Direct Imaging of “Explosively” Propagating Buried Molten Layers In Amorphous Silicon Using Optical, Tem And Ion Backscattering Measurements

The behavior of pulsed laser-induced “explosively” propagating buried molten layers (BL) in ion implantation-amorphized silicon has been studied in a time- and spatially-resolved way, using nanosecond time-resolved reflectivity measurements, “Z-contrast” scanning transmission electron microscope (STEM) imaging of implanted Cu ions transported by the BL, and helium ion backscattering measurements. Infrared (1152 nm) reflectivity measurements allow the initial formation and subsequent motion of the BL to be followed continuously in time. The BL velocity is found to be a function of both its depth below the surface and of the incident KrF laser energy density (El); a maximum velocity of about 14 m/s is observed, implying an undercoolingvelocity relationship of about 14 K/(m/s). Z-contrast STEM measurements show that the final BL thickness is less than 15 nm. Time-resolved optical, TEM and ion backscattering measurements of the final BL depth, as a function of E1, are also found to be in excellent agreement with one another.

Time-Resolved and Nicrostructural Studies of Solidification in Undercooled Liquid Silicon

Nanosecond resolution visible (633 nm) and near-infrared (1152 nm) reflectivity measurements have been used, together with transmission electronmicroscopy (TEM), to study pulsed KrF (248 nm) laser melting and subsequent solidification of thick (190–410 nm) amorphous (a) silicon layers. The measurements cover the entire laser energy density (El) range between the onset of melting (∼ 0.12 J/cm2) and the completion of epitaxial crystallization (∼1.1 J/cm2). Four distinct El-regimes of melting and solidification are found for the 410-nm thick a-Si layers. For El > 0.25 J/cm2, the time of formation, velocity and final depth of “explosively” propagating undercooled liquid layers were measured in specimens that had been uniformly implanted with Si, Ge, or Cu. TEM shows that the “fine-grained polycrystalline Si” produced by explosive crystallization (XC) actually contains large numbers of disk-shaped Si flakes that have largely amorphous centers and are visible only in plan view. The optical and TEM measurements suggest (1) that flakes are the crystallization events that initiate XC, and (2) that lateral heat flow (parallel to the sample surface) must be taken into account in order to understand flake formation. Results of new two-dimensional (2-D) model calculations of heat flow and solidification are presented. These calculations confirm the importance of 2-D heat flow and crystallite growth early in the solidification process. For 0.3 4 < El > 1.0 J/cm2, pronounced changes in both the shape and the duration of the reflectivity signals provide information about the growth of polycrystalline grains; this information can be correlated with post-irradiation plan and cross-section view TEM microstructural measurements.

Pulsed Laser Melting of Amorphous Silicon: Time-Resolved and Post-Irradiation Studies

Measurements of the time of the onset of melting of self-implantation amorphized (a) Si, during an incident laser pulse, have been combined with modified melting model calculations and measurements of surface melt duration to demonstrate that the thermal conductivity, Ka, of a-Si is very low (≃0.02 W/cm-K). Ka is also shown to be the dominant parameter determining the dynamical response of ionimplanted Si to pulsed laser radiation; the latent heat and melting temperature of a-Si are relatively unimportant. Cross-sectional transmission electron micrographs on implantation-amorphized Si layers of several different thicknesses show that for energy densities less than the threshold value for complete annealing there are usually two distinct regions in the re-solidified a-Si, consisting of fine-grained and large-grained polycrystalline Si, respectively. The presence of the fine-grained poly-Si suggests that bulk nucleation occurs directly from the highly undercooled liquid phase. Thermal melting model calculations suggest that the nucleation temperature, Tn is ≃1200°C.

Stress Effects on Raman Measurements of Pulsed Laser Annealed Silicon

It has recently been shown that the front surface region of the silicon lattice is severely strained during pulsed laser irradiation. This uniaxial strain reduces the symmetry of the front surface region, resulting in additional shifts and splittings of the phonon frequency and changes in the Raman scattering tensor. It is shown that, for the case of pulsed laser irradiation, the phonon frequency is increased, and the 3-fold degenerate optical phonon is split into a singlet and a doublet. The changes in the Raman scattering tensor make it non-symmetric, and generally invalidate the technique used by Compaan et al. to determine the cross section experimentally. The complications introduced by the presence of stress during pulsed laser annealing, coupled with the temperature dependence of the optical and Raman tensors, make a simple interpretation of the Stokes to anti-Stokes ratio in terms of lattice temperature extremely unreliable.

