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The Metabolic Cart
Published in Michael M. Rothkopf, Jennifer C. Johnson, Optimizing Metabolic Status for the Hospitalized Patient, 2023
Michael M. Rothkopf, Jennifer C. Johnson
Based on these fundamental chemistry concepts, it becomes evident that for every fuel source, there is a characteristic amount of CO2 produced in relation to the oxygen consumed. This ratio is called the respiratory quotient or RQ. The word respiratory in this term does not refer to air movement, per se. It is about cellular respiration. When we measure the RQ we are gaining insight about the collective cellular respiration. This can be summarized as the patient’s general metabolic pattern.
Micronutrient Supplementation and Ergogenesis — Metabolic Intermediates
Published in Luke Bucci, Nutrients as Ergogenic Aids for Sports and Exercise, 2020
Effects of placebo or carnitine administration on physiological parameters following strenuous treadmill exercise at sea level or high-altitude (3500 m) conditions were studied in 7 healthy male subjects in a double-blind fashion.932 No changes from carnitine supplementation at either altitude were observed for oxygen uptake, pulmonary ventilation, carbon dioxide output, heart rate, blood pressure, and serum levels of lactate, free fatty acids, glycerol, and glucose. However, significant decreases in respiratory quotient were found at each altitude. Thus, carnitine supplementation may improve lipid utilization during exercise under normoxic or hypoxic conditions.
Exercising muscle during a progressive work test
Published in Robert B. Schoene, H. Thomas Robertson, Making Sense of Exercise Testing, 2018
Robert B. Schoene, H. Thomas Robertson
The generation of ATP requires carbohydrate and fatty acid fuel sources in addition to oxygen supply. Muscle cells contain stores of both glycogen and lipid, and those local fuels are the primary metabolic resources utilized during the relatively short duration of a CPET, with lesser contributions from blood-borne glucose and triglycerides. The proportional use of carbohydrate or fat by exercising muscle depends on the level of effort required. The respiratory quotient (RQ), the ratio between CO2 production () and oxygen consumption (), reflects the balance between fat and carbohydrate metabolism. A fasting subject at rest will primarily metabolize fat, with a corresponding RQ value as low as 0.70, whereas the same subject given a large ingested glucose load will have an RQ over 0.90. During an exercise test, the ratio (termed the respiratory R rather than RQ because it is not a steady-state measurement) is measured continuously and reflects that effort-dependent changing pattern of fuel utilization. For a fasting subject, fat serves as the primary fuel source during the initial stages of exercise, giving R measurements less than 0.8 in fasting subjects, but as exercise intensity increases, there is progressively more dependence on carbohydrate utilization, producing an increase in the respiratory R value (Figure 3.3).
Effects of nocturnal light exposure on circadian rhythm and energy metabolism in healthy adults: A randomized crossover trial
Published in Chronobiology International, 2022
Youngju Choi, Yuki Nakamura, Nobuhiko Akazawa, Insung Park, Hyo-Bum Kwak, Kumpei Tokuyama, Seiji Maeda
Energy metabolism, including energy expenditure and substrate oxidation levels, was measured in a room-sized metabolic chamber (FHC-15S, Fuji Medical Science Co., Ltd. Chiba, Japan) as previously described (Kayaba et al. 2014; Park et al. 2017). The airtight chamber measured 2.00 × 3.45 × 2.10 m, with an internal volume of 14.49 m3. The chamber was furnished with a bed, desk, chair, and toilet. The temperature and relative humidity of the incoming fresh air were controlled at 25.0 ± 0.5°C and 55.0 ± 3.0%, respectively. Concentrations of oxygen and carbon dioxide in the outgoing air were measured using an online process mass spectrometer (VG Prima δB, Thermo Electron, Winsford, UK). Oxygen consumption, and carbon dioxide production rates were calculated every minute using an algorithm providing an improved transient response (Tokuyama et al. 2009). Energy expenditure; carbohydrate, fat, and protein oxidation; and, respiratory quotient (RQ) were calculated from the rates of oxygen consumption, carbon dioxide production, and urinary nitrogen (N) excretion as previously described (Ferrannini 1988). The rate of N, an index of protein oxidation, was assumed to be constant during calorimetry. Energy expenditure and substrate oxidation levels were calculated by summing up the values of the light exposure and sleeping periods, respectively (light exposure period: 21:00 to 24:00, sleeping period: 24:00 to 07:00).
Application of beta-blockers in burn management
Published in Baylor University Medical Center Proceedings, 2022
Jonathan Kopel, Gregory L. Brower, Grant Sorensen, John Griswold
One of the initial observations by Szabó et al10 evaluated the nonselective beta-blocker oxprenolol (Trasicor) in patients with approximately 20% TBSA burns. The study found that patients treated with oxprenolol lost less weight than the untreated control group (5.4%, n = 8 vs 9.2%, n = 15; respectively).10 Another study by Breitenstein et al11 compared the effect of intravenous vs oral beta-blocker administration on resting metabolic rate. In 10 patients with an average burn of 28% TBSA, the decrease in metabolism relative to the baseline resting metabolic rate produced by intravenous (1.55 kcal/min vs 1.44 kcal/min) and oral (1.45 kcal/min vs 1.36 kcal/min) administration of propranolol was similar. The resting energy expenditure was calculated from VO2, VCO2, and the energy equivalent of VO2, corrected for the nonprotein respiratory quotient. The comparable decreases in lipid oxidation indicate that the route of administration does not affect the efficacy of propranolol-mediated reductions in hypermetabolism (i.e., lipid oxidation) in burn patients.
Chronic Thromboembolic Disease: Epidemiology, Assessment with Invasive Cardiopulmonary Exercise Testing, and Options for Management
Published in Structural Heart, 2021
W. Cameron McGuire, Mona Alotaibi, Timothy A. Morris, Nick H. Kim, Timothy M. Fernandes
A V-Max metabolic cart (CareFusion, San Diego, CA) is used to measure exhaled gases throughout the procedure. First, the patient performs a maximum voluntary ventilation maneuver. After the patient recovers, the respiratory quotient (RQ, derived from VCO2/VO2) is monitored. Once a stable RQ (normally between 0.8 and 0.9) is obtained, the pulmonary artery catheter is introduced via the sheath and the right atrial, right ventricular, pulmonary artery, and pulmonary capillary wedge pressure are measured in succession. After the pressures are obtained, simultaneous arterial and pulmonary arterial blood gases are drawn and the VO2 at the time of the draws is noted. The blood gases are used to calculate the cardiac output via the Fick method and to derive the pulmonary vascular resistance, pulmonary arterial compliance, and stroke volume.