“…During the PA tracer study, blood samples for determining PA and CO 2 concentration and enrichment and breath samples for assessment of CO 2 enrichment were obtained at the following times after beginning isotope administration: 180, 240, 300, 360, 380, 400, and 420 min. During each PA tracer study, blood fl ow was measured by venous occlusion plethysmography (345, 365, 385, and 405 min) ( 23 ), and AC profi ling was carried out on blood samples collected at the end of each tracer study (in the fed state). Measurements (15 min) of oxygen consumption and CO 2 production ( V max SPECTRA 29; Sensor Medics Corp., Yorba Linda, CA) were performed at 245 min and 305 min, after the beginning of PA tracer administration.…”