Laser-Solid Interaction and Dynamics of the Laser-Ablated Materials

Rapid transformations through the liquid and vapor phases induced by laser-solid interactions are described by our thermal model with the Clausius-Clapeyron equation to determine the vaporization temperature under different surface pressure condition. Hydrodynamic behavior of the vapor during and after ablation is described by gas dynamic equations. these two models are coupled. Modeling results show that lower background pressure results lower laser energy density threshold for vaporization. the ablation rate and the amount of materials removed are proportional to the laser energy density above its threshold. We also demonstrate a dynamic source effect that accelerates the unsteady expansion of laser-ablated material in the direction perpendicular to the solid. a dynamic partial ionization effect is studied as well. a self-similar theory shows that the maximum expansion velocity is proportional to cs/α, where 1 – α is the slope of the velocity profile. Numerical hydrodynamic modeling is in good agreement with the theory. With these effects, α. is reduced. therefore, the expansion front velocity is significantly higher than that from conventional models. the results are consistent with experiments. We further study the plume propagates in high background gas condition. Under appropriate conditions, the plume is slowed down, separates with the background, is backward moving, and hits the solid surface. then, it splits to be two parts when it rebounds from the surface. the results from the modeling will be compared with experimental observations where possible.

A Detailed Examination of Time-Resolved Pulsed Raman Temeperature Measurements of Laser Annealed Silicon

Raman temperature measurements during pulsed laser annealing of Si by Compaan and co-workers are critically examined. It has been shown previously that the Stokes to anti-Stokes ratio depends critically upon the optical properties of silicon as a function of temperature. These dependences, coupled with the large spatial and temporal temperature gradients normally found immediately after the high reflectivity phase, result in large variations in the calculated temperature depending upon the probe laser pulse width and the pulse-to-pulse and spatial variations in the annealing pulse energy density.

Time Resolved Transmission and Reflectivity of Pulsed Ruby Laser Irradiated Silicon

The time resolved optical transmission, T (atλ = 1152 nm), and reflectivity, R (at 633 nm and 1152 nm), have been measured for n-type single crystalline silicon (c-Si) during and immediately after pulsed ruby laser irradiation (λ = 693 nm, FWHM pulse duration 14 nsec), for a range of pulsed laser energy densities, El. The T is found to go to zero, and to remain at zero, for a period of time that increases with increasing El, in apparent disagreement with earlier measurements elsewhere that used semi-insulating Si and a different pulsed laser wavelength. Measured reflectivities during the high R phase agree within experimental error with reflectivities calculated from the optical constants of molten Si. Quantitative agreement is also found between both our T and R measurements and detailed time– and El-dependent results of thermal melting model calculations.

Amorphous Phase Trapping as a Result of Pulsed Laser Irradiation of Silicon

It is concluded that large interface undercoolings of ˜ 300 deg are not likely to occur during pulsed laser annealing and that the observed liquid to amorphous phase transition is not a purely thermodynamic effect. It is then shown that the formation of the amorphous phase can be understood on the basis of a kinetic rate model which makes large undercoolings of the interface unnecessary.

Pulsed–Raman Measurements of Temperature When Large Temperature Variations and Gradients are Present

Pulsed Raman temperature measurements by Lo and Compaan on Si samples have been interpreted as proving that the surface region does not melt during intense pulsed laser irradiation. In this paper, it is shown by detailed calculations with the melting model that the choice of experimental parameters in the Raman measurements can severely compromise a straightforward interpretation of the data. Moreover, it is demonstrated that temperatures extracted from Raman measurements are highly sensitive to the temperature-dependent optical properties of the material. Finally, it is pointed out that the very large temperature gradients present during pulsed laser annealing may entirely invalidate the Stokes/anti-Stokes ratio as an accurate temperature probe.

Pulsed-Laser Annealing of Ion-Implanted GaAs: Theory and Exeriment

It is shown that, in the pulsed-laser irradiation of crystalline or lightly damaged GaAs, good agreement is obtained between measured and calculated thresholds for melting, for catastrophic damage due to vaporization, and for the duration of surface melting at various energy densities. Good agreement between theory and experiment is also obtained for dopant profile spreading during pulsed-laser annealing.

Calculations Pertaining to Raman Scattering During Laser Annealing of Ion-Implanted Silicon

Compaan and co-workers have reported the results of time-resolved optical experiments on ion-implanted silicon which they claim prove the melting model of pulsed laser annealing cannot be correct. These results concern the rapid onset of a Raman signal after a heating laser pulse, the simultaneous occurrence of a Raman signal and the high reflectivity phase characteristic of molten silicon, and the lattice temperature measured by the Raman Stokes/anti-Stokes intensity ratio. In this paper, we show by detailed numerical calculations with the melting model that there is, in fact, excellent agreement between the results of the calculations and the experimental results reported by Compaan and co-workers.

