Evaluating steady-state resting energy expenditure using indirect calorimetry in adults with overweight and obesity.

BACKGROUND: Determining a period of steady state (SS) is recommended when estimating resting energy expenditure (REE) using a metabolic cart. However, this practice may be unnecessarily burdensome and time-consuming in the research setting. AIM: The aim of the study was to evaluate the use of SS criteria, and compare it to alternative approaches in adults with overweight and obesity. METHODS: In this cross-sectional, ancillary analysis, participants enrolled in a bariatric (study 1; n = 13) and lifestyle (study 2; n = 51) weight loss intervention were included. Indirect calorimetry was performed during baseline measurements using a metabolic cart for 25 min, including a 5-min stabilization period at the start. SS was defined as the first 5-min period with a coefficient of variation (CV) ≤10% for both VO2 and VCO2 (hereafter REE5-SS). Body composition was measured using bioelectrical impedance analysis in study 2 participants only. REE5-SS was compared against the lowest CV (REECV-lowest), 5-min time intervals (REE6-10, REE11-15, REE16-20, REE21-25), 4-min and 3-min SS intervals (REE4-SS and REE3-SS), and time intervals of 6-15, 6-20 and 6-25 min (REE6-15, REE6-20, and REE6-25) using repeated measures ANOVA and Bland-Altman analysis to test for bias, limits of agreement and accuracy (±6% measured REE). RESULTS: Participants were 54 ± 13 years old, mostly women (75%) and had a BMI of 35 ± 5 kg/m2. Overall, 54/63 (84%) of participants reached REE5-SS, often (47/54, 87%) within the first 10-min (6-15 min). Alternative approaches to estimating REE had a relatively low bias (-16 to 13 kcals), narrow limits of agreement and high accuracy (83-98%) when compared to REE5-SS, in particular, outperforming standard prediction equations (e.g., Mifflin St. Joer). CONCLUSION: Indirect calorimetry measurements that utilize the 5-min SS approach to estimate REE are considered the gold-standard. Under circumstances of non-SS, it appears 4-min and 3-min SS periods, or fixed time intervals of atleast 5 min are accurate and practical alternatives for estimating REE in adults with overweight and obesity. However, future trials should validate alternative methods in similar populations to confirm these findings.

Remote measurement of NO2 in the brown cloud over Albuquerque, New Mexico.

Remote measurements of nitrogen dioxide (NO2) were recorded in the 'brown cloud' over Albuquerque, NM, using absorption spectroscopy in the winter of 1987-88 and summer of 1989. The NO2 burdens (optical densities) measured in this manner were found to be in excess of 100 ppm-m. These long pathlength measurements correspond to total concentrations of approximately 5-10 ppb over the integrated observation pathlengths, which ranged from 10-20 km. These concentrations compare well with single location, independent NO x analyses. Using two correlation (absorption) spectrometers simultaneously, it was shown that the NO2 distribution is not uniform over the city and can change on the order of minutes in the boundary layer late in the day, demonstrating the advantages of NO2 optical measurements for assessing the location and extent of urban nitrogen dioxide levels in the boundary layer.