Pulsed and scanned carbon dioxide laser resurfacing 2 years after treatment: comparison by means of scanning electron microscopy

Studies have reported short-term and long-term (1-year) findings for laser skin resurfacing. Two of the most popular systems used for this procedure, the continuous-wave Sharplan 40C SilkTouch system and the pulsed Coherent 5000C UltraPulse system with a computer pattern generator, were previously compared for a range of follow-up times up to 1 year, using light microscopy and transmission electron microscopy. This study analyzed the 2-year morphological differences using scanning electron microscopy. Tissue samples were obtained from 10 patients (age range, 50 to 72 years; skin types II and III) who had undergone laser resurfacing 2 years previously. One half of the face of each patient had been treated with the continuous-wave system and the other half with the pulsed system. The samples were subjected to scanning electron microscopy. On the continuous-wave-treated side, significantly better dermal collagen organization was observed at 2 years, with plump-appearing fibers that were closely knit to form a compact structure. On the side treated with the pulsed system, the collagen fibers in the papillary dermis were more loosely arranged and appeared drier. In both the continuous-wave-treated and pulsed-treated areas, the epidermis appeared healthy and exhibited some signs of age-related deterioration, with slightly flatter plaques and somewhat more flaking keratin on the pulsed-treated side. Probably because of the greater degree of residual thermal damage associated with the continuous-wave system, at 2 years after treatment there was more prolific synthesis and better orientation of collagen fibers, which were maintained for longer times, compared with the pulsed-treated specimens.     

Treatment of burn scar depigmentation by carbon dioxide laser-assisted dermabrasion and thin skin grafting

Permanent depigmentation occasionally develops after deep partial-thickness and full-thickness burn injuries, which heal by secondary intention. This problem can be solved by dermabrasion and thin split-thickness skin grafting. However, mechanical dermabrasion is a bloody procedure that risks exposing medical professionals to infectious diseases transmitted by blood products, and it is difficult to assess the extent of tissue ablation. In this study, dermabrasion of depigmented burn scar area was performed by using flash-scanned carbon dioxide laser treatment, followed by thin split-thickness skin grafting. This method was applied to 13 patients on whom burn scar depigmentation sites were located as follows: two in the facial area, four on the trunk, and seven on the extremities. Skin graft take was excellent in all patients except for one. The follow-up period for these patients ranged from 1 to 12 months, with an average of 8 months. Repigmentation appeared soon after grafting, and no depigmentation occurred again in the treated areas. In conclusion, depigmented burn scar areas can be dermabraded in a short time; depth of tissue ablation can be well controlled; and a bloodless and smooth raw surface can be created by using a flash-scanned carbon dioxide laser. These raw surfaces sustain thin skin grafts well.     

The role of carbon dioxide in free radical reactions of the organism

Carbon dioxide interacts both with reactive nitrogen species and reactive oxygen species. In the presence of superoxide, NO reacts to form peroxynitrite that reacts with CO2 to give nitrosoperoxycarbonate. This compound rearranges to nitrocarbonate which is prone to further reactions. In an aqueous environment, the most probable reaction is hydrolysis producing carbonate and nitrate. Thus the net effect of CO2 is scavenging of peroxynitrite and prevention of nitration and oxidative damage. However, in a nonpolar environment of membranes, nitrocarbonate undergoes other reactions leading to nitration of proteins and oxidative damage. When NO reacts with oxygen in the absence of superoxide, a nitrating species N2O3 is formed. CO2 interacts with N2O3 to produce a nitrosyl compound that, under physiological pH, is hydrolyzed to nitrous and carbonic acid. In this way, CO2 also prevents nitration reactions. CO2 protects superoxide dismutase against oxidative damage induced by hydrogen peroxide. However, in this reaction carbonate radicals are formed which can propagate the oxidative damage. It was found that hypercapnia in vivo protects against the damaging effects of ischemia or hypoxia. Several mechanisms have been suggested to explain the protective role of CO2 in vivo. The most significant appears to be stabilization of the iron-transferrin complex which prevents the involvement of iron ions in the initiation of free radical reactions.     

