Permeable packings and perfusion chromatography in protein separation

The use of permeable packings in perfusion chromatography for protein separation is reviewed. Mass transport mechanisms in large-pore materials include forced convection in addition to diffusive transport. The key concept in perfusion chromatography is the "augmented" diffusivity by convection which explains the improved efficiency of perfusive packings compared with conventional supports. An extended Van Deemter equation has to be applied when calculating the height equivalent to a theoretical plate (HETP) of chromatographic columns with flow-through particles. It is shown that the effect of forced convective flow in pores is to drive the separation performance between diffusion-controlled and equilibrium limits. A methodology to understand mass transfer mechanisms in permeable packings is proposed. Experimental results for protein separation by high-performance liquid chromatography in new packing media are discussed. Simulated moving bed technology is addressed.

Effect of convective stretching and folding on aerosol mixing deep in the lung, assessed by approximate entropy

There is a surprisingly substantial amount of aerosol mixing and deposition deep in the lung, which cannot be explained by classic transport mechanisms such as streamline crossing, inertial impaction, or gravitational sedimentation with reversible acinar flow. Mixing associated with "stretch and fold" convective flow patterns can, however, be a potent source of transport. We show such patterns in experimental preparations using rat lungs and in the theoretical Baker Transform. In both cases, mixing is associated with the temporal evolution of two length scales. The first is the slowly increasing diffusive length scale. The second is the rapidly decreasing lateral length scale, due to "stretching and folding," over which diffusion must take place. This interaction leads to aerosol mixing in much shorter times than previously appreciated. Finally, we propose a new method by which to quantify the state of mixing, using an approximation to the entropy of the aerosol concentration distribution. The results of the analysis suggest that stretching and folding may be a key feature underlying peripheral aerosol transport.

Convection versus conduction cooling for induction of mild hypothermia during neurovascular procedures in adults

Hypothermia for cerebral protection is usually achieved by administration of intravenous fluids at room temperature, cooling ambient air, ice packs, and a temperature-adjustable circulating water mattress. We compared cooling by conduction by using a water mattress to cool by convection by using a forced-air cooling device. Twenty patients were prospectively randomized to two groups: 10 patients cooled by convection (CC) and 10 patients cooled by traditional methods (TC). Two patients in the CC group were withdrawn from the study and excluded from the analysis; one patient for failure to cool despite the use of both techniques, and the other for the abrupt onset of arrhythmias and myocardial depression during hypothermia. Temperature was measured at the tympanic membrane, pulmonary artery, and esophageal probe sites and recorded every 15 min. The time required to reach the target temperature range of 33-34 degrees C was recorded. We found no differences in the temperatures measured at the three sites during cooling and rewarming. Baseline temperatures recorded from the pulmonary artery catheter before beginning "active cooling" were similar in both groups (TC, 35.0 +/- 0.2 degrees C vs. CC, 35.3 +/- 0.1 degrees C). We found no difference in the time to target temperature between TC and CC (TC, 178 +/- 25 min vs. CC, 142 +/- 21 min). One patient had some arrhythmias on cooling in the convective group, but her preoperative condition may have been responsible. In conclusion, cooling by convection appears to be a safe alternative to conduction cooling.

A biased random walk model for the trajectories of swimming micro-organisms

The motion of swimming micro-organisms that have a preferred direction of travel, such as single-celled algae moving upwards (gravitaxis) or towards a light source (phototaxis), is modelled as the continuous limit of a correlated and biased random walk as the time step tends to zero. This model leads to a Fokker-Planck equation for the probability distribution function of the orientation of the cells, from which macroscopic parameters such as the mean cell swimming direction and the diffusion coefficient due to cell swimming can be calculated. The model is tested on experimental data for gravitaxis and phototaxis and used to derive values for the macroscopic parameters for future use in theories of bioconvection, for example.

