[Postoperative warming therapy in the recovery room. A comparison of radiative and convective warmers]

Hypothermia (Tcore < 36 degrees C) can be observed in 60%-80% of all admissions to the post-anaesthetic recovery unit. Effective warming devices may accelerate rewarming, improve patient comfort, and suppress shivering thermogenesis. This study was designed to compare the efficiency of warming devices in extubated postoperative patients and their effect on postoperative oxygen uptake (VO2). METHODS. Thirty-five ASA I and II patients after laparoscopic hernioplastic repair with core temperatures < 36 degrees C were randomly assigned to either postoperative nursing under a radiant heater (group R, n = 11, Aragona Thermal Ceilings CTC X, Aragona Medical AB, Täby, Sweden), a forced air system (group L, n = 12, Bair Hugger, Augustine Medical Inc., Eden Prairie, Minnesota, USA), or a normal cotton hospital blanket (group K, n = 12). Anaesthesia was conducted totally intravenously with propofol, alfentanil, and vecuronium. Mean body temperature and total body heat were calculated from urinary bladder temperature and four subcutaneous temperature measurements. The rate of thermogenesis was calculated from continuous measurement of VO2 (Datex Deltatrac Metabolic Monitor, Datex Instrumentarium Corp., Helsinki, Finland). Heat balance was derived from the increase in total body heat minus body heat production. Heart rate and noninvasive blood pressure were measured by the Cardiocap (Datex Instrumentarium Corp., Helsinki, Finland). All data were transferred to an IBM-compatible computer at 60-s intervals. Measurements were stopped when core temperature reached 37 degrees C. The rate of change was calculated for each variable for the period 15 min after the beginning of rewarming to attainment of 37 degrees C. Data are presented as median, minima, and maxima (min<==>max); the Mann-Whitney U test was used to test for significance of group differences. RESULTS. All groups were comparable for body weight, height, age, and amount of postoperative infusions. Temperatures at admission were 35.2 (33.4<==>35.9), 34.7 (34.3<==>35.8), and 35.4 (34.3<==>35.9) degrees C for groups R, B, and K, respectively. No significant differences in the rate of central rewarming could be found for these groups with 0.81 (0.41<==>1.32), 0.76 (0.40<==>1.07), and 0.70 (0.37<==>1.13) degrees C/h (Fig. 1). The mean VO2 of 3.41 (3.07<==>3.73), 3.55 (2.78<==>4.06), and 3.79 (2.51<==>7.00) ml/kg/min also did not differ significantly (Fig. 3). Significant differences between groups R and B [4.39 (3.74<==>6.19) and 4.30 (3.46<==>6.67) ml/kg/min] and K [5.92 (3.79<==>10.64) ml/kg/min] were found for VO2 maxima during the course of investigation (Fig. 4). The heat balance revealed significant differences among treatment and control groups with -88 (-226<==>+30), -41 (-212<==>+12), and -191 (-265<==>-86) kJ/h for groups R, B, and K. We additionally calculated the heat balance as a quotient, which showed 0.70 (0.22<==>1.07), 0.86 (0.44<==>1.04), and 0.49 (0.31<==>0.79) for groups R, B, and K (Fig. 4). The mean rate-pressure product of all groups did not differ significantly during the period of investigation. CONCLUSIONS. Neither external heat supply by radiant heat nor by a forced warm air system significantly reduced rewarming time in extubated, awake patients. As measured by heat balance, both active treatments saved about 20% more body heat production than in the control group. Continuing peripheral vasoconstriction may be the reason for the low efficiency of heat transfer. Thermal treatment did reduce the peak load (max. VO2) on the oxygen transport systems, though shivering was treated by pethidine if it occurred. External rewarming did not reduce the average load (mean VO2). Thus, concerning the goal of accelerating rewarming, it appears more rational to prevent intraoperative heat loss. For a comparison of efficiency of different warming devices, postoperative extubated patients do not appear to be an ideal model for study.