A revision of the human XIST gene organization and structural comparison with mouse Xist

The XIST gene plays an essential role in X Chromosome (Chr) inactivation during the early development of female humans. It is believed that the XIST gene, not encoding a protein, functions as an RNA. The XIST cDNA is unusually long, as its full length is reported to be 16.5 kilobase pairs (kb). Here, comparison of sequences from the genomic interval downstream to the 3′ end of the human XIST gene against the human EST database brought to light a number of human EST sequences that are mapped to the region. Furthermore, PCR amplification of human cDNA libraries and RNA fluorescence in situ hybridization (RNA-FISH) demonstrate that the human XIST gene has additional 2.8 kb downstream sequences which have not been documented as a part of the gene. These data show that the full-length XIST cDNA is, in fact, 19.3 kb, not 16.5 kb as previously reported. The newly defined region contains an intron that may be alternatively spliced and seven polyadenylation signal sequences. Sequences in the newly defined region show overall sequence similarity with the 3′ terminal region of mouse Xist, and three subregions exhibit quite high sequence conservation. Interestingly, the new intron spans the first two subregions that are absent in one of the two isoforms of mouse Xist. Taken together, we revise the structure of human XIST cDNA and compare cDNA structures between human and mouse XIST/Xist. Received: 3 August 1999 / Accepted: 15 November 1999     

A comparison of field methods for measuring soil carbon dioxide evolution: Experiments and simulation

Three widely used methods for measuring total soil CO₂ evolution are evaluated, including the dynamic CO₂ absorption method, the static CO₂ absorption method and the closed chamber method. The study covers laboratory experiments. numerical experiments with a simulation model and field measurements. The results are used to perform an error analysis. The aim of this error analysis is to indicate the impact of each method on the CO₂ dynamics during the measurement, and to select the most suitable method for frequent field usage.Laboratory experiments and simulation results show that the dynamic CO₂ absorption method has the potential to absorb all CO₂ evolving at the soil surface. The results also prove that the method has only a minor impact on the CO₂ concentration-depth gradient and the CO₂ efflux. The static CO₂ absorption method underestimates the soil CO₂ evolution, because the absorption velocity is too low, due to slow diffusion processes. Measurements with the closed-chamber method are based on an increasing concentration with time under a closed cover. However, the accumulation of gas alters the concentration gradient in the soil profile and thus causes a rapidly decreasing efflux during the measurement. A commonly used mathematical procedure, which corrects for the altered concentration gradient, does not yield the exact surface efflux, because the effect of increasing storage in the soil profile is not incorporated. Field measurements of CO₂ evolution, using the closed-chamber method and the dynamic CO₂ absorption method confirm the trends that have been predicted by the simulation model. The results of this study indicate that the dynamic CO₂ absorption method is accurate. As it is cheap and simple, it is suitable for the study of temporal and spatial dynamics of CO₂ evolution from the soil.     

Assessing the effect of elevated carbon dioxide on soil carbon: a comparison of four meta-analyses

Soil is the largest reservoir of organic carbon (C) in the terrestrial biosphere and soil C has a relatively long mean residence time. Rising atmospheric carbon dioxide (CO₂) concentrations generally increase plant growth and C input to soil, suggesting that soil might help mitigate atmospheric CO₂ rise and global warming. But to what extent mitigation will occur is unclear. The large size of the soil C pool not only makes it a potential buffer against rising atmospheric CO₂, but also makes it difficult to measure changes amid the existing background. Meta‐analysis is one tool that can overcome the limited power of single studies. Four recent meta‐analyses addressed this issue but reached somewhat different conclusions about the effect of elevated CO₂ on soil C accumulation, especially regarding the role of nitrogen (N) inputs. Here, we assess the extent of differences between these conclusions and propose a new analysis of the data. The four meta‐analyses included different studies, derived different effect size estimates from common studies, used different weighting functions and metrics of effect size, and used different approaches to address nonindependence of effect sizes. Although all factors influenced the mean effect size estimates and subsequent inferences, the approach to independence had the largest influence. We recommend that meta‐analysts critically assess and report choices about effect size metrics and weighting functions, and criteria for study selection and independence. Such decisions need to be justified carefully because they affect the basis for inference. Our new analysis, with a combined data set, confirms that the effect of elevated CO₂ on net soil C accumulation increases with the addition of N fertilizers. Although the effect at low N inputs was not significant, statistical power to detect biogeochemically important effect sizes at low N is limited, even with meta‐analysis, suggesting the continued need for long‐term experiments.     

