Subpicosecond photon-echo spectroscopy on GaAs/AlAs short-period superlattices.
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Journal Article↗
Biomedical subjects
A Schulze
Publications and source records attributed to A Schulze.
Resistive and elastic unloading to assist spontaneous breathing does not change functional residual capacity.
Resistive and/or elastic unloading (a negative ventilator impedance, otherwise termed proportional assist ventilation) may be a useful means to assist spontaneous breathing. This only applies if the ventilator accurately provides pressure changes at the airway opening (P(ao)) proportional to the instantaneous flow and/or volume signal of spontaneous breathing and no significant phase lag. We designed such an infant ventilator, which controls the P(ao) by a negative feedback loop, and superimposes a second positive feedback circuit to generate unloading. To test this mode and the ventilator's accuracy in performing the synchronized pressure changes, we examined the functional residual capacity (FRC). We hypothesized that unloading by itself would not alter FRC because P(ao) should return to a preset baseline at end-expiration, and furthermore, that FRC could be actively altered by changing the baseline. Five anesthetized, tracheotomized, spontaneously breathing rabbits [respiratory system compliance 22.4 +/- 4.6 mL/kPa (mean +/- SEM)] were exposed to end-expiratory P(ao) levels of 0, 0.2, 0.4, and 0.6 kPa. At each of these levels a period of regular continuous positive airway pressure (CPAP) was alternated with a period of unloading (-40 mL/kPa ventilator compliance combined with -3 kPa/L/s ventilator resistance). FRC measured by a sulfur hexafluoride washout technique was virtually identical on CPAP and during unloading at equal end-expiratory P(ao) (difference, 1.41% +/- 0.95%), but FRC increased upon elevation of the end-expiratory P(ao) by 29.4 +/- 3.6 mL/kPa on CPAP and 30.2 +/- 3.2 at unloading (difference NS). We conclude that FRC is not destabilized by unloading, but that during unloading, as during CPAP, it depends on the end-expiratory P(ao).
Animals↗
The distribution of Acinetobacter species in clinical culture materials.
A total of 584 Acinetobacter strains were isolated from 420 patients from 12 different hospitals over a period of twelve months. Identification of strains at the species level was done according to the new taxonomy proposed by Bouvet and Grimont. A. baumannii strains were isolated most frequently (n = 426; 72.9%), followed by A. species 3 (n = 55), A. johnsonii (n = 29), and A. lwoffii (n = 21). Most isolates were recovered from respiratory tract specimens (n = 251; 42.9%), blood cultures (n = 116; 19.9%), wound swabs (n = 90; 15.4%), catheter tips (n = 75; 12.8%), and urinary tract specimens (n = 20; 3.4%). Strains belonging to species other than A. baumannii were isolated more frequently (n = 158; 27.1%) than previously reported, mainly from blood cultures, respiratory tract specimens, and central venous catheters.
Acinetobacter↗
Vascular catheter-related bloodstream infection due to Acinetobacter johnsonii (formerly Acinetobacter calcoaceticus var. lwoffi): report of 13 cases.
Although Acinetobacter baumannii (formerly Acinetobacter calcoaceticus var. anitratus) is known to be an important nosocomial pathogen, the clinical impact of other Acinetobacter species is not fully understood. Acinetobacter johnsonii (formerly a subset of A. calcoaceticus var. lwoffii) is considered a commensal on human skin, and infections due to this organism have not been reported previously. During a study period of 18 months, however, 13 patients at 6 hospitals developed catheter-related bloodstream infections caused by A. johnsonii. All patients had an indwelling peripheral or central venous catheter, and 11 patients were receiving a continuous intravenous infusion of heparin via the offending catheter. The clinical course of A. johnsonii bacteremia was usually benign. Infections responded readily to removal of the catheter, with or without administration of appropriate antibiotics. No insertion-site infections were documented. Thus A. johnsonii must be regarded as an organism that can cause rare cases of bloodstream infection in immunocompetent patients.
Acinetobacter Infections↗
Antimicrobial susceptibility of Acinetobacter species.