Multiscale simulations of carbon nanotube nucleation and growth: mesoscopic continuum calculations

As part of a focused computational effort on the multiscale simulations of carbon nanotube nucleation and growth, we have developed computer programs for coupled heat and mass flow in one and two dimensions. In the tip-growth mode, the sample is divided into three main regions, each of which can be further subdivided as required. In region 1, carbon is supplied to the catalytic particle from an ambient gas of carbon-containing compounds. The chemistry and thermodynamics of the decomposition of these compounds can be included in region 1, but the capability has not yet been implemented. The carbon diffuses through the catalytic particle in region 2 under concentration and temperature gradients and with a diffusion coefficient that can depend on both concentration and temperature. Region 3 consists of the interfacial region between the catalytic particle and the growing nanotube. Results to date demonstrate the key roles played by the size and shape of the catalytic particle in conjunction with the concentration and temperature gradients at the gas/solid interface and in region 2. Results also suggest how the growth of a single wall may interfere with, but not necessarily prevent, the growth of additional walls in a multi-walled nanotube. Again, the carbon concentration profile in the catalytic particle at the different growth sites is a key factor.

Multiscale simulations of carbon nanotube nucleation and growth: electronic structure calculations

Several first-principles surface and bulk electronic structure calculations relating to the nucleation and growth of single-wall carbon nanotubes are described. Density-functional theory in various forms is used throughout. In the surface-related calculations, a 38-atom Ni cluster and several low-index Ni surfaces are investigated using pseudopotentials and plane-wave expansions. The energetic ordering of the sites for C atom adsorption is found to be the same, with the Ni(100) facet favored. The bulk diffusion coefficient of C in Ni as a function of cluster size and temperature is calculated from various molecular dynamics approaches. In another group of bulk-related calculations, Gaussian orbital basis sets are used to study a cluster or "flake" containing 14 C atoms. The flake is a segment of three hexagons from an "unrolled" carbon nanotube, with an armchair termination. The binding energies of C, Ni, Co, Fe, Cu, and Au atoms to it were calculated in an effort to gain insight into the mechanism for the high catalytic activity of Ni, Co, and Fe and the lack of it in Cu and Au. The binding energies of Cu and Au are about 1 eV less than those of the three catalytic elements. Similar methods are used to study the initial stages of nanotube growth within the context of classical nucleation theory. Finally, issues relating to the establishment of a fundamental catalytic mechanism are addressed.

Effects of FK409 on intestinal ischemia-reperfusion injury and ischemia-induced changes in the rat mucosal villus microcirculation

BACKGROUND

The small intestine is extremely sensitive to ischemia-reperfusion (I/R) injury and a range of microcirculatory disturbances contribute to tissue damage. Nitric oxide (NO) seems to be involved in tissue protection after I/R injury. This study therefore assessed the effects of the NO donor, FK409, on intestinal I/R injury and changes induced in intestinal microcirculation.

METHODS

PVG rats were subjected to 30-min intestinal ischemia with a subgroup of animals receiving FK409 (10 mg/kg i.v.) 30 min before ischemia and 30 min postreperfusion. Controls underwent sham surgery. The mucosal surface was visualized via an incision made in an exteriorized ileal segment and FITC-BSA or acridine orange was used to quantitate macromolecular leak (MML) and leukocyte adhesion, respectively. MML from, and numbers of adherent leukocytes within, individual villi were determined every 15 min for 2 hr after removal of the vessel clamp. Heart rate and mean blood pressure (mBP) were monitored throughout the experiment.

RESULTS

Eleven of 12 untreated animals subjected to intestinal I/R injury failed to survive the 2 hr reperfusion period, whereas all 12 FK409-treated animals survived. MML and leukocyte adhesion were increased in untreated animals (P<0.001), and blood flow stasis eventually ensued. Although FK409 decreased mBP (P<0.001), MML and leukocyte adhesion were significantly (P<0.001) reduced, and villus blood flow was maintained throughout the observation period.

CONCLUSIONS

FK409 prevented mortality after intestinal I/R, significantly reduced leukocyte adhesion, and maintained blood flow after intestinal ischemia and may therefore be of value in reducing tissue damage and improving outcome after small bowel transplantation.

