Temperature alterations of infrared light absorption by cartilage and cornea under free-electron laser radiation

Like pure water, the water incorporated into cartilage and cornea tissue shows a pronounced dependence of the absorption coefficient on temperature. Alteration of the temperature by radiation with an IR free-electron laser was studied by use of a pulsed photothermal radiometric technique. A computation algorithm was modified to take into account the real IR absorption spectra of the tissue and the spectral sensitivity of the IR detector used. The absorption coefficients for several wavelengths within the 2.9- and 6.1-microm water absorption bands have been determined for various laser pulse energies. It is shown that the absorption coefficient for cartilage decreases at temperatures higher than 50 degrees C owing to thermal alterations of water-water and water-biopolymer interactions.

Forces for morphogenesis investigated with laser microsurgery and quantitative modeling

We investigated the forces that connect the genetic program of development to morphogenesis in Drosophila. We focused on dorsal closure, a powerful model system for development and wound healing. We found that the bulk of progress toward closure is driven by contractility in supracellular "purse strings" and in the amnioserosa, whereas adhesion-mediated zipping coordinates the forces produced by the purse strings and is essential only for the end stages. We applied quantitative modeling to show that these forces, generated in distinct cells, are coordinated in space and synchronized in time. Modeling of wild-type and mutant phenotypes is predictive; although closure in myospheroid mutants ultimately fails when the cell sheets rip themselves apart, our analysis indicates that beta(PS) integrin has an earlier, important role in zipping.

Time-resolved, light scattering measurements of cartilage and cornea denaturation due to free electron laser radiation

Light scattering is used to monitor the dynamics and energy thresholds of laser-induced structural alterations in biopolymers due to irradiation by a free electron laser (FEL) in the infrared (IR) wavelength range 2.2 to 8.5 microm. Attenuated total reflectance (ATR) Fourier-transform IR (FTIR) spectroscopy is used to examine infrared tissue absorption spectra before and after irradiation. Light scattering by bovine and porcine cartilage and cornea samples is measured in real time during FEL irradiation using a 650-nm diode laser and a diode photoarray with time resolution of 10 ms. The data on the time dependence of light scattering in the tissue are modeled to estimate the approximate values of kinetic parameters for denaturation as functions of laser wavelength and radiant exposure. We found that the denaturation threshold is slightly lower for cornea than for cartilage, and both depend on laser wavelength. An inverse correlation between denaturation thresholds and the absorption spectrum of the tissue is observed for many wavelengths; however, for wavelengths near 3 and 6 microm, the denaturation threshold does not exhibit the inverse correlation, instead being governed by heating kinetics of tissue. It is shown that light scattering is useful for measuring the denaturation thresholds and dynamics for different biotissues, except where the initial absorptivity is very high.

Free-electron laser etching of dental enamel

OBJECTIVE

The purpose of this study was to evaluate the Mark-III free-electron laser as a means of etching enamel surfaces, with potential application to resin bonding.

METHODS

The FEL was tuned to wavelengths ranging from 3.0 to 9.2 microm. Specific wavelengths that are resonantly absorbed by phosphates, proteins, and water were used. First, bovine enamel was polished and exposed to static FEL exposures. Lased enamel was examined using scanning electron microscopy (SEM). Additional bovine enamel specimens were exposed to FEL at similar wavelengths, but with rastering to create treated rectangular areas on each specimen. Surface roughness was evaluated using profilometry and atomic force microscopy (AFM). Composite was bonded to the lased enamel, and shear bond strengths were determined using an Instron universal testing machine. As a control, the surface roughness of, and shear bond strengths to, acid-etched enamel were determined.

RESULTS

Static FEL exposures caused changes in the enamel ranging from an etched appearance to pits, cracks, and frank cratering. The surface roughness of lased enamel was much greater than that of acid-etched enamel, and was qualitatively different as well. Shear bond strengths of resin to acid-etched enamel were significantly higher than bond strengths to lased enamel.

CONCLUSIONS

Under the conditions used in this study, the FEL did not offer a practical and effective method of etching enamel for resin bonding. However, the ability of the FEL to deliver many specific wavelengths makes it an interesting tool for further research of laser effects on tooth structure.