The in vitro activities of 16 antimicrobial agents against 180 Acinetobacter strains isolated from blood cultures (n = 162), central venous catheters (n = 11), and cerebrospinal fluids (n = 7) were studied. MICs were determined by a microtiter broth dilution method. Considerable differences in antimicrobial drug susceptibility against strains belonging to different species could be demonstrated. Acinetobacter baumannii isolates (n = 108) were generally more resistant than isolates identified as species other than A. baumannii. Multidrug resistance was common among A. baumannii isolates. Of the antimicrobial agents tested, imipenem was highly active against all A. baumannii isolates, and the other agents tested were only moderately active or inactive. Good activity against Acinetobacter species strain 3 was demonstrated for imipenem, amikacin, and ciprofloxacin. Most of the strains belonging to other species were susceptible to imipenem, ciprofloxacin, expanded-spectrum cephalosporins, amoxicillin-clavulanate, and the aminoglycosides but were resistant to ampicillin and older cephalosporins.
Acinetobacter↗
Assisted mechanical ventilation using elastic unloading: a study in cats with normal and injured lungs.
Elastic unloading [otherwise known as negative ventilator compliance (Cv) or proportional assist ventilation] is a new mode of assisted mechanical ventilation. The ventilator continuously measures the volume of spontaneous breathing (V) and adjusts the pressure at the airway opening in proportion to V. The quotient of pressure above the baseline end-expiratory level per unit of V (the gain of the assist) is constant at any point in time and can be preset. The apparatus used for this study can also generate elastic loading (positive Cv) by decreasing the pressure at the airway opening in proportion to V. This might be useful during the weaning process. This study compares measured values of total compliance of the combined lung-respirator system (Ctot) with values predicted according to theory, where 1/Ctot = 1/Cv + 1/Cl with Cl being the lung compliance. Respiratory mechanical data were derived from esophageal pressure and airflow in eight anesthetized, intubated, spontaneously breathing cats. Different Cv levels were set on the ventilator both before and after lung injury with xanthine oxidase. The difference (mean +/- SD) between the measured and predicted Ctot was 1.4 +/- 21.4% (healthy lungs) and -11.6 +/- 14.1% (injured lungs) during unloading and 2.5 +/- 7.5% (healthy lungs) during elastic loading. An elevation of Ctot decreased the expiratory airflow. Tidal volume increased slightly in healthy lungs and arterial PCO2 decreased. We conclude that the effects of Cv on the total compliance of the combined lung-respirator system can accurately be predicted.
Airway Resistance↗
Optical investigation of Bloch oscillations in a semiconductor superlattice.
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Journal Article↗
The mechanism by which an asymmetric distribution of plant growth hormone is attained.
Zea mays (sweet corn) seedlings attain an asymmetric distribution of the growth hormone indole-3-acetic acid (IAA) within 3 minutes following a gravity stimulus. Both free and esterified IAA (that is total IAA) accumulate to a greater extent in the lower half of the mesocotyl cortex of a horizontally placed seedling than in the upper half. Thus, changes in the ratio of free IAA to ester IAA cannot account for the asymmetric distribution. Our studies demonstrate there is no de novo synthesis of IAA in young seedlings. We conclude that asymmetric IAA distribution is attained by a gravity-induced, potential-regulated gating of the movement of IAA from kernel to shoot and from stele to cortex. As a working theory, which we call the Potential Gating Theory, we propose that perturbation of the plant's bioelectric field, induced by gravity, causes opening and closing of transport channels in the plasmodesmata connecting the vascular stele to the surrounding cortical tissues. This results in asymmetric growth hormone distribution which results in the asymmetric growth characteristics of the gravitropic response.
Biological Transport↗
Studies on the growth and indole-3-acetic acid and abscisic acid content of Zea mays seedlings grown in microgravity.
