Heat production during exercise in pregnancy: discerning the contribution of total body weight.

Studies have reported enhanced thermoregulatory function as pregnancy progresses; however, it is unclear if differences in thermoregulation are attributed to weight gain or other physiological changes. This study aimed to determine if total body weight will influence thermoregulation (heat production (Hprod)), heart rate, and perceptual measurements in response to weight-bearing exercise during early to late pregnancy. A cross-sectional design of healthy pregnant women at different pregnancy time points (early, T1; middle, T2; late, T3) performed a 7-stage weight-bearing incremental exercise protocol. Measurements of Hprod, HR, and RPE were examined. Two experimental groups were studied: (1) weight matched and (2) non-weight matched, in T1, T2, and T3. During exercise, equivalent Hprod at T1 (326 ± 88 kJ), T2 (330 ± 43 kJ), and T3 (352 ± 52 kJ) (p = 0.504); HR (p = 0.830); and RPE (p = 0.195) were observed in the WM group at each time point. In the NWM group, Hprod (from stages 1-6 of the exercise) increased across pregnancy time points, T1 (291 ± 76 kJ) to T2 (347 ± 41 kJ) and T3 (385 ± 47 kJ) (p < 0.001). HR increased from T1 to T3 in the warm-up to stage 6 (p = 0.009). RPE did not change as pregnancy time point progressed (p = 0.309). Total body weight, irrespective of pregnancy time point, modulates Hprod and HR during exercise. Therefore, accounting for total body weight is crucial when comparing thermoregulatory function during exercise across pregnancy.

Proportional increment of oxygen consumption, heart rate and core body temperature in the digesting Python bivittatus.

The Burmese python has a remarkable digestive physiology with large elevations of metabolic rate and heart rate following feeding. Here, we investigated the relationship between heart rate, oxygen consumption and core body temperature during digestion in five pythons (Python bivittatus) by implantation of data loggers. The snakes were placed in respirometers at 30±0.1°C for 26 days and voluntarily ingested three meals of different size, whilst heart rate, core body temperature and oxygen consumption rate were measured continuously. Both oxygen consumption and heart rate increased severalfold during digestion, and metabolic heat production increased core body temperature by 2°C, explaining 12% of the observed tachycardia. The rise in core body temperature means that standard metabolic rate increased during digestion, and we estimate that failure to account for core body temperature leads to a 4% overestimation of the specific dynamic action (SDA) response. Our study reveals a close correlation between oxygen consumption and heart rate during digestion, further supporting the use of heart rate as a proxy for metabolism.

Highland deer mice support increased thermogenesis in response to chronic cold hypoxia by shifting uptake of circulating fatty acids from muscles to brown adipose tissue.

During maximal cold challenge (cold-induced V̇O2,max) in hypoxia, highland deer mice (Peromyscus maniculatus) show higher rates of circulatory fatty acid delivery compared with lowland deer mice. Fatty acid delivery also increases with acclimation to cold hypoxia (CH) and probably plays a major role in supporting the high rates of thermogenesis observed in highland deer mice. However, it is unknown which tissues take up these fatty acids and their relative contribution to thermogenesis. The goal of this study was to determine the uptake of circulating fatty acids into 24 different tissues during hypoxic cold-induced V̇O2,max, by using [1-14C]2-bromopalmitic acid. To uncover evolved and environment-induced changes in fatty acid uptake, we compared lab-born and -raised highland and lowland deer mice, acclimated to either thermoneutral (30°C, 21 kPa O2) or CH (5°C, 12 kPa O2) conditions. During hypoxic cold-induced V̇O2,max, CH-acclimated highlanders decreased muscle fatty acid uptake and increased uptake into brown adipose tissue (BAT) relative to thermoneutral highlanders, a response that was absent in lowlanders. CH acclimation was also associated with increased activities of enzymes citrate synthase and ß-hydroxyacyl-CoA dehydrogenase in the BAT of highlanders, and higher levels of fatty acid translocase CD36 (FAT/CD36) in both populations. This is the first study to show that cold-induced fatty acid uptake is distributed across a wide range of tissues. Highland deer mice show plasticity in this fatty acid distribution in response to chronic cold hypoxia, and combined with higher rates of tissue delivery, this contributes to their survival in the cold high alpine environment.

