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Biomedical subjects

C Wick

Publications and source records attributed to C Wick.

13 recordsLinked to original sources
PubMed2003

High pressure effects on proteolytic and glycolytic enzymes involved in cheese manufacturing.

The activity of chymosin, plasmin, and Lactococcus lactis enzymes (cell envelope proteinase, intracellular peptidases, and glycolytic enzymes) were determined after 5-min exposures to pressures up to 800 MPa. Plasmin was unaffected by any pressure treatment. Chymosin activity was unaffected up to 400 MPa and decreased at 500 to 800 MPa. Fifty percent of control chymosin activity remained after the 800 MPa treatment. The lactococcal cell envelope proteinase (CEP) and intracellular peptidase activities were monitored in cell extracts of pressure-treated cells. A pressure of 100 MPa increased the CEP activity, whereas 200 MPa had no effect. At 300 MPa, CEP activity was reduced, and 400 to 800 MPa inactivated the enzyme. X-Prolyl-dipeptidyl aminopeptidase was insensitive to 5-min pressure treatments of 100 to 300 MPa, but was inactivated at 400 to 800 MPa. Aminopeptidase N was unaffected by 100 and 200 MPa. However, 300 MPa significantly reduced its activity, and 400 to 800 MPa inactivated it. Aminopeptidase C activity increased with increasing pressures up to 700 MPa. High pressure did not affect aminopeptidase A activity at any level. Hydrolysis of Lys-Ala-p-NA doubled after 300-MPa exposure, and was eliminated at 400 to 800 MPa. Glycolytic enzyme activities of pressure-treated cells were evaluated collectively by determining the titratable acidity as lactic acid produced by cell extracts in the presence of glucose. The titratable acidities produced by the 100 and 200 MPa samples were slightly increased compared to the control. At 300 to 800 MPa, no significant acid production was observed. These data demonstrate that high pressure causes no effect, activation, or inactivation of proteolytic and glycolytic enzymes depending on the pressure level and enzyme. Pressure treatment of cheese may alter enzymes involved in ripening, and pressure-treating L. lactis may provide a means to generate attenuated starters with altered enzyme profiles.

Cheese↗
PubMed2001

An enabling system for echocardiography providing adaptive support through behavioral analysis.

Echocardiography requires the integrated application of a broad spectrum of cognitive and practical skills, e.g. diagnostic knowledge (symbolic), image interpretation (visual perception) and handling of the ultrasound probe (sensorimotor). This complex expertise is acquired through extensive practical training guided by a skilled cardiologist that is often incompatible with clinical reality. Especially for beginners, the most critical point during an echocardiographic examination is the steering of the ultrasound probe to navigate between different cardiological standard planes (sensorimotor skill) without loosing orientation. These transitions or "standard trajectories" can roughly be described by specific movement patterns. We propose an enabling system based on an Augmented Reality simulator for two-dimensional echocardiography imitating this apprenticeship [1]-[3]. During a simulated ultrasound examination the system monitors the activities of the trainee and analyzes the motion pattern of the ultrasound probe. The simulator reacts by mapping the motion patterns onto cognitive orientation demands and providing adaptive feedback in the form of context sensitive help (animations). It partly takes the role of the critical teacher.

Computer-Assisted Instruction↗
PubMed2000

Augmented reality simulator for training in two-dimensional echocardiography.

In two-dimensional echocardiography the sonographer must synthesize multiple tomographic slices into a mental three-dimensional (3D) model of the heart. Computer graphics and virtual reality environments are ideal to visualize complex 3D spatial relationships. In augmented reality (AR) applications, real and virtual image data are linked, to increase the information content. In the presented AR simulator a 3D surface model of the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to establish spatial and temporal congruence. The heart model, together with an animated ultrasound sector represents a reference scenario, which displays the currently selected two-dimensional echocardiographic cutting plane calculated from the volume data set. Modifications of the cutting plane within the echocardiographic data are transferred and visualized simultaneously and in real time within the reference scenario. The trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by an animated ultrasound probe, whose position is controlled by an electromagnetic tracking system. The tracking system is attached to a dummy transducer and placed on a plastic puppet to give a realistic impression of a two-dimensional echocardiographic examination.

Computer Graphics↗
PubMed2000

[Augmented reality in echocardiography. A new method of computer-assisted training and image processing using virtual and real three-dimensional data sets].

