Skin temperatures at the nape in infants at high altitude.

Skin temperatures were measured on three Quechua Indian infants resident at 4,000 meters above sea level in Peru. Nape temperatures were warmer than other skin sites, suggesting that the brown adipose tissue associated with non-shivering thermogenesis is metabolically active despite the reduced oxygen availability at high altitude. The question of the role of non-shivering thermogenesis in infant thermoregulation under the covariant stresses of hypoxia and cold is still open.     

A study of human skin and surface temperatures in stable and unstable thermal environments

Skin temperature is a common physiological parameter that reflects human thermal responses. The purpose of this research was to investigate the effects of radiant temperature on human skin temperature and surface temperature in stable and unstable thermal environments. For a clothed human body, the skin temperature is the surface temperature of the skin, while the surface temperature is the outer surface temperature of the clothes. For this aim, the radiant temperature from 26 to 38 °C and then from 38 to 26 °C was controlled in three different ways; in stable condition keeping stable above 40 min, in unstable condition at a rate of 2 °C/5 min, and in another unstable condition at a rate of 2 °C/10 min. Experimental data showed that at the same radiant temperature, the local skin/surface temperatures during the radiant temperature decrease were higher compared to those during the radiant temperature increase. During the radiant temperature increase/decrease, the increments/decrements of the mean skin temperature and the mean surface temperature decreased gradually from the stable condition, 2 °C/10 min to 2 °C/5 min. Compared to surface temperature, the faster the radiant temperature changed, the more obviously the change in skin temperature was delayed. These data demonstrated that the human body has physiological adaptability to unstable thermal environments.     

An assessment of skin temperature gradients in a tropical primate using infrared thermography and subcutaneous implants

Infrared thermography has become a useful tool to assess surface temperatures of animals for thermoregulatory research. However, surface temperatures are an endpoint along the body's core-shell temperature gradient. Skin and fur are the peripheral tissues most exposed to ambient thermal conditions and are known to serve as thermosensors that initiate thermoregulatory responses. Yet relatively little is known about how surface temperatures of wild mammals measured by infrared thermography relate to subcutaneous temperatures. Moreover, this relationship may differ with the degree that fur covers the body. To assess the relationship between temperatures and temperature gradients in peripheral tissues between furred and bare areas, we collected data from wild mantled howling monkeys (Alouatta palliata) in Costa Rica. We used infrared thermography to measure surface temperatures of the furred dorsum and bare facial areas of the body, recorded concurrent subcutaneous temperatures in the dorsum, and measured ambient thermal conditions via a weather station. Temperature gradients through cutaneous tissues (subcutaneous-surface temperature) and surface temperature gradients (surface-ambient temperature) were calculated. Our results indicate that there are differences in temperatures and temperature gradients in furred versus bare areas of mantled howlers. Under natural thermal conditions experienced by wild animals, the bare facial areas were warmer than temperatures in the furred dorsum, and cutaneous temperature gradients in the face were more variable than the dorsum, consistent with these bare areas acting as thermal windows. Cutaneous temperature gradients in the dorsum were more closely linked to subcutaneous temperatures, while facial temperature gradients were more heavily influenced by ambient conditions. These findings indicate that despite the insulative properties of fur, for mantled howling monkeys surface temperatures of furred areas still demonstrate a relationship with subcutaneous temperatures. Given that most mammals possess dense fur, this provides insight for using infrared imaging in thermoregulatory studies of wild animals lacking bare skin.     

The effect of Sub-MAC anesthesia and the radiation setting on repeated tail flick testing in rats.