Predicting CO2 production of lactating dairy cows from animal, dietary, and production traits using an international dataset.

Automated measurements of the ratio of concentrations of methane and carbon dioxide, [CH4]:[CO2], in breath from individual animals (the so-called "sniffer technique") and estimated CO2 production can be used to estimate CH4 production, provided that CO2 production can be reliably calculated. This would allow CH4 production from individual cows to be estimated in large cohorts of cows, whereby ranking of cows according to their CH4 production might become possible and their values could be used for breeding of low CH4-emitting animals. Estimates of CO2 production are typically based on predictions of heat production, which can be calculated from body weight (BW), energy-corrected milk yield, and days of pregnancy. The objectives of the present study were to develop predictions of CO2 production directly from milk production, dietary, and animal variables, and furthermore to develop different models to be used for different scenarios, depending on available data. An international dataset with 2,244 records from individual lactating cows including CO2 production and associated traits, as dry matter intake (DMI), diet composition, BW, milk production and composition, days in milk, and days pregnant, was compiled to constitute the training dataset. Research location and experiment nested within research location were included as random intercepts. The method of CO2 production measurement (respiration chamber [RC] or GreenFeed [GF]) was confounded with research location, and therefore excluded from the model. In total, 3 models were developed based on the current training dataset: model 1 ("best model"), where all significant traits were included; model 2 ("on-farm model"), where DMI was excluded; and model 3 ("reduced on-farm model"), where both DMI and BW were excluded. Evaluation on test dat sets with either RC data (n = 103), GF data without additives (n = 478), or GF data only including observations where nitrate, 3-nitrooxypropanol (3-NOP), or a combination of nitrate and 3-NOP were fed to the cows (GF+: n = 295), showed good precision of the 3 models, illustrated by low slope bias both in absolute values (-0.22 to 0.097) and in percentage (0.049 to 4.89) of mean square error (MSE). However, the mean bias (MB) indicated systematic overprediction and underprediction of CO2 production when the models were evaluated on the GF and the RC test datasets, respectively. To address this bias, the 3 models were evaluated on a modified test dataset, where the CO2 production (g/d) was adjusted by subtracting (where measurements were obtained by RC) or adding absolute MB (where measurements were obtained by GF) from evaluation of the specific model on RC, GF, and GF+ test datasets. With this modification, the absolute values of MB and MB as percentage of MSE became negligible. In conclusion, the 3 models were precise in predicting CO2 production from lactating dairy cows.

Derivation of the maintenance energy requirements in Jersey cows differing in body condition score.

Research in a variety of species including cattle has suggested energy required for maintenance may be affected by body condition. The objective of this study was to use indirect calorimetry and total fecal and urine collections to estimate maintenance energy and fasting heat production (FHP) of cows differing in BCS. Twelve multiparous nonpregnant and nonlactating Jersey cows were randomly assigned to one of 2 treatment groups. To construct these groups, cows were fed 2 different TMR in a preexperimental period for 84 d resulting in a BCS of >5 (HiBCS) and a BCS <3 (LoBCS), and no difference was observed in initial BW or BCS between treatments, averaging 509 ± 26.0 kg and 4.1 ± 0.23. To begin the experiment all animals were fed at maintenance [NELmaint, (Mcal/d) = 0.10 × metabolic BW (BW0.75)] for 24 d followed by 4 d of data collection for energy balance, cows were then fasted of 96 h with data collection for energy balance once again taken over the final 24 h. During the maintenance collection period, differences in BW and BCS existed (439 and 566 ± 19.0 kg BW, and 3.0 and 5.0 ± 0.13 BCS) for LoBCS and HiBCS, respectively. Heat production increased with increasing BCS (13.1 to 16.2 ± 0.55 Mcal/d), but when expressed per unit of BW0.75 no difference was observed (0.14 ± 0.002 Mcal/d per BW0.75). When fasted, BW loss did not differ averaging 28.9 ± 0.181 kg. The FHP did not differ, averaging 0.10 ± 0.004 Mcal/d per BW0.75 and resulted in the following representation of maintenance: [NELmaint, (Mcal/d) = 0.10 ± 0.004 × BW0.75]. During fasting the nitrogen free respiratory quotient tended to differ (0.69 and 0.73 ± 0.014) and O2 consumption and CO2 production for protein oxidation differed for LoBCS and HiBCS (5.44 and 2.35 ± 0.988 O2 and 4.52 and 1.95 ± 0.821 CO2 L/BW0.75). Overall, FHP increased with increasing BCS, but FHP per unit of BW0.75 did not differ. Although BW change was similar during fasting, differences O2 consumption and CO2 production per unit of BW0.75 used for protein oxidation may indicate differences in the nature of body tissue utilization in cows differing in BCS.