Elevated levels of circulating heat shock protein 70 (Hsp70) in peripheral and renal vascular disease

Heat shock proteins (Hsp) are families of phylogenetically conserved molecules that have a range of cytoprotective and intracellular functional roles. Reactivity to heat shock proteins has been implicated in the development of autoimmune disease and tissue expression of heat shock proteins and increased levels of anti-Hsp antibodies have also been reported in vascular disease. This study compared circulating levels of Hsp60 and Hsp70 and antihuman Hsp60, antihuman Hsp70, and antimycobacterial Hsp65 antibodies in peripheral (PVD) and renal (RVD) vascular disease with those in age- and sex-matched controls. Levels of Hsp70 were higher in both PVD (median 580 vs 40; P < 0.01) and RVD (median 160 vs 0; P < 0.03), whereas there were no differences in Hsp60 levels. Anti-Hsp60 antibody levels were elevated in PVD (146 vs 81 arbitrary units/ml; P < 0.04), but not RVD. This is the first study to demonstrate increased levels of circulating Hsp70 in pathological disease states; however, its physiological role remains to be determined.

Effect of anti-CD4 monoclonal antibody administration on rat small bowel allograft survival and circulating leukocyte populations

This study assessed the effect of an anti-rat CD4 monoclonal antibody (OX38) on heterotopic small bowel allograft rejection. Fully allogeneic small bowel transplants were performed in the PVG-to-DA-rat strain combination. Animals received either i) short course (days -1, 0 and 1) of 1 mg/kg per day OX38, ii) short course of 5 mg/kg per day or iii) extended course (days -2, -1, 0, 1, 2 and twice weekly thereafter) of 1 mg/kg per day. Both the high dose (13 days) and extended low-dose (12 days) courses prolonged graft survival compared to untreated control animals (7 days). The low-dose, short-course treatment had no effect. Similar regimens were given to animals that did not receive transplants and in which peripheral blood CD4+ cell counts fell to between 20 and 55 % of pretreatment levels and 20-30% of binding sites were blocked. In summary, anti-CD4 monoclonal antibody therapy delayed rejection of rat small bowel allografts; however, long-term survival was not achieved.

The inflammatory response to upper and lower limb exercise and the effects of exercise training in patients with claudication

PURPOSE

We have previously shown that a program of upper limb exercise training can induce significant improvements in walking distance in patients with claudication. This study assessed whether upper limb exercise avoids the systemic inflammatory responses associated with lower limb exercise and also whether the inflammatory response to acute lower limb exertion is modified by a program of supervised exercise training.

METHODS

Fifty-two patients with stable intermittent claudication were randomized into two groups who underwent 6 weeks of supervised upper (n = 26) or lower (n = 26) limb cardiorespiratory exercise training. A parallel control group (n = 15) was provided with lifestyle advice only. Neutrophil activation markers (CD11b and CD66b) and plasma levels of von Willebrand factor (marker of endothelial damage) in response to an acute bout of sustained upper and lower limb exercise were assessed before and after the period of training. Plasma levels of soluble E-selectin (marker of endothelial activation) were also determined before and after the training period.

RESULTS

An acute bout of sustained lower limb exercise significantly increased the intensity of CD11b and CD66b expression by peripheral blood neutrophils in all groups, whereas upper limb exercise had no effect. Resting neutrophil expression of CD11b and CD66b and circulating von Willebrand factor levels were unaffected by the training program, as were the inflammatory responses to an acute bout of sustained upper and lower limb muscular work, despite the fact that both training programs significantly increased walking distances.

CONCLUSIONS

These findings indicate that upper limb exercise training programs may offer certain advantages over currently prescribed lower limb programs. Our results show that exercising nonischemic muscles in a way that promotes improved cardiorespiratory function and walking capacity can avoid the potentially deleterious systemic inflammatory responses associated with lower limb exertion in patients with stable intermittent claudication.

Induction of antigraft and antirecipient antibody responses after fully allogeneic and semiallogeneic rat small bowel transplantation

BACKGROUND

Given the potential influence of alloantibodies on organ graft outcome, this study investigated the induction of antigraft and antirecipient antibodies after allogeneic and semiallogeneic rat small bowel transplantation.

METHODS

Fully allogeneic, unidirectional rejection and unidirectional graft-versus-host disease (GvHD) heterotopic small bowel transplantation was performed using DA, PVG, and (PVGxDA)F1 donor-recipient combinations. Serum was obtained before and at time points after transplantation and incubated with blood from untransplanted DA and PVG rats. Antibody binding to T cells was detected by whole blood flow cytometry using FITC-conjugated anti-rat IgM murine monoclonal antibody. Antibody levels were determined by reference to a standard curve of fluorescent intensity generated using a serum sample with known anti-target cell IgM activity. Data are presented as arbitrary units/ml (AU/ml).

