Measurement Of Evaporative Water Loss Research Articles

Physiological responses of a rodent to heliox reveal constancy of evaporative water loss under perturbing environmental conditions.

Total evaporative water loss of endotherms is assumed to be determined essentially by biophysics, at least at temperatures below thermoneutrality, with evaporative water loss determined by the water vapor deficit between the animal and the ambient air. We present here evidence, based on the first measurements of evaporative water loss for a small mammal in heliox, that mammals may have a previously unappreciated ability to maintain acute constancy of total evaporative water loss under perturbing environmental conditions. Thermoregulatory responses of ash-grey mice (Pseudomys albocinereus) to heliox were as expected, with changes in metabolic rate, conductance, and respiratory ventilation consistent with maintaining constancy of body temperature under conditions of enhanced heat loss. However, evaporative water loss did not increase in heliox. This is despite our confirmation of the physical effect that heliox augments evaporation from nonliving surfaces, which should increase cutaneous water loss, and increases minute volume of live ash-grey mice in heliox to accommodate their elevated metabolic rate, which should increase respiratory water loss. Therefore, mice had not only a thermoregulatory but also a hygroregulatory response to heliox. We interpret these results as evidence that ash-grey mice can acutely control their evaporative water loss under perturbing environmental conditions and suggest that hygroregulation at and below thermoneutrality is an important aspect of the physiology of at least some small mammals.

New functions and applications of walter, the sweating fabric manikin.

In this paper, latest developments on Walter, a sweating fabric manikin, are reported. These include the improved simulation of "walking motion", the design and construction of an automated water supply, and real-time measurement of evaporative water loss and regulation of "skin" temperature through the regulation of the pumps inside the manikin body. Testing of commercial garment ensembles showed that the measurement of thermal insulation and moisture-vapour resistance of clothing is very reproducible with the coefficient of variation being generally less than 5%. It was also shown that, in addition to the thermal insulation and moisture-vapour resistance, the percentage of moisture accumulation within clothing is a very useful parameter of clothing comfort. The improved manikin has been used to investigate the effects of walking motion on thermal insulation and evaporative resistance of clothing. The trend of the effects of walking speed up to 1.13 m s(-1) for the nude manikin and when it was wearing garments of different sizes are reported.

Evaporative and excretory water loss during free flight in pigeons

Body water conservation is important in flying birds because the very high metabolic demands and heat dissipation requirements during flight depend on plasma-volume integrity. Wind tunnel experiments and theoretical model predictions show that evaporative water loss (EWL) depends on air temperature (Ta) and water vapor density (ρa), but these relationships have not been examined in free-flying birds. The contribution of excretory water loss to the total water loss of a flying bird is thought to be negligible but this assumption is untested. To study the dependence of water losses on environmental conditions in free-flying birds and to quantify the contribution of excretory water loss to total water loss, we estimated evaporative and excretory water losses in 16 trained, free-flying tippler pigeons (Columba livia, 250–340 g). We collected excreta by attaching a light latex, water-impermeable receptacle around each bird's vent. By gravimetry, we measured evaporative and excretory water losses of birds for eight flights at different Tas and compared flying to resting (control) birds for two of these flights. EWL was constant with respect to Ta when less than 15 °C, and increased with increasing Ta above 19 °C, indicating that evaporative cooling was invoked when the heat load increased. EWL increased with increasing ρa, possibly due to the strong correlation between ρa and Ta. Excretory water loss was independent of ρa or Ta and averaged almost 10% of the total water loss. Measurements of EWL made on pigeons during wind tunnel experiments and previous free-flight studies are consistent with our free-flight measurements made at similar Tas.

Evaporative water loss and the role of cocoon formation in Australian frogs

Measurements of evaporative water loss (EWL; mg min-1) and resistance (R; sec cm-1) for various Australian frogs indicate three general allometric patterns: non-cocooned and non-‘waterproof’ frogs with EWL ∝ Mass0.30 and R independent of body mass at about 1–3 sec cm-1, cocooned frogs with EWL reduced about 50–200-fold and R about 50–200 sec cm-1, and ‘waterproof’ frogs with EWL reduced about 5–100- fold and R about 5–100 sec cm-1. Cocooned frogs have an exponential reduction in EWL and fairly linear increase in R over time, corresponding to the temporal addition of layers to the cocoon. The biophysical properties of cocoon are generally similar for various species, although there is some variation in both resistance per thickness (5–20 × 104 s cm-2) and diffusion coefficient (0.4–2.4 × 10 –5 cm2 s-1). The hygroscopic property of frog cocoon resembles that of mammalian stratum corneum, hair and wool, and mucopolysaccharides; there is a slight increase in water content of cocoon over a wide range of humidities but a very steep increase in water content and substantial hydration and swelling at >96% RH. This extreme hygroscopic behaviour of frog cocoon at very high RH may reflect less polymer cross-linking in frog cocoon and its high digestibility. The prevention of over-hydration of frog cocoon in vivo may be attributed to the restriction of high water content to only very high RH (>96%).

Dew-point hygrometry system for measurement of evaporative water loss in infants.

