Mathematical model of Rayleigh-Taylor and Richtmyer-Meshkov instabilities for viscoelastic fluids

We extended the Goncharov model [V. N. Goncharov, Phys. Rev. Lett. 88, 134502 (2002)] for nonlinear Rayleigh-Taylor instability of perfect fluids to the case of Rivlin-Ericksen viscoelastic fluids [R. S. Rivlin and J. L. Ericksen, Rat. Mech. Anal. 4, 323 (1955)], with surface tension. For Rayleigh-Taylor instability, viscosity, surface tension, and viscoelasticity decrease the exponential growth rate predicted by linear stability analysis. In particular, we find that viscosity and surface tension decrease the terminal bubble velocity, whereas viscoelasticity is found to have no effect. All three properties increase the saturation height of the bubble. In Richmyer-Meshkov instability, the decay of the asymptotic velocity depends on the balance between viscosity and surface tension, and viscoelasticity tends to slow the asymptotic velocity decay.

Development and validation of a turbulent-mix model for variable-density and compressible flows

The modeling of buoyancy driven turbulent flows is considered in conjunction with an advanced statistical turbulence model referred to as the BHR (Besnard-Harlow-Rauenzahn) k-S-a model. The BHR k-S-a model is focused on variable-density and compressible flows such as Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH) driven mixing. The BHR k-S-a turbulence mix model has been implemented in the RAGE hydro-code, and model constants are evaluated based on analytical self-similar solutions of the model equations. The results are then compared with a large test database available from experiments and direct numerical simulations (DNS) of RT, RM, and KH driven mixing. Furthermore, we describe research to understand how the BHR k-S-a turbulence model operates over a range of moderate to high Reynolds number buoyancy driven flows, with a goal of placing the modeling of buoyancy driven turbulent flows at the same level of development as that of single phase shear flows.

Small Atwood number Rayleigh-Taylor experiments

Consideration is given to small Atwood number (non-dimensional density difference) experiments to investigate mixing driven by Rayleigh-Taylor (R-T) instability. The past 20 years have seen the development of novel experiments to investigate R-T mixing and, simultaneously, the advent of high-fidelity diagnostics. Indeed, the developments of experiments and diagnostics have gone hand in hand, and as a result modern R-T experiments rival the capabilities and research scope of shear-driven mixing experiments. Thus, research into the small Atwood number limit has made significant progress over the past 20 years, and has offered important insights into natural mixing processes as well as the general R-T problem. This review of small Atwood number experiments serves as an opportunity to discuss progress, and also to provoke thoughts about future high Atwood number designs and difficulties.

Optimization of PLG microspheres for tailored drug release

Here we explore the opportunity to design and then produce tailored release of therapeutic drugs from microcapsules. By use of "building blocks," formed from well characterized microcapsule populations, an inverse design algorithm has been developed that provides an optimal (in a least squares sense) combination of building blocks to achieve a desired release history. Previously we have reported experiments and a well validated mathematical model for computing drug release histories from PLG microcapsules, and these form the backbone of the present optimization algorithm. To expand our available basis for finding useful optimal solutions, we also report work to validate the mathematical model for two different molecular weights. Thus, our building blocks comprise populations that differ by microsphere mean diameter, polydispersity, and polymer molecular weight, giving three separate parameters that effect drug release rate, and from which we build a foundation for our tailored release. Here we have taken a basis of six different microcapsule release systems, from which we build a tailored release history using constrained optimization to fit a prescribed release profile. Comparison of predicted release with measurements from the tailored microcapsule populations was found to produce excellent results, with correlation coefficients greater than 0.98. By way of demonstration, a triple pulse design is described that illustrates the power of the method.

About mean diameter and size distributions of poly(lactide-co-glycolide) (PLG) microspheres

Despite the importance of microsphere size for controlled drug delivery, little work has been done to quantitatively predict the distribution of microspheres from manufacturing techniques. This work presents a quantitative study that describes the size distribution of poly(lactide-co-glycolide) (PLG) microspheres. A fluid mechanics based correlation for the mean microsphere diameter is formulated based on the theory of emulsification in turbulent flow under non-coalescing conditions. The correlation was constructed and validated with experimentally obtained mean microsphere diameters prepared at different stirring speeds. In addition, a Rosin Rammler distribution function was found to give an accurate representation of the microsphere distribution. The spread of the microsphere size distribution was found to decrease with stirring speed. With the validation of the mathematical correlation, it is now possible to have a good estimate of the average microsphere size prior to microsphere preparation. This is directly relevant to the pharmaceutical industry where microspheres of specified mean diameter and size distribution are desirable.