RESULTS

In the PVG-->DA combination, five of six DA recipients had detectable anti-graft (PVG) antibodies by day 4 after transplantation (mean 72 AU/ml) and all animals were positive by day 6 (976 AU/ml). Antirecipient (DA) antibodies were also induced, however, they were only apparent after 6 days in five of eight animals (90 AU/ml). Antigraft (DA) antibody responses were also induced in the DA-->PVG combination (day 6-218 AU/ml), however no antirecipient (PVG) response was apparent. Transplantation induced antirecipient (DA) antibodies in the unidirectional GvHD model (day 6-90 AU/ml) and an anti-graft (PVG) response in the unidirectional rejection model (day 6-60 AU/ml). However, the latter was quantitatively lower than that generated in the PVG-->DA combination (day 6-976 AU/ml).

CONCLUSIONS

Antigraft and antirecipient antibody responses are simultaneously induced after fully allogeneic small bowel transplantation, despite rejection being the predominant clinical feature. Further studies are required to elucidate their influence on graft outcome.

Stress responses in graft and native intestine after rat heterotopic small bowel transplantation

BACKGROUND

Cardiac transplantation has been shown to induce heat shock protein expression, and reactivity to these stress proteins has been implicated in acute and chronic allograft rejection. This study assessed Hsp60 and Hsp70 expression in graft and native small intestine after rat small bowel transplantation.

METHODS

Heterotopic small bowel transplantation was performed between PVG donor and DA recipient rats, a subgroup of which received tacrolimus immunosuppression (1 mg x kg(-1) x day(-1)). Untransplanted and isografted (PVG-->PVG) animals served as controls. Paraffin sections of graft and native intestine on day 5 after transplantation were stained by immunohistochemistry, and heat shock protein expression was graded blindly by three observers.

RESULTS

Villus epithelial cell expression of Hsp60, but not Hsp70, was increased in allografts. The induction of Hsp60 in the villus epithelium was not controlled by tacrolimus. Hsp60 and Hsp70 expression was induced in the lamina propria of isografts and allografts. This response was more pronounced in allografts and was significantly reduced, but not totally abrogated, by tacrolimus. Interestingly, heat shock protein expression was also induced in the native intestine lamina propria and epithelium of allograft recipients, suggesting the induction of stress responses at sites other than the transplanted organ.

CONCLUSIONS

Small bowel transplantation induces a stress response in both the graft and native intestine. The early and prolonged expression of these proteins may influence the induction of anti-heat shock protein reactivity and have an adverse effect on graft outcome after small bowel transplantation.

Influence of upper- and lower-limb exercise training on cardiovascular function and walking distances in patients with intermittent claudication

PURPOSE

The effects of upper-limb (arm cranking) and lower-limb (leg cranking) exercise training on walking distances in patients with intermittent claudication was assessed.

METHODS

Sixty-seven patients (33 to 82 years old) with moderate to severe intermittent claudication were recruited, and the maximum power generated during incremental upper- and lower-limb ergometry tests was determined, as were pain-free and maximum walking distances (by using a shuttle walk test). Patients were randomly assigned to an upper-limb training group (n = 26) or a lower-limb training group (n = 26). An additional untrained group (n = 15) was recruited on an ad hoc basis in parallel with the main trial by using identical inclusion criteria. This group was subsequently shown to possess a similar demographic distribution to the two exercise groups. Supervised training sessions were held twice weekly for 6 weeks.

RESULTS

Both training programs significantly improved the maximum power generated during the incremental upper- and lower-limb ergometry tests (P <. 001), which may reflect an increase in central cardiovascular function that was independent of the training mode. More importantly, pain-free and maximum walking distances also improved in both training groups (P <.001). The improvements in the training groups were similar; there were no changes in the untrained control group. These findings suggest that the symptomatic improvement after upper-limb exercise training may result, in part, from systemic cardiovascular effects rather than localized metabolic or hemodynamic changes.

CONCLUSION

Carefully prescribed upper-limb exercise training can evoke a rapid symptomatic improvement in patients with claudication, while avoiding the physical discomfort experienced when performing lower-limb weight-bearing exercise.

Effect of anti-LFA-1 monoclonal antibody on rat small bowel allograft survival and circulating leukocyte populations

Anti-LFA-1 monoclonal antibodies (mAb) prolong graft survival in several animal models. This study assessed the effect of an anti-LFA-1 mAb (WT.1) on small bowel allograft rejection, circulating leukocyte subsets and in vivo target cell antigen blockade. Heterotopic small bowel transplantation was performed between PVG donor and DA recipient rats. Transplanted animals received 1 mg/kg per day WT.1 on days -1, 0 (day of transplantation) and 1. Three doses of WT.1 were also administered to a group of untransplanted animals to monitor circulating leukocyte populations and in vivo binding. WT.1 prolonged recipient survival from 7 to 14 days. Peripheral leukocyte counts increased more than twofold, primarily due to marked increases in both CD4+ and CD8+ lymphocytes. Approximately 85% of WT.1 binding sites on lymphocytes and monocytes were blocked/modulated after the course of therapy. WT.1 has marked effects on circulating leukocytes and target cell binding capacities and can affect the survival of rat small bowel transplant recipients.