Estimation of the thermal effect of blood flow in a branching countercurrent network using a three-dimensional vascular model

A three-dimensional thermal model is presented in which convective heat transfer is defined in terms of the physical details of the vascular system. The convective heat exchange between prearteriole and postvenule vessels and the tissue across the vessel walls is calculated explicitly without using shape factors. Conduction in x-, y-, and z-direction is considered. This vascular model is applied to a human extremity. The spatial variations in the arterial, venous and tissue temperatures under basal conditions, hyperthermic conditions and in a cold environment are computed. Conclusions are drawn as to the validity of bioheat approaches.

[Radiant-convection heat flow studied during the performance of a mud therapy procedure]

Original technique is described of recording radiative convective heat flow- (RCHF) over various sites of the patient's body surface while he or she is receiving a mud treatment. The dynamics of the RCHF in the course of applying mud to the patient is demonstrated, which is best recorded over the surfaces of the forehead and hands. The proposed technique permits the objectivization of thermoenergetic response of the organism to thermal therapeutic interventions to be done.

Inhalation risk in low-gravity spacecraft

Inhalation risks on long-duration manned spaced flight include gasses chronically released by outgassing of materials, gasses released during spills, thermodegradation events (including fires) with their attendant particulates, and fire extinguishment. As an example, an event in which electronic insulation consisting of polytetrafluoroethylene undergoes thermodegradation on the Space Station Freedom was modeled experimentally and theoretically from the initial chemistry and convective transport through pulmonary deposition in humans. The low-gravity environment was found to impact various stages of event simulation. Critical unknowns were identified, and these include the extent of production of ultrafine particles and polymeric products at the source in low gravity, the transport of ultrafine particles in the spacecraft air quality control system, and the biological response of the lung, including alveolar macrophages, to this inhalation risk in low gravity.

Changes of ampulla pressure in the semicircular canal of pigeons by caloric stimulation

Still now several hypotheses about the mechanisms of the caloric nystagmus have been in conclusive. In this study we confirmed the convection effect and the volume change effect of the endolymph in horizontal semicircular canal following the caloric stimulation using pigeons (Columba livia). Although the direction of the caloric nystagmus depended on the head position and the stimulus site of calorization, the caloric nystagmus disappeared after plugging of horizontal semicircular canal. On the other hand, the ampulla pressure increased by cold calorization and decreased by hot calorization and these pressure changes had no relation to the head position. These results show that the main role of the mechanisms of the caloric nystagmus under 1G is the convection effect but the volume change effect may act on the caloric nystagmus not only under 1G but also under microgravity.

Transperitoneal transport of creatinine. A comparison of kinetic models

Six kinetic models of transperitoneal creatinine transport were formulated and validated on the basis of experimental results obtained from 23 non-diabetic patients undergoing peritoneal dialysis. The models were designed to elucidate the presence or absence of diffusive, non-lymphatic convective and lymphatic convective solute transport. The validation procedure included an assessment of theoretical (a priori) and practical (a posteriori) identifiability, goodness of fit, residual error analysis and plausibility of parameter estimates. The results of the validation procedure demonstrate that the model including all three forms of transport is superior to other models. We conclude that the best model of transperitoneal creatinine transport includes diffusion, non-lymphatic convective transport and lymphatic convective transport.

Changes of endolymphatic pressure in the semicircular canal of pigeon by caloric stimulation

It gets into difficult to explain the mechanism of caloric nystagmus only by convection theory from results of microgravity experiments. One of the other theories is an occurrence of a relative volume change due to a temperature change. Since the volume change must lead to a pressure change after caloric stimulation, we tried to measure the ampulla pressure of the horizontal semicircular canal in pigeons (Columba livia) using an improved servo micropipette system. The main result was that the ampulla pressure increased by cooling and decreased by heating. The changes of the ampulla pressure depended on the temperature change but were not influenced by the pigeon's head position.

