Apparatus to attain and maintain target end tidal partial pressure of a gas

Abstract

A processor obtains input of a logistically attainable end tidal partial pressure of gas X (PetX[i]T) for one or more respective breaths [i] and input of a prospective computation of an amount of gas X required to be inspired by the subject in an inspired gas to target the PetX[i]T for a respective breath [i] using inputs required to utilize a mass balance relationship, wherein one or more values required to control the amount of gas X in a volume of gas delivered to the subject is output from an expression of the mass balance relationship. The mass balance relationship is expressed in a form which takes into account (prospectively), for a respective breath [i], the amount of gas X in the capillaries surrounding the alveoli and the amount of gas X in the alveoli, optionally based on a model of the lung which accounts for those sub-volumes of gas in the lung which substantially affect the alveolar gas X concentration affecting mass transfer.

Description

FIELD OF THE INVENTION[0001]The present invention relates to an apparatus and method for controlling end tidal gas partial pressures in spontaneously breathing or ventilated subjects and to the use of such an apparatus and method for research, diagnostic and therapeutic purposes.BACKGROUND OF THE INVENTION[0002]Techniques for controlling end-tidal partial pressures of carbon dioxide, oxygen and other gases are gaining increasing importance for a variety of research, diagnostic and medicinal purposes. Methods for controlling end tidal pressures of gases have gained particular importance as a means for manipulating arterial levels of carbon dioxide (and also oxygen), for example to provide a controlled vasoactive stimulus to enable the measurement of cerebrovascular reactivity (CVR) e.g. by MRI.[0003]Conventional methods of manipulating arterial carbon dioxide levels such as breath holding, hyperventilation and inhalation of fixed concentration of carbon dioxide balanced with medical ...

AI Technical Summary

Benefits of technology

[0012]Based on this prospective determination control of the amount of gas X in a volume of gas delivered to the subject in a respective breath [i] is implemented to target the respective PetX[i]T for a breath [i]. Implementing a calibration step as necessary in advance may improve targeting.

[0155]The time course of predicted mixed-venous gases is used to compute the series of inspired gas mixtures required to realize the target end-tidal partial pressures of gases. In this way, assuming that the end-tidal partial pressures of gases adhere to the targets allows prediction of the mixed-venous gases, and prediction of the mixed-venous gases allows a priori calculation of the inspired gas mixtures required to accurately implement the end-tidal targets. There is no requirement to modify the series of the inspired gas mixtures calculated before execution of the sequence based on deviations of the measured end-tidal partial pressures of gases from the targets during execution of the sequence.

Problems solved by technology

Conventional methods of manipulating arterial carbon dioxide levels such as breath holding, hyperventilation and inhalation of fixed concentration of carbon dioxide balanced with medical air or oxygen are deficient in their ability to rapidly and accurately attain targeted arterial carbon dioxide partial pressures for the purposes of routinely measuring vascular reactivity in a rapid and reliable manner.

Previous attempts at controlling the end-tidal partial pressures of gases have failed to account for these complex dynamics, and have therefore produced mediocre results.

However, without any additional intervention, the end-tidal partial pressures of gases vary slowly and irregularly as exchange occurs at the lungs and tissues.

Furthermore, the ventilatory response to perturbations in the end-tidal partial pressures of gases is generally unpredictable and potentially unstable.

Therefore, any changes in the end-tidal partial pressures of gases are immediately challenged by a disruptive response in the alveolar ventilation.

Technically, such a system suffers from the same limitations as all negative feedback control systems—an inherent trade-off between response time and stability.

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