Latex vessels with customized compliance for use in arterial flow models

The physical characteristics of the arterial wall exert a major influence over blood flow patterns and the pulse wave velocity is strongly affected by the elasticity of the vessel. We have developed a technique for manufacturing latex tubing which has physical characteristics similar to those of human arteries. Tubes were produced by painting a plastic rod of diameter 7 x 10(-3) m (the internal diameter of the superficial femoral artery) with liquid latex. The number of coats applied controlled the thickness, and hence the elasticity of the resulting tube. Values of compliance and pulse wave velocity were similar to those observed in vivo. The tubing was tested in a model of the femoral arterial circulation and the typical triphasic arterial now was seen. The mean flow in the vessels was also analysed, and found to be higher for the more elastic vessels, supporting existing mathematical theories and qualitative physiological data. These vessels provide a reliable method of producing physiologically accurate test segments for use in a range of arterial flow models.

Time-averaged mean velocity for volumetric blood flow measurements: an in vitro model validation study using physiological femoral artery flow waveforms

This study assesses the accuracy of the volume flow measurement of the ATL HDI 3000 duplex ultrasound scanner using a model of the femoral arterial circulation. The beam profile of the transducer was measured, and used to identify regions of the beam where there may be poor insonation characteristics. The flow measurement accuracy was not found to be influenced by the vessel depth between 1.0 cm and 8.0 cm in a 0.7 cm diameter vessel. Overall accuracy was 3%+/-9%. Vessels in excess of 0.9 cm produced larger errors. In the model system, pulse rates between 60 bpm and 120 bpm had no significant effect on the measurement accuracy (p > 0.01). The results of this study suggest that accurate measurements of femoral arterial blood flow are possible. Further work will be required to assess the accuracy of the technique in vivo.

Identification of localized anti-host responses in the graft mesenteric lymph node and Peyer's patches after rat small bowel transplantation

This study determined the activation status of recipient and donor lymphocyte populations in the graft mesenteric lymph node (MLN) and Peyer's patches (PP) after allogeneic, heterotopic rat small bowel transplantation without immunosuppression. Untransplanted and isografted animals served as controls. The activation status of lymphocyte subsets was determined by flow cytometric evaluation of lymphoblastoid transformation (forward light scatter; FSc). The proportion of activated lymphocytes in the MLN and PP of allografted animals progressively increased. There was also an early transient activation of MLN lymphocytes in isografted animals which probably resulted from surgery-related inflammation. Activated alpha/beta TCR+ and CD4+ cells were detected in the MLN as early as day 3, whereas there was little activation of CD8+ cells. Interestingly, donor lymphocytes became more activated than recipient lymphocytes. Allografting also led to activation of graft-derived PP alpha/beta TCR+ and CD8+ cells, yet there was no detectable activation of recipient-derived lymphocytes. In summary, this study has identified activated donor lymphocytes in the graft MLN and PP after allogeneic small bowel transplantation. Although rejection predominates without immunosuppression, the presence of an underlying anti-recipient response within the small bowel allograft may contribute to graft damage via the localized release of cytokines and inflammatory mediators.

Identification of migratory graft and host cell populations after allogeneic rat small bowel transplantation

This study used flow cytometry to identify graft cells in the recipient peripheral blood and spleen and host cells infiltrating the graft mesenteric lymph node and Peyer's patches after heterotopic rat small bowel transplantation. Transplantation had little effect on the overall cell subset composition of these compartments and no changes appeared characteristic or indicative of developing rejection, suggesting that physiological control of cell migration remained unaltered. A small and transient population of graft cells was detected in the peripheral blood and spleen of the recipient which disappeared after 5 and 3 days respectively. Graft-derived cells in the peripheral blood comprised predominantly CD4+ cells on day 1 with B cells predominating on day 5. Graft cells infiltrating the spleen were predominantly B cells. Host cells infiltrated the graft mesenteric lymph nodes and Peyer's patches to a lesser extent than previously reported using immunohistochemical analysis. For both tissues, infiltrating host-derived cells initially comprised mainly CD4+ cells. On day 4 approximately equal proportions of CD4+ and B cells were present in the mesenteric lymph node, whereas B cells were predominant in the host cell infiltrate of the graft Peyer's patches. In summary, these findings indicate that the cell subset composition of recipient and graft lymphoid compartments does not change after small bowel transplantation, even in the presence of a substantial recipient cell infiltration. The reasons for the apparent discrepancies in the degree of host cell infiltration when assessed using immunohistochemical and flow cytometric techniques are currently uncertain, but may result from the localised release of soluble MHC class I in graft tissues as a consequence of infiltrating host cell activation or localised cell destruction.