Formation and resolution of brain edema associated with brain tumors. A comprehensive theoretical model and clinical analysis

The purpose of this study is to quantify the relative contribution of the mechanisms in the absorption of edema fluid. The convection/diffusion and the comprehensive bulk flow model were applied for the finite element analysis of peritumoral brain edema. For clinical analysis, 90 meningiomas studied by MRI were selected. Serial CT scan and MRI were performed at 0, 2, 4, 6 hours after injection of Iopamidol or Gadpenteic acid respectively. Then the tracer distributions in the edematous brain was analyzed. The tracer movement in the brain is well represented by the convection/diffusion equation. The absence of the preferential fluid flow directing toward the ventricle indicates that a limited role of CSF sink action into the ventricle. From capillary surface area (240 cm2/g brain), capillary hydraulic conductivity (1.8 x 10(-8) ml/cmH2O/cm2/min) and the simulated average tissue pressure of 9.8 mmHg, maximum absorption rate into capillaries was estimated to be 0.003 ml/h/cm3 brain tissue. Considering the limited role of edema fluid clearance into the ventricle, the results indicate a possible role of subarachnoid CSF space for the clearance of edema fluid. The clearance of edema fluid into subarachnoid CSF space should be studied quantitatively. Finally, unification of the convection/diffusion and the comprehensive bulk flow model will provide a more quantitative analysis of edema formation and resolution by using MRI and tracer studies.

Effects of a microgravity environment on the crystallization of biological macromolecules

Macromolecules crystals are indispensable intermediates in the analysis of macromolecular structure, are essential for the application of x-ray diffraction methods, and are at the same time the greatest obstacle to success. Protein crystals are generally difficult to grow, often of imperfect form or small size, and frequently lack sufficient order. Their growth has become the rate limiting step in x-ray crystallography. Evidence has emerged from protein crystallization experiments carried out in space that suggests macromolecular crystals of improved order and quality can be grown in a microgravity environment. Presumably the absence of density driven convection and sedimentation permits a more deliberate and graceful entry of individual molecules into the crystal lattice. This in turn results in improvements in both morphology and the diffraction patterns of the crystals. The precise mechanisms for these improvements and the means for their optimization are, however, not understood at more than a rudimentary level. I attempt here to review microgravity effects that may play a role in protein crystal growth, sedimentation, convection and surface contact, and suggest their possible mechanisms.

The simulation of microgravity conditions on the ground

This chapter defines weightlessness as the condition where the acceleration of an object is independent of its mass. Applying this definition to the clinostat, it argues that the clinostat is very limited as a simulator of microgravity because it (a) generates centrifugal forces, (b) generates particle oscillations with mass-dependent amplitudes of speed and phase shifts relative to the clinorotation, (c) is unable to remove globally the scalar effects of gravity such as hydrostatic pressure, which are independent of the direction of gravity in the first place, and, (d) generates more convective mixing of the gaseous or liquid environment of the test object, rather than eliminating it, as would true weightlessness. It is proposed that attempts to simulate microgravity must accept the simulation of one aspect of microgravity at a time, and urges that the suppression of convective currents be a major feature of experimental methods that simulate microgravity.

Influence of buoyancy-driven convection on protein separation by free-flow electrophoresis

In free-flow electrophoresis, the stability and reproducibility of the flow field are prerequisites for a satisfactory separation. Due to the presence of the species to be separated and due to mass- and heat-transfer phenomena, non-uniformities in density inevitably appear, both within the carrier buffer and between the carrier buffer and the sample stream. On earth they give rise to buoyancy-driven convection which interferes with the separation. These effects have been quantified by numerical modelling. Agreement has been found between the numerical results and experimental observations.

Possible mechanism of microgravity impact on Carausius morosus ontogenesis

Experiments aboard "Spacelab-D1" and "Cosmos-1887" revealed an adverse effect of space flight on Carausius morosus embryos. The main influencing factor for stick insect eggs turned out to be microgravity, while the contribution of HZE particles of cosmic radiation was relatively low. Flight experiments indicated an increased vulnerability of stick insect eggs to microgravity at intermediate stages of development, that could support the "convection" hypothesis.