Hollow-glass waveguide delivery of an infrared free-electron laser for microsurgical applications

The purpose of this research is to deliver free-electron-laser (FEL) pulses for intraocular microsurgery. The FEL at Vanderbilt University is tunable from 1.8 to 10.8 microm. To deliver the FEL beam we used a metallic-coated hollow-glass waveguide of 530-mum inner diameter. A 20-gauge cannula with a miniature CaF2 window shielded the waveguide from water. Open-sky retinotomy was performed on cadaver eyes. The system delivered as much as 6 x 10(5) W of FEL peak power to the intraocular tissues without damage to the waveguide or to the surgical probe.

Right versus left symmetry of ulnar variance. A radiographic assessment

One hundred skeletally mature healthy volunteers underwent standardized bilateral posteroanterior radiographs in unloaded (static) and loaded (dynamic) conditions to determine the symmetry of ulnar variance. The mean age was 32 +/- 9 years (range, 19-61 years), with 58 women and 42 men. Ulnar variance was measured to the closest 0.5 mm using the method of perpendiculars. Three separate measurements were made of each radiograph in a blinded fashion by the same investigator. An intraobserver standard deviation of 0.21 was used to calculate a 95% tolerance interval of 0.7 mm (rounded up to 1 mm) as a measure of significance. The average static ulnar variance was -0.13 +/- 1.5 mm on the left and -0.29 +/- 1.6 mm on the right. The average dynamic ulnar variance was 0.93 +/- 1.5 mm on the left and 0.82 +/- 1.5 mm on the right. When compared individually, there was a greater than or equal to 1 mm side to side difference in 37% of volunteers under static and 38% under dynamic conditions. There were no significant correlations between ulnar variance measurements and patient age, gender, race, or handedness. Use of the normal wrist radiograph as a baseline for static radial length measurements is valid in only 63% of cases.

Growth and nutrition of Quercus rubra L. seedlings and mature trees after three seasons of ozone exposure

Seedling growth and nutritional status have been shown to be sensitive to ozone, but the influence of multi-season ozone exposure on mature tree growth and nutrition has not been examined. To determine if seedlings and mature trees were similarly affected by ozone exposure, growth and nutrient concentrations in northern red oak (Quercus rubra L.) 4-year-old seedlings and 32-year-old mature trees were examined after treatment with subambient, ambient and twice ambient concentrations of ozone for three growing seasons. SUM00 values summed over the three growing seasons were 147, 255 and 507 ppm-h, respectively, for the subambient, ambient and twice ambient exposures. For mature trees, no influence of ozone treatment on lower stem diameter growth, stem growth within the mid-canopy and foliar biomass was observed. Seedling height was increased by ozone, but biomass and diameter were unaffected. A reduction in the specific leaf weight of leaves in response to ozone coincident with the loss of recurrent flushing was observed in seedlings. Ozone exposure reduced foliar nitrogen concentrations and increased woody tissue nutrient concentrations in seedlings and mature trees at the end of the third growing season. These results suggest an influence of ozone on retranslocation processes in seedlings and mature trees.

Seasonal patterns of light-saturated photosynthesis and leaf conductance for mature and seedling Quercus rubra L. foliage: differential sensitivity to ozone exposure

Extrapolation of the effects of ozone on seedlings to large trees and forest stands is a common objective of current assessment activities, but few studies have examined whether seedlings are useful surrogates for understanding how mature trees respond to ozone. This two-year study utilized a replicated open-top chamber facility to test the effects of subambient, ambient and twice ambient ozone concentrations on light-saturated net photosynthesis (P(max)) and leaf conductance (g(l)) of leaves from mature trees and genetically related seedlings of northern red oak (Quercus rubra L.). Gas exchange measurements were collected four times during the 1992 and 1993 growing seasons. Both P(max) and g(l) of all foliage followed normal seasonal patterns of ontogeny, but mature tree foliage had greater P(max) and g(l) than seedling foliage at physiological maturity. At the end of the growing season, P(max) and g(l) of the mature tree foliage exposed to ambient ( approximately 80-100 ppm-h) and twice ambient ( approximately 150-190 ppm-h) exposures of ozone were reduced 25 and 50%, respectively, compared with the values for foliage in the subambient ozone treatment ( approximately 35 ppm-h). In seedling leaves, P(max) and g(l) were less affected by ozone exposure than in mature leaves. Extrapolations of the results of seedling exposure studies to foliar responses of mature forests without considering differences in foliar anatomy and stomatal response between juvenile and mature foliage may introduce large errors into projections of the response of mature trees to ozone.

