Bacterial carbon sources in coastal sediments: a cross-system analysis based on stable isotope data of biomarkers

International audienceCoastal ecosystems are typically highly productive, and the sediments in these systems receive organic matter from a variety of local and imported sources. To assess if general patterns are present in the origin of carbon sources for sedimentary bacteria and their relation to the origin of the sediment organic carbon pool, we compiled both literature and new data on ?13C of bacterial biomarkers (the phospholipid derived fatty acids i+a15:0), along with ?13C data on sediment organic carbon (?13CTOC) and macrophyte biomass from a variety of typical near-coastal systems. These systems included mangroves, salt marshes (both C3 and C4-dominated sites), seagrass beds, and macroalgae-based systems, as well as unvegetated sediments. First, our ?13Ci+a15:0 data showed large variability over the entire range of ?13CTOC, indicating that in many settings, bacteria may depend on carbon derived from various origins. Secondly, systems where local macrophyte production is the major supplier of organic carbon for in situ decomposition are generally limited to organic carbon-rich, peaty sites (TOC>10 wt%), which are likely to make up only a small part of the global area of vegetated coastal systems. These carbon-rich sediments also provided a field based estimate of isotopic fractionation between bacterial carbon sources and biomarkers (-3.7±2.1), which is similar to the expected value of about -3 associated with the biosynthesis of fatty acids. Thirdly, only in systems with low TOC (below ~1 wt%), we consistently found that bacteria were selectively utilizing an isotopically enriched carbon source, which may be root exudates but more likely is derived from microphytobenthos. In other systems with between ~1 and 10 wt% TOC, bacteria appear to show on average little selectivity and ?13Ci+a15:0 data generally follow the ?13CTOC, even in systems where the TOC is a mixture of algal and macrophyte sources that generally are believed to have a very different degradability

Carbon sources supporting benthic mineralization in mangrove and adjacent seagrass sediments (Gazi Bay, Kenya)

The origin of carbon substrates used by in situ sedimentary bacterial communities was investigated in an intertidal mangrove ecosystem and in adjacent seagrass beds in Gazi bay (Kenya) by d13C analysis of bacteria-specific PLFA (phospholipid fatty acids) and bulk organic carbon. Export of mangrove-derived organic matter to the adjacent seagrass-covered bay was evident from sedimentary total organic carbon (TOC) and d13CTOC data. PLFA d13C data indicate that the substrate used by bacterial communities varied strongly and that exported mangrove carbon was a significant source for bacteria in the adjacent seagrass beds. Within the intertidal mangrove forest, bacterial PLFA at the surface layer (0-1cm) typically showed more enriched d13C values than deeper (up to 10cm) sediment layers, suggesting a contribution from microphytobenthos and/or inwelled seagrass material. Under the simplifying assumption that seagrasses and mangroves are the dominant potential end-members, the estimated contribution of mangrove-derived carbon to benthic mineralization in the seagrass beds (16-74%) corresponds fairly well to the estimated contribution of mangrove C to the sedimentary organic matter pool (21-71%) across different seagrass sites. Based on the results of this study and a compilation of literature data, we suggest that trapping of allochtonous C is a common feature in seagrass beds and often represents a significant source of C for sediment bacteria - both in cases where seagrass C dominates the sediment TOC pool and in cases where external inputs are significant. Hence, it is likely that data on community respiration rates systematically overestimate the role of in situ mineralization as a fate of seagrass production

Wirkortäquilibration, Anschlagzeit, "time to peak effect": Bedeutung pharmakokinetisch-dynamischer Prinzipien für die tägliche klinische Praxis

Zusammenfassung: In der anästhesiologischen Pharmakologie spielen im Gegensatz zur internistischen Pharmakologie "Non-steady-state-Phänomene" eine herausragende Rolle. Ihr Verständnis ist eine Conditio sine qua non für die sichere und effiziente Applikation von anästhesierelevanten Medikamenten. Insbesondere die Verfügbarkeit der "optimierten target controlled infusion" ("optimized TCI"), von TCI-Systemen mit Ansteuerung des Effektkompartiments und dem relativ geringen Dosierungsspielraum bei "conscious sedation" unter erhaltener Spontanatmung verlangen von Anästhesisten, sich mit dem Konzept des Konzentrationsverlaufes am Wirkort auseinander zu setzen. Der Leser wird in die grundlegende Problematik eingeführt. Anwendungen der Prinzipien bei der Applikation von Muskelrelaxanzien, Propofol mit TCI-Systemen, volatilen Anästhetika und Opiaten werden erläuter