Augmented reality (AR) applications link real with virtual image data, in order to increase their information content. In medicine they are especially useful for education and for supporting the interpretation of three-dimensional (3D) image data. Simulators are used to train risky or expensive procedures. In the AR application EchoCom2 a 3D surface model of the human heart is linked with echocardiographic volume data sets. The 3D echocardiographic data sets are registered with the heart model to synchronize it's temporal and spatial orientation. The heart model together with an animated ultrasound sector represents a reference scenario, which displays the currently selected cutting plane within the echocardiographic volume data set. Modifications of the cutting plane within the echocardiographic data are transferred simultaneously and in real time to the reference scenario. The AR application is used as a simulator to train two-dimensional echocardiographic examinations and as an orientation and navigation aid for the exploration of 3D echocardiographic data sets. Beginners in echocardiography have only a rudimentary conception of the spatial relationship between the actual ultrasound image and the 3D anatomy of the heart. They are unable to translate multiple two-dimensional slices into a coherent 3D mental image of the heart. In EchoCom2 the trainee can interactively explore the 3D heart model and the registered 3D echocardiographic data sets by the animated ultrasound sector, whose position is controlled by an electromagnetic orientation and position system (EPOS). The data from the EPOS are used to calculate the echocardiographic images that are analogue to the position of the animated ultrasound sector. EchoCom2 is also used to support the interpretation of 3D echocardiographic data sets. The analysis of 3D echocardiographic data has to be done during a post processing. Defining the exact position of a cutting plane within the volume is difficult due to the lack of a standardized representation, the independence of the cutting plane of any transducer position and the possibility to calculate an indefinite number of views. The simultaneous representation of the current cutting plane both in the volume data, and in the heart model enables the examiner ad hoc to recognize it's position and the visualized structures.

Computer Simulation↗
PubMed1991

[Mechanical ventilation in an anesthetic circle system using the lowest tidal volume--studies of 3 anesthesia ventilators in a lung model and an animal experiment].

No anesthesia ventilator attached to a circle system is manufactured for use in neonates. However, a small bellows can be supplied for the following anesthesia ventilators: Spiromat NS 656 (NS), Ventilog 2 (V2) and AV1 (Draeger Co.) We investigated the minimal tidal volume delivered by each of the three ventilators. In addition, we tested the performance of the AV1 in neonatal piglets for manual and controlled ventilation, and in decreased lung compliance. MATERIALS AND METHODS. All circuits were equipped with one CO2 canister (750 ml) and the low-compliance tubes of the "Ulmer Kinder Set" (Ruesch Co.) The circuits were connected to a lung model consisting of a glass cylinder filled with copper wool with a compliance of 3.0 ml/mbar. By using calibrated glass syringes we created a pressure-volume correlation for the entire system, i.e., the lung model, the anesthesia circuit and the ventilator, which was linear for each of the three ventilators. The pressure was measured in the test lung. The pressure increase caused by the tidal volume therefore reflected the actual tidal volume delivered, which was calculated using the pressure-volume correlation. Tidal volumes were determined for varying the fresh gas flow (FGF), the respiratory rate (RR), which was varied between 20 and 60/min and the I:E ratio (IE), which was varied between 1:1 and 1:2. Six newborn piglets aged 2-12 h and with body weight 1000-1300 g were anesthetized, tracheotomized and ventilated with an oxygen-nitrous oxide mixture (FIO2 0.25). The manual ventilation lasted 30 min (period 1) and was followed by mechanical ventilation for 60 min (period 2). Thereafter, a left pneumothorax with constant pressure of 20 mbar and then 40 mbar for 15 min each was created (period 3). A fall in blood pressure was treated with 10 ml colloids in five of the six animals. During the experiment arterial blood pressure in the carotid artery, mean airway pressure at the distal end of the tracheal tube and end-tidal CO2 were continuously recorded. Arterial blood gases were analyzed at the end of each period. RESULTS. The tidal volumes delivered with an identical position of the bellows varied in ventilators NS and V2 with changes in FGF, RR and IE. Decrease in FGF, higher RR and longer expiration resulted in a decrease in the tidal volume. The "smallest" tidal volume delivered by NS varied from 50 ml (FGF 2 l/min, RR 60, IE 1:2) to 188 ml (FGF 4 l/min, RR 20, IE 1:1) and from 11 ml (FGF 2 l/min, RR 60, IE 1:2) to 110 (FGF 4 l/min, RR 20, IE 1:1) in the V2. The AV1 showed a minimal tidal volume of about 5 ml, and no changes in tidal volume attributable to alterations in FGF, RR or IE could be observed. No problems occurred during manual or mechanical ventilation in the piglets. With the experimental decrease in lung compliance no increase in airway pressure was noted, but an increase in arterial pCO2 by 8 mmHg (mean) reflects hypoventilation that was not corrected by the ventilator. DISCUSSION. We believe that the changes in tidal volume in ventilators NS and V2 are caused by adding FGF to the volume delivered by the below during inspiration. Because of the unpredictability of the tidal volumes, these ventilators are not suitable for the use in neonates. The AV1 has a very low systemic compliance which makes it suitable for use in neonatal anesthesia. However, a decrease in lung compliance is not compensated by an increase in airway pressure and leads to hypoventilation. When small tidal volumes are used in patients with low lung compliance, it does not act as expected of a volume-cycled ventilator.