Convection as one of the limiting factors of human respiration during normoxic exercise

Each of the pathways within respiration has been suspected of limiting maximal performance, suggesting that O2 transport may be affected by each single pathway. The use of the stable, isotopic O2 molecules 16O2 and 16O18O is presented as a novel method for assessing respiration. Because of their different molecular weights, 16O2 diffuses 3% more rapidly than 16O18O, whereas 16O2 is convectively transported as rapidly as 16O18O. This can be quantified by using the overall fractionation factor alpha O. The more diffusion becomes limiting, the more 16O2 is transported in preference to 16O18O and alpha O is increased to 1.03. By contrast, the more respiration is limited by convection, the closer alpha O comes to 1.0 during the entire O2 transport. Six untrained subjects underwent normoxic exercise on a cycle ergometer. Isotopic analysis was performed at rest and during exercise loads of 50, 100, 150, 200, and 250 W using respiratory mass spectrometry. With increasing workload, a decrease in alpha O from 1.0072 at rest to 1.0033 at 250 W was determined in all subjects. On the basis of a serial resistance model of respiration, we concluded that, in our subjects, O2 transport was increasingly affected by convection but decreasingly limited by diffusion. The relative contribution of convection to the entire resistance to O2 flow ranged from > or = 44.6% at rest to > or = 74.6% at the most strenuous level of exercise, whereas the diffusive pathways decreasingly contributed to resistance to O2 flow by < or = 24% at rest and < or = 11% at 250 W.

A model for interpreting the tracer labeling of interendothelial clefts

We extended the model describing the low molecular weight electron dense tracer wake in the interendothelial cleft and surrounding tissue to describe the time-dependent transport of intermediate size solutes of 1.0-3.5 nm radius by convection and diffusion in an interendothelial cleft containing a fiber matrix. This model provides a quantitative basis on which to reinterpret electron microscopic studies of the distribution of tracers such as horseradish peroxidase (HRP; molecular weight = 40,000; Stokes radius = 3.0 nm) along the interendothelial cell cleft from the lumen to the tissue. For example, we show that, in contrast to our results with low molecular weight tracers, the wake of large molecular weight tracers on the abluminal side of the junctional strand is not likely to be detected, because the concentration of the tracer is predicted to be very low in most experiments. Thus the lack of a tracer such as HRP on the abluminal side of the junctional strand and in the tissue is not as strong evidence against the presence of a cleft pathway as suggested previously. The model does provide the basis for the design of experiments to locate both the principal molecular sieve and breaks in the junctional strand from the standing gradient on the luminal side of the junctional strand. An important experimental variable is the pressure in the vessel lumen which can be varied between 0 and 30 cm H2O to change the contributions of diffusive and convective transport to transcapillary exchange through he interendothelial cleft. This approach will also allow the testing of models for transcapillary pathways for large molecules by measuring the distribution of fluorescent traces across the microvessel wall and in the tissue surrounding the microvessel using confocal microscopy.

Effects of ultrasound and convection cooking to different end point temperatures on cooking characteristics, shear force and sensory properties, composition, and microscopic morphology of beef longissimus and pectoralis muscles

Longissimus and pectoralis muscles were removed from 10 steer carcasses at 4 d postmortem, aged for 14 d at 2 degrees C, then assigned to either ultrasound or convection cooking to either 62 degrees C or 70 degrees C internal end point temperature. During cooking, time-temperature profiles and energy consumption were monitored. Ultrasound cooking resulted in greater (P < .05) cooking speed, greater (P < .05) moisture retention and less (P < .05) cooking loss, greater (P < .05) efficiency of energy consumption, a more uniform cooking environment, and less (P < .05) instrumental peak-force work to shear muscle samples than convection cooking. The ultrasound treatment also resulted in a reduction (P < .05) in soluble collagen content and superior (P < .05) myofibrillar tenderness, as determined by a trained sensory panel, than convection cooking. Electron micrographs indicated that ultrasound-cooked muscles had longer sarcomeres, larger diameter fibers, and more myofibrillar disruption and shattering. Longissimus muscles cooked faster (P < .05) and more (P < .05) energetically efficient, had less (P < .05) total collagen, and were superior (P < .05) in instrumental evaluated texture and sensory tenderness than pectoralis muscles. Cooking to 70 degrees C caused greater (P < .05) moisture and cooking losses, required more (P < .05) time and energy input to cook, and negatively (P < .05) affected instrumental textural and sensory tenderness characteristics. Electron micrographs indicated a shortening of sarcomeres, more deterioration of the banding structure, reduction in fiber diameter, and breakdown of endomysial and perimysial connective tissue at an internal temperature of 70 degrees C vs 62 degrees C. This research identifies ultrasound cooking as a new, rapid, energy-efficient method that may improve some meat textural attributes.

