Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees.

Because lignin limits the use of wood for fiber, chemical, and energy production, strategies for its downregulation are of considerable interest. We have produced transgenic aspen (Populus tremuloides Michx.) trees in which expression of a lignin biosynthetic pathway gene Pt4CL1 encoding 4-coumarate:coenzyme A ligase (4CL) has been downregulated by antisense inhibition. Trees with suppressed Pt4CL1 expression exhibited up to a 45% reduction of lignin, but this was compensated for by a 15% increase in cellulose. As a result, the total lignin-cellulose mass remained essentially unchanged. Leaf, root, and stem growth were substantially enhanced, and structural integrity was maintained both at the cellular and whole-plant levels in the transgenic lines. Our results indicate that lignin and cellulose deposition could be regulated in a compensatory fashion, which may contribute to metabolic flexibility and a growth advantage to sustain the long-term structural integrity of woody perennials.

pH in physiological salt solutions: direct measurements.

Calculations of pH in modified Krebs solutions by inserting PCO2 and total-CO2 in the Henderson-Hasselbalch (H.-H.) equation are obvious as the equation originally served for this purpose. An exact calculation of the relation between pH and PCO2 is complicated as the concentration of bicarbonate, the dissociation constant and the solubility of CO2 change. Furthermore, the dissociation constant in the H.-H. equation is constant only if activities are used in the equation instead of stoichiometric concentrations. We therefore investigated the influence of different carbon dioxide tensions and bicarbonate concentrations on directly measured pH of organ baths aerated with mass-spectrometric analyzed O2-CO2 gases. For reference precision buffers were used. The measured pH values differed distinctly from calculated pH values in the acidic and alkaline parts of the pH interval investigated (6.57-8.15). Measurements of actual pH with proper calibration standards therefore seem mandatory.

Carbon dioxide tensions in physiological salt solutions: direct measurements.

Carbon dioxide tensions were measured directly in organ baths and a tonometer aerated in parallel with 6 different gas mixtures of O2 and CO2, 3 gas flows, 3 equilibration periods, and 3 bicarbonate concentrations. The measured partial pressure of carbon dioxide differed systematically from expected values, probably due to errors in the carbon dioxide measurement system. In conclusion, carbon dioxide equilibrates with the bubbling gas in the baths as well as in the tonometer to an almost perfect equilibration.

Carbon dioxide distribution in Mapleson A and D systems: an experimental study.

The distribution of CO2 in the Mapleson A and D rebreathing systems was investigated experimentally during controlled ventilation and with the expiratory valve closed during inspiration. Maximal and minimal levels of CO2-concentration obtained from capnograms along the tubing were used to construct "gas profiles". For both systems, high tidal volumes and low fresh gas flows resulted in a high degree of gas separation with a pool of alveolar gas near the expiratory valve, and longitudinal gas mixing was minimal. In this manner fresh gas loss was prevented and fresh gas utilization optimized. The end of the tubing nearest the patient was found to act as a reservoir for alveolar gas in the Mapleson A system and fresh gas in the Mapleson D system. Fresh gas utilization in the Mapleson D system was somewhat less efficient than in the Mapleson A system due to the fresh gas admixture to exhaled alveolar gas in the patient-near end of the tubing during expiration. The replacement of the usual expiratory valve of the Mapleson A system by a valve which is closed during inspiration makes the A system an alternative to the D system for controlled ventilation.

Calcium, magnesium and phosphate during and after hypothermic cardiopulmonary bypass without temperature correction of acid base status.

The plasma concentration variations of calcium, magnesium and phosphate were studied in ten patients during and after hypothermic cardiopulmonary bypass (CPB) without temperature correction of acid base status. During the study, pH remained stable, but all the other studied components varied significantly (P less than 0.001). At the start of CPB, the mean ionized calcium concentration increased 25%, and magnesium and phosphate decreased 29% and 40%, respectively, from their control values. At the end of blood cooling, ionized calcium was still 11% above its initial value, magnesium 50% above, and phosphate 39% below. Before weaning from CPB, ionized calcium remained 10% above its initial level, magnesium 41% above, and phosphate 26% below. After CPB, the different divalent ions returned to their initial levels within 1 h for ionized calcium, 6 h for phosphate and 9 h for magnesium. One day post-CPB, ionized calcium was at its start level, magnesium 13% lower, and phosphate 36% higher. During cardiac surgery, the acid base regulation without temperature correction (so-called "alpha stat mode") avoided the appearance of carbon dioxide acidosis. There were widespread disturbances of the divalent ions concentrations, due principally to the different fluids used during CPB, pump priming fluids and cardioplegic solution.