Bacterial carbon sources in coastal sediments: a review based on stable isotope data of biomarkers

International audienceCoastal ecosystems are typically highly productive, and recieve organic matter from a variety of local and imported sources. To assess if general patterns are present in the origin of carbon sources for sedimentary bacteria and their relation to the origin of the sediment organic carbon pool, we compiled both literature and new data on ?13C of bacterial biomarker PLFA (the phospholipid derived fatty acids i+a15:0) along with ?13C data on sediment organic carbon ?13CTOC and macrophyte biomass. Such data were collected from a variety of typical near-coastal systems, including mangroves, salt marshes (both C3 and C4-dominated sites), seagrass beds, and macroalgae-based systems, as well as unvegetated sediments. First, our ?13Ci+a15:0 data showed a large variability over the entire range of ?13CTOC, indicating that in many settings, bacteria may depend on carbon derived from various origins. Secondly, systems where local macrophyte production is the major supplier of organic carbon for in situ decomposition are generally limited to organic carbon-rich, peaty sites (TOC>10 wt%) which are likely to make up only a small part of the global area of vegetated coastal systems. These carbon-rich sediments also provided a field based estimate of isotopic fractionation in bacterial lipid synthesis (-3.7±2.1), that is similar to the expected value. Thirdly, only in systems with low TOC (below ~1 wt%), we consistently found that bacteria were on average selectively utilizing an isotopically enriched carbon source, which may be root exudates but more likely is derived from microphytobenthos. In other systems with between ~1 and 10 wt% TOC, bacteria appear to show on average little selectivity and ?13Ci+a15:0 data generally follow the ?13CTOC, even in systems where the TOC is a mixture of algal and macrophyte sources that generally are believed to have a very different degradability

Compartmental pharmacokinetics of nefopam during mild hypothermia

Background Nefopam is a non-opioid, non-steroidal, centrally acting analgesic which has an opioid-sparing effect. It also reduces the threshold (triggering core temperature) for shivering without causing sedation or respiratory depression. The drug is therefore useful as both an analgesic and to facilitate induction of therapeutic hypothermia. However, compartmental pharmacokinetics during hypothermia are lacking for nefopam. Methods We conducted a prospective, randomized, blinded study in eight volunteers. On two different occasions, one of two nefopam concentrations was administered and more than 30 arterial blood samples were gathered during 12 h. Plasma concentrations were determined using gas chromatography/mass spectrometry to investigate the pharmacokinetics of nefopam with non-linear mixed-effect modelling. Results A two-compartment mammillary model with moderate inter-individual variability and inter-occasional variability independent of covariates was found to best describe the data [mean (se): V1=24.13 (2.8) litre; V2=183.34 (13.5) litre; Clel=0.54 (0.07) litre min−1; Cldist=2.84 (0.42) litre min−1]. Conclusions The compartmental data set describing a two-compartment model was determined and could be implemented to drive automated pumps. Thus, work load could be distributed to a pump establishing and maintaining any desired plasma concentration deemed necessary for a treatment with therapeutical hypothermi

