A Novel, Low-Cost Mobile Metabolic Measurement (M3) System - Summary/Abstract Indirect calorimetry (IC) is based on measurement of the exchange of respiratory gases. All aerobic energy- releasing reactions in the body use oxygen; oxygen consumption, V.O2, is proportional to energy expenditure (EE). Research-grade IC systems measure V.O2, carbon dioxide production, V.CO2, and minute ventilation, V.E, breath by breath and then average results over multiple breaths to obtain accurate measures of cardiorespira- tory function. Subjects' V.O2max (i.e., maximum attainable V.O2) is the gold standard for assessing cardiorespiratory fitness (CRF). Indirect calorimetry is a part of cardiopulmonary exercise testing (CPET), providing a comprehen- sive assessment of physiology at rest and during stress. Further, derived variables (e.g., V.E=V.CO2, V.E=V.O2) have significant prognostic implications. For example, V.E=V.CO2 and V.E=V.O2, which can be obtained under maximal and submaximal conditions, provide measures of ventilatory efficiency; higher ratios indicate reduced breathing efficiency (e.g., due to pulmonary shunting or increased dead space ventilation). Like V.O2peak (i.e., the maximum V.O2 attained by a patient in an exercise stress test), V.E=V.CO2 and V.E=V.O2 improve with treatment/training. In cardiac rehabilitation (CR), for example, patients with coronary artery disease or chronic heart failure undergo supervised exercise training to improve heart health. Most CR is performed in outpatient settings, where the lack of equipment and specially-trained staff have precluded quantitative measurement of key values. To obtain such measures, patients have to be scheduled for CPET, which is expensive and generally not covered by insurance after an initial test. In practice, due to the nonavailability of V.O2peak and other derived measures in outpatient settings, suboptimal, semi-quantitative substitute measures are generally employed (e.g., 6-minute walk test). The Mobile Metabolic Measurement (M3) system will enable this limitation to be overcome, enabling objectively-measured V.O2, V.CO2, and V.E values to be available to provide CR patients with their initial exercise intensities, to track their progress, and to optimize their exercise prescriptions to maximize safe progress. The M3 system represents a substantial and practicable advance in quantitative CR patient monitoring. Phase I Results All Phase I objectives were successfully achieved. Specifically, the statistical equivalence of the M3 system's V.O2, V.CO2, and V.E measurements was demonstrated vis-à-vis two criterion systems: (1) the VacuMed Metabolic Simulator with Mass Flow Controller system [158]; and (2) the Oxycon Mobile system [49]. Phase II Goal Phase II will involve: (1) developing and validating the M3 system product using the VacuMed Metabolic Simulator, including the clinical software that will run on tablets and other computers; (2) evaluating M3 system performance in healthy adults; and (3) evaluating M3 system performance in patients with chronic stable coronary artery disease (CAD). Rigorous comparisons with commercial IC systems (viz., Oxycon Mobile and Vyntus CPX metabolic cart) will be made during aerobic exercise. Performance testing will be conducted in collaboration with the Arizona State University (healthy subjects) and the University of Virginia (CAD patients).