Modelling and simulation to support the design of a Dutch Protein Crystallization Facility

This paper reports on the progress made in the development of the Netherlands Protein Crystallization Facility. The facility allows two crystallization techniques: Vapour diffusion and micro-dialysis. The design and development is accompanied by a project in which it tried to model and simulate the events which occur during the vapour diffusion process within the crystallization cell.

A potentialgradient-conductivity-scanner for the investigation of effects leading to buoyancy-driven convection on continuous-flow-electrophoresis

Continuous flow electrophoresis (CFE) is a mild and high-resolving method for the separation of sensitive biomolecules like peptides and proteins. The resolution is decreased by several effects, of which density gradients are important since they lead to buoyancy-driven convection. A tool for the measurement of physical quantities that cause the separation process, a potentialgradient/conductivity-scanner has been developed. With this PC-scanner consecutive potential- and concentration profiles can be measured inside the CFE-chamber. Local current densities and local joule heat yielding density gradients are calculated from the measurement data. With the PC-scanner the influence of gravity on separations by CFE can be evaluated more easily by the knowledge of the thermal and electrical conditions inside the separation slit.

Evolution of bioconvective patterns in variable gravity

Measurements are reported of the evolution of bioconvective patterns in shallow, dense cultures of microorganisms subjected to varying gravity. Various statistical properties of this random, quasi-two-dimensional structure have been found: Aboav's law is obeyed, the average vertex angles follow predictions for regular polygons, and the area of a pattern varies linearly with its number of sides. As gravity varies between 1 g and 1.8g (g = 9.8 m s-1), these statistical properties continue to hold despite a tripling of the number of polygons and a reduced average polygon dimension by a third. This work compares with experiments on soap foams, Langmuir monolayer foams, metal grains, and simulations.

Our experience in the evaluation of the thermal comfort during the space flight and in the simulated space environment

The paper presents the results of the mathematical modelling the effects of hypogravity on the heat output by the spontaneous convection. The theoretical considerations were completed by the experiments "HEAT EXCHANGE 1" performed on the biosatellite "KOSMOS 936". In the second experiment "HEAT EXCHANGE 2" accomplished on the board of the space laboratory "SALYUT 6" was studied the effect of the microgravity on the thermal state of a man during the space flight. Direct measurement in weightlessness prowed the capacity of the developed electric dynamic katathermometer to check directly the effect of the microgravity on the heat output by the spontaneous convection. The role of the heat partition impairment's in man as by the microgravity, so by the inadequate forced convection are clearly expressed in changes of the skin temperature and the subjective feeling of the cosmonaut's thermal comfort. The experimental extension of the elaborated methods for the flexible adjustment of the thermal environment to the actual physiological needs of man and suggestions for the further investigation are outlined.

Rhythmic biological systems under microgravity conditions

Rhythmic phenomena in biology cover a wide frequency spectrum. In Space, the rhythms will encounter microgravity conditions which can, therefore, be a valuable tool for their understanding. A review and discussion of important effects of gravity/absence of gravity on biological systems will be given. Convection will be emphasized as a mechanism which is drastically reduced in Space. Microgravity might also affect the coupling between individual oscillators in a multi-oscillatory system. The environmental interference with rhythms will be discussed with a simple feedback as a starting point. Model simulations will be presented and clinostat and microgravity-conditions will be discussed in a specific case, viz. the gravitropical system of plants which can show sustained oscillations.

The Protein Crystallization Facility (PCF) for EURECA

Research on the structure of molecules by X-ray diffraction analysis requires large single crystals. However, the dynamic behavior of proteins caused by their high molecular weight prevents the growth of large single crystals if this process is disturbed by thermal convection. For example, protein single crystals grown under terrestrial (1 g) conditions are limited to dimensions in the order of 0.1 mm, whereas the size of crystals, grown under (quasi) space conditions has been 5 times larger (pilot experiment CRYOSTAT, Spacelab). Under EURECA conditions (e.g. no microgravity disturbances), the result in regularity of crystal growth and size is expected to be much better. In this paper an overview is given of the protein crystallization facility which includes Experiment-, Service- and Secondary Cooling Module, and its interfaces to the EURECA Carrier. At the end, there will be presented a short mission profile concerning cooling-, power- and data exchange requirements.

