Pulse-modulated photoacoustic measurements reveal strong gas-uptake component at high CO2-concentrations

The effect of high CO₂-concentration on photoacoustic signals from tobacco leaves is studied by means of a recently developed pulse modulation method which provides simultaneous information on photothermal and photobaric components in the millisecond time domain. High CO₂-concentrations are found to induce large gas-uptake signals. Simultaneous measurements of chlorophyll fluorescence suggest that the uptake signals are correlated with energy-dependent fluorescence quenching. Very similar CO₂-concentration dependencies are found in the absence and presence of methylviologen, which is known to catalyze O₂-reduction, and in the presence of glyceraldehyde, which blocks Calvin cycle and photorespiration. It is suggested that the CO₂-enhanced uptake signal is likely to reflect O₂-uptake in the Mehler reaction. However, it is not ruled out that also rapid CO₂-solubilisation or CO₂-binding caused by light-induced stroma alkalisation are involved. Strong uptake is also induced when the CO₂-concentration in the closed photoacoustic chamber increases due to dark-respiration. The consequences of these findings with respect to the interpretation of photoacoustic data (e.g., low-light effect) and to the regulatory role of O₂-dependent electron flow are discussed.     

Scanning CO2 laser bacterial inactivation systems

AIMS: The performance of three scanning CO(2) laser inactivation systems was assessed and included: a gantry system, a rapidly rotating mirror and a low-power hybrid system combining an oscillating mirror and rotary motion of the sample. METHODS AND RESULTS: Escherichia coli and Staphylococcus aureus were the target organisms on stainless steel, nutrient agar or moist collagen film and the laser power was varied from 2 to 1060 W (two laser sources). In general, a threshold energy density was identified, above which no inactivation was observed because the scanning velocity was too high (10 cm s(-1) for stainless steel, 660 W). Reducing the velocity increased the inactivation process until complete inactivation was observed at 1.3 cm s(-1) (E. coli, approximately 10(6) CFU per sample) and 0.82 cm s(-1) (S. aureus, approximately 10(8) CFU per sample); consequently, S. aureus organisms showed a greater resistance to laser irradiation. For the nutrient agar and collagen samples, the averages of the width of clearing were measured as a function of the translation velocity and the rates of inactivation (I(R), cm(2) s(-1)) were found; an optimum velocity was observed that produced the maximum rate of inactivation. At a laser power of 1060 W, the maximum value of I(R) was 140 cm(2) s(-1) ( approximately 10(7) CFU cm(-2)) for S. aureus on collagen and slightly less on nutrient agar (114 cm(2) s(-1), estimated from a best-fit polynomial, r(2) = 0.98). CONCLUSIONS: A comparison of the low- and high-power lasers produced values of 0.09 cm(2) s(-1) W(-1) (i.e. I(R) per Watt delivered) for S. aureus on nutrient agar with the low-power laser at 13 W and on collagen 0.13 cm(2) s(-1) W(-1) for 1060 W. The rate of inactivation was found to be a function of the laser power, translation velocity and properties of the substrate media. The three laser inactivation systems successfully demonstrated the potential speed, efficiency and application of such systems. SIGNIFICANCE AND IMPACT OF THE STUDY: Laser scanning systems offer the potential for rapid and efficient inactivation of surfaces, eliminating the need for chemical treatment.     

Retinoic acid and CO2 laser resurfacing

The purpose of this study was to analyze the effect of retinoic acid on wound healing and depth of injury in an animal skin model resurfaced with a CO2 laser. The dorsal skin of 21 Hartley guinea pigs was divided into halves. One-half received a daily application of 0.05% retinoic acid for 28 days, whereas the other half served as the control. The animals were divided into three treatment groups of seven animals. Group A was laser resurfaced with one pass of the Coherent UltraPulse CO2 laser (300 mJ, 60 W, density 40 percent). Group B received two passes, and group C received three passes. Histologic studies were obtained before laser resurfacing and days 1, 4, and 7 after resurfacing. Depth of injury, thickness, number of squamous cell and granular cell layers, and epithelialization rates were measured. We found that the depth of injury was statistically less in animals pretreated with retinoic acid. Granular cells were thicker and more numerous at day 4 in pretreated animals but similar to controls by day 7. Animals pre-treated with retinoic acid overall seemed to heal wounds earlier. In conclusion, pretreatment with retinoic acid may reduce the depth of injury in laser resurfacing and speed healing rates.     

