Measuring V̇O2 kinetics

The common perception of V̇O₂ kinetics analysis is that it is too complex and difficult to grasp. Consequently, in laboratories around the world a great deal of data has been collected and either incompletely analysed or ignored. This is an almost criminal shame because the dynamic phases of the gas exchange responses at exercise onset are a rich source of information that can provide unique insights into metabolic function and dysfunction. This chapter walks the reader through various analysis techniques for kinetics data from simple identification of some parameters of the V̇O₂ response such as t ₅₀ (time to 50% of the final response) and t₆₃ (τ, time to 63% of the final response) to calculation of these parameters using semi-logarithmic analysis. Finally, some of the complex models that require computer-driven least squares iterative techniques are presented. Over the past half-century, data collection techniques have progressed considerably from periodic collection (every 15, 30 or 60 s) and analysis of expired gases in Douglas bags to measurement of breath-to-breath gas exchange. In part, this progress has been facilitated by the development of rapidly responding gas analysers and economical flow meters (pneumotachographs, anemometers, turbines and ultrasonic flow probes) and has forced the development and refinement of efficient gas exchange algorithms that can estimate alveolar gas exchange by accounting for changes in lung gas stores between consecutive breaths (e.g. Auchincloss et al., 1966; Linnarsson, 1974; Wessel et al., 1979; Beaver et al., 1981; Giezendanner et al., 1983; Swanson and Sherrill, 1983; di Prampero and Lafortuna, 1989). Whereas breath-to-breath resolution of the metabolic responses at exercise onset is extremely powerful, it generates unique problems related to the often high variability between breaths that leads sometimes to a low signal-to-noise ratio. In addition, there is the desire to resolve multiple kinetics parameters (i.e. up to three time delays and three time constants) some of which may have a high degree of interdependence. The majority of these issues are dealt with in this chapter which interdigitates closely with Chapter 3.