Determination and prediction of the net energy content of wheat bran for pregnant sow.

Two experiments were conducted to determine net energy (NE) values of wheat bran ingredients and develop a prediction equation for NE of wheat bran. In each experiment, 12 multiparous pregnant sows were allocated to two 3 × 6 Youden squares with three consecutive periods and six diets in each square. The study consisted of six diets, including a corn-soybean meal basal diet and five diets formulated with 29.2% wheat bran. Each period lasted for 10 d, with 5 d allocated for adaptation and followed by 5 d for heat production measurement. Sows were provided feed at 604 kJ/kg BW0.75·d-1. On day 10, sows underwent fasting to measure fasting heat production. Results indicated that the inclusion of wheat bran in the diets significantly reduced digestibility of energy and nutrients in (p < 0.05). The average net energy (NE) content of wheat bran was determined to be 8.8 MJ/kg DM. A regress equation NE = 7.968 + 0.28 × CP + 0.607 × EE - 0.782 × ash - 0.05 × hemicellulose (R2 = 0.98, p < 0.01) was found to accurately predit the NE value when feeding pregnant sows with wheat bran-based diets. In conclusion, the net energy content of wheat bran fed to pregnant sows ranged from 7.24 to 10.67 MJ/kg DM and can be effectively estimated using proximate analysis methods.

The use of infrared thermography as an indicator of methane production in hair sheep.

Infrared thermography may be an alternative technology for measuring the amount of CH4 produced and has the advantages of low cost, speed and efficiency in obtaining results. The study's objective was to determine if the infrared thermography is adequate for predicting the emission of CH4 in hair sheep and the best time after feeding to carry out the measurement. Twelve Santa Inês lambs (females, non-pregnant, with twelve months old and mean body weight of 39.3 ± 2.1 kg) remained for two days in respirometric chambers, in a semi-closed system, to determine the CH4 production. The animals were divided into two treatments, according to the diet provided. During this period, seven thermographic photographs were taken, at times - 1 h, -0.5 h, 0 h, 0.5 h, 1 h, 2 h, 3 h, 5 h, and 7 h, according to the feeding time, defined as 0 h. CH4 production was measured over 24 h. Thermographic images measured the maximum, minimum, average and point temperatures at the left and right flanks. The temperature difference between the left and right flanks (left minus right) was calculated each time. Pearson correlation coefficients, multiple regression and principal component analysis were carried out in SAS®. The best prediction of emission intensity of CH4 (kg of CH4 per dry matter intake) was obtained at 3 h after feeding: CH4/DMI = 13.9016-0,38673 * DifP2 + 3.39089 * DifMed2 (R² = 0.48), using the difference between left and right flanks for point and average temperature measures. Therefore, infrared thermography can be used as an indicator of CH4 production in hair sheep three hours after feeding.

Effects of discontinuous blue light stimulation on the electrophysiological properties of neurons lacking opsin expression in vitro: Implications for optogenetic experiments.