Measurements were made of the fresh weight, dry weight, dry weight-fresh weight ratio, free and conjugated indole-3-acetic acid, and free and conjugated abscisic acid in seedlings of Zea mays grown in darkness in microgravity and on earth. Imbibition of the dry kernels was 17 h prior to launch. Growth was for 5 d at ambient orbiter temperature and at a chronic accelerational force of the order of 3 x 10(-5) times earth gravity. Weights and hormone content of the microgravity seedlings were, with minor exceptions, not statistically different from seedlings grown in normal gravity. The tissues of the shuttle-grown plants appeared normal and the seedlings differed only in the lack of orientation of roots and shoots. These findings, based upon 5 d of growth in microgravity, cannot be extrapolated to growth in microgravity for weeks, months, and years, as might occur on a space station. Nonetheless, it is encouraging, for prospects of bioregeneration of the atmosphere and food production in a space station, that no pronounced differences in the parameters measured were apparent during the 5 d of plant seedling growth in microgravity.
Abscisic Acid↗
Comparison of the effect of GIP and GLP-1 (7-36amide) on insulin release from rat pancreatic islets.
After ingestion of glucose both GIP (gastric inhibitory polypeptide, glucose-dependent insulinotropic polypeptide) and GLP-1(7-36amide) (glucagon-like polypeptide-1, 7-36amide) may play a physiological role in augmenting insulin release. Their insulinotropic effect was compared in isolated rat islets after 24-h maintenance in tissue culture (11 mmol l-1 glucose). Ten islets per vial were then incubated in Krebs-Ringer-Hepes buffer for 30 min; insulin was measured radioimmunologically. Both hormones were always compared in the same experiment. At 16.7 mmol l-1 glucose both GIP and GLP-1(7-36amide) 2 x 10(-10) mol l-1 significantly increased insulin release; 10(-10) mol l-1 of either hormone had no significant effect. The response at 10(-9) and 10(-8) mol l-1 was similar for both; at 4 x 10(-10) mol l-1 GLP-1(7-36amide), however, was clearly more effective than GIP. At low glucose (2.8 or 5.0 mol l-1) no significant differences were found. A concentration of 10(-8) mol l-1 of both hormones was slightly stimulatory. At 8.3 mmol l-1 glucose, 10(-9) mol l-1 GLP-1(7-36amide) was 60% more effective than GIP (4.8 +/- 0.4 vs. 3.0 +/- 0.4, n = 13, P less than 0.005), the response to 10(-8) mol l-1 was similar. These data show comparable effects of high concentrations of GIP and GLP-1(7-36amide) on glucose-induced insulin release; at presumably physiological concentrations, however, GLP-1(7-36amide) was clearly more effective. The combination of the two peptides was not more than additive, suggesting that they act via the same final mechanism.
Animals↗
[Psychosomatic determinants of graphospasm].
As there is a variety of psychic and somatic variables in its genesis, the writer's cramp could be a syndrome of different subtypes. Therefore 62 former psychotherapy-patients with writer's cramp were examined according to a design of several dimensions in order to find out if there were any subtypes. The parts of the examination were exploration, structural interview, neurological examination, psychological examination of the personality, examination of some electrolytes in serum and radiograph of neck spinal column. Different multivariate statistical methods isolated two subtypes of patients with writer's cramp. The first group comprises patients with fine and/or big dysfunctions of motor activity, the symptoms are independent of psychic factors or of psychotherapy. The second group is characterized of a monosymtomatic writer's cramp, of a neurosis and of remissions of motoric symptoms following psychotherapy. The examination shows that fine and/or big dysfunctions of motor activity which often co-occur the writer's cramp are important criteria for differential diagnosis and indications.
Adolescent↗
High frequency oscillatory ventilation near resonant frequency of the respiratory system in rabbits with normal and surfactant depleted lungs.