On the diameter and size distributions of Bovine Serum Albumin (BSA)-based microspheres

A fluid mechanics-based correlation for the average size of Bovine Serum Albumin (BSA) microspheres, prepared using a water-in-oil emulsion technique, is presented. The correlation is formulated based on the theory of turbulent dispersion and a non-dimensional Weber number. Measured average diameters of the BSA microspheres prepared in olive oil at different stirring speeds are used to construct the correlation formula. The correlation gives good agreement with experimentally measured average diameters for a wide range of Weber numbers. This correlation is particularly useful to the pharmaceutical industry for predicting the size of encapsulated microspheres used in drug delivery prior to microsphere preparation. The effect of additives on microsphere size was also explored. The average diameter of the BSA microspheres was doubled by the addition of a bioadherent vitelline protein B solution. In addition, a Rosin-Rammler statistical distribution function is shown to accurately represent the microsphere size distribution obtained at different stirring speeds.

On the mechanical properties of bovine serum albumin (BSA) adhesives

Biological adhesives, natural and synthetic, are of current active interest. These adhesives offer significant advantages over traditional sealant techniques, in particular, they are easier to use, and can play an integral part in the healing mechanism of tissue. Thus, biological adhesives can play a major role in medical applications if they possess adequate mechanical behavior and stability over time. In this work, we report on the method of preparation of bovine serum albumin (BSA) into a biological adhesive. We present quantitative measurements that show the effect of BSA concentration and cross-linker content on the bonding strength of BSA adhesive to wood. A comparison is then made with synthetic poly(glycidyl methacrylate) (PGMA) adhesive, and a commercial cyanoacrylate glue, which was used as a control adhesive. In addition, BSA samples were prepared and characterized for their water content, tensile strength, and elasticity. We show that on dry surface, BSA adhesive exhibits a high bonding strength that is comparable with non-biological commercial cyanoacrylate glues, and synthetic PGMA adhesive. Tensile testing on wet wood showed a slight increase in the bonding strength of BSA adhesive, a considerable decrease in the bonding strength of cyanoacrylate glue, and negligible adhesion of PGMA. Tests performed on BSA samples demonstrate that initial BSA concentration and final water content have a significant effect on the stress-strain behavior of the samples.

Effect of mean diameter and polydispersity of PLG microspheres on drug release: Experiment and theory

The need to tailor release rate profiles from polymeric microspheres is a significant problem. Microsphere size, which has a significant effect on drug release rate, can potentially be varied to design a controlled drug delivery system with desired release profile. In this work the effects of microspheres mean diameter, polydispersity, and polymer degradation on drug release rate from poly(lactide-co-glycolide) (PLG) microspheres are described. Piroxicam containing PLG microspheres were fabricated at 20% loading, and at three different impeller speeds. A portion of the microspheres was then sieved giving five different size distributions. In vitro release kinetics were determined for each preparation. Based on these experimental results, a suitable mathematical theory has been developed that incorporates the effect of microsphere size distribution and polymer degradation on drug release. We show from in vitro release experiments that microsphere size has a significant effect on drug release rate. The initial release rate decreased with an increase in microsphere size. In addition, the release profile changed from first order to concave-upward (sigmoidal) as the microsphere size was increased. The mathematical model gave a good fit to the experimental release data. For highly polydisperse populations (polydispersity parameter b<3), incorporating the microsphere size distribution into the mathematical model gave a better fit to the experimental results than using the representative mean diameter. The validated mathematical model can be used to predict small-molecule drug release from PLG microsphere populations.