[Air-convection heater for abdominal surgery. Study of the relation between surgical time and the efficacy of body temperature maintenance]

OBJECTIVES

1) To quantify the efficacy of forced air warming for maintaining body temperature during general anesthesia of adults, and 2) to study the relation between the duration of surgery and the level of thermal protection provided by the device used.

PATIENTS AND METHODS

We studied 30 adult patients of both sexes who were scheduled for abdominal surgery involving laparotomy. After three patients were excluded because surgery was unfeasible, the remaining 27 were allocated randomly to a control group (n = 14) or a group (n = 13) to be warmed by a Bair Hugger (Augustine Medical Inc.) heater. Esophageal temperature was checked every 30 min by one probe of a modular thermometric channel (Mon-a-therm) 6510 Mallincrodt, while ambient temperature was monitored by the second probe.

RESULTS

Significant differences in esophageal temperature were observed between the two groups from the second hour after start of surgery, and the differences increased over time. Differences were observed at the end of surgery (Bair group: 36.4 +/- 0.5 degrees C; control group: 34.7 +/- 1.1 degrees C) and upon admission to the intensive care recovery unit (Biar group: 36.3 +/- 0.6 degrees C; control 34.8 +/- 1.0 degrees C) (p < 0.0001).

CONCLUSIONS

The Bair Hugger heater is effective during abdominal operations lasting two or more hours. The device not only prevented hypothermia from deepening during surgery, but also reversed hypothermia in spite of being used after anesthetic induction and in spite of the loss of heat produced by secondary vasodilation.

Optimization of sodium removal in paired filtration dialysis by single pool sodium and conductivity kinetic models

Sodium removal is one of the main factors affecting intradialytic cardiovascular stability and interdialytic hypertension, and its removal should therefore be individualized. The aims of this study were: (1) to test the ability of a single-pool variable volume (SPVV) sodium kinetic model (NaKM) to optimize sodium removal in paired filtration dialysis (PFD), and (2) to test a SPVV conductivity kinetic model (CKM) in order to verify whether CKM can be used as an alternative for NaKM in estimating sodium balance. The mean difference between the NaKM-predicted and measured end-PFD plasma water ionized sodium concentrations was 0.00 +/- 0.55 mEq/l, which means that the model has an imprecision of < or = 1.1 mEq/ l. The mean difference between predicted and measured sodium removal was 0.21 +/- 16.86 mEq/session, which means a model overestimate of 0.21 mEq/session. The mean difference between the CKM-predicted and measured end-PFD ultrafiltrate conductivity was 0.01 +/- 0.05 mS/cm, which means an inaccuracy of the model of 0.01 mS/cm and an imprecision of < or = 0.1 mS/cm. The regression in the ionized sodium concentration measured in plasma or blood on the conductive values of the ultrafiltrate shows an error of < or = 2 mEq/l in the prediction of the ionized sodium concentration in blood by means of ultrafiltrate conductivity measurements. These results demonstrate that both models make it possible to obtain a level of dialytic sodium removal that is almost equivalent to interdialytic sodium loading. Moreover, given that it does not require blood sampling and the possibility of making repeated and inexpensive ultrafiltrate conductivity measurements, the CKM allows online monitoring of programmed sodium removal.