Neuronal sensitivity to light stimulation can be a significant confounding factor for assays that use light to study neuronal processes, such as optogenetics and fluorescent imaging. While continuous one-photon (1P) blue light stimulation has been shown to be responsible for a decrease in firing activity in several neuronal subtypes, discontinuous 1P blue light stimulation commonly used in optogenetic experiments is supposed to have a negligible action. In the present report, we tested experimentally this theoretical prediction by assessing the effects produced by the most commonly used patterns of discontinuous 1P light stimulation on several electrophysiological parameters in brain slices. We found that, compared with continuous stimulation, the artefactual effect of light is reduced when discontinuous stimulation is used, especially when the duty cycle and light power are low.

A century of exercise physiology: key concepts in muscle energetics.

In the mid-nineteenth century, the concept of muscle behaving like a stretched spring was developed. This elastic model of contraction predicted that the energy available to perform work was established at the start of a contraction. Despite several studies showing evidence inconsistent with the elastic model, it persisted into the twentieth century. In 1923, W. O. Fenn published a paper in which he presented evidence that appeared to clearly refute the elastic model. Fenn showed that when a muscle performs work it produces more heat than when contracting isometrically. He proposed that energy for performing work was only made available in a muscle as and when that work was performed. However, his ideas were not adopted and it was only after 15 years of technical developments that in 1938 A. V. Hill performed experiments that conclusively disproved the elastic model and supported Fenn's conclusions. Hill showed that the rate of heat production increased as a muscle made the transition from isometric to working contraction. Understanding the basis of the phenomenon observed by Fenn and Hill required another 40 years in which the processes that generate force and work in muscle and the associated scheme of biochemical reactions were established. Demonstration of the biochemical equivalent of Hill's observations-changes in rate of ATP splitting when performing work-in 1999 was possible through further technical advances. The concept that the energy, from ATP splitting, required to perform work is dynamically modulated in accord with the loads a muscle encounters when contracting is key to understanding muscle energetics.

Influence of lactation stage on heat production and macronutrient oxidation in dairy cows during a 24-hour fasting period.

Understanding nutrient utilization and partitioning is essential for advancing the efficiency of dairy cattle. Our objective was to determine if dairy cows exposed to a 24-h fasting period differ in heat production (HP) and macronutrient oxidation at different stages of lactation. Twelve primiparous, lactating German Holstein dairy cows were used in a longitudinal study design spanning from 2013 to 2014. Dairy cows were housed in respiration chambers during 3 stages of the lactation cycle: early (mean ± SD; 28.8 ± 6.42 d), mid- (89.4 ± 4.52 d), and late (293 ± 7.76 d) lactation. Individual CO2, O2, and CH4 gas exchanges were measured every 6 min for two 24-h periods, an ad libitum period and fasting period (RES). Blood was sampled at the start and end of the RES period. Gas measurements were used to calculate HP, net carbohydrate oxidation (COX), and net fat oxidation (FOX). Measurements were corrected with metabolic BW (kg of BW0.75; cBW). The RES period for each stage of lactation was further subdivided into the start (RESstart) and end (RESend) by averaging the first and last 2 h of the RES period. The net change was calculated as RESend - RESstart. All energy variables differed among lactation stage within the RES period except for HP/cBW. As expected, COX, COX/cBW, COX/HP, HP, and HP/cBW, were greater at the RESstart compared with RESend, whereas FOX, FOX/cBW, and FOX/HP were greater at the RESend except for FOX and FOX/cBW during mid lactation, which was only a tendency for a difference. The net change for COX, COX/cBW, HP, HP/cBW, and FOX/cBW did not differ among stages of lactation. Despite detecting a tendency for a difference among stage of lactation for FOX, pairwise analysis revealed no differences. Plasma triglyceride, urea, and nonesterified fatty acid concentrations were greater at RESend than RESstart. The net change for plasma glucose, urea, ß-hydroxybutyrate, and nonesterified fatty acid concentrations were greater in early than late lactation. Our results demonstrate that despite differences in absolute measurements of energy variables and plasma metabolites, the change in whole-body macronutrient oxidation and HP as cows' transition from a fed-like state to a starvation-like state during a 24-h fasting period is consistent throughout lactation.