Long-term histologic effects of the CO2 laser

The long-term histologic effects of CO2 laser resurfacing previously were unknown. Prior investigations have clearly defined the photothermal effect. Collagen shrinkage as a reaction to increased tissue temperature between 60 and 70 degrees C has also been previously described. Twenty-two patients completed a 1-year study in which biopsy specimens from the upper lip were taken preoperatively and 6 weeks, 6 months, and 1 year after CO2 laser resurfacing. Trichrome stains and Verhoeff-van Gieson stains were used to demonstrate tissue collagen and tissue elastin. Neocollagenesis beginning at 6 weeks and progressively increasing at 6 months and 1 year was clearly demonstrated. Neoelastogenesis showed significant increases at 6 months and 1 year. It is hypothesized that the additive effects of initial collagen shrinkage and the long-term effect of neocollagenesis and neoelastogenesis are the significant factors contributing to the long-lasting and excellent results of CO2 laser skin resurfacing.     

Double-mixing kinetic studies of the reactions of methyl isocyanide and CO with diliganded intermediates of hemoglobin: alpha 2CO beta 2 and alpha 2 beta 2CO

Kinetics of the reactions of CO and methyl isocyanide with two diliganded intermediates of hemoglobin, alpha 2CO beta 2 and alpha 2 beta 2CO, have been studied by double-mixing and microperoxidase methods. The valency hybrids were prepared by high-pressure liquid chromatography. The reaction time courses of ligand combination and dissociation with both of the ligands were biphasic, and in CO combination reaction the zero-time amplitudes of the two phases were independent of the protein concentration. In the presence of 2 M urea the reaction time course was clearly dependent on protein concentration, as the zero-time amplitude of the fast phase increased at lower protein concentrations. These two observations indicate that little dissociation of tetramers into dimers occurs in the absence of urea. Consistent with this, the kinetic data for the reactions of CO best fit a reaction model consisting of two tetrameric species not in rapid equilibrium with each other. Various considerations, however, suggest that the reaction model is more appropriately described as 2D in equilibrium R in equilibrium T. The reaction of triliganded species (Hb4(CO)2Me1) with methyl isocyanide was monophasic, and the reaction model suggested a fast T in equilibrium R structural change after the binding of the third ligand. Although the precise structural nature of the two species remains undefined, it is concluded that the biphasicity in the reactions of the two hybrids is characteristic of the diliganded species only and is independent of the nature of the ligand.     

Benefits of the CO2 laser in oral hemangioma excision

Twenty-one patients with small localized oral cavity hemangiomas of the lips, tongue, and buccal mucosa are reported in this series. Although the lesions were not massive or high-flow/high-pressure vascular tumors, the simultaneous cutting and coagulation capabilities of the CO2 laser were demonstrated, rendering such excisional surgery more precisely and easily accomplished with a great deal less bleeding and a marked reduction in postoperative pain and edema. Many of the patients in this series were done as outpatients under local anesthesia. Results were acceptable and complications were minimal. Thus this laser is recommended both for the patient care and comfort aspects and the ability to render oral cavity hemangioma excisional surgery much more safely and easily done with a significant decrease in hospital utilization and overall medical expenses.     

CO2激光治疗重度宫颈糜烂

作者用ＣＯ２激光治疗了重度宫颈糜烂２９２例,单纯型２４例,颗粒型１６６例,乳突型１０２例。结果：２８２例获治愈（９６．２％）,其中２４９例（８５．２％）一次性痊愈,１０例好转,无一例无效。说明该疗法简便,迅速,无明显副作用,疗效显著,是治疗重度宫颈糜烂的有效方法。     

CO2激光治疗26例甲真菌病临床观察

目的探讨CO2激光治疗甲真菌病的临床疗效。方法对44例甲真菌病病例共92只病甲采用每2周1次CO2激光烧灼打孔,疗程共24周。结果治疗有效率90%。结论CO2激光治疗甲真菌病安全、有效、副作用小。     

RF discharge in CO2 laser mixtures at moderate pressures

The voltage-power characteristics and spatial structure of an RF discharge in the mixtures of CO₂ and N₂ molecular gases with He at total pressures of tens of torr are studied. One-dimensional numerical simulations of an RF discharge are carried out within two approaches: (i) the distribution function and the related kinetic coefficients are assumed to be functions of the local reduced field, and (ii) the kinetic coefficients are functions of the electron mean energy, which is calculated with allowance for both electron heat conduction and diffusion. The latter approach is shown to better describe the existing experimental dependence of the discharge voltage and the phase shift between the discharge current and voltage on the driving power.     