Removal of constitutive and inducible nitric oxide synthase-active compounds in a modified hemodiafiltration with on-line production of substitution fluid: the contribution of convection and diffusion

Chronic renal failure and the uremic state lead to accumulation of various endogenous inhibitors of nitric oxide synthase. Previous studies on end-stage uremic patients nitric oxide synthase activity in murine vascular endothelium and cytokine-induced macrophage cell lines was shown to be modulated during treatment (Nephrol Dial Transplant 1995; 10: 1386-96). Paired filtration dialysis, a modified hemodiafiltration technique, physically separates convection from diffusion. Plasmas, ultrafiltrates and dialysates from seven uremic patients undergoing paired filtration dialysis performed using ultrapure apyrogen substitution fluid in the absence (first 120 min) or presence (last 120 min) of extracellular fluid reduction were tested for their inhibitory/stimulatory effect on ecNOS, constitutively expressed on t.End 1 cell line, a murine vascular endothelium, or for their inducing effect on iNOS, inducible on J774 cells, a macrophage cell line. On ecNOS, Group 1 (stimulatory, 3/7 patients) markedly enhanced the ecNOS activity as compared to control plasma, whereas group 2 plasma (inhibitory, 4/7 patients) inhibited ecNOS plasma. Post-dialysis plasma samples from all Group 1 and 2 patients showed a marked decrease of the predialysis stimulatory and inhibitory activity, respectively. On iNOS: all patient plasmas stimulated iNOS activity. The UF and particularly the dialysate had a remarkable iNOS inducing effect (Group 1). The substitution fluid obtained at 120 min during treatment in Group 1 and 2 had no effect on NOS activity. No correlation was found between predialysis ecNOS or iNOS activity values with mean systolic or diastolic pressures. These studies suggest a complex balance of ecNOS inhibitors/stimulators and iNOS inducers in uremia. Dialysis may remove ecNOS inhibitors and stimulators by convection and, in the latter case, by diffusion. iNOS inducers are removed during dialysis, suggesting the biocompatibility of the dialysis system with the on-line production of ultrapure substitution fluid.

[The effect of convection warming during abdominal surgery on the early postoperative heat balance]

Hypothermia (core temperature < 36 degrees C) is common after longer-lasting surgical procedures. Heat loss mainly occurs during anaesthesia and surgery and leads to increased risk, especially in the early recovery period of elderly patients. In the present study we investigated the effects of intraoperative forced-air warming, administered via an upper-body blanket ("Warm Touch", Mallinckrodt, USA), with the specific aims of: (1) drawing up heat balances; and (2) analysing postoperative thermoregulation, oxygen consumption (VO2) and cardiovascular reactions of mechanically ventilated patients. The general aim of our study was to compare intraoperative forced-air-warming and conventional patient-insulation with cotton blankets.

METHODS

Twenty four ASA II and III patients scheduled for elective colon surgery were randomly assigned to a control group (n = 12, no warming therapy, upper body covered with a cotton hospital blanket) or a convective warming group (n = 12). Anaesthesia was administered with etomidate (0.2 mg/kg), fentanyl (approximately 10 micrograms/kg) and vecuronium bromide (0.1 mg/kg). During surgery the lungs were mechanically ventilated with 70% nitrous oxide in oxygen and enflurane (end-tidal-concentration max. 0.7%) using a semiclosed circuit with a fresh gas flow of 3 l/min. A hygrophobe heat and moisture exchanger ("Sterivent," Darex Corp., Italy) was used. At the end of surgery patients were transferred to the ICU, covered with a hospital cotton-quilt and normo-ventilated using a Bennett 7200 a. Patients were sedated/kept free of pain by administering titrated doses of midazolam and/or piritramide. Postoperative oxygen consumption (VO2) was recorded continuously with a Deltatrac Metabolic Monitor (Datex Corp., Finland). Pre-, intra- and postoperative measurements included heart rate, invasive blood pressure, core-temperature (before and after operation: urinary bladder-temperature, during surgery: oesophageal temperature) and mean-skin-temperature (according to Ramanathan) up to 180 min from the end of surgery. Shivering, pharmacological interventions (e.g. pethidine) and time of extubation were noted. Data are presented as median, minima and maxima. The results were analysed using the Mann-Whitney U test or Chi-Square test (shivering). Statistical significance was assumed when P < 0.05.

