constants. Two common disease types are the acute respiratory distress syndrome (ARDS) and the chronic obstructive pulmonary disease (COPD). ARDS is characterized by stiff or noncompliant lungs with low compliance and normal or lower resistance which results in shorter τ. COPD is characterized by impaired airflow or high airways resistance and high compliance which results higher τ. τ reveals information about respiratory mechanics and the time required for the lungs to empty. Traditional pulmonary function tests provide global information only. EIT is a non-invasive real-time imaging technology which determines changes of lung volumes on a regional basis assuming that local impedance changes are proportional to local changes in lung volume. Pikkemaat [1] introduced the method to calculate regional τ, what we improved and applied in 10 patients.

Highlights

During relaxed breathing expiration can be compared to a RC-circuit with R being the airway resistance, C the respiratory system compliance and τ = R∙C the expiratory time constant
Time constants were calculated from global and regional volume signals measured with EIT in 10 patients with hypoxemic or hypercapnic (COPD) lung failure
EIT data were measured with Swisstom BB2 (Swisstom AG, Switzerland) and the time constants of ensemble averaged of 10 consecutive breaths of 5 patients with chronic obstructive pulmonary disease (COPD) and 5 with acute respiratory distress syndrome (ARDS) were determined

Summary

Introduction

During relaxed breathing expiration can be compared to a RC-circuit with R being the airway resistance, C the respiratory system compliance and τ = R∙C the expiratory time constant. Different lung pathologies have different time constants. Two common disease types are the acute respiratory distress syndrome (ARDS) and the chronic obstructive pulmonary disease (COPD). ARDS is characterized by stiff or noncompliant lungs with low compliance and normal or lower resistance which results in shorter τ. COPD is characterized by impaired airflow or high airways resistance and high compliance which results higher τ. Τ reveals information about respiratory mechanics and the time required for the lungs to empty. EIT is a non-invasive real-time imaging technology which determines changes of lung volumes on a regional basis assuming that local impedance changes are proportional to local changes in lung volume. Pikkemaat [1] introduced the method to calculate regional τ, what we improved and applied in 10 patients

Methods

Results and Conclusions

Pikkemaat R