The tail flick (TF) response is regarded as a spinal reflex that is influenced by supraspinal structures. The TF test using radiant heat is the most common way to assess pain perception; however, there are few reports dealing with the heat source's properties and score consistency. This study examined the usefulness of light anesthesia for suppressing supraspinal signals and the effects of radiant heat on skin temperature during TF testing. The fluctuations of TF latency over one hour were evaluated while the rats were given oxygen and 0%, 0.5%, 1.0%, or 1.5% isoflurane. The stimulator's infrared radiant (IR) power flux was measured over time, and the tail skin surface temperature was predicted using a non-linear regression equation. TF latencies were measured at various heat source intensities, and response temperatures were estimated. Inhalation anesthesia suppressed the TF reflex according to the inspiratory concentration of the volatile anesthetic. IR power fluxes reached constant power 2.5 s after the stimulator was turned on, and the predicted skin temperature depended on the maximum IR power flux of the IR intensity and the radiation time. One percent isoflurane inhalation and an IR20 heat intensity (which was 161.5 mW/cm(2) and resulted in a skin temperature of 65 degrees C after 10 s of radiation) provided reliable TF latencies on repeated TF testing. Given these results, it can be concluded that the stimulator setting influenced TF latency, and that the inhalation of light anesthesia provided consistent scores on repeated TF testing.     

Climatic controls of the cool human thermal sensation in a summertime onshore wind

 Afternoon observations in summer comparing shoreline with inland atmospheric conditions were made during onshore winds at Victoria, British Columbia, Canada. The onshore wind came from a cool water surface. Mean monthly water temperatures near to shore were between 11 and 11.5° C. The onshore wind brought lower air, ground surface radiant and sky radiant temperatures; lower humidity and greater wind speed. All of these combine to produce a cooler human environment at the shoreline than inland. The relative importance of climatic elements in producing the cooler environment was assessed using sensitivity analyses with eight different human thermal exchange models/indices. Air temperature and wind speed had the greatest effect, followed by ground surface radiant temperature, sky radiant temperature and humidity. Wind speed is the most practical element to consider when trying to maximize human comfort along the shoreline. Received: 9 July 1996 / Revised: 31 March 1997 / Accepted: 14 April 1997     

Bed climate of Korean using ondol heating system

1. 1. To examine the influence of different bed conditions (ondol sleep, bed sleep on ondol with same bedding) of the Korean ondol traditional heating system on human response during sleep, bed climates and physiological responses such as skin and rectal temperatures, weight loss, body movement and subjective sensation were measured with 4 grown-up females as subjects while they were sleeping for 7 h.

2. 2. Bed climate: Temperatures under the mattress and inside the quilt were higher on ondol while temperatures on the mattress and humidity inside the quilt were higher on the bed.

3. 3. Rectal temperature was significantly higher on ondol; skin temperature showed no major differences in relation to bed conditions. The frequency of body movements had the highest correlation with bed climate of the parameters measured.

4. 4. Mattress weight decreased on ondol and increased on the bed.

5. 5. The frequency of body movements was significantly higher in ondol sleep.

6. 6. The subjects sensation showed difference on cushion sensation between the two types of bed condition.

7. 7. To obtain the same level of comfort on both ondol and bed sleeping conditions less thermal insulating value is needed for ondol sleep.

Inferring pathogen inactivation from the surface temperatures of compost heaps

A sufficiently high composting temperature should inactivate many common pathogens likely to be present in solid animal waste. Monitoring core temperatures inside compost heaps is not straightforward, which means that heaps are not generally monitored. An alternative is to monitor surface temperatures and use those data to infer core temperatures, and thus whether pathogen inactivation has occurred. This paper describes two methods (thermal imaging and thermocouples) for the measurement of surface temperature, and a modelling approach using time series analysis to predict the temperatures obtained in the core of aerated heaps of composting pig farmyard manure (FYM) from surface temperature data. The model was able to predict core temperatures in the heap quite closely for a period of time for well insulated parts of the heap, although predictions were further from observed values close to the surface of the heap and the aeration pipe.     

Homeothermy and primate bipedalism: Is water shortage or solar radiation the main threat to baboon (Papio hamadryas) homeothermy?