Warm Cells, Hot Mitochondria: Achievements and Problems of Ultralocal Thermometry.

Temperature is a crucial regulator of the rate and direction of biochemical reactions and cell processes. The recent data indicating the presence of local thermal gradients associated with the sites of high-rate thermogenesis, on the one hand, demonstrate the possibility for the existence of "thermal signaling" in a cell and, on the other, are criticized on the basis of thermodynamic calculations and models. Here, we review the main thermometric techniques and sensors developed for the determination of temperature inside living cells and diverse intracellular compartments. A comparative analysis is conducted of the results obtained using these methods for the cytosol, nucleus, endo-/sarcoplasmic reticulum, and mitochondria, as well as their biological consistency. Special attention is given to the limitations, possible sources of errors and ambiguities of the sensor's responses. The issue of biological temperature limits in cells and organelles is considered. It is concluded that the elaboration of experimental protocols for ultralocal temperature measurements that take into account both the characteristics of biological systems, as well as the properties and limitations of each type of sensor is of critical importance for the generation of reliable results and further progress in this field.

Energy cost of physical activities in growing broilers.

1. The time-energy budget method estimates the energy used for physical activity (PA) by integrating behaviour PA patterns with energy cost for specific PAs. Nevertheless, information about individual energy cost by type of PA are not available and so this study estimated the energy cost of PA for growing broilers.2. An indirect calorimetry system for single birds was constructed to measure the variation in the rate of O2 consumption (V˙O2, L/min) and rate of CO2 production (V˙CO2, L/min) produced by these PAs.3. A total of five birds were used in a replicated trial where their body weight (BW) ranged from 1.5 to 2.5 kg to measure the increase in heat production (HP) above resting levels as a result of PA. The procedure in the chamber was divided into five steps: (1) initial baselining, (2) resting metabolic rate, (3) PA such as feeding, drinking and other standing activities, (4) removal of gas exchange produced in step 3, and (5) final baselining. The PA was recorded using a video camera fixed at the chamber's top (and outside).4. The area under V˙CO2 and V˙O2 curves was used to calculate the CO2 production (vCO2, L) and O2 consumption (vO2, L). Then, the HP (cal/kg-0.75) was calculated according to the Brouwer equation. Two observers analysed the video records to estimate the time spent for each PA (seconds and frequency).5. To calculate the energetic coefficients, the HP was regressed with the function of time spent to perform each PA allowing to estimate the energy cost for eating, drinking and stand activities, which were 0.607, 0.352 and 0.938 cal/kg-0.75/s, respectively.

Radiogeochemistry, mineralogy, lithology, radiogenic heat production, and health implication using airborne radiometric data of Ilesha and its surroundings.

The current study analyzed and interpreted airborne radiometric data from Ilesha's basement complex rock and its surroundings. At the surface, the concentrations of the most frequent primordial radionuclides notably K, elemental concentration of uranium eU, and elemental concentration of thorium eTh were measured. The weighted mean elemental and activity concentrations were 0.85%, 2.75 ppm, 10.22 ppm, and 267.54 Bq kg-1, 34.41 Bq kg-1, 41.51 Bq kg-1 for 40 K, 238U, and 232Th, respectively. The low concentration of 40 K was certainly due to the effects of weathering, kaolinization of granites, and pedogenesis activities. The abundance of uranium was ascribed to the availability of uranium minerals such as allanite, apatite, and sphene with accessories minerals, while that of thorium was due to minerals such as cheralite, thorite, uranothorite, thorianite, and uranothorianite with accessories minerals. The RPHR weighted mean 1.48 µWm-3 compared to the earth's crust mean between 0.8 and1.2 µWm-3 was higher due to significant presence of gneiss rocks in all the studied profiles. Radiological hazard, in particular, dose rates, external hazard index, internal hazard index, radium equivalent, annual gonadal dose, effective dose dispensed to various organs of the body were computed to determine the deleterious effects of rocks in the area. The weighted means of annual gonadal dose of 363.98 µSv y-1 and outdoor 0.91 × 10×3 and indoor 1.65 × 10-3 excessive life cancer risks were more than the global average 300 µSv y-1, 0.29 × 10-3 and 1.16 × 10-3. As a result, proper surveillance is required in the area in order to prevent epidemics occurrence in future.