It has been suggested that high frequency oscillatory ventilation (HFV) might improve gas exchange and reduce the risk of pressure-related side-effects compared to conventional mechanical ventilation (CMV). Whereas most studies have used arbitrarily set frequencies for HFV, we evaluated the effects of HFV near resonant frequency (fr). Anaesthetised and tracheotomized adult rabbits (n = 10; 3.8-5.1 kg body weight) were ventilated by alternating periods of CMV and HFV near fr. Negative ventilator resistance was used for complete resistive unloading of the respiratory system before each HFV period. This enabled a continuous swinging at resonance thus allowing measurement of fr and selection of exactly that frequency for the HFV run. Intra-animal CMV-HFV comparisons (n = 4) were performed on each animal: with healthy lungs at a mean airway pressure (MAP) of 0.5 kPa and after saline lung lavage at MAPs of less than 1.5 kPa; 1.5-1.8 kPa; greater than 1.8 kPa. Surfactant removal caused total respiratory system compliance (Ctot) to decrease from 44 +/- 5 to 22 +/- 3 ml/kPa. Corresponding fr was 244 +/- 48 and 360 +/- 30 min-1, respectively. HFV produced effective pulmonary gas exchange but did not improve arterial oxygenation in comparison with CMV at matched MAPs both before and after surfactant depletion. Volume amplitudes of oscillation necessary to achieve normocapnia were slightly above the natural plus equipment (2 ml) dead space. Maximum intra-alveolar pressure (Pmax) was calculated for the HFV runs from MAP, Ctot, and the volume amplitude of oscillation. Pmax during CMV was nearly twice that during HFV at equivalent PaCO2 and equivalent MAPs throughout the experiments.
Animals↗
Interaction of 5-azacytidine and dexamethasone in the control of hepatic tyrosine aminotransferase.
The nucleoside analog 5-azacytidine is able to induce tyrosine aminotransferase several-fold in the liver of suckling rats. Bilateral adrenalectomy abolishes this inducing effect. The drug also decreases significantly the concentration of cytosolic glucocorticoid receptor accompanied by an increase of the glucocorticoid receptor concentration in the nuclei. The antiglucocorticoid RU 486 which abolishes the induction of tyrosine aminotransferase and serine dehydratase by dexamethasone very effectively is not able to inhibit either the induction of tyrosine aminotransferase or the translocation of the glucocorticoid receptor into the nuclei by 5-azacytidine.
Animals↗
A ventilator generating a positive or negative internal compliance.
This paper describes technical details of a ventilator for altering the resistive and elastic load placed on respiratory muscles during spontaneous breathing in intubated infants. Positive or negative values for ventilator resistance and/or ventilator compliance can be chosen by superimposing the weighted sum of the flow and/or the volume signal over the input to a pressure controller within the pressure feedback control system of the ventilator. The aim of the study was to compare values of the ventilator's compliance (Cv), as measured with a ventilation mechanics calculator, with those Cv values set by the ventilator's Cv control knob on the front panel. Another aim was to compare measured values of total compliance of a combined ventilator-lung model system (Ct) with the values expected according to theory where 1/Ct = 1/Cv + 1/C1m (Eq. alpha; C1m is the lung model's compliance). The Cv values set on the front panel were nearly identical to those measured (Cvm = 0.97 * Cvs + 0.54) over the whole tested range from -20 to +20 ml/kPa. Similarly, the measured Ct values were almost equal to those expected according to Eq. alpha; the standard deviation of the relative residuals was 2.7% for elastic loading and 12.4% for elastic unloading. We conclude that the ventilator described in this study can effectively provide both elastic loading and elastic unloading of spontaneous breathing, as expected according to theory.
Biomedical Engineering↗
[Determination of respiratory system compliance from resonance frequency--animal experiment].
10 anaesthetized and tracheotomized rabbits were used to test the possibility for calculation of total respiratory system compliance from resonance frequency (CR). Reference values were obtained by inflation method compliance (CI). A new servocontrolled infant ventilator was used with an integrated negative ventilator resistance mode for resistive unloading of combined resistances of lung, endotracheal tube and ventilator. This evoked oscillation at resonant frequency. By analogy with electrical circuit theory compliance was calculated as follows: CR = 1/(4 pi 2 x square root I.RF2). Pairs of CI and CR values were obtained from each animal during spontaneous breathing, after pancuronium relaxation and after surfactant depletion by lavage. There was found a significant linear correlation between CR and CI values (CR = 1.1 x CI-0.74; r = 0.97).
Animals↗
Titration of continuous positive airway pressure by the pattern of breathing: analysis of flow-volume-time relationships by a noninvasive computerized system.