Other than the hominin lineage, baboons are the diurnally active primates that have colonized the arid plains of Africa most successfully. While the hominin lineage adopted bipedalism before colonizing the open, dry plains, baboons retained a quadrupedal mode of locomotion. Because bipedalism has been considered to reduce the thermoregulatory stress of inhabiting open dry plains, we investigated how baboons cope with thermal loads and water restriction. Using implanted data loggers, we measured abdominal temperature every 5 min in six unrestrained baboons while they were exposed to simulated desert conditions (15 °C at night rising to 35 °C during the day, with and without extra radiant heating), or an ambient temperature of 22 °C. At 22 °C, core temperature averaged 37.9 °C and cycled nychthemerally by 1.7 °C. Mean, minimum, and maximum daily core temperatures in euhydrated baboons in the simulated desert environments did not differ from the temperatures displayed in the 22 °C environment, even when radiant heating was applied. At 22 °C, restricting water intake did not affect core temperature. During the desert simulations, maximum core temperature increased significantly on each day of water deprivation, with the highest temperatures (>40 °C) on the third day in the simulation that included radiant heat. When drinking water heated to 38 °C was returned, core temperature decreased rapidly to a level lower than normal for that time of day. We conclude that baboons with access to water can maintain homeothermy in the face of high air temperatures and radiant heat loads, but that a lack of access to drinking water poses a major threat to baboon homeothermy. We speculate that any competitive thermoregulatory advantage of bipedalism in early hominins was related to coping with water shortage in hot environments, and that their freed hands might have enabled them to transport enough water to avoid dangerous hyperthermia.     

Quantitative differences in sperm cells and organelles of tobacco (Nicotiana tabacum L.) grown under differing environmental conditions

In flowers grown at warm temperatures in environmental chambers and at cooler temperatures in the greenhouse, eight parameters of the sperm-cell organization of Nicotiana tabacum were examined during sperm cell maturation using serial ultrathin sectioning, transmission electron microscopy and quantitative cytology. Despite employing the same seed source, and similar soil and nutrient conditions, the surface area and volume of the cell, the nucleus and the chondriome were larger in flowers grown in growth chambers under warmer controlled conditions, whereas the number of plastids appeared to be the same, or slightly higher, in flowers grown under cooler greenhouse conditions. These results suggest that environmental conditions may influence the quantity of cytoplasmic organelles, including mitochondria and plastids, thus potentially influencing the likelihood of male cytoplasmic inheritance.     

Endpiece: Genius (1815)

ObjectiveTo examine the proposition that a used infant mattress is associated with an increased risk of sudden infant death syndrome.DesignCase-control study.SettingScotland (population 5.1 million, with about 53 000 births a year).Participants131 infants who died of sudden infant death syndrome between 1 January 1996 and 31 May 2000 and 278 age, season, and obstetric unit matched control infants.ResultsRoutine use of an infant mattress previously used by another child was significantly associated with an increased risk of sudden infant death syndrome (multivariate odds ratio 3.07, 95% confidence interval 1.51 to 6.22). Use of a used infant mattress for last sleep was also associated with increased risk (6.10, 2.31 to 16.12). The association was significantly stronger if the mattress was from another home (4.78, 2.08 to 11.0) than if it was from the same home (1.64, 0.64 to 4.2).ConclusionA valid significant association exists between use of a used infant mattress and an increased risk of sudden infant death syndrome, particularly if the mattress is from another home. Insufficient evidence is available to judge whether this relation is cause and effect.

What is already known about this topic

The major risk factors for sudden infant death syndrome are sleeping prone and parental smokingOne study has suggested that the syndrome is associated with sleeping on an infant mattress previously used by another child

What this study adds

New case-control data show that the association between a previously used infant mattress and sudden infant death syndrome is validWhen source of used mattress is categorised, the association is significant only if the mattress is from another homeInsufficient evidence is available to judge whether this is a cause and effect relation     