RESULTS

Both groups were comparable for gender, body weight, height, age, duration of their operations and amount of intraoperative fluids, narcotics and muscle relaxants. Room temperatures in the control group were significantly higher than in the forced air group (24 vs 22 degrees C). Initial setting of the forced-air blower was "high" (42-46 degrees high air flow). When the oesophageal-temperature reached 36.5 degrees C, the blower temperature was reduced to 36-40 degrees C. Reduction was necessary approximately 60 min from start in the operation. At the end of surgery/administration to the ICU core-temperatures of both groups differed significantly (35.2/ 35.4 degrees C vs 36.3/36.2 degrees C). Mean-skin temperatures were higher, too, but no statistical analysis was carried out for the intraoperative period, because warm air influenced skin thermometers located on the upper body. At admission to the ICU patients in the control group had a heat loss of 4.4 kJ/kg; those in the convective warming group had a heat-gain of 0.8 kJ/kg. Further measurements of postoperative core temperatures did not differ significantly, but the skin-temperatures of patients who received forced-air warming in the theatre remained higher (P < 0.05) until 120 min from the end of surgery. Shivering was more frequent and lasted longer in the control group (8 patients, 20 min vs 4 patients, 9 min; P < 0.05). Patients in the control group needed more drugs to stop increased cardiovascular reactions (hypertension, tachycardia) or shivering.(ABSTRACT TRUNCATED)

Transport processes in fibrinolysis and fibrinolytic therapy

Transport of fibrinolytic agents into thrombi represents a rate limiting step in therapeutic thrombolysis. Mathematical modeling predicts and in vitro experiments demonstrate that effective delivery of fibrinolytic agents into clots is the most important determinant of fibrinolytic rate. Transport by diffusion is slow and limited by the need for a high concentration gradient. Transport by convection is more efficient and depends on both the intrinsic resistance of the thrombus and on the effective pressure gradient. Animal experiments indicate that delivery of activator into a thrombus accelerates fibrinolysis and that fibrinolytic rate is dependent on the pressure gradient to which the clot is exposed. Clinical observations are consistent with a dominant role of transport in determining thrombolytic efficacy. Systemic thrombolysis is most successful in short clots exposed to a high pressure gradient, such as coronary artery thrombi in normotensive or hypertensive patients. Rapid lysis is also achieved by intrathrombic delivery of plasminogen activator into peripheral arterial clots and thrombosed dialysis access fistulas. In contrast, systemic thrombolysis is much less successful in clots that are exposed to an insufficient pressure gradient, such as venous thrombi and coronary thrombi of patients in cardiogenic shock.

Clothing insulation in a hypobaric environment

HYPOTHESIS

Clothing insulation is the result of complex interactions between heat transfer mechanisms and clothing material thermal resistances. Hypobaria changes the heat transfer processes therefore should have observable effects on the clothing insulation.

METHODS

The effect of hypobaria on the thermal insulative properties of U.S. Army fatigue uniform (BDU) and U.S. Army chemical protective overgarment (BDO) were examined Barometric pressure of 429 mmHg, comparable to the condition at terrestrial elevation of 4570 m (15,000 ft) above sea level was created in a hypobaric chamber. The sea level environment was used as a baseline condition.

RESULTS

Our data support a diminished convective heat transfer and an enhanced evaporative heat transfer at higher altitude. We also found that hypobaria had only a small effect on the intrinsic clothing insulation values. For the less insulative BDU, hypobaria did not appreciably affect clothing insulation values. For the more insulative BDO, a maximum difference of 0.2 clo (clo = 0.155 m2.K.W-1) was found between hypobaric and normobaric environments.