Growth and physiology of Northern Red Oak: preliminary comparisons of mature tree and seedling responses to ozone

Considerable progress has been made during the past decade in the development of mechanistic models that allow complex chemical, physical, and biological processes to be evaluated in the global change context. However, quantitative predictions of the response of individual trees, stands, and forest ecosystems to pollutants and climatic variables require extrapolation of existing data sets, derived largely from seedling studies, to increasing levels of complexity with little or no understanding of the uncertainties associated with these extrapolations. Consequently, a project designed to address concerns associated with scaling from seedling to mature tree responses was initiated. During the 1990 and 1991 growing seasons, mature northern red oak (Quercus rubra L.) trees and seedlings were exposed to subambient, ambient, and twice ambient ozone (O(3)) concentrations. The initial focus of the study was to identify possible trends and obvious differences between mature trees and seedlings, both in terms of growth and physiology and in response to O(3). Generally, mature trees exhibited a greater decrease in photosynthesis rates over the growing season than did the seedlings. Ozone treatments had no consistent effect on gas exchange rates of seedlings, but the twice ambient O(3) treatment resulted in reduced photosynthesis rates in the mature tree. Despite no effect of O(3) on seedling gas exchange rates, total seedling biomass was significantly less at the end of the 1991 growing season for those seedlings exposed to twice ambient O(3) levels. Disproportionate reductions in root biomass also resulted in reduced root to shoot ratios at elevated O(3) concentrations.

A comparison of sensitivity to ozone in seedlings and trees of Quercus rubra L

Assessments of ozone sensitivity in tree species have been based primarily on studies of Seedlings without any knowledge of the similarities between seedling and mature tree responses. To determine if seedlings and trees responded similarly to ozone, 2-yr-old seedlings and 30-yr-old trees of Quercus rubra L. were fumigated with subambient, ambient and twice-ambient ozone for one growing season (cumulative doses of 18, 45 and 87 ppm h^-1 , respectively). Carboxylation efficiency, apparent quantum yield and light-saturated net photosynthesis of leaves from the lower canopy of the 30-yr-old trees were reduced by ambient and twice-ambient ozone treatment. However, physiological characteristics of leaves from the upper canopy of trees showed no signs of ozone injury. Canopy leaf dry weight of trees was reduced by the twice-ambient ozone treatment through reductions in leaf area rather than specific leaf weight, but bole diameter and branch growth of trees were unaffected by ozone treatment. In contrast, ozone did not influence leaf physiology of second flush leaves, stem diameter, and height and biomass growth of 2-yr-old seedlings. These results indicate that for deciduous hardwood species, studies of seedlings may underestimate the ozone sensitivity of larger and more physiologically mature trees. For large trees with developed canopies, leaf position within the canopy may influence the sensitivity of physiological processes to ozone.

Ectomycorrhizal colonization of loblolly pine seedlings during three growing seasons in response to ozone, acidic precipitation, and soil Mg status

A three-year study was initiated in 1987 to evaluate the impact of O3, acidic precipitation, and soil Mg on ectomycorrhizal colonization of loblolly pine (Pinus taeda L.) seedlings. Thirty-six open-top chambers equipped with a rainfall exclusion/addition system were utilized to administer three levels of O3 (subambient, ambient, or twice ambient) and two precipitation acidity levels (pH 3.8 or 5.2) to seedlings growing in 24-liter plastic pots containing soil having either 35 or 15 mg kg(-1) of exchangeable Mg. Seedlings exposed to the twice ambient O3 treatment exhibited smaller percentages of total ectomycorrhizal short roots at the end of each year of the study, but trends were statistically significant in 1989 only. Changes in number of specific ectomycorrhizal morphotypes in response to O3 were not consistent from year to year. Acidic precipitation treatments had no effect on number or percent of mycorrhizal short roots, and responses of two morphotypes to soil Mg treatments were probably due to differences in the soil environment rather than a result of changes in aboveground processes. Temporal shifts in morphotype frequencies were observed for seedlings in all treatments and indicate that mycorrhizal succession occurred during the study period.