Prediction of mean skin temperature in warm environments

The data collected by the authors in four experimental series have been analysed together with data from the literature, to study the relationship between mean skin temperature and climatic parameters, subject metabolic rate and clothing insulation. The subjects involved in the various studies were young male subjects, unacclimatized to heat. The range of conditions examined involved mean skin temperatures between 33 degrees C and 38 degrees C, air temperatures (Ta) between 23 degrees C and 50 degrees C, ambient water vapour pressures (Pa) between 1 and 4.8 kPa, air velocities (Va) between 0.2 and 0.9 m.s-1, metabolic rates (M) between 50 and 270 W.m-2, and Clo values between 0.1 and 0.6. In 95% of the data, mean radiant temperature was within +/- 3 degrees C of air temperature. Based on 190 data averaged over individual values, the following equation was derived by a multiple linear regression technique: Tsk = 30.0 + 0.138 Ta + 0.254 Pa-0.57 Va + 1.28.10(-3) M-0.553 Clo. This equation was used to predict mean skin temperature from 629 individual data. The difference between observed and predicted values was within +/- 0.6 degrees C in 70% of the cases and within +/- 1 degrees C in 90% of the cases. It is concluded that the proposed formula may be used to predict mean skin temperature with satisfactory accuracy in nude to lightly clad subjects exposed to warm ambient conditions with no significant radiant heat load.     

Global climate change increases risk of crop yield losses and food insecurity in the tropical Andes

One of the greatest current challenges to human society is ensuring adequate food production and security for a rapidly growing population under changing climatic conditions. Climate change, and specifically rising temperatures, will alter the suitability of areas for specific crops and cultivation systems. In order to maintain yields, farmers may be forced to change cultivation practices, the timing of cultivation, or even the type of crops grown. Alternatively, farmers can change the location where crops are cultivated (e.g., to higher elevations) to track suitable climates (in which case the plants will have to grow in different soils), as cultivated plants will otherwise have to tolerate warmer temperatures and possibly face novel enemies. We simulated these two last possible scenarios (for temperature increases of 1.3°C and 2.6°C) in the Peruvian Andes through a field experiment in which several traditionally grown varieties of potato and maize were planted at different elevations (and thus temperatures) using either the local soil or soil translocated from higher elevations. Maize production declined by 21%–29% in response to new soil conditions. The production of maize and potatoes declined by >87% when plants were grown under warmer temperatures, mainly as a result of the greater incidence of novel pests. Crop quality and value also declined under simulated migration and warming scenarios. We estimated that local farmers may experience severe economic losses of up to 2,300 USOne of the greatest current challenges to human society is ensuring adequate food production and security for a rapidly growing population under changing climatic conditions. Climate change, and specifically rising temperatures, will alter the suitability of areas for specific crops and cultivation systems. In order to maintain yields, farmers may be forced to change cultivation practices, the timing of cultivation, or even the type of crops grown. Alternatively, farmers can change the location where crops are cultivated (e.g., to higher elevations) to track suitable climates (in which case the plants will have to grow in different soils), as cultivated plants will otherwise have to tolerate warmer temperatures and possibly face novel enemies. We simulated these two last possible scenarios (for temperature increases of 1.3°C and 2.6°C) in the Peruvian Andes through a field experiment in which several traditionally grown varieties of potato and maize were planted at different elevations (and thus temperatures) using either the local soil or soil translocated from higher elevations. Maize production declined by 21%–29% in response to new soil conditions. The production of maize and potatoes declined by >87% when plants were grown under warmer temperatures, mainly as a result of the greater incidence of novel pests. Crop quality and value also declined under simulated migration and warming scenarios. We estimated that local farmers may experience severe economic losses of up to 2,300 US$ ha^?1 yr^?1. These findings reveal that climate change is a real and imminent threat to agriculture and that there is a pressing need to develop effective management strategies to reduce yield losses and prevent food insecurity. Importantly, such strategies should take into account the influences of non‐climatic and/or biotic factors (e.g., novel pests) on plant development.     

