Stability of respiratory quotient and growth outcomes of very low birth weight infants

Evolution of Resting Energy Expenditure, Respiratory Quotient, and Adiposity in Infants Recovering from Corrective Surgery of Major Congenital Gastrointestinal Tract Anomalies: A Cohort Study

This cohort study describes the evolution of resting energy expenditure (REE), respiratory quotient (RQ), and adiposity in infants recovering from corrective surgery of major congenital gastrointestinal tract anomalies. Energy and macronutrient intakes were assessed. The REE and RQ were assessed by indirect calorimetry, and fat mass index (FMI) was assessed by air displacement plethysmography. Longitudinal variations over time are described. Explanatory models for REE, RQ, and adiposity were obtained by multiple linear regression analysis. Twenty-nine infants were included, 15 born preterm and 14 at term, with median gestational age of 35.3 and 38.1 weeks and birth weight of 2304 g and 2935 g, respectively. In preterm infants, median REE varied between 55.7 and 67.4 Kcal/kg/d and median RQ increased from 0.70 to 0.86–0.92. In term infants, median REE varied between 57.3 and 67.9 Kcal/kg/d and median RQ increased from 0.63 to 0.84–0.88. Weight gain velocity was slower in term than preterm infants. FMI, assessed in a subset of 15 infants, varied between a median of 1.7 and 1.8 kg/m² at term age. This low adiposity may be related to poor energy balance, low fat intakes, and low RQ¸ that were frequently recorded in several follow-up periods.

Routine resting energy expenditure measurement increases effectiveness of dietary intervention in obesity

AIMS

Primary outcome of this observational study was to compare weight changes in two groups of overweight and obese individuals: subjects who had a diet prescribed on the base of resting energy expenditure (REE) measured by indirect calorimetry and subjects whose REE was estimated by a predictive equation. In addition, we analyzed differences in weight and metabolic parameter variation in subjects with and without an adequate to predicted REE.

METHODS

We retrospectively analyzed data of 355 overweight and obese patients: 215 on a diet based on REE measured by indirect calorimetry and 140 following a diet based on REE estimated by the Harris-Benedict equation. Anthropometric and metabolic parameters were evaluated for 18 months from baseline. Propensity score adjustment was used to adjust for known differences between the groups being compared.

RESULTS

A significant greater decrease in body weight was observed in the group that underwent indirect calorimetry compared to the group that did not undergo it (p < 0.001). No significant differences were observed between patients with not adequate to predicted REE compared to patients with adequate to predicted REE.

CONCLUSIONS

A weight reduction program based on REE measurement appears more effective than a dietary program based on predictive formulas. This study suggests the routine use of indirect calorimetry in all weight reduction procedures.

Thermometry, calorimetry, and mean body temperature during heat stress

Heat balance in humans is maintained at near constant levels through the adjustment of physiological mechanisms that attain a balance between the heat produced within the body and the heat lost to the environment. Heat balance is easily disturbed during changes in metabolic heat production due to physical activity and/or exposure to a warmer environment. Under such conditions, elevations of skin blood flow and sweating occur via a hypothalamic negative feedback loop to maintain an enhanced rate of dry and evaporative heat loss. Body heat storage and changes in core temperature are a direct result of a thermal imbalance between the rate of heat production and the rate of total heat dissipation to the surrounding environment. The derivation of the change in body heat content is of fundamental importance to the physiologist assessing the exposure of the human body to environmental conditions that result in thermal imbalance. It is generally accepted that the concurrent measurement of the total heat generated by the body and the total heat dissipated to the ambient environment is the most accurate means whereby the change in body heat content can be attained. However, in the absence of calorimetric methods, thermometry is often used to estimate the change in body heat content. This review examines heat exchange during challenges to heat balance associated with progressive elevations in environmental heat load and metabolic rate during exercise. Further, we evaluate the physiological responses associated with heat stress and discuss the thermal and nonthermal influences on the body's ability to dissipate heat from a heat balance perspective.

Assessing neonatal heat balance and physiological strain in newborn infants nursed under radiant warmers in intensive care with fentanyl sedation

PURPOSE

To assess heat balance status of newborn infants nursed under radiant warmers (RWs) during intensive care.

METHODS

Heat balance, thermal status and primary indicators of physiological strain were concurrently measured in 14 newborns nursed under RWs for 105 min. Metabolic heat production (M), evaporative heat loss (E), convective (C) and conductive heat flow (K), rectal temperature (T re) and mean skin temperatures (T sk) were measured continuously. The rate of radiant heat required for heat balance (R req) and the rate of radiant heat provided (R prov) were derived. The rate of body heat storage (S) was calculated using a two-compartment model of 'core' (T re) and 'shell' (T sk) temperatures.

RESULTS

Mean M, E, C and K were 10.5 ± 2.7 W, 5.8 ± 1.1 W, 6.2 ± 0.8 W and 0.1 ± 0.1 W, respectively. Mean R prov (1.7 ± 2.6 W) and R req (1.7 ± 2.7 W) were similar (p > 0.05). However, while the resultant mean change in body heat content after 105 min was negligible (-0.1 ± 3.7 kJ), acute time-dependent changes in S were evidenced by a mean positive heat storage component of +6.4 ± 2.6 kJ and a mean negative heat storage component of -6.5 ± 3.7 kJ. Accordingly, large fluctuations in both T re and T sk occurred that were actively induced by changes in RW output. Nonetheless, no active physiological responses (heart rate, breathing frequency and mean arterial pressure) to these bouts of heating and cooling were observed.

CONCLUSIONS

RWs maintain net heat balance over a prolonged period, but actively induce acute bouts of heat imbalance that cause rapid changes in T re and T sk. Transient bouts of heat storage do not exacerbate physiological strain, but could in the longer term.

Dynamic coordination of macronutrient balance during infant growth: insights from a mathematical model

BACKGROUND

Complex dynamic changes in body composition, dietary intake, energy expenditure, and macronutrient oxidation occur during infant growth. Although previous investigators have focused on energy requirements for normal growth, little is known about the dynamic coordination of macronutrient balance.

OBJECTIVE

Our objective was to develop a mathematical model of the dynamic relations between diet, macronutrient oxidation, and energy expenditure during normal infant growth.

DESIGN

We developed a mathematical model that integrates longitudinal data on changes of body composition and carbon dioxide production determined with the doubly labeled water method to calculate both energy intake requirements and macronutrient oxidation rates during normal infant growth.

RESULTS

The calculated fat oxidation rate was initially <20 kcal x kg(-1) x d(-1), despite the consumption of >60 kcal x kg(-1) x d(-1) of dietary fat. This discrepancy was maintained until approximately 6 mo, after which fat intake was only slightly greater than fat oxidation. Nonfat oxidation closely followed nonfat dietary intake for the duration of the period studied. Model calculations of the energy intake requirements for normal growth were slightly lower than previous estimates. The calculations were robust to variations of body weight, body composition, and diet composition input data, but depended sensitively on variations of carbon dioxide production data.

CONCLUSIONS

Our model presents a dynamic picture of how macronutrient oxidation adapts in concert with dietary changes and energy expenditure to give rise to normal tissue deposition. The model integrates a variety of data in a self-consistent way, simulating the complex metabolic adaptations occurring during normal growth while extracting important physiologic information from the data that would otherwise be unavailable.