Anesthesiology↗
PubMed1987

[Comparative humidity measurements in semiclosed and semiopen systems with the additional use of artificial noses].

The administration of dry anesthetic gases for ventilation lasting more than 1 h leads to morphological changes of the tracheobronchial epithelium that may cause postoperative pulmonary complications. Therefore, additional humidification is suggested for ventilation during anesthesia, particularly when using semiopen breathing systems. Recommendations concerning the use of semiclosed systems are controversial: previous studies have shown sufficient humidification on the one hand, and insufficient water content in the inspired air on the other hand. In this study, comparative humidity measurements in a semiopen and a semiclosed system were carried out during anesthesia and mechanical ventilation. We particularly wanted to find out whether placement of the fresh gas inlet into the circle before or behind the soda lime canister influences the humidity of the inspired gas. In addition, we tested three types of "heat and moisture exchanges"--Engström "Edith", Siemens "Servo Humidifier", and Portex "Humid Vent". A total of 58 patients between 23 and 78 years of age were studied. They were divided into three groups. Group I: In 10 patients comparative humidity measurements were carried out using both a semiopen and a semiclosed system. Group II: The time course of water saturation during a 3-h period was determined in 10 patients ventilated with a semiopen and 8 patients ventilated with a semiclosed circle system. Group III: In 20 patients we tested the effect of "heat and moisture exchangers". All patients were intubated and ventilated with the Spiromat 656 and the Circle System 8 (Drger) that made ventilation in both a semiclosed and a semiopen system possible. The humidity measurements were carried out using a psychometric method.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

[Comparative study of the behavior of intraocular pressure in anesthesia induction by diazepam and midazolam].

20 patients scheduled for cataract extraction were randomly assigned to two groups. Before anaesthesia was induced, group A patients received 0.3 mg/kg body weight diazepam, whereas group B was given 0.15 mg/kg body weight midazolam. The ocular pressure, blood pressure, pulse and respiratory rate were determined and a capillary blood gas analysis was performed prior to the administration of the tranquilizer (time I), after the patient fell asleep (time II) as well as 5 min. after intubation (time III). Before intubation the patients received fentanyl and succinylcholin. The reduction in ocular pressure is initially somewhat less in the midazolam group, but is identical to that in the diazepam group at time III where it fell to 57% of the preinduction value. In combination with fentanyl, these two drugs are suitable for anaesthesia in intraocular surgery.

Cataract Extraction↗
PubMed1985

[The semi-closed filter circuit].

In a semi-closed circle system, the inspiratory and expiratory limbs are completely separated and part of the patient's expired air recirculates. CO2 rebreathing is prevented by CO2- absorption with soda lime, which is always incorporated in such a circle. The inspiratory and expiratory valves ensure that gas flow is unidirectional and also prevent rebreathing, even at tidal volumes of 10 ml and ventilation frequencies of 60 c . min-1. This circuit can be used as an universal anaesthetic system for all age groups, simply by changing the hoses and connecting pieces. The values of expiratory resistance are within the recommended limits of the ISO; prewarming and humidification of the inspiratory gas mixture are sufficient without additional equipment. Standard monitoring of the circuit such as measurement of inspiratory O2 concentration and ventilation pressure, including a disconnection alarm, can be used for all age groups; spirometry or end-tidal CO2 measurements ensure normoventilation. The fresh gas flow required in a semi-closed circle system is about 2-4 1 . min-1, so that costs and environmental contamination with anaesthetic gases are relatively low in comparison with a semi-open system.

Airway Resistance↗
PubMed1980

Induction of sister chromatid exchanges by hydroxylamine, hydrazine and isoniazid and their inhibition by cysteine.

Experiments were performed in order to gain information about the primary process leading to the production of sister chromatid exchanges (SCEs). Radical-forming substances (hydroxylamine, hydrazine and the antituberculous drug isoniazid) were examined for their effectiveness in inducing SCEs. All three substances proved successful in the induction of SCEs in the V-79 cell line of the Chinese hamster. By simultaneous application of a sulfhydryl compound (cysteine), a reduction of the hydrazine- and isoniazid-induced SCEs was achieved. Isoniazid was additionally examined in the in vivo SCE-test. At concentrations of 2-100 mg/kg body weight, it does not increase the rate of SCEs in the bone marrow of the Chinese hamster.

Animals↗