Statistical Modelling of Physiological Heat Stress Response by Means of a Nonlinear Two‐Stage Model

In the context of medical or biological studies, very often parameters of interest are measured repeatedly over time under a given set of conditions. This results in a set of (often similarly shaped) time series. Then, the objective is the determination of the functional relationship between the parameter of interest and time on the one hand, and the analysis of the variation of this functional relationship between experiments, on the other hand. This may be done by means of a two‐stage model. The present work describes the theory of the two‐stage model and its application to the increase of human core temperature for a set of 678 experiments where the subjects were exposed to warm and hot environments. The data originating from 6 European research institutes, have been pooled into one database for the Heat Stress Project within the scope of the BIOMED 2 programme of the European Union. A nonlinear two‐stage model was applied, with a logistic function modelling the nonlinear time course of the core temperature, and with its parameters depending on air temperature, mean radiant temperature, air velocity, partial vapour pressure, clothing insulation, metabolic rate, gender, acclimatisation status and body surface area. We conclude that acclimatisation, clothing insulation, body surface area, air temperature, air velocity, partial vapour pressure, metabolic rate, and the difference between mean radiant temperature and air temperature play an important role for work in warm and hot environments. We show how our results can be used for the estimation of allowable exposure times for work in hot environments.     

Plastic collective endothermy in a complex animal society (army ant bivouacs: Eciton burchellii parvispinum)

Endothermic animals do not always have a single adaptive internal temperature; some species exhibit plastic homeostasis, adaptively allowing body temperature to drop when thermoregulatory costs are high. Like large‐bodied endotherms, some animal societies exhibit collective thermal homeostasis. We tested for plasticity of thermoregulation in the self‐assembled temporary nests (bivouacs) of army ants. We measured core bivouac temperatures under a range of environmental conditions and at different colony developmental (larval vs pupal brood) stages. Contrary to previous assertions, bivouacs were not perfect thermoregulators in all developmental stages. Instead, bivouacs functioned as superorganismal facultative endotherms, using a combination of site choice and context‐dependent metabolic heating to adjust core temperatures across an elevational cline in ambient temperature. When ambient temperature was low, the magnitude of metabolic heating was dependent on colony developmental stage: pupal bivouacs were warmer than larval bivouacs. At cooler high elevations, bivouacs functioned like some endothermic animals that intermittently lower their body temperatures to conserve energy. Bivouacs potentially conserved energy by investing less metabolic heating in larval brood because the high costs of impaired worker development may require more stringent thermoregulation of pupae. Our data also suggest that site choice played an important role in bivouac cooling under high ambient temperatures at low elevations. Climate warming may expand upper elevational range limits of Eciton burchellii parvispinum, while reducing the availability of cool and moist bivouac sites at lower elevations, potentially leading to future low‐elevation range contraction.     

A new approach using the Pierce two-node model for different body parts

This paper presents a new approach, in applying the Pierce two-node model, to predict local skin temperatures of individual body parts with good accuracy. In this study, local skin temperature measurements at 24 sites on the bodies of 11 human subjects were carried out in a controlled environment under three different indoor conditions (i.e. neutral, warm and cold). The neutral condition measurements were used to adjust the local skin set-points in the model for each body part. Additional modifications to the calculation algorithm were introduced corresponding to different body parts. The local core set-points were then calculated, using a line search method, as the input values that allow the model to predict the skin temperatures with maximum deviation of ±0.1°C for the neutral condition. The model predictability was verified for the other two indoor conditions, and the results show that the modified model predicts local skin temperatures with average deviation of ±0.3°C.     