Ondansetron does not reduce the shivering threshold in healthy volunteers

Background. Ondansetron, a serotonin-3 receptor antagonist, reduces postoperative shivering. Drugs that reduce shivering usually impair central thermoregulatory control, and may thus be useful for preventing shivering during induction of therapeutic hypothermia. We determined, therefore, whether ondansetron reduces the major autonomic thermoregulatory response thresholds (triggering core temperatures) in humans. Methods. Control (placebo) and ondansetron infusions at the target plasma concentration of 250 ng ml−1 were studied in healthy volunteers on two different days. Each day, skin and core temperatures were increased to provoke sweating; then reduced to elicit peripheral vasoconstriction and shivering. We determined the core-temperature sweating, vasoconstriction and shivering thresholds after compensating for changes in mean-skin temperature. Data were analysed using t-tests and presented as means (sds); P<0.05 was taken as significant. Results. Ondensetron plasma concentrations were 278 (57), 234 (55) and 243 (58) ng ml−1 at the sweating, vasoconstriction and shivering thresholds, respectively; these corresponded to ≈50 mg of ondansetron which is approximately 10 times the dose used for postoperative nausea and vomiting. Ondansetron did not change the sweating (control 37.4 (0.4)°C, ondansetron 37.6 (0.3)°C, P=0.16), vasoconstriction (37.0 (0.5)°C vs 37.1 (0.3)°C; P=0.70), or shivering threshold (36.3 (0.5)°C vs 36.3 (0.6)°C; P=0.76). No sedation was observed on either study day. Conclusions. Ondansetron appears to have little potential for facilitating induction of therapeutic hypothermi

Cross-validation of two prognostic trauma scores in severely injured patients

Introduction Trauma scoring systems are important tools for outcome prediction and severity adjustment that informs trauma quality assessment and research. Discrimination and precision of such systems is tested in validation studies. The German TraumaRegister DGU® (TR-DGU) and the Trauma Audit and Research Network (TARN) from the UK agreed on a cross-validation study to validate their prediction scores (RISC II and PS14, respectively). Methods Severe trauma patients with an Injury Severity Score (ISS) ≥ 9 documented in 2015 and 2016 were selected in both registries (primary admissions only). The predictive scores from each registry were applied to the selected data sets. Observed and predicted mortality were compared to assess precision; area under the receiver operating characteristic curve was used for discrimination. Hosmer–Lemeshow statistic was calculated for calibration. A subgroup analysis including patients treated in intensive care unit (ICU) was also carried out. Results From TR-DGU, 40,638 patients were included (mortality 11.7%). The RISC II predicted mortality was 11.2%, while PS14 predicted 16.9% mortality. From TARN, 64,622 patients were included (mortality 9.7%). PS14 predicted 10.6% mortality, while RISC II predicted 17.7%. Despite the identical cutoff of ISS ≥ 9, patient groups from both registries showed considerable difference in need for intensive care (88% versus 18%). Subgroup analysis of patients treated on ICU showed nearly identical values for observed and predicted mortality using RISC II. Discussion Each score performed well within its respective registry, but when applied to the other registry a decrease in performance was observed. Part of this loss of performance could be explained by different development data sets: the RISC II is mainly based on patients treated in an ICU, while the PS14 includes cases mainly cared for outside ICU with more moderate injury severity. This is according to the respective inclusion criteria of the two registries. Conclusion External validations of prediction models between registries are needed, but may show that prediction models are not fully transferable to other health-care settings

Model‐based control of mechanical ventilation: design and clinical validation

Background. We developed a model‐based control system using end‐tidal carbon dioxide fraction (FE′CO2) to adjust a ventilator during clinical anaesthesia. Methods. We studied 16 ASA I-II patients (mean age 38 (range 20-59) yr; weight 67 (54-87) kg) during i.v. anaesthesia for elective surgery. After periods of normal ventilation the patients were either hyper‐ or hypoventilated to assess precision and dynamic behaviour of the control system. These data were compared with a previous group where a fuzzy‐logic controller had been used. Responses to different clinical events (invalid carbon dioxide measurement, limb tourniquet release, tube cuff leak, exhaustion of carbon dioxide absorbent, simulation of pulmonary embolism) were also noted. Results. The model‐based controller correctly maintained the setpoint. No significant difference was found for the static performance between the two controllers. The dynamic response of the model‐based controller was more rapid (P<0.05). The mean rise time after a setpoint increase of 1 vol% was 313 (sd 90) s and 142 (17) s for fuzzy‐logic and model‐based control, respectively, and after a 1 vol% decrease was 355 (127) s and 177 (36) s, respectively. The new model‐based controller had a consistent response to clinical artefacts. Conclusion. A model‐based FE′CO2 controller can be used in a clinical setting. It reacts appropriately to artefacts, and has a better dynamic response to setpoint changes than a previously described fuzzy‐logic controller. Br J Anaesth 2004; 92: 800-