Effect of ocular pressure on choroidal circulation in the cat and Rhesus monkey.
Using the heated thermocouple principle to monitor blood flow-rate in the choroid of the anesthetized cat and Rhesus monkey revealed that elevation of ocular pressure reduces blood flow-rate in the choroidal circulation. The magnitude of this effect at varying levels of ocular pressure led to the conclusion that the vascular bed of the choroid in these experimental animals is a passive one without evidence of active regulation. (+info)
Pulmonary and bronchial circulations: contributions to heat and water exchange in isolated lungs.
The relative contribution of the pulmonary and bronchial circulatory systems to heat and water exchange in normal lungs was evaluated in 20 isolated, in situ perfused dog lungs and in four patients undergoing elective cardiopulmonary bypass. In isolated dog lungs, if the pulmonary artery was perfused at a nominal flow rate (0.5 l/min), bronchial artery perfusion (up to 70 ml/min) did not significantly affect the expired gas temperature. When the lungs were not perfused through either system, 8 min of ventilation with cool, dry gas decreased the temperature of the expired gas by 6.2 +/- 1.4 degrees C. Selective perfusion of bronchial arteries at 68 +/- 10 mmHg resulted in a mean flow rate of 28 +/- 16 ml/min and increased the average temperature of the expired gas by 0.6 degrees C. An increase in the rate of bronchial arterial perfusion to 55 +/- 14 ml/min increased the average temperature of the expired gas by 1.3 degrees C. The time constant for equilibration of tritiated water between the perfusate and the lung parenchyma was 130 +/- 33 min for pulmonary arterial perfusion and 35 +/- 13 min for combined bronchial and pulmonary perfusion, which indicated that filtration of water from high-pressure bronchial vessels facilitated water exchange in the lung interstitium. The rate of tracer equilibration was similar between the perfusate and gas in both variants of perfusion, but the ratios of tracer gas to perfusate were different (0.42 +/- 0.06 for pulmonary, 0.98 +/- 0.07 for combined), which indicates that bronchial vessels contribute mainly to the hydration of the bronchial mucosa. In humans, the bronchial blood flow was capable of maintaining heat supply after the initiation of cardiopulmonary bypass. Before bypass, when both pulmonary and bronchial blood flow were present, the mean time constant of the temperature decay after a switch to ventilation with cool, dry gas was 35 +/- 12 s. The average temperature difference between the blood and expired gas was 2.4 +/- 0.50 degrees C. After 5 min of dry gas ventilation, the temperature difference between the expired gas and initial blood temperature decreased an average of 3.8 +/- 0.06 degrees C (P < 0.05). The time constant of temperature decay increased to 56 +/- 14 s (P < 0.05). We conclude that bronchial perfusion has a less important role in the temperature balance of the respiratory tract compared with pulmonary arterial perfusion because heat flux is "flow limited" but is important in providing water for hydration of the mucosal surface and interstitial compartments of peribronchial tissues. (+info)
Public health implications of components of plastics manufacture. Flame retardants.
The four processes involved in the flammability of materials are described and related to the various flame retardance mechanisms that may operate. Following this the four practical approaches used in improving flame retardance of materials are described. Each approach is illustrated with a number of typical examples of flame retardants or synthetic procedures used. This overview of flammability, flame retardance, and flame retardants used is followed by a more detailed examination of most of the plastics manufactured in the United States during 1973, their consumption patterns, and the primary types of flame retardants used in the flame retardance of the most used plastics. The main types of flame retardants are illustrated with a number of typical commercial examples. Statistical data on flame retardant market size, flame retardant growth in plastics, and price ranges of common flame retardants are presented. (+info)
Water sorption isotherms and enthalpies of water sorption by lysozyme using the quartz crystal microbalance/heat conduction calorimeter.
The water sorption isotherm and the water vapor activity dependence of the enthalpy of water sorption Delta(sorp)Hdegrees of lysozyme have been measured at 25 degrees C. A thin film of lysozyme of mass 250 microg was exposed to H2O/N2 mixtures in a quartz crystal microbalance/heat conduction calorimeter (QCM/HCC). The QCM/HCC is a new gravimetric/calorimetric method that measures simultaneously and with high precision the mass change and the corresponding heat flow in a thin film exposed to a gas. Delta(sorp)Hdegrees for lysozyme agrees with previous determinations, although hysteresis effects are evident in the data. No van't Hoff analysis is necessary because sorption enthalpies are measured calorimetrically. The water vapor activity dependence of Delta(sorp)Hdegrees agrees with that measured previously by Bone. As the water content of the lysozyme film drops below 10 mass%, Delta(sorp)Hdegrees becomes more exothermic, indicating that water is being bound to the charged or highly polar groups of the solvent-accessible surface of lysozyme. The dynamics of water uptake and release from lysozyme thin films are much slower than in polymer films of comparable thickness. Because the QCM/HCC operates with sub-milligram samples, any protein is now amenable to study by this technique. (+info)
Allometry of post-flight cooling rates in moths: a comparison with vertebrate homeotherms.