Differential effects of phosphodiesterase inhibitors on platelet activating factor (PAF)- and adenosine diphosphate (ADP)-induced equine platelet aggregation

Compounds that activate adenylate cyclase, increasing intracellular cyclic adenosine monophosphate (cAMP), inhibit equine platelet aggregation. Cyclic AMP is broken down by phosphodiesterase (PDE) and, in the present study, the effects of theophylline, a nonselective PDE inhibitor, and selective inhibitors of PDE isoenzymes PDE3, PDE4 and PDE5, on equine platelet aggregation in response to platelet activating factor (PAF) and adenosine diphosphate (ADP) have been examined. Theophylline and the PDE3 inhibitors, trequinsin and quazinone, inhibited both PAF and ADP-induced aggregation in a concentration dependent manner. The inhibition of PAF-induced aggregation was, however, significantly greater than that of the response to ADP. The inhibitory effects of theophylline and the PDE3 inhibitors on ADP- but not PAF-, induced aggregation were reversed by addition of the calcium ionophore, A23187. Rolipram and zaprinast, inhibitors of PDE4 and PDE5, respectively, had no effect on either PAF- or ADP-induced aggregation. These results demonstrate that inhibition of aggregation caused by PAF or ADP can be achieved by selective inhibition of PDE3 but suggest that there may be agonist-specific differences in the intracellular signalling pathways that regulate equine platelet aggregation.

Honduras: Caribbean Coast

The coast of Honduras, Central America, represents the southern end of the Mesoamerican Barrier Reef System, although its marine resources are less extensive and studied than nearby Belize and Mexico. However, the coastal zone contains mainland reef formations, mangroves, wetlands, seagrass beds and extensive fringing reefs around its offshore islands, and has a key role in the economy of the country. Like most tropical areas, this complex of benthic habitats experiences limited annual variation in climatic and oceanographic conditions but seasonal and occasional conditions, particularly coral bleaching and hurricanes, are important influences. The effects of stochastic factors on the country's coral reefs were clearly demonstrated during 1998 when Honduras experienced a major hurricane and bleaching event. Any natural or anthropogenic impacts on reef health will inevitably affect other countries in Latin America, and vice versa, since the marine resources are linked via currents and the functioning of the system transcends political boundaries. Much further work on, for example, movement of larvae and transfer of pollutants is required to delineate the full extent of these links. Anthropogenic impacts, largely driven by the increasing population and proportion of people living in coastal areas, are numerous and include key factors such as agricultural run-off, over-fishing, urban and industrial pollution (particularly sewage) and infrastructure development. Many of these threats act synergistically and, for example, poor watershed management via shifting cultivation, increases sedimentation and pesticide run-off onto coral reefs, which increases stress to corals already affected by decreasing water quality and coral bleaching. Threats from agriculture and fishing are particularly significant because of the size of both industries. The desire to generate urgently required revenue within Honduras has also led to increased tourism which provides an overarching stress to marine resources since most tourists spend time in the coastal zone. Hence the last decade has seen a dramatic increase in coastal development, a greater requirement for sewage treatment and more demand for freshwater, particularly in the Bay Islands. Although coastal zone management is relatively recent in Honduras, it is gaining momentum from both large-scale initiatives, such as the Ministry of Tourism's 'Bay Islands Environmental Management Project', and national and international NGO projects. For example, a series of marine protected areas and legislative regulations have been established, but management capacity, enforcement and monitoring are limited by funding, expertise and training. Existing and future initiatives, supported by increased political will and environmental awareness of stakeholders, are vital for the long-term economic development of the country.

Peptides constrained by an aliphatic linkage between two C(alpha) sites: design, synthesis, and unexpected conformational properties of an i,(i + 4)-linked peptide

A novel route for the synthesis of cyclic peptides constrained by an aliphatic bridge between two C(alpha)sites, using a triply orthogonal protecting group strategy, is described. The synthesis of the orthogonally protected bis-amino acid 1, via an enantioselective route utilizing the Schöllkopf and Evans methodologies, is first described. This is then incorporated into a short, alanine-rich peptide 13, using a novel triply orthogonal protecting group strategy to couple first one, then the other, amino acid moiety in such a way that an aliphatic bridge is formed between the i and i + 4 positions. Unexpectedly, the resulting constrained peptide does not adopt a helical conformation: instead, it is shown by CD at low temperature to adopt a left-handed type II beta-turn conformation in aqueous media and a right-handed type I beta-turn conformation in TFE.

Differential activation of platelets from normal and allergic ponies by PAF and ADP

OBJECTIVE AND DESIGN

Altered platelet responsiveness has been demonstrated in human atopic dermatitis. This study has compared the in vitro function of platelets from normal ponies and those with the allergic skin disease, sweet itch.