Brain temperature and limits on transcranial cooling in humans: quantitative modeling results

Selective brain cooling (SBC) of varying strengths has been demonstrated in a number of mammals and appears to play a role in systemic thermoregulation. Although primates lack obvious specialization for SBC, the possibility of brain cooling in humans has been debated for many years. This paper reports on the use of mathematical modeling to explore whether surface cooling can control effectively the temperature of the human cerebrum. The brain was modeled as a hemisphere with a volume of 1.33 1 and overlying layers of cerebrospinal fluid, skull, and scalp. Each component was assigned appropriate dimensions, physical properties and physiological characteristics that were determined from the literature. The effects of blood flow and of thermal conduction were modeled using the steady-state form of the bio-heat equation. Input parameters included core (arterial) temperature: normal (37°C) or hyperthermic (40°C), air temperature: warm (30°C) or hot (40°C), and sweat evaporation rate: 0, 0.25, or 0.50 l · m⁻² · h⁻¹. The resulting skin temperatures of the model ranged from 31.8°C to 40.2°C, values which are consistent with data obtained from the literature. Cerebral temperatures were generally insensitive to surface conditions (air temperature and evaporation rate), which affected only the most superficial level of the cerebrum (≤1.5 mm) The remaining parenchymal temperatures were 0.2–0.3°C above arterial temperatures, regardless of surface conditions. This held true even for the worst-case conditions combining core hyperthermia in a hot environment with zero evaporative cooling. Modeling showed that the low surface-to-volume ratio, low tissue conductivity, and high rate of cerebral perfusion combine to minimize the potential impact of surface cooling, whether by transcranial venous flow or by conduction through intervening layers to the skin or mucosal surfaces. The dense capillary network in the brain assures that its temperature closely follows arterial temperature and is controlled through systemic thermoregulation independent of head surface temperature. A review of the literature reveals several independent lines of evidence which support these findings and indicate the absence of functionally significant transcranial venous flow in either direction. Given the fact that humans sometimes work under conditions which produce face and scalp temperatures that are above core temperature, a transcranial thermal link would not necessarily protect the brain, but might instead increase its vulnerability to environmentally induced thermal injury. Accepted: 11 March 1998     

Effects of reproductive condition,roost microclimate,and weather patterns on summer torpor use by a vespertilionid bat

A growing number of mammal species are recognized as heterothermic, capable of maintaining a high‐core body temperature or entering a state of metabolic suppression known as torpor. Small mammals can achieve large energetic savings when torpid, but they are also subject to ecological costs. Studying torpor use in an ecological and physiological context can help elucidate relative costs and benefits of torpor to different groups within a population. We measured skin temperatures of 46 adult Rafinesque's big‐eared bats (Corynorhinus rafinesquii) to evaluate thermoregulatory strategies of a heterothermic small mammal during the reproductive season. We compared daily average and minimum skin temperatures as well as the frequency, duration, and depth of torpor bouts of sex and reproductive classes of bats inhabiting day‐roosts with different thermal characteristics. We evaluated roosts with microclimates colder (caves) and warmer (buildings) than ambient air temperatures, as well as roosts with intermediate conditions (trees and rock crevices). Using Akaike's information criterion (AIC), we found that different statistical models best predicted various characteristics of torpor bouts. While the type of day‐roost best predicted the average number of torpor bouts that bats used each day, current weather variables best predicted daily average and minimum skin temperatures of bats, and reproductive condition best predicted average torpor bout depth and the average amount of time spent torpid each day by bats. Finding that different models best explain varying aspects of heterothermy illustrates the importance of torpor to both reproductive and nonreproductive small mammals and emphasizes the multifaceted nature of heterothermy and the need to collect data on numerous heterothermic response variables within an ecophysiological context.     

Water warming garment versus forced air warming system in prevention of intraoperative hypothermia during liver transplantation: a randomized controlled trial [ISRCTN32154832