SSC microgravity sounding rocket program MASER

The Swedish Microgravity Sounding Rocket program MASER is presented. Especially the MASER 1 payload is depicted, but also an outlook for the future possibilities within the Short Duration Flight Opportunities is given. Furthermore the coordination and relation with the German TEXUS program is touched upon. With the two TEXUS and MASER programs--possibly together with other fascinating projects like M-ARIES and MG-M-ARIANNE--the microgravity scientific community in Europe should get reasonable amounts of flight opportunities in preparation for the big space venture the European Space Station.

The growth of bioconvection patterns in a uniform suspension of gyrotactic micro-organisms

'Bioconvection' is the name given to pattern-forming convective motions set up in suspensions of swimming micro-organisms. 'Gyrotaxis' describes the way the swimming is guided through a balance between the physical torques generated by viscous drag and by gravity operating on an asymmetric distribution of mass within the organism. When the organisms are heavier towards the rear, gyrotaxis turns them so that they swim towards regions of most rapid downflow. The presence of gyrotaxis means that bioconvective instability can develop from an initially uniform suspension, without an unstable density stratification. In this paper a continuum model for suspensions of gyrotactic micro-organisms is proposed and discussed; in particular, account is taken of the fact that the organisms of interest are non-spherical, so that their orientation is influenced by the strain rate in the ambient flow as well as the vorticity. This model is used to analyse the linear instability of a uniform suspension. It is shown that the suspension is unstable if the disturbance wavenumber is less than a critical value which, together with the wavenumber of the most rapidly growing disturbance, is calculated explicitly. The subsequent convection pattern is predicted to be three-dimensional (i.e. with variation in the vertical as well as the horizontal direction) if the cells are sufficiently elongated. Numerical results are given for suspensions of a particular algal species (Chlamydomonas nivalis); the predicted wavelength of the most rapidly growing disturbance is 5-6 times larger than the wavelength of steady-state patterns observed in experiments. The main reasons for the difference are probably that the analysis describes the onset of convection, not the final, nonlinear steady state, and that the experimental fluid layer has finite depth.

[Heat transfer, convection and altitudinal gradient]

Measurements of heat loss from fur covered aluminium cylinders were made under barometric pressures ranging from 760 to 368 torr (sea level up to 5.8 km, simulated altitudes). Heat transfer diminished at high altitudes and a relative greater diminution was observed when forced convection was applied. The virtual increase in thermal insulation at high altitudes may be useful to compensate the expected larger difference between body and ambient temperatures.

Physical parameters affecting living cells in space

The question is posed: Why does a living cell react to the absence of gravity? What sensors may it have? Does it note pressure, sedimentation, convection, or other parameters? If somewhere in a liquid volume sodium ions are replaced by potassium ions, the density of the liquid changes locally: the heavier regions sink, the lighter regions rise. This may contribute to species transport, to the metabolism. Under microgravity this mechanism is strongly reduced. On the other hand, other reasons for convection like thermal and solutal interface convection are left. Do they affect species transport? Another important effect of gravity is the hydrostatic pressure. On the macroscopic side, the pressure between our head and feet changes by 0.35 atmospheres. On the microscopic level the hydrostatic pressure on the upper half of a cell membrane is lower than on the lower half. This, by affecting the ion transport through the membrane, may change the surrounding electric potential. It has been suggested to be one of the reasons for graviperception. Following the discussion of these and other effects possibly important in life sciences in space, an order of magnitude analysis of the residual accelerations tolerable during experiments in materials sciences is outlined. In the field of life sciences only rough estimates are available at present.