SUBJECTS

Ponies with a clinical history of sweet itch and normal ponies were used as blood donors.

METHODS

PAF and ADP-induced platelet aggregation was measured and TxB2 production quantitated at the time of maximal aggregation; 12-HETE was additionally measured in some samples. Agonist-induced release of 3[H]5-HT was also studied.

RESULTS

Although both PAF and ADP caused equine platelet aggregation, only PAF stimulated eicosanoid and 5-HT release. There were no differences between the responses of platelets from allergic and normal ponies to PAF or ADP (analysis of variance).

CONCLUSIONS

There is no evidence of altered platelet responsiveness in ponies with sweet itch. The profile of responses to PAF and ADP suggest differential activation of intracellular signalling pathways in equine platelets.

Actions and interactions of ADP, 5- HT, histamine and PAF on equine platelets

Platelets are thought to play a role in equine diseases such as acute laminitis and verminous arteritis and may be involved in allergic disease. Mediators implicated in the pathophysiology of these conditions activate platelets and responses may be enhanced by interactions between mediators. The present study compared platelet aggregation, thromboxane production and release of radiolabelled [(3)H]5- HT in response to 5- HT, histamine, ADP and PAF alone and in combination in vitro.PAF caused concentration-related aggregation, [(3)H]5- HT release and thromboxane production. In contrast, ADP caused aggregation and 5- HT induced the release of [(3)H]5- HT with little effect on other platelet functions. Histamine had little or no effect on equine platelets. Addition of 5- HT (10 microM) prior to ADP significantly displaced the aggregation response curve to the left. The profile of responses to PAF, ADP and 5- HT suggests differential activation of intracellular signalling pathways regulating these events. The enhanced response to ADP in the presence of 5- HT may have implications in thromboembolic disease in the horse.

A comparison of the actions of platelet activating factor (PAF) antagonists WEB 2170 and WEB 2086 in the horse

The effects of the selective platelet activating factor (PAF) receptor antagonist WEB 2170 on PAF-induced responses in equine cells and tissues have been examined and compared with those of WEB 2086. In initial experiments WEB 2170 was shown to inhibit in vitro platelet aggregation in a dose-dependent, competitive reversible manner (pA2 = 7.21). Co-administration of the antagonists with either PAF or histamine also inhibited PAF, but not histamine, induced wheal formation and PAF-induced neutrophil accumulation in vivo in equine skin. Intravenous (i.v.) administration of both drugs at a dose of 0.1 mg/kg blocked PAF-induced ex vivo platelet aggregation. The inhibition produced by WEB 2170 was greater and, at 30 min, this drug also reduced the slope and maximal response. Wheal formation in the skin was significantly inhibited for up to 6 h by WEB 2170 administered i.v., the reduction being more prolonged than that obtained with WEB 2086. Neutrophil accumulation in the skin was also significantly reduced for up to 24 h by WEB 2170, whilst no significant inhibition was produced by WEB 2086. These results demonstrate that WEB 2170, like WEB 2086, is an effective antagonist of PAF in the horse. Moreover, when given i.v., WEB 2170 appears to be a more potent PAF inhibitor than WEB 2086.

Effects of WEB 2086, an antagonist to the receptor for platelet-activating factor (PAF), on PAF-induced responses in the horse

Platelet-activating factor (PAF) causes oedema and neutrophil accumulation when injected into the skin of normal horses. PAF is also known to induce aggregation of horse platelets in vitro. The selective PAF receptor antagonist WEB 2086 has now been used to determine whether these effects are mediated by PAF receptor activation. Addition of WEB 2086 to equine platelets in vitro inhibited PAF-induced aggregation in a competitive reversible manner (pA2 = 7.14). Inhibition of in vivo inflammatory responses to PAF occurred after local administration of WEB 2086: wheal formation induced by 0.1 micrograms PAF/site was reduced by 1-10 micrograms WEB 2086/site. PAF (1 micrograms/site)-induced neutrophil accumulation was also inhibited by co-administration of 10 micrograms WEB 2086/site. Systemic administration of WEB 2086 (3 mg/kg iv) to 4 normal ponies inhibited PAF-induced wheal formation and ex vivo platelet aggregation. At 30 min after drug administration the concentration of PAF required to produce a half maximal aggregation response was increased 496 +/- 137 fold. At 6 h the degree of inhibition was markedly reduced and responses had returned to pre-treatment values by 24 h. PAF-induced increases in cutaneous vascular permeability were also reduced by 80% as early as 30 min after iv administration of WEB 2086 in these animals, the inhibition persisting for at least 6 h. These results suggest that in vitro and in vivo responses to PAF in the horse are mediated via activation to PAF receptors. WEB 2086 will therefore be a useful agent for studying the role of PAF in the pathogenesis of equine inflammatory conditions.