BACKGROUND: The authors compared two strategies for the maintenance of intraoperative normothermia during orthotopic liver transplantation (OLT): the routine forced-air warming system and the newly developed, whole body water garment. METHODS: In this prospective, randomized and open-labelled study, 24 adult patients were enrolled in one of two intraoperative temperature management groups during OLT. The water-garment group (N = 12) received warming with a body temperature (esophageal) set point of 36.8 degrees C. The forced air-warmer group (N = 12) received routine warming therapy using upper- and lower-body forced-air warming system. Body core temperature (primary outcome) was recorded intraoperatively and during the two hours after surgery in both groups. RESULTS: The mean core temperatures during incision, one hour after incision and during the skin closing were significantly higher (p < 0.05, t test with Bonferroni corrections for the individual tests) in the water warmer group compared to the control group (36.7 PlusMinus; 0.1, 36.7 PlusMinus; 0.2, 36.8 PlusMinus; 0.1 vs 36.1 PlusMinus; 0.4, 36.1 PlusMinus; 0.4, 36.07 PlusMinus; 0.4 degrees C, respectively). Moreover, significantly higher core temperatures were observed in the water warmer group than in the control group during the placement of cold liver allograft (36.75 PlusMinus; 0.17 vs 36.09 PlusMinus; 0.38 degrees C, respectively) and during the allograft reperfusion period (36.3 PlusMinus; 0.26 vs 35.52 PlusMinus; 0.42 degrees C, respectively). In addition, the core temperatures immediately after admission to the SICU (36.75 PlusMinus; 0.13 vs 36.22 PlusMinus; 0.3 degrees C, respectively) and at one hr (36.95 PlusMinus; 0.13 vs 36.46 PlusMinus; 0.2 degrees C, respectively) were significantly higher in the water warmer group, compared to the control group, whereas the core temperature did not differ significantly afte two hours in ICU in both groups. CONCLUSIONS: The investigated water warming system results in better maintenance of intraoperative normothermia than routine air forced warming applied to upper- and lower body.     

Aerial release of bacteria from cot mattress materials and the sudden infant death syndrome

AIM: To investigate aerial release of bacteria from used cot mattresses and to assess factors that may influence this process. METHODS AND RESULTS: Movement on used mattresses, simulating that of an infant's head, significantly enhanced aerial release of naturally acquired bacteria from the polyurethane foams (total count data, P = 0.008; Staphylococcus aureus, P = 0.004) or from polyvinyl chloride covers (total count data, P = 0.001). Aerial release of naturally acquired bacteria from used cot mattresses showed high variability and was poorly correlated (R2 < or = 0.294) with bacterial cell density within the materials. In experiments involving inoculation of S. aureus and Escherichia coli onto the polyurethane of unused cot mattresses, aerial release of the species correlated well (R2 > or = 0.950) with inoculation density when simulated infant head movement was applied. Aerial release of these bacterial species from the material decreased with increase in width or aqueous content of the material, and was lower from polyurethane foam of a used cot mattress. CONCLUSIONS: Simulated infant movement and mattress related factors influence aerial release of bacteria from cot mattress materials. With simulated infant movement on cot mattress polyurethane foam, levels of airborne bacteria above the material are proportional to bacterial population levels inoculated onto the material. SIGNIFICANCE AND IMPACT OF THE STUDY: Cot mattresses harbouring relatively high levels of naturally acquired toxigenic bacteria, such as S. aureus, could pose a relatively high risk of infection to the infant's respiratory tract through increased aerial contamination. This has impact in the context of recent findings on cot mattress related risk factors for sudden infant death syndrome.     

Influence of temperature and soil drying on respiration of individual roots in citrus: integrating greenhouse observations into a predictive model for the field

In citrus, the majority of fine roots are distributed near the soil surface – a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant’s below‐ground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring the respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q₁₀ = 1·8–2·0), provided that the changes in temperature were short‐term. However, when temperatures were held constant, root respiration did not increase exponentially with increasing temperatures. Instead, the roots acclimated to controlled temperatures above 23 °C, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually beginning at 6% soil water content and reached a minimum at <2% soil water content in sandy soil. A model was constructed from greenhouse data to predict diurnal patterns of fine root respiration based on temperature and soil water content. The model was then validated in the field using data obtained by CO₂ trapping on root systems of mature citrus trees. The trees were grown at a site where the soil temperature and water content were manipulated. Respiration predicted by the model was in general agreement with observed rates, which indicates the model may be used to estimate entire root system respiration for citrus.