Evaporation of water from the skin is an important mechanism in thermal homeostasis. Resistance hygrometry, in which the water vapor pressure gradient above the skin surface is calculated, has been the measurement method of choice in the majority of pediatric investigations. However, resistance hygrometry is influenced by changes in ambient conditions such as relative humidity, surface temperature, and convection currents. We have developed a ventilated capsule method that minimized these potential sources of measurement error and that allowed second-by-second, long-term, continuous measurements of evaporative water loss in sleeping infants. Air with a controlled reference humidity (dew-point temperature = 0 degree C) is delivered to a small, lightweight skin capsule and mixed with the vapor on the surface of the skin. The dew point of the resulting mixture is measured by using a chilled mirror dew-point hygrometer. The system indicates leaks, is mobile, and is accurate within 2%, as determined by gravimetric calibration. Examples from a recording of a 13-wk-old full-term infant obtained by using the system give evaporative water loss rates of approximately 0.02 mgH2O.cm-2.min-1 for normothermic baseline conditions and values up to 0.4 mgH2O.cm-2. min-1 when the subject was being warmed. The system is effective for clinical investigations that require dynamic measurements of water loss.

An inexpensive portable monitor for measuring evaporative water loss.

The measurement of evaporative water loss from the skin, using a ventilated chamber, usually requires two high-accuracy devices for the measurement of the inflow and outflow relative humidity. The water-loss rate is proportional to the difference between the inflow and outflow relative humidity, and a sensor with low absolute accuracy can be used if the same sensor measures both relative humidities. The system described uses an inexpensive sensor to measure the water-loss rate with an accuracy of 10%.

Simultaneous measurement of evaporative water loss, oxygen consumption, and thoracic temperature during flight in a carpenter bee

AbstractThe carpenter bee Xylocopa capitata has a high wing loading (425 mg cm−2 in females with empty crops) and exhibits a very high mass‐specific oxygen consumption during flight (mean for free flight 52.3 ml O2 gm−1 hour−1). Evaporative water loss is also high during flight (26.6 mg gm−1hour−1) and is significantly correlated with rate of oxygen consumption (r = 0.73) as well as with temperature of the ambient air (r = 0.80) and the water vapor deficit (r = 0.66). No indication of active evaporative cooling was evident and the bees are true endotherms capable of rapid preflight thermogenesis. Analysis of the osmotic and ionic concentrations of the body fluids showed that no water stress was experienced by the bees.The use of suitable thermocouples and a sensitive capacitance‐type humidity meter in an open flow‐through system allowed instantaneous and simultaneous measurement of oxygen consumption, evaporative water loss, and thoracic temperature. All three variables fluctuated in close synchrony during preflight warmup, flight, and subsequent cooling.

Effects of dehydration on thermoregulation in cats exposed to high ambient temperatures.

Measurements of evaporative water loss (EWL), metabolic rate (MR), body core temperature (Tc), and respiratory rate (RR) were made in nine hydrated cats exposed to several high ambient temperatures. Measurements were made in animals hydrated ad libitum and during progressive dehydration. At 43 and 40 degrees C, no significant change in EWL occurred during dehydration. At 38 and 35 degrees C, EWL in animals dehydrated for 4 days was reduced to about 50% of hydrated levels. Reductions in RR correlated highly with reduced EWL, suggesting that control of evaporation in dehydrated cats is dependent largely on control of RR. Significant elevations in Tc occurred in dehydrated animals at 43, 40, and 38 degrees C, and an insignificant upward trend was observed at 35 degrees C. Multiple linear regression analysis of data for EWL, Tc, and level of dehydration indicates that dehydration reduces the evaporative response to elevations in Tc and suggests that a change in the sensitivity of the thermoregulatory system is occurring. A similar analysis for MR, Tc, and level of dehydration shows that dehydration results in a lower MR at a given Tc. Changes in MR, corrected for body temperature, during dehydration are principally related at altered ventilatory energy expenditure. A model has been formed for estimating the metabolic cost of ventilation in the cat.

Measurements of evaporative water loss

Measurements of evaporative water loss

Measurement of evaporative water loss in small animals by dew-point hygrometry.

This paper presents the procedures and equations to be utilized for measurement of evaporative water loss (mw), by use of the dew-point hygrometer, in small animals exposed to air containing water vapor in an open-flow system. The system accounted accurately for the water evaporated from a bubble flask. In addition, hygrometric measurements of pulmocutaneous mw in pigeons (Columba livia, mean mass 0.31 kg) agreed closely with simultaneous gravimetric measurements, utilizing a desiccant in the sample stream, in a manner independently of air temperature (Ta, 20 or 40 degrees C), ambient water vapor pressure (PW, 4-16 10(2) Pa), or mw (5-66 mg-min-1). Evaporation in pigeons was independent of PW at 20 degrees C, but increased with decreasing PW at 40 degrees C, suggesting differences in ventilatory adjustments to changes in PW at the two temperatures.

An Apparatus and Method for the Continuous Measurement of Evaporative Water Loss from Human Subjects

The rate of evaporative water loss is measured by recording the difference in water vapor concentration in a stream of air before and after it passes over a man enclosed in a sealed chamber. An infra-red gas analyzer is employed for measuring the difference in water vapor concentration. Construction and application of the apparatus are discussed.