CONCLUSION

Heavy clothing insulation forced the heat transfer processes at the skin surface to operate almost independently from those at the clothing surface. At the skin surface, evaporation was the dominant process, while at the outer clothing surface, convection dominated. At higher altitude, enhanced evaporative heat transfer resulted in a lower skin temperature, while reduced convective heat transfer hampered heat dissipation from clothing surface to the ambient environment, hence elevating the clothing temperature. Therefore, in hypobaric environment, the skin temperature was found to be lower, but the clothing temperature higher than at sea level.

Multiple-breath washout and washin experiments in steers

Multiple-breath N2 washouts (WO) and washins (WI) were performed during regular tidal breathing in 11 unsedated healthy steers approaching pulmonary functional maturity (mean body weight = 271 kg). They inspired 20% O2 in 80% Ar during the WO and air during the WI. For each steer, we computed two indexes of ventilation inhomogeneity from the N2 WO curves: 1) the curvilinearity of the logarithm of end-tidal N2 concentrations as a function of cumulative expired volume reflected in the ratio of two slopes fitted between 100 and 50% and between 50 and 10%, respectively, of end-tidal N2 concentration of the first breath of the WO; and 2) the N2 phase III slope divided by the mean expired concentration (Sn) of each breath also plotted as a function of cumulative expired volume. Equivalent computation of both parameters was done on WI and WO curves, and similar results were obtained. The mean slope ratio was 0.812 +/- 0.119 (SD) for all the steers, which is consistent with topographic gravity-dependent specific ventilation distribution inhomogeneity. Sn was independent of the breath number both for WO and WI (mean Sn = 0.130 +/- 0.057 liters-1), suggesting that emptying between unequally ventilated units, is synchronous. This behavior resembles that observed in rats postmortem (S. Verbanck, E.R. Weibel, and M. Paiva. J. Appl Physiol. 71: 847-854, 1991) but contrasts with experiments in humans, in whom convection-dependent ventilation inhomogeneities generate a marked increase in Sn throughout the entire WO (A. B. H. Crawford, M. Makowska, M. Paiva, and L. A. Engel. J. Appl. Physiol. 59: 838-846, 1985). This is surprising because one would expect gravity-dependent sequential emptying in animals of this size.

Bolus contaminant dispersion for oscillatory flow in a curved tube

The dispersion of a bolus of soluble contaminant in a curved tube during volume-cycled oscillatory flows is studied. Assuming a small value of delta (the ratio of tube radius to radius of curvature), the Navier-Stokes equations are solved by using a perturbation method. The convection-diffusion equation is then solved by expanding the local concentration in terms of the cross-sectionally averaged concentration and its axial derivatives. The time-averaged dimensionless effective diffusivity, <Deff/D>, is calculated for a range of Womersley number alpha and different values of stroke amplitude A and Schmidt number Sc, where D is the molecular diffusivity of contaminant. For the parameter values considered, the results show that axial dispersion in a curved tube is greater than that in a straight tube, and that it has a local maximum near alpha = 5 for given fixed values of Sc = 1, A = 5 and delta = 0.3. Finally, it is demonstrated how the time history of concentration at a fixed axial position can be used to determine the effective diffusivity.

Separation of arterial pressure waves into their forward and backward running components

A new separation technique has been developed to determine the forward and backward running arterial pressure wave components. It takes into account friction as well as nonlinear effects due to convective acceleration and to the pressure dependence of the arterial compliance. The new method is a combination of two methods treating friction and nonlinearities separately. The method requires the measurements of pressure and flow at one location as well as the knowledge of the area-pressure relationship. The validity of the method was tested by a simulation experiment in which the forward and backward waves were known a priori. It was shown that the new method is significantly more accurate in the predictions of the forward and backward waves when compared to the classical method assuming linearity and no dissipation. The new wave separation method was also applied to simulated aortic waves for (a) a healthy subject and (b) a subject with decreased compliance. Comparison with the classical linear method showed that neglecting nonlinearities leads to an overestimation of the forward and backward pressure wave amplitudes. The errors, however, were in the order of 5 to 10 percent. We concluded that, for most clinical purposes, the improvement using the nonlinear method is of the same magnitude as experimental errors, and thus the linear method would suffice.