The legacy of A. V. Hill's Nobel Prize winning work on muscle energetics.

A. V. Hill was awarded the 1922 Nobel Prize, jointly with Otto Meyerhof, for Physiology or Medicine for his work on energetic aspects of muscle contraction. Hill used his considerable mathematical and experimental skills to investigate the relationships among muscle mechanics, biochemistry and heat production. The main ideas of the work for which the Nobel Prize was awarded were superseded within a decade, and the legacy of Hill and Meyerhof's Nobel work was not a set of persistent, influential ideas but rather a prolonged period of extraordinary activity that advanced the understanding of how muscles work far beyond the concepts that led to the Nobel Prize. Hill pioneered the integration of mathematics into the study of physiology and pharmacology. Particular aspects of Hill's own work that remain in common use in muscle physiology include mathematical descriptions of the relationships between muscle force output and shortening velocity and between force output and calcium concentration, and the model of muscle as a contractile element in series with an elastic element. We describe some of the characteristics of Hill's broader scientific activities and then outline how Hill's work on muscle energetics was extended after 1922, as a result of Hill's own work and that of others, to the present day.

Contrasting recruitment of skin-associated adipose depots during cold challenge of mouse and human.

KEY POINTS: Several distinct strategies produce and conserve heat to maintain the body temperature of mammals, each associated with unique physiologies, with consequences for wellness and disease susceptibility Highly regulated properties of skin offset the total requirement for heat production  We hypothesize that the adipose component of skin is primarily responsible for modulating heat flux; here we evaluate the relative regulation of adipose depots in mouse and human, to test their recruitment to heat production and conservation We found that insulating mouse dermal white adipose tissue accumulates in response to environmentally and genetically induced cool stress; this layer is one of two adipose depots closely apposed to mouse skin, where the subcutaneous mammary gland fat pads are actively recruited to heat production In contrast, the body-wide adipose depot associated with human skin produces heat directly, potentially creating an alternative to the centrally regulated brown adipose tissue ABSTRACT: Mammalian skin impacts metabolic efficiency system-wide, controlling the rate of heat loss and consequent heat production. Here we compare the unique fat depots associated with mouse and human skin, to determine whether they have corresponding functions and regulation. For humans, we assay a skin-associated fat (SAF) body-wide depot to distinguish it from the subcutaneous fat pads characteristic of the abdomen and upper limbs. We show that the thickness of SAF is not related to general adiposity; it is much thicker (1.6-fold) in women than men, and highly subject-specific. We used molecular and cellular assays of ß-adrenergic-induced lipolysis and found that dermal white adipose tissue (dWAT) in mice is resistant to lipolysis; in contrast, the body-wide human SAF depot becomes lipolytic, generating heat in response to ß-adrenergic stimulation. In mice challenged to make more heat to maintain body temperature (either environmentally or genetically), there is a compensatory increase in thickness of dWAT: a corresponding ß-adrenergic stimulation of human skin adipose (in vivo or in explant) depletes adipocyte lipid content. We summarize the regulation of skin-associated adipocytes by age, sex and adiposity, for both species. We conclude that the body-wide dWAT depot of mice shows unique regulation that enables it to be deployed for heat preservation; combined with the actively lipolytic subcutaneous mammary fat pads they enable thermal defence. The adipose tissue that covers human subjects produces heat directly, providing an alternative to the brown adipose tissues.

Respirometry protocols for avian thermoregulation at high air temperatures: stepped and steady-state profiles yield similar results.

