Respiratory gas analysis

Abstract

This chapter outlines key aspects for ensuring the accuracy of respiratory gas data collection and describes methods of data analysis for the subsequent derivation of parameters of physiological function. Respiratory gas analysis is a cornerstone of physiological testing procedures, perhaps most commonly for the determination of pulmonary gas exchange variables, particularly oxygen uptake and carbon dioxide production. The Douglas bag technique incorporates a mouth-piece or face-mask attached via a sample tube to a 100–200 litre polyvinyl chloride sealed ‘bag’ which captures the expirate via a one-way valve operated by the practitioner. Commercial metabolic carts for respiratory gas analysis on a breath-by-breath basis typically incorporate a measurement of ventilatory flow with simultaneous, continuous sampling of gas fractions by directing samples of expirate to gas analysers. Breath-by-breath respiratory gas analysis enables the determination of physiological parameters requiring a more rapid sampling rate than can be accurately achieved using the Douglas bag technique.