Effects of altered FIO2 on maximum VO2 in the horse

Although the horse is considered an elite athlete with a specific VO2max some 2-4 times higher than man, maximal O2 transport is compromised both by moderately severe arterial desaturation and by failure to extract all O2 from blood perfusing exercising muscle. This prompted the present study to ascertain whether correction of arterial desaturation would proportionally augment VO2max and, if so, would O2 extraction behave in a manner predicted by diffusional transport limitation. Six two year old thoroughbreds were exercised to VO2max on a treadmill each on three separate occasions breathing gases of FIO2 = 0.15, 0.21 and 0.35, each used once in balanced order. VO2, ventilation, arterial and pulmonary arterial blood gases, pressures and lactate levels were measured both submaximally and maximally at each FIO2 and cardiac output was computed by mass balance for O2. At FIO2 = 0.21, VO2max = 143.9 +/- 4.8 ml kg-1 min-1, arterial saturation (SaO2) was 81.6 +/- 3.3% while venous PO2 (PvO2) was 15.3 +/- 1.4 Torr. At FIO2 = 0.35, VO2max was 172.6 +/- 8.2 ml kg-1 min-1, SaO2 reached 97.4 +/- 0.4% and PvO2 was 23.4 +/- 0.7 Torr. VO2max at FIO2 = 0.15 was 109.8 +/- 4.1 ml kg-1 min-1, SaO2 fell to 68.1 +/- 2.5% and PvO2 was 10.6 +/- 1.0 Torr, all changes being significant, p < 0.01. As FIO2 was varied, VO2max changed proportionally to calculated mean capillary Po2 as well as to total O2 delivery. These data confirm substantial O2 supply dependence of VO2max in the horse, and in such a manner as to be consistent with the hypothesis of combined diffusive and convective transport limitation within muscle.

Classification of pulsating flow patterns in curved pipes

The fully developed periodic laminar flow of incompressible Newtonian fluids through a pipe of circular cross section, which is coiled in a circle, was simulated numerically. The flow patterns are characterized by three parameters: the Womersley number Wo, the Dean number De, and the amplitude ratio beta. The effect of these parameters on the flow was studied in the range 2.19 < or = Wo < or = 50.00, 15.07 < or = De < or = 265.49 and 0.50 < or = beta < or = 2.00, with the curvature ratio delta fixed to be 0.05. The way the secondary flow evolved with increasing Womersley number and Dean number is explained. The secondary flow patterns are classified into three main groups: the viscosity-dominated type, the inertia-dominated type, and the convection-dominated type. It was found that when the amplitude ratio of the volumetric flow rate is equal to 1.0, four to six vortices of the secondary flow appear at high Dean numbers, and the Lyne-type flow patterns disappear at beta > or = 0.50.

Protein separation by continuous-flow electrophoresis in microgravity

During the IML-2 space shuttle mission, the RAMSES instrument was operated in the Spacelab module. This continuous-flow electrophoresis device performs separation and purification of protein solutions on a preparative scale. Samples containing artificial mixtures of pure proteins were used to test the capabilities of the device, and useful separations were obtained for proteins having a mobility difference of only 3 x 10(-9) m2 V-1 s-1. Operating conditions that cannot be applied on earth were explored for two different sample concentrations, one of which is too high to allow treatment on earth. It agrees well with a previously published numerical model in that the main cause of loss in resolution in this process is the electrohydrodynamic spreading of the protein filaments.

