Implementing the Three-Equation Method of Measuring Single Breath Carbon Monoxide Diffusing Capacity

Abstract

Conventional methods of measuring the single breath diffusing capacity of the lung for carbon monoxide (DLcoSB) are based on the Krogh equation, which is valid only during breath holding. Rigid standardization is used to approximate a pure breath hold manoeuvre, but variations in performing the manoeuvre cause errors in the measurement of DLcoSB. The authors previously described a method of measuring DLcoSBusing separate equations describing carbon monoxide uptake during each phase of the manoeuvre: inhalation, breath holding and exhalation. The method is manoeuvre-independent, uses all of the exhaled alveolar gas to improve estimates of mean DLcoSBand lung volume, and is more accurate and precise than conventional methods. A slow, submaximal, more physiological single breath manoeuvre can be used to measure DLcoSBin patients who cannot achieve the flow rates and breath hold times necessary for the standardized manoeuvre. The method was initially implemented using prototype equipment but commercial systems are now available that are capable of implementing this method. The authors describe how to implement the method and discuss considerations to be made in its use.