The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide synthases

Acetylation of Ser-530 of sheep prostaglandin endoperoxide (PGG/H) synthase by aspirin causes irreversible inactivation of the cyclooxygenase activity of the enzyme. To determine the catalytic function of the hydroxyl group of Ser-530, we used site-directed mutagenesis to replace Ser-530 with an alanine. Cos-1 cells transfected with expression vectors containing the native (Ser-530) or mutant (Ala-530) cDNAs for sheep PGG/H synthase expressed comparable cyclooxygenase and hydroperoxidase activities. Km values for arachidonate (8 microM) and ID50 values for reversible inhibition by the cyclooxygenase inhibitors, flurbiprofen (5 microM), flufenamate (20 microM), and aspirin (20 mM), were also the same for both native and mutant PGG/H synthases; however, only the native enzyme was irreversibly inactivated by aspirin. Thus, the "active site" Ser-530 of PGG/H synthase is not essential for catalysis or substrate binding. Apparently, acetylation of native PGG/H synthase by aspirin introduces a bulky sidechain at position 530 which interferes with arachidonate binding. In related studies, a cDNA for mouse PGG/H synthase was cloned and sequenced. A sequence of 35 residues with Ser-530 at the midpoint was identical in the two proteins. Thus, Ser-530 does lie in a highly conserved region, probably involved in cyclooxygenase catalysis. Sequence comparisons of mouse and sheep PGG/H synthase also provided information about the heme-binding site of the enzyme. The sheep HYPR sequence (residues 274-277), which had been proposed to form a portion of the distal heme-binding site, is not conserved in the mouse PGG/H synthase, suggesting that this region is not the distal heme-binding site. One sequence, TIWLREHNRV (residues 303-312 of the sheep enzyme), is very closely related to the sequence TLW(L)LREHNRL common to thyroid peroxidase and myeloperoxidase. The histidine in this latter sequence is the putative axial heme ligand of these peroxidases. We suggest that the histidine (His-309) of sheep PGG/H synthase sequence is the axial heme ligand of this enzyme.

Fluorine in the UK environment

Relatively low concentrations of fluorine in drinking water (≤ 1 mg F/l) have been shown to significantly reduce the degree of dental caries in children and fluorine would also appear to have a beneficial effect on bone formation in both humans and farm animals. However, it is apparent that elevated levels of fluorine in the diet have sometimes resulted in problems of increased dental caries and of the development of bone deformities. Much of the fluorine in rocks and soils occurs in apatite and hydroxysilicate minerals, fluorite being the only relatively common rock forming mineral containing fluorine as an essential constituent.Little systematic data are available on fluorine concentrations in soils, plants and natural waters in the UK. General background soil concentrations lie in the range 200 - 400 mg F/kg. For waters the average fluorine content is low, <0.1 mg F/l.In the British Isles there are several areas where there are enhanced levels of fluorine. In the northern Pennines, Derbyshire, northeast Wales and Cornwall, fluorite occurs as a significant component of mineralisation and much fluorine has been added to the environment from mining waste dumps. Soils in northeast Wales contain up to 3,650 mg F/kg and in the northern Pennines up to 20,000 mg F/kg. Waters contain up to 2.3 mg F/l. In southwest England, the granites are generally fluorine-rich with the fluorite granites of the St Austell pluton containing as much as 1 percent fluorine. These rocks are frequently kaolinised and intensively worked as a source of china clay. Soils in the vicinity of the waste tips contain up to 3,300 mg F/kg and grasses up to 2,950 mg F/kg. Surface waters in the St Austell area contain up to 1.25 mg F/l.Atmospheric fluorine pollution around brickworks in the Peterborough and Bedford areas has resulted in fluorosis in farm animals. Other sources of atmospheric fluorine pollution are aluminium smelters, steelworks and fossil fuel burning.

