Key points
Human placental function is evaluated using non‐invasive Doppler ultrasound of umbilical and uterine artery pulsatility indices as measures of resistance in placental vascular beds, while ...measurement of placental oxygen consumption (VO2) is only possible during Caesarean delivery.
This study shows the feasibility of using magnetic resonance imaging (MRI) in utero to measure blood flow and oxygen content in uterine and umbilical vessels to calculate oxygen delivery to and VO2 by the gravid uterus, uteroplacenta and fetus.
Normal late gestational human uteroplacental VO2 by MRI was ∼4 ml min−1 kg−1 fetal weight, which was similar to our MRI measurements in sheep and to those previously measured using invasive techniques.
Our MRI approach can quantify uteroplacental VO2, which involves the quantification of maternal‐ and fetal‐placental blood flows, fetal oxygen delivery and VO2, and the oxygen gradient between uterine‐ and umbilical‐venous blood, providing a comprehensive assessment of placental function with clinical potential.
It has not been feasible to perform routine clinical measurement of human placental oxygen consumption (VO2) and in vitro studies do not reflect true metabolism in utero. Here we propose an MRI method to non‐invasively quantify in utero placental and fetal oxygen delivery (DO2) and VO2 in healthy humans and sheep. Women (n = 20) and Merino sheep (n = 10; 23 sets of measurements) with singleton pregnancies underwent an MRI in late gestation (36 ± 2 weeks and 128 ± 9 days, respectively; mean ± SD). Blood flow (phase‐contrast) and oxygen content (T1 and T2 relaxometry) were measured in the major uterine‐ and umbilical‐placental vessels, allowing calculation of uteroplacental and fetal DO2 and VO2. Maternal DO2 (ml min−1 kg−1 fetus) to the gravid uterus was similar in humans and sheep (human = 54 ± 15, sheep = 53 ± 21, P = 0.854), while fetal DO2 (human = 25 ± 4, sheep = 22 ± 5, P = 0.049) was slightly lower in sheep. Uteroplacental and fetal VO2 (ml min−1 kg−1 fetus; uteroplacental: human = 4.1 ± 1.5, sheep = 3.5 ± 1.9, P = 0.281; fetus: human = 6.8 ± 1.3, sheep = 7.2 ± 1.7, P = 0.426) were similar between species. Late gestational uteroplacental:fetal VO2 ratio did not change with age (human, P = 0.256; sheep, P = 0.121). Human umbilical blood flow (ml min−1 kg−1 fetus) decreased with advancing age (P = 0.008), while fetal VO2 was preserved through an increase in oxygen extraction (P = 0.046). By contrast, sheep fetal VO2 was preserved through stable umbilical flow (ml min−1 kg−1; P = 0.443) and oxygen extraction (P = 0.582). MRI derived measurements of uteroplacental and fetal VO2 between humans and sheep were similar and in keeping with prior data obtained using invasive techniques. Taken together, these data confirm the reliability of our approach, which offers a novel clinical ‘placental function test’.
Key points
Human placental function is evaluated using non‐invasive Doppler ultrasound of umbilical and uterine artery pulsatility indices as measures of resistance in placental vascular beds, while measurement of placental oxygen consumption (VO2) is only possible during Caesarean delivery.
This study shows the feasibility of using magnetic resonance imaging (MRI) in utero to measure blood flow and oxygen content in uterine and umbilical vessels to calculate oxygen delivery to and VO2 by the gravid uterus, uteroplacenta and fetus.
Normal late gestational human uteroplacental VO2 by MRI was ∼4 ml min−1 kg−1 fetal weight, which was similar to our MRI measurements in sheep and to those previously measured using invasive techniques.
Our MRI approach can quantify uteroplacental VO2, which involves the quantification of maternal‐ and fetal‐placental blood flows, fetal oxygen delivery and VO2, and the oxygen gradient between uterine‐ and umbilical‐venous blood, providing a comprehensive assessment of placental function with clinical potential.