A comparison of carbon dioxide production and oxygen uptake in sediment cores from four south Swedish lakes

Carbon dioxide production and oxygen uptake were measured in undisturbed sediment cores taken during winter from four lakes of different trophic state. Respiration was measured at 5, 10, 15 and 20°C at high oxygen saturation (75–100%). The respiratory quotient, calculated from the mean values of carbon dioxide production and oxygen uptake at each temperature for each lake, was 0.83–0.96 with a mean value for the four lakes of 0.90. At very low oxygen saturations (<10%) carbon dioxide production was 21–42% of the production at 20°C and high oxygen saturations. The results indicate that under aerobic conditions, oxygen uptake and carbon dioxide production are closely-coupled processes in these lake sediments.     

End-tidal carbon dioxide tension reflects arterial carbon dioxide tension in the heat-stressed human with and without simulated hemorrhage

End-tidal carbon dioxide tension (Pet(CO(2))) is reduced during an orthostatic challenge, during heat stress, and during a combination of these two conditions. The importance of these changes is dependent on Pet(CO(2)) being an accurate surrogate for arterial carbon dioxide tension (Pa(CO(2))), the latter being the physiologically relevant variable. This study tested the hypothesis that Pet(CO(2)) provides an accurate assessment of Pa(CO(2)) during the aforementioned conditions. Comparisons between these measures were made: 1) after two levels of heat stress (N = 11); 2) during combined heat stress and simulated hemorrhage [via lower-body negative pressure (LBNP), N = 8]; and 3) during an end-tidal clamping protocol to attenuate heat stress-induced reductions in Pet(CO(2)) (N = 7). Pet(CO(2)) and Pa(CO(2)) decreased during heat stress (P < 0.001); however, there was no group difference between Pa(CO(2)) and Pet(CO(2)) (P = 0.36) nor was there a significant interaction between thermal condition and measurement technique (P = 0.06). To verify that this nonsignificant trend for the interaction was not due to a type II error, Pet(CO(2)) and Pa(CO(2)) at three distinct thermal conditions were also compared using paired t-tests, revealing no difference between Pa(CO(2)) and Pet(CO(2)) while normothermic (P = 0.14) and following a 1.0 ± 0.2°C (P = 0.21) and 1.4 ± 0.2°C (P = 0.28) increase in internal temperature. During LBNP while heat stressed, measures of Pet(CO(2)) and Pa(CO(2)) were similar (P = 0.61). Likewise, during the end-tidal carbon dioxide clamping protocol, the increases in Pet(CO(2)) (7.5 ± 2.8 mmHg) and Pa(CO(2)) (6.6 ± 3.4 mmHg) were similar (P = 0.31). These data indicate that mean Pet(CO(2)) reflects mean Pa(CO(2)) during the evaluated conditions.     

Reduction of oxygen by the electron transport chain of chloroplasts during assimilation of carbon dioxide

In photosynthetically competent chloroplasts from spinach the quantum requirements for oxygen evolution during CO₂ reduction were higher, by a factor often close to 1.5, than for oxygen evolution during reduction of phosphoglycerate. Mass spectrometer experiments performed under rate-limiting light indicated that an oxygen-reducing photoreaction was responsible for the consumption of extra quanta during carbon dioxide assimilation. Uptake of ¹⁸O₂ during reduction of CO₂ was considerably higher than could be accounted for by oxygen consumption during glycolate formation and by the Mehler reaction of broken chloroplasts which were present in the preparations of intact chloroplasts. The oxygen reducing reaction occurring during CO₂ assimilation resulted in the formation of H₂O₂. This was indicated by a large stimulation of CO₂ reduction by catalase, but not of phosphoglycerate reduction. Catalase could be replaced as a stimulant of photosynthesis by dithiothreitol or ascorbate, compounds known to react with superoxide radicals. There was no effect of dithiothreitol and ascorbate on phosphoglycerate reduction. A main effect of superoxide radicals and/or H₂O₂ was shown to be at the level of phosphoglycerate formation. Evidence for electron transport to oxygen was also obtained from ¹⁴CO₂ experiments. The oxidation of dihydroxyacetonephosphate during a dark period or after addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone in the light was studied. The results indicated a link between the chloroplast pyridine nucleotide system and oxygen. Oxygen reduction during photosynthesis under conditions where light is rate limiting is seen as important in supplying the ATP which is needed for CO₂ reduction but is not provided during electron transport to NADP. A mechanism is discussed which would permit proper distribution of electrons between CO₂ and oxygen during photosynthesis.     

