Validity and reliability of selected commercially available metabolic analyzer systems

Automated metabolic gas analysis systems have advanced considerably over the past decade. They provide an abundance of information, which is not possible by using the traditional Douglas bag method and have become an essential tool in both physiological monitoring and in the diagnosis of cardiopulmonary disease. The validity and reliability of the different online metabolic analyzer systems are not well known, with relatively few independent studies being published. The purpose of this review was to examine and evaluate current literature regarding the validity and reliability of commercially available metabolic analyzer systems. This review reveals significant differences between the available systems in the way that they capture and process basic respiratory measurements. Online metabolic analyzer systems were found to vary significantly when compared with Douglas bag methods. These variations have the potential to introduce error into the accuracy with which the health of cardiovascular system can be assessed or training loads can be assigned. Compounding this is the fact that many automated systems are a "black box", which makes it easy to generate data without the user having much understanding of how the data were generated. In conclusion automated metabolic analyser systems are a scientifically robust method for the evaluation of cardiopulmonary function. Individual researchers and clinicians must, however, be able to make their own decisions about the level of error that is tolerable for their individual needs. This presents a significant practical challenge in light of the speed with which technical developments in the field occur and we make some suggestions for the formulation of intersystem comparison studies.