Dynamic End-Tidal Forcing Technique: Modelling the Ventilatory Response to Carbon Dioxide

Abstract

The chemical regulation of breathing, the primary purpose of which is to ensure CO₂, O₂ and H⁺ homeostatis in arterial blood and brain tissue, involves two major chemosensitive structures, the central chemoreceptors and the peripheral chemoreceptors. In spite of much experimental work a definite answer to the question of the relative importance of the peripheral and the central chemoreceptors in the control of breathing is still lacking. Different classes of techniques have been used to separate the contributions of these receptors to the ventilatory responses following changes in blood gas tensions and acid-base disturbances (see ref. 1 and references cited therein). Among the different classes of techniques dynamic analysis methods are particularly attractive because they can be applied non invasively. The dynamic end-tidal forcing (DEF) technique, developed by Swanson and Bellville in 1970’s, is perhaps the most promising. This technique consists of three elements: 1) accurate breath-to- breath control of the end-tidal CO₂ and O₂, so that they can be forced to follow a prescribed pattern in time together with the measurement of the breath-to-breath ventilation; 2) mathematical modelling of the input-output relationship of the respiratory controller; 3) techniques to estimate the model parameters from the noisy input-output data.