Infants can defend or even dynamically elevate their functional residual capacity with additional respiratory muscle work by retarding early expiratory airflow (V) with postinspiration inspiratory muscle activity and/or laryngeal narrowing, or by starting inspiration before expiration to the relaxation volume has been completed. In order to study the effect of continuous positive airway pressure (CPAP) on both phenomena in 23 infants (birthweight 1,746 +/- 417 g), we elevated the airway pressure stepwise in 0.2 kPa increments. A computerized bedside flow-volume (V/V) analysis was used for evaluation. In 16 "responders" early expiration braking decreased and "premature inspiratory interruption" was postponed at an "appropriate CPAP level." The linear segment (relaxation line) of the V/V-loop was lengthened until expiratory time reached a maximum. Elevation of CPAP beyond this level again produced a rapid, shallow pattern, often combined with flow acceleration late in expiration (recruitment of expiratory muscles). In the remaining seven infants (non-responders) these latter signs of excessive airway pressure already occurred at the lowest CPAP levels applied during the "titration trials." Respiratory rate without CPAP was different between responders (84 +/- 17/min) and non-responders (46 +/- 17/min). This approach for determining the appropriate CPAP level might reduce the risk of respiratory muscle fatigue.
Computer Systems↗
An infant ventilator technique for resistive unloading during spontaneous breathing. Results in a rabbit model of airway obstruction.
The combined system of ventilator circuit, endotracheal tube, and lung commonly imposes a resistive load on spontaneous breathing efforts. It is possible to compensate for this positive resistance by a device generating a "negative ventilator resistance" (NVR), i.e. delivering a positive pressure during inspiration and a negative pressure during expiration in constant proportion to the instantaneous flow of the spontaneous breathing. The concept of NVR implies that there must not be any phase lag between flow and pressure signals. In eight anesthetized, intubated, spontaneously breathing rabbits (mean body wt 3570 g, range 2900-4600 g), challenged either by aerosolized histamine or an extrapulmonary resistive load, lung mechanical data were calculated from esophageal pressure and flow signals. Each animal served as its own control with and without NVR. In a total of 39 experiments, NVR was applied in amounts between 1 and 15 kPa.s/L. During both types of additional resistive load, NVR immediately reduced the resistive work of breathing. There was a strong linear correlation between the amount of NVR applied and the decrease in total resistance, where the total resistance equals the resistive load on the animal's respiratory muscles (sum of the resistances of all components of the combined respirator-lung system): r = 0.93, p less than 0.001. The relationship between NVR and the drop in resistive work per mL of tidal volume was similar: r = 0.85, p less than 0.001. Throughout the experiments, NVR operated in perfect synchronization with the animal's spontaneous breathing activity.
Airway Obstruction↗
A method of calculating total respiratory system compliance from resonant frequency: validity in a rabbit model.
Ten anesthetized, tracheotomized, adult rabbits were used to test the validity of a method for calculation of total respiratory system compliance from resonant frequency (Cr). Reference values were obtained during constant flow inflation of the relaxed respiratory system by dividing the volume gain by the related difference in pressure at the airway opening (inflation method compliance, Ci). The animals were connected to a new type of servo-controlled infant ventilator. Besides volume-controlled mechanical ventilation at constant inspiratory flow rate and intermittent mandatory ventilation, there is a negative ventilator resistance mode integrated in this device for resistive unloading (Schulze A, Schaller P, Gehrhardt B, Mädler H-J, Gmyrek D: Pediatr Res 28:79-82, 1990). To measure resonant frequency (fr), the respiratory system was totally unloaded for a short period by a negative ventilator resistance exceeding the combined resistances of the endotracheal tube and airways. This evoked a continuous oscillation at fr. By analogy with electrical circuit theory, Cr was calculated according to C = 1/(4 pi 2.I.fr2) where C is compliance and I is inertance. The inertance of the endotracheal tube is given and that of the bronchial tree was ignored assuming a much greater total cross-sectional area and therefore much lower inertance when compared with the endotracheal tube. Three pairs of Ci - Cr values were obtained from each animal: 1) during intact respiratory muscle activity; 2) after pancuronium relaxation, and 3) after surfactant depletion by saline washout.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