Blood flow in the lower limb after balloon angioplasty of the superficial femoral artery

Using duplex ultrasonography lower-limb blood flow measurements were obtained in 20 patients with intermittent claudication. Assessments of flow were made in the common femoral artery, profunda femoris artery (PFA) and superficial femoral artery (SFA) before and after angioplasty for stenoses of short segments of the SFA. Blood flow was measured at rest and after exercise on a cycle ergometer. Collateral flow was calculated using an established mathematical model. Results were compared with the ankle:brachial systolic pressure index (ABPI) after exercise. Although there was no overall increase in resting limb blood flow, an increase in mean(s.d.) SFA flow from 148(79) to 312(94) ml min-1, with a concomitant decrease in PFA flow from 224(84) to 98(43) ml min-1 was noted 1 week after angioplasty (P < 0.05). At rest there was an increase in mean(s.d.) ABPI from 0.62(0.12) to 0.89(0.23) (P < 0.05). Collateral flow was estimated to have decreased from 186(34) to 18(8) ml min-1; the pattern of change in flow was similar after exercise. Angioplasty of the SFA remains controversial because of the risk of restenosis. The above methodology allows assessment of whether patients can re-establish collateral flow or whether limb blood flow will be significantly compromised if restenosis occurs.

Haemodynamic and metabolic responses of the lower limb after high intensity exercise in humans

This study assessed blood flow in the common femoral, superficial femoral and profunda femoris arteries, the effects of vasodilator metabolites and changes in blood pressure and pulse during recovery after high intensity exercise (Wingate test). Mean common femoral artery flow increased sevenfold in response to the exercise. The subsequent decline in mean common femoral artery flow was mono-exponential with a mean time constant of 19 min. The post-exercise increase in profunda femoris artery flow (ninefold) was significantly greater than the superficial femoral artery flow (fourfold, P < 0.05). Systolic blood pressure and heart rate decreased monotonically throughout recovery. In contrast, diastolic blood pressure showed a significant fall below baseline at 3 min (P < 0.05) with a return to baseline at 60 min. The greatest drop below baseline (approximately 20 mmHg) occurred around 7 min. Lactate reached a maximum of 13.6 +/- 2.3 mmol -1 at 8 min (P < 0.05) and was still significantly above baseline at 60 min. pH remained below 7.2 until 20 min of recovery. The results demonstrate that following high intensity exercise, blood flow to the limbs appears to be controlled by complex interactions of various vaso-active metabolites, each contributing proportionally more at different times during recovery.

Evidence that orthotopic transposition following rat heterotopic small bowel transplantation corrects overgrowth of potentially pathogenic bacteria

An overgrowth of pathogenic organisms occurs following rat heterotopic small bowel transplantation. This study assessed whether the bacterial microflora return to normal following subsequent orthotopic transposition of the graft. After 14 days the heterotopic graft was placed into continuity following resection of 15 cm of the host midintestinal loop. Quantitative and qualitative analyses of the intraluminal bacteria were performed studying the resected host intestine, the heterotopic graft at 14 days, and the graft 14 days after transposition. A group of normal rats were used as controls. An overgrowth of Staphylococcus epidermidis evident in the heterotopic graft at 14 days returned to a more normal bacterial profile following orthotopic transposition. These findings suggest that early interposition of a small bowel graft into an orthotopic position may prevent an alteration in the small bowel ecology toward potentially pathogenic organisms capable of translocation.

Observer variability in volumetric blood flow measurements in leg arteries using duplex ultrasound

Duplex ultrasound volumetric flow measurements have not found a major clinical use because of variability caused by errors in estimating cross-sectional area (CSA) and in measuring time averaged mean velocity (TAMeV). We determined inter- and intraobserver variation in volumetric blood flow measured at rest in the common femoral artery (CFA) and its main branches, the superficial femoral (SFA) and profunda femoris (PFA) arteries, in 20 normal subjects. The product of TAMeV and CSA was taken as volumetric flow. The coefficient of variation of TAMeV was consistently greater than that of CSA. Interobserver variation for blood flow (16.2%, 20.2% and 40.3% for CFA, SFA and PFA, respectively) was larger than intraobserver variation (13.0%, 15.1%, 21.2%). In conclusion, these data define the minimum changes in VQ that can be realistically detected and indicate that, with modern duplex Doppler equipment, volumetric flow can be used as a reliable haemodynamic measure for monitoring patients before and after surgical or radiological intervention.