Acid-base interactions with noradrenaline-induced contractile response of the rabbit isolated aorta.

The effect of acidosis and alkalosis on vascular smooth muscle contractions evoked by noradrenaline was studied. Helical strips of rabbit aorta were mounted for isometric tension recording. Acidosis (pH 7.24-6.51) was obtained by either increasing the PCO2 (hypercapnic) and/or lowering the HCO3-concentration (hypobicarbonatic). Acidosis shifted the noradrenaline concentration-response curve to the right in a competitive manner. The maximal developed tension was unchanged at pH 7.24-6.90 and decreased by 30% at pH 6.51. Alkalosis (pH 7.61-8.04) did not alter noradrenaline-evoked contractions. The results suggest that hydrogen ions during acidosis (pH less than 7.40) but not during alkalosis (pH greater than 7.40) exert alpha-adrenoceptor blocking properties.

Carbon dioxide tensions in manually ventilated, prone patients.

The distribution of arterial carbon dioxide tensions (PaCO2) in 288 anaesthetized, healthy patients in the prone position was investigated during non-monitored manual ventilation. Four equal groups of 72 patients were compared employing a conventional anaesthetic system with and without CO2-absorption and a modified Mapleson D rebreathing system using high and low fresh gas flows. No fundamental difference between the Mapleson D system and the circle system without CO2-absorption could be demonstrated. With the Mapleson D system a high fresh gas flow resulted in a loss of rebreathing characteristics, the scatter of PaCO2-values then approaching that of a conventional circle system with CO2-absorption. The results demonstrate that during manual ventilation a CO2-absorption results in unpredictable levels of PaCO2 with unacceptably wide ranges. On the other hand, prevention of hypocapnia could be obtained with the rebreathing systems using a low fresh gas flow. Hypercapnia was modest and similar in all groups, PaCO2 never exceeding 7.3 kPa. In terms of PaCO2-levels it seems, compared to recent literature, of no importance whether the patient is prone or supine or whether or not ventilation is monitored, performed by hand or by means of anaesthetic ventilators. Accurate levels of PaCO2 can probably only be obtained by frequent analyses of PaCO2, or monitoring of the end-tidal CO2 concentration.

Efficiency of two variable performance techniques of oxygen therapy in relieving postoperative hypoxaemia.

The efficiency of two patient-dependent, variable performance techniques of oxygen therapy in relieving hypoxaemia after upper abdominal surgery was compared. A high-flow system delivered a humidified mixture of oxygen 2 litre min-1 and air 13 litre min-1 through a cannula inserted into the anterior nares. The low-flow system delivered 2 litre min-1 of dry oxygen into the nasopharynx through a catheter. Thirteen otherwise healthy patients received either high-flow oxygen therapy for 30 min followed by low-flow oxygen therapy for a further 30 min after operation or the same therapy in reverse order. With the patients breathing room air, arterial hypoxaemia could be demonstrated with Pao2 inversely related to age. The increase of Pao2 during either oxygen treatment was significantly greater with the low flow system.

Cross-infection from contaminated anaesthetic equipment. A real hazard?

A definite relationship between the use of contaminated anaesthetic equipment and subsequent pulmonary infection remains to be established. There is however indirect and circumstantial evidence suggesting that cross-infection may occur, and further an increased susceptibility of surgical patients to pulmonary infections has been demonstrated. Decontamination should be recommended before the equipment is re-used. Pasteurisation may prove sufficient and this can be obtained employing a specially designed dish-washing machine.

Accuracy of new gas flowmeters.

The accuracy of five new oxygen and nitrous oxide flowmeter units was investigated using the bubble meter method. The results were compared with those previously found in flowmeters withdrawn from clinical use. New oxygen flowmeters demonstrated less inaccuracies than old flowmeters. No differences were found between the nitrous oxide flowmeters. Unacceptable errors were demonstrated at oxygen presettings less than 1 litre min-1, suggesting the grading within this range to be of no value. Marked deviations which exceeded the limits stated by the manufacturer could still be shown at presettings greater than 1 litre min-1. If an exact FIO2 is required, continuous monitoring with a high accuracy oxygen analyser is essential, even using new flowmeters.