Cystic partially differentiated nephroblastoma and polycystic Wilms tumor: a spectrum of related clinical and pathologic entities

Cystic partially differentiated nephroblastoma is a rare neoplasm occurring in young children and demonstrating features of classic nephroblastoma (Wilms tumor) and multilocular cysts. Cystic partially differentiated nephroblastoma actually represents a spectrum of cystic renal tumors in which varying amounts of blastema, stroma and epithelial structures are present. Some of these lesions should, perhaps, be classified more accurately as polycystic nephroblastoma. The clinical and pathologic findings, and management of 2 infants with cystic partially differentiated nephroblastoma are presented. The controversy over the histogenesis of these lesions and whether they should be considered benign or potentially malignant is discussed.

The contribution of atrial contraction to right heart function before and after right ventriculotomy. Experimental and clinical observations

Effective atrial contraction was abolished by simultaneous atrial and ventricular (A-V) pacing in an acute canine preparation. At constant cardiac output, aortic pressure, and heart rate, only a small rise (1.4 mm. Hg) in mean right atrial pressure was observed before vertical right ventriculotomy, but a larger rise (9.5 mm Hg) occurred after ventriculotomy (p less than 0.01). Right heart failure with tricuspid regurgitation was induced after ventriculotomy by volume overload and A-V pacing. Restoration of atrial contraction (sequential A-V pacing) eliminated regurgitation and lowered average mean right atrial pressure from 22 to 4 mm. Hg (p less than 0.001). After right ventriculotomy, loss of atrial contraction at a constant right atrial pressure resulted in a 42 per cent reduction in cardiac output. In 8 patients who had had right ventriculotomies, abolition of effective atrial contraction by A-V pacing caused an average reduction in cardiac output of 22 per cent, whereas cardiac output fell only 5 per cent in 5 control patients (p less than 0.01).

Long-term morphologic and hemodynamic evaluation of the left ventricle after cardiopulmonary bypass. A comparison of normothermic anoxic arrest, coronary artery perfusion, and profound topical cardiac hypothermia

In order to assess the long-term effects of cardiopulmonary bypass (CPB) in combination with pupular methods of myocardial protection, 37 dogs were placed on CPB for 100 minutes with the use of a bubble oxygenator without hemodilution. A separate group (I) of eight normal dogs served as a control for assessment of hemodynamic changes. The operative groups were as follows: II, continuous coronary perfusion with an empty, beating heart for 60 minutes at 35 degrees C.; III, hypothermic anoxic arrest (aortic occlusion) for 60 minutes with topical cold saline lavage (4 degrees C.); IV, anoxic arrest for 60 minutes at 35 degrees C. Subgroups of Groups III and IV received intracoronary perfusion with Ringer's lactate or Sacks' solution during aortic occlusion and were compared with those animals receiving no perfusion. Survival in Groups II and III was significantly better than in Group IV (82 and 92 per cent vs. 45 per cent). Coronary perfusion with Ringer's lactate or Sack's solution did not influence survival. The 23 survivors from all groups underwent left heart catheterization and LV cineangiography 5 months after operation. All three operative groups had significant elevation of LVEDP and depression of maximum developed dp/dt when compared with normal dogs. Ejection fraction was significantly depressed in Groups III and IV, and there was evidence of left ventricular hypokinesia and/or akinesia in all three operative groups. Differences in function between Groups II, III, and IV were not significant. The use of intracoronary solutions during anoxic arrest did not significantly influence these functional alterations. Evidence of subendocardial fibrosis was found in each of the operative groups, with the most marked changes found in the normothermic arrest group. Moderate fibrosis was present, however, in some survivors in both the continuous coronary perfusion and topical hypothermic arrest groups. These data indicate that although survival is greatly enhanced when coronary artery perfusion or topical hypothermia is used, neither method prevents chronic deterioration in ventricular function nor the development of subendocardial fibrosis.