Intra-articular fractures of the distal part of the radius treated with the small AO external fixator

Thirty adults who had a severely comminuted intra-articular closed fracture of the distal part of the radius were treated by closed reduction and AO external fixation consisting of a converging-pin configuration with a double row of connecting bars. The patients were followed for an average of 2.6 years (range, two to four years). Twenty-seven patients had an excellent result; two, a good result; and one, a poor result, on the basis of pain, motion, strength, and radiographic appearance. Complications were rare, and there was no loss of fixation of the pins. The average grip strength was 92 per cent of normal. Motion of the wrist and rotation of the forearm averaged more than 90 per cent of that of the normal side. Carpal height was used as an indicator of distraction force produced by the fixator. There was an average increase in carpal height of four millimeters initially and 3.7 millimeters immediately before removal of the fixator, indicating near-constant distraction throughout the treatment. Radial length was well maintained, with shortening averaging less than one millimeter. The converging pins of the AO fixator prevent loosening, thereby diminishing the risks of infection, loss of reduction of the fracture, and breakage of the pins. This geometry of the pins allows the use of smaller-diameter (2.5-millimeter) pins and provides rigid fixation, even in osteoporotic bone.

Radial head fractures with acute distal radioulnar dislocation. Essex-Lopresti revisited

Seven adults with displaced radial head fractures had concurrent dislocation of the distal radioulnar joint. Because support of the radius was lost at both the elbow and wrist, proximal migration of the radius from 5 to 10 mm occurred. Different types of fractures were classified to designate the best method of restoring radial length to prevent chronic wrist pain and stiffness. Type I fractures had large displaced radial head fragments with minimal or no comminution and amenable to interfragmentary fixation. Type II fractures had severe comminution requiring radial head excision and prosthetic replacement. Type III were old injuries with irreducible proximal migration of the radius managed by ulnar shortening and radial head prosthetic replacement. There were three Type I, two Type II, and two Type III fractures. Results of treatment were graded as 3, excellent; 2, good; 1, fair; and 1, poor. The three excellent results were in patients in which restoration of radial length was achieved within one week of injury. Suboptimal results occurred in the remaining four patients when definitive surgery was delayed four to ten weeks. The poor result was in a patient treated only by radial head excision and who refused further surgery. Recommendations include meticulous clinical and roentgenographic examination of the distal radioulnar joint in all patients with displaced radial head fractures. Preservation of the radial head with anatomic reduction and rigid internal fixation is preferred, but radial head replacement may be necessary in cases with extensive comminution. Radial head excision alone, though contraindicated, may be restructured by ulnar shortening and radial head prosthetic replacement.

Intercarpal arthrodesis for static and dynamic volar intercalated segment instability

Since 1982 seven patients with volar intercalary segment instability (VISI) have been operated on at the Massachusetts General Hospital. All had preoperative wrist pain and described a painful "clunk" with ulnar deviation. In each case there was palpable evidence of instability when the wrist was deviated ulnarly that produced a "buckling" sensation as the distal and proximal rows rotated with ulnar deviation. Arthrograms in six patients and a cineradiography in one patient confirmed that this buckling correlated with volar rotation of the lunate and triquetrum and dorsal rotation of the capitate and hamate. All the patients had some type of intercarpal arthrodesis including four capitate-lunate-triquetrum hamate (CLTH), one lunate-triquetrum (LT), one lunate-triquetrum-hamate (LTH), and one triquetrum-hamate (TH). Surgical findings included the position of the lunate that had rotated on the capitate so that it was tilting volarly and the major ligament instability was between the proximal and distal rows although ligament tears were also present between lunate and triquetrum. Arthrodesis of the proximal and distal rows provided relief of wrist pain in five of six patients. The one patient with the arthrodesis limited to the proximal row had a poor result. Of the five successful cases, the postoperative range of wrist motion was 81 degrees of extension/flexion arc (63% of the normal contralateral) and 35 degrees of radial and ulnar deviation arc (57% of the normal contralateral wrist). The grip strength postoperatively averaged 58 pounds (74% of the normal contralateral side).