Relationships between air temperature (Tair) and avian body temperature (Tb), resting metabolic rate (RMR) and evaporative water loss (EWL) during acute heat exposure can be quantified through respirometry using several approaches. One involves birds exposed to a stepped series of progressively increasing Tair setpoints for short periods (<20-30 min), whereas a second seeks to achieve steady-state conditions by exposing birds to a single Tair for longer periods (>1-2 h). To compare these two approaches, we measured Tb, RMR and EWL over Tair=28°C to 44°C in the dark-capped bulbul (Pycnonotus tricolor). The two protocols yielded indistinguishable values of Tb, RMR and EWL and related variables at most Tair values, revealing that both are appropriate for quantifying avian thermal physiology during heat exposure over the range of Tair in the present study. The stepped protocol, however, has several ethical and practical advantages.

Estimates of daily oxygen consumption, carbon dioxide and methane emissions, and heat production for beef and dairy cattle using spot gas sampling.

A simulation study was conducted to examine accuracy of estimating daily O2 consumption, CO2 and CH4 emissions, and heat production (HP) using a spot sampling technique and to determine optimal spot sampling frequency (FQ). Data were obtained from 3 experiments where daily O2 consumption, emissions of CO2 and CH4, and HP were measured using indirect calorimetry (respiration chamber or headbox system). Experiment 1 used 8 beef heifers (ad libitum feeding; gaseous exchanges measured every 30 min over 3 d in respiration chambers); Experiment 2 used 56 lactating Holstein-Friesian cows (restricted feeding; gaseous exchanges measured every 12 min over 3 d in respiration chambers); Experiment 3 used 12 lactating Jersey cows (ad libitum feeding; gaseous exchanges measured every hour for 1 d using headbox style chambers). Within experiment, averages of all measurements (FQALL) and averages of measurements selected at time points with 12, 8, 6, or 4 spot sampling FQ (i.e., sampling every 2, 3, 4, and 6 h in a 24-h cycle, respectively; FQ12, FQ8, FQ6, and FQ4, respectively) were compared. Within study a mixed model was used to compare gaseous exchanges and HP among FQALL, FQ12, FQ8, FQ6, and FQ4, and an interaction of dietary treatment by FQ was examined. A regression model was used to evaluate accuracy of spot sampling within study [i.e., FQALL (observed) vs. FQ12, FQ8, FQ6, or FQ4 (estimated)]. No interaction of diet by FQ was observed for any variables except for CH4 production in experiment 1. No FQ effect was observed for gaseous exchanges and HP except in experiment 2 where CO2 production was less (5,411 vs. 5,563 L/d) for FQ4 compared with FQALL, FQ12, and FQ8. A regression analysis between FQALL and each FQ within study showed that slopes and intercepts became farther from 1 and 0, respectively, for almost all variables as FQ decreased. Most variables for FQ12 and FQ8 had root mean square prediction error (RMSPE) less than 10% of the mean and concordance correlation coefficient (CCC) greater than 0.80, and RMSPE increased and CCC decreased as FQ decreased. When a regression analysis was conducted with combined data from the 3 experiments (mixed model with study as a random effect), results agreed with those from the analysis for the individual studies. Prediction errors increased and CCC decreased as FQ decreased. Generally, all the estimates from FQ12, FQ8, FQ6, and FQ4 had RMSPE less than 10% of the means and CCC greater than 0.90 except for FQ6 and FQ4 for O2 consumption and CH4 production. In conclusion, the spot sampling simulation with 3 indirect calorimetry experiments indicated that FQ of at least 8 samples (every 3 h in a 24-h cycle) was required to estimate daily O2 consumption, CO2 and CH4 production, and HP and to detect changes in those in response to dietary treatments. This sampling FQ may be considered when using techniques that measure spot gas exchanges such as the GreenFeed and face mask systems.

On the power per mitochondrion and the number of associated active ATP synthases.