Comfort studies of rail passengers

Nicol, J. F., Doré, C., Weiner, J. S., Lee, D. E., Prestidge, S. P., and Andrews, M. J. (1973).British Journal of Industrial Medicine,30, 325-334. Comfort studies of rail passengers. A short series of trials is described in which a specimen car of the new High Density Rolling Stock was laden with passengers at different densities and under different environmental constraints, designed to simulate `shut-down' conditions.

The results suggest that the limit for comfort, 21·8°C corrected effective temperature (CET), proposed by Bell and Watts (1971) is reasonable but that temperatures some 3 or 4°C higher can be tolerated without undue discomfort.

The physiological limit for safety recommended by Bell and Watts is a CET of 30·6°C. This will be reached in less than 20 minutes if there is a power failure in warm conditions in crowded trains.

An undesirable, possibly dangerous, level of discomfort will be experienced by passengers in ventilated but crowded trains after 30 minutes.

In any case it is recommended that the globe temperature in a carriage should not exceed 30°C.

An analysis of 59 cases of tracheal stenosis following tracheostomy with cuffed tube and assisted ventilation, with special reference to diagnosis and treatment

An analysis of 59 cases of tracheal stenosis after tracheostomy with cuffed tube and assisted ventilation is reported. Special emphasis is placed upon diagnosis and treatment. The detection of severe strictures is usually easily achieved, but mild to moderate degrees of stenosis may present difficulties in diagnosis and may remain undetected for some time.

Management of the strictures included dilatation (14 cases), segmental tracheal resection with primary end-to-end anastomosis (34 cases), staged plastic reconstruction (2 cases), and permanent tracheostomy (4 cases). No treatment was given in 5 cases.

Dilatation achieved a good result in 6 cases and a satisfactory one in 8. Of 34 strictures treated by segmental resection, a good result was obtained in 29 cases, although 7 required a second operation for restenosis. Three cases had an unsatisfactory result and there were 2 operative deaths. Postoperative complications are discussed.

Mild strictures may be satisfactorily managed by dilatation, but some mild strictures and all severe strictures are best treated by segmental resection with primary end-to-end anastomosis. Segmental defects ranging from 0.5 to 5.5 cm. in length can be satisfactorily resected.

The incidence and pathogenesis of tracheal injury following tracheostomy with cuffed tube and assisted ventilation. Analysis of a 3-year prospective study

Observations are reported from a 3-year prospective study of tracheal injury occurring in patients managed by cuffed-tube tracheostomy and assisted ventilation in the Respiratory Failure Unit at Toronto General Hospital. When the cuffed tracheostomy tube was finally removed an initial bronchoscopic examination of the trachea was performed. Further clinical and radiological assessments were made 3 weeks and 3 months later, using bronchoscopy when indicated.

The incidence of symptomatic tracheal stenosis in 153 patients studied was 21 per cent. Of these strictures, 18 occurred at the level of the tracheostome and 14 at the level of the inflatable cuff. Disability due to airway obstruction was severe in 18 and mild in 14 patients. These mild lesions might easily have remained undetected. Two patients with severe strictures died of airway obstruction before treatment could be instituted, a mortality of 6·2 per cent in patients developing strictures. The remaining 30 strictures required treatment either by dialtation alone or by dilatation and resection of the stricture with tracheal reanastomosis. Two of the 153 patients studied developed chronic tracheo-oesophageal fistulas.

The observations indicate that stenosis can be anticipated before the lesion has developed by the finding of circumferential mucosal ulceration or segmental collapse at the initial per stomal bronchoscopy.

Observations from the study prompted the following changes in technique:- A modification of the connexions between the tracheostomy tube and the respirator, with a subsequent reduction in symptomatic stenosis at the stomal level.A reduction in the diameter of tracheostomy tubes.A search for a less injurious inflatable cuff.

The conclusions reached by this study were as follows:– Tracheostomy tubes of large diameter predispose to the development of strictures at the level of the tracheostome in male patients.The presence of airway infection predisposes to stomal stenosis, and probably to cuff stenosis.Cuff strictures are commoner in female patients than in male patients.Age and pre-existing lung disease may be important in the production of stomal stenosis.The use of a deliberate routine follow-up examination to evaluate tracheal injury following tracheostomy and assisted ventilation is a necessary undertaking.

Incidence and pathogenesis of tracheal injury following cuffed tube tracheostomy with assisted ventilation: analysis of a two-year prospective study

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