Abstract: A physiologic analyzer is disclosed for continuous measurement of a subject's metabolic functions in which signals from ventilatory flow rate sensors and gas analyzers are processed to provide continuous measurement of the subject's ventilatory volume, carbon dioxide production, oxygen consumption, respiratory exchange ratio, and other metabolic functions of interest. An expiratory oxygen concentration sampler is enabled only when oxygen concentration deviates from the inspired value. When enabled, the sampler provides at its output a series of discrete signals proportional to successive instantaneous values of oxygen concentration in expired breath. A similar sampler is used in the processing of the carbon dioxide concentration signals. A respiratory cycle timer measures elapsed time between successive inspirations and provides a breath duration signal which is used for rate computations.