1. The rates of post-flight cooling in 25 saturniid moths of 8 genera ranging in weight from 81 to 2650 mg were measured and compared with cooling rates in sphingids, birds and mammals. 2. The initial and terminal cooling rates of the saturniids did not differ significantly. 3. Large saturniids have relatively smaller thoraxes than small ones. 4. In saturniids the rate of post-flight cooling is inversely related both to thoracic volume and total weight. 5. Cooling rate is less dependent on thoracic volume in saturniids than in sphingids. 6. Weight-specific conductance calculated on the basis of total weight, shows that moths are not as well insulated as birds or mammals. However, when considered on the basis of thoracic weight, the weight-specific conductance of saturniids and sphingids closely approximates that predicted by the regression of weight-specific conductance on total body weight in birds and mammals. 7. Since the insulation of saturniids and sphingids is no more effective for animals of their size than is that of birds and mammals, their high body temperatures during activity appear to depend primarily on high levels of heat production. (+info)
Temperature response of mesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo.
CO(2) transfer conductance from the intercellular airspaces of the leaf into the chloroplast, defined as mesophyll conductance (g(m)), is finite. Therefore, it will limit photosynthesis when CO(2) is not saturating, as in C3 leaves in the present atmosphere. Little is known about the processes that determine the magnitude of g(m). The process dominating g(m) is uncertain, though carbonic anhydrase, aquaporins, and the diffusivity of CO(2) in water have all been suggested. The response of g(m) to temperature (10 degrees C-40 degrees C) in mature leaves of tobacco (Nicotiana tabacum L. cv W38) was determined using measurements of leaf carbon dioxide and water vapor exchange, coupled with modulated chlorophyll fluorescence. These measurements revealed a temperature coefficient (Q(10)) of approximately 2.2 for g(m), suggesting control by a protein-facilitated process because the Q(10) for diffusion of CO(2) in water is about 1.25. Further, g(m) values are maximal at 35 degrees C to 37.5 degrees C, again suggesting a protein-facilitated process, but with a lower energy of deactivation than Rubisco. Using the temperature response of g(m) to calculate CO(2) at Rubisco, the kinetic parameters of Rubisco were calculated in vivo from 10 degrees C to 40 degrees C. Using these parameters, we determined the limitation imposed on photosynthesis by g(m). Despite an exponential rise with temperature, g(m) does not keep pace with increased capacity for CO(2) uptake at the site of Rubisco. The fraction of the total limitations to CO(2) uptake within the leaf attributable to g(m) rose from 0.10 at 10 degrees C to 0.22 at 40 degrees C. This shows that transfer of CO(2) from the intercellular air space to Rubisco is a very substantial limitation on photosynthesis, especially at high temperature. (+info)
Analyzing heat capacity profiles of peptide-containing membranes: cluster formation of gramicidin A.
The analysis of peptide and protein partitioning in lipid membranes is of high relevance for the understanding of biomembrane function. We used statistical thermodynamics analysis to demonstrate the effect of peptide mixing behavior on heat capacity profiles of lipid membranes with the aim to predict peptide aggregation from c(P)-profiles. This analysis was applied to interpret calorimetric data on the interaction of the antibiotic peptide gramicidin A with lipid membranes. The shape of the heat capacity profiles was found to be consistent with peptide clustering in both gel and fluid phase. Applying atomic force microscopy, we found gramicidin A aggregates and established a close link between thermodynamics data and microscopic imaging. On the basis of these findings we described the effect of proteins on local fluctuations. It is shown that the elastic properties of the membrane are influenced in the peptide environment. (+info)
Biophysical properties of the pelt of a diurnal marsupial, the numbat (Myrmecobius fasciatus), and its role in thermoregulation.
Numbats are unusual marsupials in being exclusively diurnal and termitivorous. They have a sparse (1921 hairs cm(-2)) and shallow (1.19 mm) pelt compared with other marsupials. Coat reflectivity is low (19%) for numbats compared with nocturnal marsupials, but absorptivity is similar to that of diurnal North American ground squirrels (72%), indicating that the coat of the numbat may be adapted for acquisition of solar heat. Numbat coat thermal resistance decreases significantly with wind speed from 45.9 s m(-1) (at 0.5 m s(-1)) to 29.8 s m(-1) (at 3 m s(-1)). Erecting the fur significantly increases pelt depth (6.5 mm) and coat resistance (79.2-64.2 s m(-1)) at wind speeds between 0.5 m s(-1) and 3 m s(-1). Numbat coat resistance is much lower than that of other marsupials, and wind speed has a greater influence on coat resistance for numbats than for other mammals, reflecting the low pelt density and thickness. Solar heat gain by numbats through the pelt to the level of the skin (60-63%) is similar to the highest value measured for any mammal. However the numbat's high solar heat gain is not associated with the same degree of reduction in coat resistance as seen for other mammals, suggesting that its pelt has structural and spectral characteristics that enhance both solar heat acquisition and endogenous heat conservation. Maximum solar heat gain is estimated to be 0.5-3.6 times resting metabolic heat production for the numbat at ambient temperatures of 15-32.5 degrees C, so radiative heat gain is probably an important aspect of thermoregulation for wild numbats. (+info)