Arterial carbon dioxide tensions during anaesthesia with manual ventilation. A descriptive study of the effects of various non-polluting circuits.

In 660 supine, intubated and anaesthetized, healthy patients scheduled for various elective surgical procedures, the distribution of arterial carbon dioxide tension (PaCO2) was investigated during manual non-monitored ventilation. The study comprised six equal groups: group 1: ventilation with a circle circuit absorber system; group 2: ventilation with the Hafnia A circuit using a total fresh gas flow (FGF) of 100 ml . kg-1 . min-1; groups 3-6: ventilation with a Hafnia D circuit with fresh gas flows of 100, 80, 70 and 60 ml . kg-1 . min-1, respectively. The mean PaCO2's of the first three groups were situated in the lower range of normocapnia (the observations in the first group having the greatest total range), whereas the rebreathing (Hafnia A and D) circuits resulted in a clustering of observed data. Employing the rebreathing circuits, protection against hypocapnia can be achieved by lowering the fresh gas flow. The most satisfying result was obtained with the Hafnia D circuit with a fresh gas flow of 70 ml . kg-1 . min-1 resulting in normocapnia with a modest and limited spread towards hypo- and hypercapnia. FGF in excess of this level must be considered as wasted. The study indicates that corrections of fresh gas flows for age are superfluous. Use of relaxants and type of surgery had no influence on the observations.

Method for continuous measurement of carbon dioxide output during anesthesia. An assessment.

Employing the Mapleson D circuit, a modified closed-circuit flow-through technique for the continuous measurement of carbon dioxide production (VCO2) was tested for accuracy and precision in a lung model. The recovery of carbon dioxide production was found to be between 90 and 110%, the maximized errors for a single estimate of carbon dioxide production were between +/- 4 and +/- 28%, with the highest errors at high gas flows and low carbon dioxide inputs. Accepting arbitrarily chosen limits of maximized errors of +/- 10%, it could be shown that the system did not work acceptably when the mean carbon dioxide concentration was below 1.5 vol.% within the fresh gas flow rates (2.2--7.7 1 min-1) and the range of minute ventilation (4--10 1 min-1) employed. The half-life of carbon dioxide washout varied between 41 and 138 s, thus limiting the suitability of the system for detecting changes in carbon dioxide output. The method may be used as an approximate monitor of VCO2 in anaesthetized patients, but cannot be regarded as sufficient for research purposes.

Accuracy of gas flowmeters determined by the bubble meter method.

THe accuracy of 15 oxygen and nitrous oxide flowmeter units in daily use was investigated using the bubble meter method. At preset oxygen flow rates of less than 1 litre min-1 unacceptable errors were found. At flow settings greater than 1 litre min-1 the deviations varied within closer limits, but the actural flows were inaccurate irrespective of the presettings and of the gas delivered, and independent of the indicator being adjusted to be opposite or between the graduation marks on the flowmeter.

[A new safe system for the prevention of peroperative hypothermia (author's transl)]. / Ein neues, sicheres System zur Verhinderung peroperativer Hypothermie.

On the basis of our experiences and data from the literature concerning thermal injury by warming blankets in anaesthetized patients, a new and safe system for the maintenance of body temperature during the operation is described. The following advantages are emphasized: 1. Adjustable double-thermostat with audible alarm. 2. Easy-to-read control thermometer of water bath. 3. Thermal blanket water temperature cannot rise above 43 degrees C.

Bacterial contamination of anaesthetic gases.

The bacterial content of oxygen and nitrous oxide immediately before and after passing through clean and used breathing systems (circuits) was measured using a specially constructed agar chamber (Bourdillon's slit sampler). The content per litre of oxygen from the outlet of the anaesthetic machine was 4.0 X 10-2, and 2.9 X 10-2 for nitrous oxide, corresponding to 3.5 X 10-2 for a 50% mixture of the gases. After passing through cleaned circuits, the bacterial pollution of the gas mixture had increased by 30%, but more than elevenfold after passing through used circuits. The content from cleaned circuits was less than that measured previously in the air of hospital wards and operating theatres, whereas gases from used circuits were polluted to approximately the same extent. It is concluded that used circuits may increase the risk of cross-infection. The cleaning method employed by us (dish-washer--hot airy drying) appeared to be acceptable.