Microsurgical anastomosis of rat carotid arteries with the CO2 laser

In order to further evaluate the role of lasers in microvascular tissue closure, we modified an existing CO2 surgical laser (Xanar XA-20) by adding a partially reflecting mirror to attenuate the beam. This allowed the laser to operate at an output of approximately 100 mW, which was appropriate to achieve microvascular closures. In each of 43 rats, one carotid artery was transected and then anastomosed with standard suture technique with 10 to 12 simple interrupted sutures of size 10-0 Ethilon nylon suture (Ethicon, Inc.). The opposite carotid in each rat was anastomosed by the placement of three stay sutures followed by the application of laser irradiation to the tissue between the stay sutures at 90 to 100 mW, spot size of 0.2 mm, pulse duration 0.2 seconds, approximately 20 to 30 pulses per anastomosis. In vivo test periods were 1 hour, 1 day, 3 days, 7 days, 10 days, 14 days, 28 days, 91 days, and 180 days. All anastomoses were evaluated for patency, and selected samples were utilized for light microscopy, and mechanical testing (intraluminal pressure raised to 300 mmHg). It was determined that similar patency rates and slightly faster time to perform the same procedure could be achieved with the use of the low-powered CO2 laser. However, histologic evidence of significant medial damage raises concern about the long-term risk of a higher aneurysm rate. Vessel damage and the lack of simple intraoperative methods to verify the quality of the laser technique restrict these authors from advocating the clinical introduction of the procedure until further advances are made.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition by ethoxyzolamide of a photoacoustic uptake signal in leaves: Evidence for carbonic anhydrase catalyzed CO2-solubilisation

A photoacoustic pulse-modulation technique is applied for the study of a CO₂-stimulated gas uptake signal in leaves (Reising and Schreiber, Photosynthe Res 31: 227–238, 1992). It is shown that this uptake signal can be substantially suppressed by application of the carbonic anhydrase inhibitor, ethoxyzolamide, to leaf discs. This inhibitor does not affect the O₂-evolution signal in air or the chlorophyll fluorescence induction pattern at high CO₂, when non-saturating light intensities are used. On the basis of these findings it is concluded that at least a major part of the CO₂-stimulated photoacoustic uptake signal results from light-modulated CO₂-solubilisation catalysed by carbonic anhydrase. Modulated CO₂-solubilisation appears likely to be induced by light driven H⁺-translocation from the stroma into the thylakoid lumen. Comparison of the induction patterns of chlorophyll fluorescence quenching and the uptake signal suggests a correlation between membrane energisation and CO₂-uptake. The importance of O₂-dependent electron flow as a major cause of membrane energisation is discussed. It is proposed that in the absence of CO₂ the combination of Mehler- and ascorbate peroxidase reactions does not result in a photobaric signal, as O₂-uptake and O₂-evolution components cancel each other. Two main conclusions, which are of considerable importance for future practical applications of the photoacoustic method, are drawn from these findings: (1) When high CO₂ is applied to leaves, the photobaric uptake component may provide a unique means of monitoring the function of stromal carbonic anhydrase in vivo. (2) Brief flushing of the photoacoustic cell with air may prevent the occurrence of an uptake signal, thus allowing a straight-forward deconvolution into photothermal and O₂-evolution components.     

Conformational dynamics associated with photodissociation of CO from dehaloperoxidase studied using photoacoustic calorimetry

Herein, we present photoacoustic calorimetry and transient absorption studies of the dynamics and energetics associated with dissociation of a ligand from Fe(2+) dehaloperoxidase (DHP) from Amphitrite ornata. Our data show that CO photodissociation is associated with an endothermic (DeltaH = 8 +/- 3 kcal mol(-1)) volume expansion (DeltaV = 9.4 +/- 0.6 mL mol(-1)) that occurs within 50 ns upon photodissociation. No additional thermodynamics were detected on slower time scales (up to 10 micros), suggesting that the dissociated ligand rapidly escapes from the heme-binding pocket into the surrounding solvent. Similar volume and enthalpy changes were observed for CO photodissociation in the presence of the substrate, 2,4-dichlorophenol or 4-bromophenol, indicating that either the substrate does not bind in the protein distal cavity at ambient temperature or its presence does not impact the thermodynamic profile associated with ligand dissociation. We attribute a fast ligand exchange between the protein active site and the surrounding solvent to the high flexibility of the distal histidine residue, His55, that provides a direct pathway between the heme-binding pocket and the protein exterior. The dynamics and energetics of conformational changes observed for dissociation of a ligand from DHP differ significantly from those measured previously for photodissociation of CO from the structural homologue myoglobin, suggesting that structural dynamics in DHP are fine-tuned to enhance the peroxidase function of this protein.     

Clinical experience with the CO2 laser during carpal tunnel decompression

Scar tissue formation along the cut edges of the transverse carpal ligament has been found to be among the primary causes for persistent median nerve compression following carpal tunnel release with the steel scalpel. Since laser surgery has been shown to be effective in reducing incisional inflammatory reactions, hypertrophic scarring, and postoperative pain and edema, in achieving better hemostasis, the application of the carbon dioxide laser may be a more efficient surgical tool than the steel scalpel for carpal tunnel release. In 46 cases of carpal tunnel syndrome, the carbon dioxide laser was utilized to vaporize the transverse carpal ligament and seal its edges. The patients were then reevaluated at 1 week, 2 weeks, 6 months, 1 year, and 2 years. No intraoperative complications were encountered. Patients reported minimal postoperative pain, rapid return of sensibility, decreased paresthesia, and increased motor function. After 2 years, there have been no recurrent symptoms of median nerve compression in these patients.