Irreducible trans-scaphoid perilunate dislocation

Two cases of irreducible trans-scaphoid perilunate dislocation are described. In each case there was soft tissue interposition between the proximal and distal elements of the fracture-dislocation and this prevented capitolunate and scaphoid reduction. The dorsal capsule was impaled on the distal scaphoid fragment in one case, and a flap of dorsal capsule was entrapped between the capitate and the lunate in the other. In light of these findings, we recommend a dorsal approach for open reduction of trans-scaphoid perilunate dislocation when the capitolunate joint cannot be reduced by closed manipulation.

Microwave-field-driven acoustic modes in DNA

The direct coupling of a microwave field to selected DNA molecules is demonstrated using standard dielectrometry. The absorption is resonant with a typical lifetime of 300 ps. Such a long lifetime is unexpected for DNA in aqueous solution at room temperature. Resonant absorption at fundamental and harmonic frequencies for both supercoiled circular and linear DNA agrees with an acoustic mode model. Our associated acoustic velocities for linear DNA are very close to the acoustic velocity of the longitudinal acoustic mode independently observed on DNA fibers using Brillouin spectroscopy. The difference in acoustic velocities for supercoiled circular and linear DNA is discussed in terms of solvent shielding of the nonbonded potentials in DNA.

Genotoxic activity of nitroaromatic explosives and related compounds in Salmonella typhimurium

A number of nitroaromatic explosives and related compounds were examined for mutagenic activity with the Salmonella/mammalian microsome test. 9 of 11 nitroaromatics tested were mutagenic, including 2,4,6-trinitrotoluene, the most widely produced military explosive. All the nitroaromatics, except 2,4,6-trinitrophenol and 2,3,5-trinitroresorcinol, were at least an order of magnitude more mutagenic than 3 dinitrotoluene (DNT) isomers. The most active compound was 2,3,5-trinitronaphthalene, which was approximately 5000 times more mutagenic than DNT isomers. These compounds induced predominantly frameshift mutations. The mutagenic activity did not require S9 activation, but was largely dependent on the presence of an intact nitroreductase capability in the test bacteria. This implied that reduced metabolites, possibly hydroxylamines, are the proximal mutagenic intermediates.

Ankle diastasis without fracture

Ankle diastasis without associated fracture occurs in a latent form in which the diastasis is detected only by stress radiographs, and in a frank form with the diastasis visible on routine, unstressed radiographs. Whereas latent ankle diastasis requires no reduction and can be treated by cast immobilization, frank diastasis requires anatomical reduction of the ankle mortise. The method of reduction depends upon the particular type of frank diastasis. We have identified four types of frank ankle diastasis without fracture. Type I injuries demonstrate straight lateral fibular subluxation without plastic deformation of the fibula and are best treated by open reduction, removal of any interposed soft tissue, and stabilization with a tibiofibular screw. Type II injuries present with straight lateral subluxation of the fibula due to plastic deformation of the distal fibula and may require a fibular osteotomy for reduction prior to internal fixation. Plastic deformation of the fibula as a cause of ankle diastasis has not been previously reported. The uncommon type III injury consists of posterior rotatory subluxation of the fibula. In type IV injuries the talus is dislocated superiorly, resulting in divergence of the tibia and fibula. Type III and IV injuries can usually be treated by closed manipulation and plaster immobilization. The authors treated four type I and two type II patients by open reduction and internal fixation. Both type II injuries required fibular osteotomy to restore the normal tibiofibular relationship. Good results were obtained in four patients. Fair results secondary to stiffness and pain on activity were present in two patients. All patients maintained anatomical reduction of the ankle mortise following removal of the tibiofibular screw.

Retrograde cross-pinning of transverse metacarpal and phalangeal fractures

Six different techniques of Kirschner wire fixation are compared in experimental transverse diaphyseal fractures of metacarpals and phalanges. Open retrograde cross-pinning provides a relatively simple means of obtaining consistently accurate pin placement with maximal stability. The technique is described, and the use of a preview pin and hypodermic needle guide are introduced. The indications, advantages, potential complications and clinical application are discussed.