Both oxygen and temperature are fundamental factors determining metabolic performance, fitness, ecological niches, and responses of many aquatic organisms to climate change. Despite the importance of ...physical and physiological constraints on oxygen supply affecting aerobic metabolism of aquatic ectotherms, ecological theories such as the metabolic theory of ecology have focused on the effects of temperature rather than oxygen. This gap currently impedes mechanistic models from accurately predicting metabolic rates (i.e., oxygen consumption rates) of aquatic organisms and restricts predictions to resting metabolism, which is less affected by oxygen limitation. Here, we expand on models of metabolic scaling by accounting for the role of oxygen availability and temperature on both resting and active metabolic rates. Our model predicts that oxygen limitation is more likely to constrain metabolism in larger, warmer, and active fish. Consequently, active metabolic rates are less responsive to temperature than are resting metabolic rates, and metabolism scales to body size with a smaller exponent whenever temperatures or activity levels are higher. Results from a metaanalysis of fish metabolic rates are consistent with our model predictions. The observed interactive effects of temperature, oxygen availability, and body size predict that global warming will limit the aerobic scope of aquatic ectotherms and may place a greater metabolic burden on larger individuals, impairing their physiological performance in the future. Our model reconciles the metabolic theory with empirical observations of oxygen limitation and provides a formal, quantitative framework for predicting both resting and active metabolic rate and hence aerobic scope of aquatic ectotherms.
To understand the oxidation reaction of coal and predict and control generation and development of coal fires, a one-step global dynamic model of the chemical reaction between coal and oxygen ...considering multi-material actions was established. A volume-averaged oxygen consumption rate (OCR) to evaluate the characteristics of the oxidation reaction of coal was proposed. The results demonstrate that, in the reaction between coal and oxygen, the dominant effects of temperature and oxygen concentration on the reaction rate of coal oxidation also change. There is a certain time-lag between changes of the temperature during coal oxidation and combustion and the reaction rate: the changes of temperature parameters fail to reflect the instantaneous reaction rate in real time. By changing the volume fraction of oxygen and the programmed heating rate, it is found that increasing the volume fraction of oxygen and the heating rate both can promote the reaction between coal and oxygen and reduce the hysteretic effects of heating in the reaction under external heating. Therefore, controlling the temperature storage conditions is beneficial to preventing the oxidation reaction of coal in its early stage, while changing the oxygen supply conditions can control the development of coal spontaneous combustion in its later stage.
Display omitted
•The dominant effects of temperature and oxygen concentration were changed in the process of coal oxidation.•There was a certain time-lag between changes of the temperature and the reaction rate.•A volume-averaged oxygen consumption rate was proposed.•The temperature storage and oxygen supply could prevent the oxidation reaction of coal in different stages.
Hibernating mammals actively lower their body temperature to reduce energy expenditure when facing food scarcity
. This ability to induce a hypometabolic state has evoked great interest owing to its ...potential medical benefits
. Here we show that a hypothalamic neuronal circuit in rodents induces a long-lasting hypothermic and hypometabolic state similar to hibernation. In this state, although body temperature and levels of oxygen consumption are kept very low, the ability to regulate metabolism still remains functional, as in hibernation
. There was no obvious damage to tissues and organs or abnormalities in behaviour after recovery from this state. Our findings could enable the development of a method to induce a hibernation-like state, which would have potential applications in non-hibernating mammalian species including humans.