Integrative model for predicting thermal balance in exercising horses

A theoretical integrative model was developed to determine the heat balance of horses working in a given environment. This model included the following parameters: metabolic heat gain, solar heat gain, evaporative heat loss due to sweating, respiratory tract heat loss, radiation from the body and heat gain or loss due to convection and conduction. The model developed in this study includes an unique approach for estimating heat loss via evaporation of sweat from the animal's skin surface. Previous studies modelling evaporative heat dissipation were based on the volume of sweat loss. While it is known that the ambient conditions affect evaporation rate, these effects have not been adequately described. The present model assumes the horse's skin surface is adequately represented by a body of water and it describes the interaction of that water body with the atmosphere. It is assumed that sweat has thermodynamic characteristics equivalent to distilled water. Sweat, however, has high electrolyte and protein concentrations and anecdotal evidence has shown that the thermodynamic characteristics may be significantly affected. Further research is, therefore, required to confirm these characteristics for equine sweat. The model describes all factors known to affect the thermal balance of the horse working in a given environment. The relative significance of the various variables on the whole integrative model has been illustrated. The effect of ambient temperature and humidity on the evaporative heat loss, the most significant and critical avenue of heat dissipation, is defined and quantified. The model illustrates clearly how increasing relative humidity limits evaporative heat loss, which can be further compromised when horses exercise on treadmills with no air movement.

[Comparative rheoencephalographic and convective radiation encephalic thermometric studies]

It is for the first time that thermoassimetry of heart flows of brain right and left hemispheres presenting as predominance of radiative-convective heat radiation from the left has been revealed, the thermoassimetry gradient being rostral-caudal. Disclosed in cerebral hemispheres was complimentarity of energetic processes: the right hemisphere secures the background energy state, the left one functions in ensuring the discrete adaptive thermoenergy reactions. The thermoassimetry revealed may be the basis of other functional asymmetries of the brain. There was no parallelism between the studied parameters of circulation and heat flow.

Influence of intrinsic particle properties on the assessment of convective gas transport by aerosol bolus technique

Aerosol bolus measurements are increasingly being used in patients and healthy subjects to assess convective gas transport and mixing in the lungs. To investigate the extent to which intrinsic particle properties confound parameters derived for the assessment of intrapulmonary transport, bolus inhalation experiments were performed in six anesthetized, intubated, and mechanically ventilated beagle dogs using DEHS particles of 0.5, 1, or 2 microns diameter. Therefore, particle displacement by diffusion varied by a factor of two, settling velocity by a factor of 13, and particle inertia as inferred from the stopping distance by a factor of 16. By using a standardized breathing maneuver 6-mL boluses were inhaled into lung depths between 75 and 475 mL. Mode, half-width, and intrapulmonary particle deposition along with mean, standard deviation, and skewness of the particle concentration distributions in the expired air were determined. For all particle sizes studied particle deposition increased with increasing lung depth not exceeding 25% for 0.5-micron particles, but being 80% in deep lung regions for 2-micron particles. Whereas half-width and standard deviation exhibited only small differences between particle sizes (less than 20%), mode and mean of the exhaled bolus were clearly dependent on particle size, in particular for particles inhaled deep into the lung. No significant effects were detectable for the skewness. Hence, convective mixing assessed by half-width or standard deviation is only slightly dependent on particle size, but the estimate of convective bulk transport as inferred from the mean volume from which the bolus is exhaled is highly dependent on particle size. Yet, the intrinsic mobility of unit-density 0.5-micron particles was found to be small enough to consider these particles as ideal tracers for probing convective gas transport in the lungs.

[The quantitative parameters of the vertical migration of radionuclides in the soils in different types of meadows]

The two-component convective-diffusional model was used for determination of vertical migration parameters of 90Sr [correction of 90Cs] and 137Cs in meadow ecosystems and dependence from meadow type and soil properties was shown. The migration coefficients decrease in the order: peat land, lowland meadows, flood-plain meadows, dry meadows. The ecological half-life in the root zone ranges from 55 to 143 y for dry meadows and from 15 to 21 y for peat lands. Analogous parameters for 90Sr was 30-96 and 13-18 y, respectively. Since 1987 to 1994 the ecological half-life of 137Cs increased by a factor of 1.7-6.0.