Differential expression of adhesion molecules during rat small bowel allograft rejection

The adhesion molecules intercellular adhesion molecule 1 (ICAM-1), lymphocyte function-associated antigen-1 (LFA-1) (alpha and beta chains), and very late activation antigen-4 (VLA-4) have an essential role in cell-cell interactions and the initiation of immune responses. This study used an indirect immunoperoxidase technique to investigate the expression of these molecules in the lamina propria of allografts and isografts after heterotopic rat small bowel transplantation. Normal untransplanted small bowel served as additional controls. Overall, ICAM-1 and LFA-1 alpha expression was significantly higher in allografts, although there was variable expression of these molecules in isografted animals. There were temporal differences in the expression of ICAM-1 and LFA-1 alpha in that increased ICAM-1 expression was more pronounced in the the early posttransplant period, whereas there was a progressive increase in LFA-1 alpha as rejection developed. In contrast, there was no difference between allograft and isograft expression of LFA-1 beta and VLA-4. This study has demonstrated a preferential increase in adhesion molecule expression with developing rat small bowel allograft rejection and suggests that adhesion molecules are involved in the development and progression of allograft rejection. Although the observed differences in antigen expression are not as marked as those previously reported in other organ transplants, appropriate adhesion molecules may present suitable targets for immunotherapeutic protocols after small bowel transplantation.

CD44 expression in rejecting rat small bowel allografts

CD44 is a widely expressed cell surface protein that recognizes multiple ligands and is involved in extra- and intercellular adhesion. The precise role of CD44 in immune interactions is currently unknown, but it is believed to be a homing receptor involved in lymphocyte trafficking and inflammatory responses. This study investigated CD44 expression in intestinal tissue after heterotopic rat small bowel transplantation and assessed the effect of transplantation on intestinal epithelial cell proliferation using an antibody to the nuclear activation Ag Ki67. Lamina propria and intestinal epithelial cell expression of CD44 was graded blindly by five observers, and villus epithelial cells were noted as being positive or negative for Ki67 staining. CD44 expression was high in the lamina propria of both allografted and isografted animals; however, there was no significant difference between the two groups. In contrast, the expression of CD44 on the villus epithelium was greater in allografted animals and progressed toward the villus tips as rejection developed, declining thereafter because of loss of villus integrity. Ki67 positivity was also greater in allografted animals but did not progress toward the villus tip. This is the first reported observation of CD44 expression on intestinal epithelium that is not restricted to the crypts. The findings indicate the involvement of CD44 in the rejection process and demonstrate changes in the proliferative profile of rejecting small intestinal epithelium. Further studies into adhesion molecules, such as CD44, may help to improve understanding of graft failure and promote the development of new therapeutic approaches for controlling and preventing graft rejection.

Flow cytometric analysis of peripheral blood lymphocyte subset light scatter characteristics as a means of monitoring the development of rat small bowel allograft rejection

This investigation used flow cytometry to monitor peripheral blood lymphocyte morphology after rat small bowel transplantation. Preliminary studies demonstrated that in vitro activated peripheral blood lymphocytes exhibited increased cell size and granularity as measured by flow cytometric analysis of forward (FSc) and side (SSc) light scatter characteristics. The formation of distinct 'activated' light scatter regions by such lymphoblastoid transformation occurred concomitantly with up-regulated p55IL-2R expression. Heterotopic small bowel transplantation was performed between PVG donor and DA recipient rats without immunosuppression. Animals receiving isografts served as controls. Peripheral blood lymphocyte subsets were identified using appropriate MoAbs, and the light scatter characteristics of each cell subset were determined by backgating strategies. Increased proportions of activated alpha/beta T cell receptor (TCR)-positive cells could be detected in allografted animals as early as day 2 post-transplantation. B cells showed peak activation by day 4, at which time the proportion of activated cells was over two-fold greater than that seen in untransplanted animals--few activated B cells were detected in isografted animals. Resting natural killer (NK) cell light scatter regions only partially overlap with those of resting T and B lymphocytes, but in allografted animals almost the entire NK population fell outside the resting lymphocyte gate by day 2 post-transplantation, an activation state which was maintained until day 4. These findings associate peripheral blood cell subset lymphoblastoid transformation with developing small bowel allograft rejection. Importantly, changes were detected early and prior to the onset of overt rejection. These data suggest that analysis of peripheral blood lymphocyte light scatter properties may provide an insight into in vivo immune status after small bowel transplantation.