Observations of climate impacts on ecosystems highlight the need for an understanding of organismal thermal ranges and their implications at the ecosystem level. Where changes in aquatic animal ...populations have been observed, the integrative concept of oxygen- and capacity-limited thermal tolerance (OCLTT) has successfully characterised the onset of thermal limits to performance and field abundance. The OCLTT concept addresses the molecular to whole-animal mechanisms that define thermal constraints on the capacity for oxygen supply to the organism in relation to oxygen demand. The resulting 'total excess aerobic power budget' supports an animal's performance (e.g. comprising motor activity, reproduction and growth) within an individual's thermal range. The aerobic power budget is often approximated through measurements of aerobic scope for activity (i.e. the maximum difference between resting and the highest exercise-induced rate of oxygen consumption), whereas most animals in the field rely on lower (i.e. routine) modes of activity. At thermal limits, OCLTT also integrates protective mechanisms that extend time-limited tolerance to temperature extremes - mechanisms such as chaperones, anaerobic metabolism and antioxidative defence. Here, we briefly summarise the OCLTT concept and update it by addressing the role of routine metabolism. We highlight potential pitfalls in applying the concept and discuss the variables measured that led to the development of OCLTT. We propose that OCLTT explains why thermal vulnerability is highest at the whole-animal level and lowest at the molecular level. We also discuss how OCLTT captures the thermal constraints on the evolution of aquatic animal life and supports an understanding of the benefits of transitioning from water to land.
Display omitted
•A method to calculate the key parameters of coal oxidation reaction was proposed.•The course of coal oxidation reaction shows the characteristics of different stages.•Complexity of ...coal spontaneous combustion were enhanced by substance transfer and temperature-rise.•High-temperature gas and contact wall could heat the surrounding coal.
Coal spontaneous combustion (CSC) is one of major disasters that threaten the safety and production of coal mines. A method to calculate the key parameters of coal oxidation reaction based on temperature-programmed tests was proposed. Moreover, a one-step global numerical model for exploring coal oxidation considering the effects of multi-component material was established. The evolution of the oxygen consumption rates (OCRs) in multiple stages of coal oxidation was investigated and the changes in temperature and reaction rate were assessed by changing thermal boundary conditions including gas temperature supplied and wall temperature. The results show that the coal oxidation can be simulated based on the obtained parameters; the process of coal oxidation can be partitioned into three stages (i.e. temperature-dominated, co-dominated by temperature and oxygen, and oxygen-dominated) as the reaction continues. Under thermal conditions involving high-temperature gas, the coal always exhibits a high temperature at the gas inlet and the dimensionless number Φ of the coal self-heating temperature presents three trends including slight variation, a gradual increase, and gradual reduction. Under conditions involving the high-temperature wall of coal-storage tanks in contact with coal (briefly called the contact wall hereinafter), the dimensionless number Φ of the coal self-heating temperature increases exponentially.
Oxygen plays an essential role in the photodynamic therapy (PDT) of cancer. However, hypoxia inside tumors severely attenuates the therapeutic effect of PDT. To address this issue, a novel strategy ...is reported for cutting off the oxygen consumption pathway by using sub‐50 nm dual‐drug nanoparticles (NPs) to attenuate the hypoxia‐induced resistance to PDT and to enhance PDT efficiency. Specifically, dual‐drug NPs that encapsulate photosensitizer (PS) verteporfin (VER) and oxygen‐regulator atovaquone (ATO) with sub‐50 nm diameters can penetrate deep into the interior regions of tumors and effectively deliver dual‐drug into tumor tissues. Then, ATO released from NPs efficiently reduce in advance cellular oxygen consumption by inhibition of mitochondria respiratory chain and further heighten VER to generate greater amounts of 1O2 in hypoxic tumor. As a result, accompanied with the upregulated oxygen content in tumor cells and laser irradiation, the dual‐drug NPs exhibit powerful and overall antitumor PDT effects both in vitro and in vivo, and even tumor elimination. This study presents a potential appealing clinical strategy in photodynamic eradication of tumors.
A novel strategy for reducing oxygen consumption to attenuate the hypoxia‐induced resistance to photodynamic therapy (PDT) by using sub‐50 nm dual‐drug nanoparticles (ATO/VER NPs) is described. ATO has the ability of alleviating hypoxic regions and can eliminate tumors by enhancing PDT, which provides a valuable reference for research on targeted treatment of hypoxic tumor tissues.