Recent experiments and thermodynamic arguments suggest that mitochondrial temperatures are higher than those of the cytoplasm. A "hot mitochondrion" calls for a closer examination of the energy balance that endows it with these claimed elevated temperatures. As a first step in this effort, we present here a semi-quantitative bookkeeping whereby, in one stroke, a formula is proposed that yields the rate of heat production in a typical mitochondrion and a formula for estimating the number of "active" ATP synthase molecules per mitochondrion. The number of active ATP synthase molecules is the equivalent number of ATP synthases operating at 100% capacity to maintain the rate of mitochondrial heat generation. Scaling laws are shown to determine the number of active ATP synthase molecules in a mitochondrion and mitochondrial rate of heat production, whereby both appear to scale with cell volume. Four heterotrophic protozoan cell types are considered in this study. The studied cells, selected to cover a wide range of sizes (volumes) fromca.100µm3to 1 millionµm3, are estimated to exhibit a power per mitochondrion ranging fromca.1 pW to 0.03 pW. In these cells, the corresponding number of active ATP synthases per mitochondrion ranges from 5000 to just about a hundred. The absolute total number of ATP synthase molecules per mitochondrion, regardless of their activity status, can be up to two orders of magnitudes higher.

Components of activation heat in skeletal muscle.

Activation heat (qA) production by muscle is the thermal accompaniment of the release of Ca2+ from the sarcoplasmic reticulum (SR) into the cytoplasm, its interactions with regulatory proteins and other cytoplasmic Ca2+ buffers and its return to the SR. The contribution of different Ca2+-related reactions to qA is difficult to determine empirically and therefore, for this study, a mathematical model was developed to describe Ca2+ movements and accompanying thermal changes in muscle fibres in response to stimulation. The major sources of heat within a few milliseconds of the initiation of Ca2+ release are Ca2+ binding to Tn and Pv. Ca2+ binding to ATP produces a relatively small amount of heat. Ca2+ dissociation from ATP and Tn, with heat absorption, are of similar time course to the decline of force. In muscle lacking Pv (e.g. mouse soleus), Ca2+ is then rapidly pumped into the SR. In muscles with Pv, Ca2+ that dissociates from Tn and ATP binds to Pv and then dissociates slowly (over 10 s of seconds) and is then pumped into the SR; the net effect of these two processes is heat absorption. It is proposed that this underlies Hill's "negative delayed heat". After all the Ca2+ is returned to the SR, qA is proportional to the amount of Ca2+ released into the cytoplasm. In muscles with Pv this is 20-60 s after Ca2+ release; in muscles without Pv, all Ca2+ is returned to the SR soon after the end of force relaxation.

Total body and regional surface area: Quantification with low-cost three-dimensional optical imaging systems.

OBJECTIVES: Body surface area (SA) is a widely used physical measure incorporated into multiple thermophysiology and evolutionary biology models currently estimated in humans either with empirical prediction equations or costly whole-body laser imaging systems. The introduction of low-cost 3D scanners provides a new opportunity to quantify total body (TB) and regional SA, although a critical question prevails: can these devices acquire the quality of depth information and process this initial data to form a mesh that has the fidelity needed to generate accurate SA estimates? MATERIALS AND METHODS: This question was answered by comparing SA estimates calculated using images from four commercial 3D scanners in 108 adults to corresponding estimates acquired with a whole-body laser system. This was accomplished by processing initial mesh data from all devices, including the laser system, with the same universal software adapted specifically for repairing mesh gaps, identifying landmarks, and generating SA measurements. RESULTS: TB SA measured on all four 3D scanners was highly correlated with corresponding laser system estimates (R2 s, 0.98-0.99; all p < 0.001) with some small but significant mean differences (-0.19 to 0.06 m2 ); root-mean square errors (RMSEs) were small (0.02-0.03 m2 ); and significant bias was present for one device. Qualitatively similar results (e.g., R2 s, 0.78-0.95; mean Δs, -0.05 to 0.02 m2 ; RMSEs, 0.01-0.03 m2 ) were present for trunk, arm, and leg SA comparisons. DISCUSSION: The current study observations demonstrate that low-cost and practical 3D optical scanners are capable of accurately quantifying TB and regional SA, thus opening new opportunities for evaluating human phenotypes and related physiological characteristics.