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Biomedical subjects

J Theissen

Publications and source records attributed to J Theissen.

6 recordsLinked to original sources
PubMed1990

[Inhalation anesthesia with halogenated hydrocarbons: value of isoflurane].

The halogenated hydrocarbons halothane, enflurane and isoflurane are used extensively. Like every other anaesthetic, these inhaled agents are not devoid of side effects, most of which are undesirable. This review summarises the similarities and differences between the actions of these vapours. Although isoflurane appears to be more advantageous than enflurane and halothane in certain patients, isoflurane is no panacea and the question of which agent to choose still has to be answered for every patient. A note of caution is warranted against the further use of halothane in adults, as halothane offers no advantages when compared to enflurane and isoflurane but carries a higher risk of hepatotoxicity. However, in children halothane remains the halogenated agent of first choice, when anaesthesia is induced via face mask.

Anesthesia, General↗
PubMed1988

The problem created by myocardial structure in assessing function.

The clinical understanding of the dynamics of myocardial contraction is hampered by an over-simplified interpretation of the intramural pattern of force generation. This limits the anaesthetist's knowledge of the direct effects of commonly used anaesthetics. A discrimination between a negative inotropic effect and changes in pre- and afterload is usually impossible in clinical conditions. By using needle force probes, it is now possible to measure intramyocardial mesh tension in volumes as small as 3 mm3. Force mapping in 20 to 30 layers of the hearts of five normal dogs has shown that there are different patterns in the basal, middle and apical portions of the free wall of the left ventricle. An inhomogeneity is also observed when myocardial hypertrophy is produced by a 6-week period of aortic banding. However, this decreased the gradient in wall tension between the basal and the other portions of the ventricle. Inhomogeneities in wall tension increase the difficulty of assessing the contractile state of heart muscle. It may, however, be useful to compare local wall dynamics in the more isometrically-contracting basal segment with those in the middle portion which brings about most of the emptying of the ventricle. In the future, transoesophageal echocardiography may be used to measure variations in wall thickness which change the global loading conditions in the basal midwall compartments of the left ventricle.

Animals↗
PubMed1988

[High-frequency artificial respiration. II. Intratracheal high-frequency pressure changes with a rotation-valve catheter].

From the history of ventilatory support, the early studies of Auer und Meltzer only now seem to find a functional explanation. A rotating valve mounted on the tip of an endotracheal tube delivers a widespread gas bolus. The turbulent flow acts as a stirring device on the intrapulmonary gas volume. The method reduces the directional selectivity that typically limits the efficiency of jet ventilation. Systematically changing the rotational frequency between 10 and 80 Hz allows sequential stimulation, compartment by compartment, of the entire lung, which also gives rise to frequency-dependent local air-trapping that sequentially inflates different compartments. Jet ventilation and high-frequency oscillation were compared in dogs with the rotating valve tube by taking blood gas samples from 4-6 intrapulmonary veins: jet ventilation is characterized by preponderant ventilation of lung compartments opposite the lower aperture of the endotracheal tube. High-frequency oscillation induces a frequency dependent repartition of alveolar ventilation. The rotating valve tube definitely contributes to the homogenisation of alveolar ventilation in a manner that is less dependant upon segmental compliance than conventional ventilation.

Animals↗
PubMed1987

[High-frequency ventilation. I. Distribution of alveolar pressure amplitudes during high frequency oscillation in the lung model].

The pattern of intrapulmonary pressure distribution was studied during high-frequency ventilation in order to explain the inconsistent results reported in the literature. Methods. Pressure and flow velocity (hot-wire anemometry) were measured in different lung compartments: 1. In transalveolar chambers sealed to the perforated pleural surfaces of dried pig lungs; 2. In emphysema-simulating airbags sealed to the isolated bronchial trees of dried pig lungs; and 3. In transalveolar chambers sealed to the perforated pleural surfaces of freshly excised pig lungs. Results. 1. The pressure amplitudes change from one area to another and depending on the exciting frequency. 2. High-frequency oscillation is associated with an increase in pressure amplitude when the exciting frequency rises, whereas with conventional high-frequency jet ventilation the pressure amplitude is more likely to decrease with frequency. 3. During high-frequency jet ventilation the local pressure amplitude changes with the position of the tube in the trachea rather than with the exciting frequency. 4. When the volume of the measuring chamber is doubled the resulting pressure amplitude falls to half the control value. 5. The pressure amplitude and mean pressure measured in the transalveolar chamber vary more or less independently from the peak flow velocity. High-frequency ventilation is thus seen to be a frequency-dependant, inhomogeneous mode of ventilation that can essentially be homogenized by systematically changing the exciting frequency. The frequency-dependant response to different lung areas to excitation is likely to result from an intrabronchially-localized aerodynamic effect rather than the mechanical properties of the lung parenchyma.

Animals↗
PubMed1986

[Drug intolerance reactions in the perioperative phase--pathophysiology, diagnosis, therapy].

The increase in allergic reactions compels the anaesthetist to exercise great care when administering anaesthetics exclusively intravenously, because anaphylactic or anaphylactoid reactions can become a life-threatening problem for the patient within a very short time. Unfortunately the information given by patients is often very incomplete and the risk of allergic reactions is not eliminated by false positive or negative results in the skin test. There are only a few drugs available as antigens for the RAST test. Apart from avoiding histamine-releasing drugs, this information gap can only be countered in high-risk patients by preoperative prophylaxis with H1 and H2 receptor antagonists.

Anaphylaxis↗