Maximum (aerobic) metabolic rate (MMR) is defined here as the maximum rate of oxygen consumption (M˙O2max) that a fish can achieve at a given temperature under any ecologically relevant circumstance. ...Different techniques exist for eliciting MMR of fishes, of which swim‐flume respirometry (critical swimming speed tests and burst‐swimming protocols) and exhaustive chases are the most common. Available data suggest that the most suitable method for eliciting MMR varies with species and ecotype, and depends on the propensity of the fish to sustain swimming for extended durations as well as its capacity to simultaneously exercise and digest food. MMR varies substantially (>10 fold) between species with different lifestyles (i.e. interspecific variation), and to a lesser extent (<three‐fold) between individuals of the same species (i.e. intraspecific variation). MMR often changes allometrically with body size and is modulated by several environmental factors, including temperature and oxygen availability. Due to the significance of MMR in determining aerobic scope, interest in measuring this trait has spread across disciplines in attempts to predict effects of climate change on fish populations. Here, various techniques used to elicit and measure MMR in different fish species with contrasting lifestyles are outlined and the relevance of MMR to the ecology, fitness and climate change resilience of fishes is discussed.
Background
There is increasing evidence that physical activity supports healthy ageing. Exercise is helpful for cardiovascular, respiratory and musculoskeletal systems, among others. Aerobic ...activity, in particular, improves cardiovascular fitness and, based on recently reported findings, may also have beneficial effects on cognition among older people.
Objectives
To assess the effect of aerobic physical activity, aimed at improving cardiorespiratory fitness, on cognitive function in older people without known cognitive impairment.
Search methods
We searched ALOIS ‐ the Cochrane Dementia and Cognitive Improvement Group's Specialized Register, the Cochrane Controlled Trials Register (CENTRAL) (all years to Issue 2 of 4, 2013), MEDLINE (Ovid SP 1946 to August 2013), EMBASE (Ovid SP 1974 to August 2013), PEDro, SPORTDiscus, Web of Science, PsycINFO (Ovid SP 1806 to August 2013), CINAHL (all dates to August 2013), LILACS (all dates to August 2013), World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (http://apps.who.int/trialsearch), ClinicalTrials.gov (https://clinicaltrials.gov) and Dissertation s International (DAI) up to 24 August 2013, with no language restrictions.
Selection criteria
We included all published randomised controlled trials (RCTs) comparing the effect on cognitive function of aerobic physical activity programmes with any other active intervention, or no intervention, in cognitively healthy participants aged over 55 years.
Data collection and analysis
Two review authors independently extracted the data from included trials. We grouped cognitive outcome measures into eleven categories covering attention, memory, perception, executive functions, cognitive inhibition, cognitive speed and motor function. We used the mean difference (or standardised mean difference) between groups as the measure of the treatment effect and synthesised data using a random‐effects model. We conducted separate analyses to compare aerobic exercise interventions with no intervention and with other exercise, social or cognitive interventions. Also, we performed analyses including only trials in which an increase in the cardiovascular fitness of participants had been demonstrated.
Main results
Twelve trials including 754 participants met our inclusion criteria. Trials were from eight to 26 weeks in duration.
We judged all trials to be at moderate or high risk of bias in at least some domains. Reporting of some risk of bias domains was poor.
Our analyses comparing aerobic exercise to any active intervention showed no evidence of benefit from aerobic exercise in any cognitive domain. This was also true of our analyses comparing aerobic exercise to no intervention. Analysing only the subgroup of trials in which cardiorespiratory fitness improved in the aerobic exercise group showed that this improvement did not coincide with improvements in any cognitive domains assessed. Our subgroup analyses of aerobic exercise versus flexibility or balance interventions also showed no benefit of aerobic exercise in any cognitive domain.
Dropout rates did not differ between aerobic exercise and control groups. No trial reported on adverse effects.
Overall none of our analyses showed a cognitive benefit from aerobic exercise even when the intervention was shown to lead to improved cardiorespiratory fitness.
Authors' conclusions
We found no evidence in the available data from RCTs that aerobic physical activities, including those which successfully improve cardiorespiratory fitness, have any cognitive benefit in cognitively healthy older adults. Larger studies examining possible moderators are needed to confirm whether or not aerobic training improves cognition.
PDF