Characteristics of free air carbon dioxide enrichment of a northern temperate mature forest

In 2017, the Birmingham Institute of Forest Research (BIFoR) began to conduct Free Air Carbon Dioxide Enrichment (FACE) within a mature broadleaf deciduous forest situated in the United Kingdom. BIFoR FACE employs large‐scale infrastructure, in the form of lattice towers, forming ‘arrays’ which encircle a forest plot of ~30 m diameter. BIFoR FACE consists of three treatment arrays to elevate local CO₂ concentrations (e[CO₂]) by +150 µmol/mol. In practice, acceptable operational enrichment (ambient [CO₂] + e[CO₂]) is ±20% of the set point 1‐min average target. There are a further three arrays that replicate the infrastructure and deliver ambient air as paired controls for the treatment arrays. For the first growing season with e[CO₂] (April to November 2017), [CO₂] measurements in treatment and control arrays show that the target concentration was successfully delivered, that is: +147 ± 21 µmol/mol (mean ± SD) or 98 ± 14% of set point enrichment target. e[CO₂] treatment was accomplished for 97.7% of the scheduled operation time, with the remaining time lost due to engineering faults (0.6% of the time), CO₂ supply issues (0.6%) or adverse weather conditions (1.1%). CO₂ demand in the facility was driven predominantly by wind speed and the formation of the deciduous canopy. Deviations greater than 10% from the ambient baseline CO₂ occurred <1% of the time in control arrays. Incidences of cross‐contamination >80 µmol/mol (i.e. >53% of the treatment increment) into control arrays accounted for <0.1% of the enrichment period. The median [CO₂] values in reconstructed three‐dimensional [CO₂] fields show enrichment somewhat lower than the target but still well above ambient. The data presented here provide confidence in the facility setup and can be used to guide future next‐generation forest FACE facilities built into tall and complex forest stands.     

Histopathologic and morphometric evaluation of the skin abnormalities induced by erbium:YAG and carbon dioxide lasers in 10 patients

In the 1960s, carbon dioxide (CO2) laser therapy started to be applied to eliminate wrinkles, actinic scars, and acne because of its capacity of induce intracellular water vaporization. However, recent studies have shown the efficacy of the erbium laser in removing delicate and moderate scars. Furthermore, the postoperative lesions induced by the erbium laser seem to resolve faster and with less erythematous pattern compared with lesions induced by the CO2 laser. The purpose of this study was to determine the immediate pathologic alterations caused by single applications of CO2 and erbium lasers and their association in human skin shreds.Ten white female patients aged 30 to 63 years underwent rhytidectomy, and their respective shreds, which were prepared for excision, were tattooed with the CO2 laser, the erbium laser, or a combination of both in random order and number of applications, before final removal. This project was approved by the local ethical committee. After surgical removal, these tattooed shreds were fixed in 10% buffered formalin and submitted to histopathologic analysis. Morphometric studies demonstrated the normal skin thickness and thickness of the laser-treated area, and their subtraction resulted in the ablation damage values. Residual thermal damage corresponded to the thickness of the affected skin from the most superficial layer of tissue in the laser-treated area down to the deepest dermal area with basophilic degeneration of collagen fibers.Our results showed that two CO2 applications resulted in greater ablation and residual thermal damage when compared with only one CO2 application. The same was true in comparisons of one and two applications of the erbium laser. Both results were statistically significant (p < 0.05). When one isolated erbium and one isolated CO2 application were compared, ablation damage was greater in the former group, although with no statistical significance. One CO2 plus one erbium application compared with one isolated CO2 application showed similar ablation damage but greater residual thermal damage in the latter group (p < 0.05). These observations might contribute to our understanding of the lesions caused in the human skin by erbium and CO2 lasers and eventually help determine the ideal laser combination for the appropriate surgical treatment.