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  • 1
    ISSN: 0304-4165
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1238
    Keywords: Work of breathing ; Positive pressure respiration methods ; Lung disease ; Obstructive therapy ; Ventilator weaning ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective Evaluation of low-level PEEP (5 cm H2O) and the two different CPAP trigger modes in the Bennett 7200a ventilator (demand-valve and flow-by trigger modes) on inspiratory work of breathing (Wi) during the weaning phase. Design Prospective controlled study. Setting The intensive care unit of a university hospital. Patients Six intubated patients with normal lung function (NL), ventilated because of non-pulmonary trauma or post-operative stay in the ICU, and six patients recovering from acute respiratory failure due to exacerbation of chronic obstructive pulmonary disease (COPD), breathing either FB-CPAP or DV-CPAP with the Bennett 7200a ventilator. Interventions The patients studied were breathing with zero end-expiratory pressure (ZEEP), as well as CPAP of 5 cm H2O (PEEP), with the following respiratory modes: the demand-valve trigger mode, pressure support of 5 cm H2O, and the flow-by trigger mode (base flow of 20 l/min and flow trigger of 2 l/min). Furthermore, Wi during T-piece breathing was evaluated. Measurements and results Wi was determined using a modified Campbell's diagram. Total inspiratory work (Wi), work against flow-resistive resistance (Wires), work against elastic resistance (Wiel), work imposed by the ventilator system (Wimp), dynamic intrinsic positive end-expiratory pressure (PEEPidyn), airway pressure decrease during beginning inspiration (Paw) and spirometric parameters were measured. In the NL group, only minor, clinically irrelevant changes in the measured variables were detected. In the COPD group, in contrast, PEEP reduced Wi and its components Wires and Wiel significantly compared to the corresponding ZEEP settings. This was due mainly to a significant decrease in PEEPidyn when external PEEP was applied. Flow-by imposed less Wi on the COPD patients during PEEP than did demand-valve CPAP. Differences in Wimp between the flow-by and demand-valve trigger models were significant for both groups. However, in relation to Wi these differences were small. Conclusion We conclude that the application of low-level external PEEP benefits COPD patients because it reduces inspiratory work, mainly by lowering the inspiratory threshold represented by PEEPidyn. Differences between the trigger modes of the ventilator used in this study were small and can be compensated for by the application of a small amount of pressure support.
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  • 3
    ISSN: 1432-055X
    Keywords: Schlüsselwörter Atemarbeit ; Beatmung ; Pressure Support Ventilation ; COPD ; Key words Pressure support ventilation ; Work of breathing ; Chronic obstructive pulmonary disease ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract During pressure support ventilation (PSV), the timing of the breathing cycle is mainly controlled by the patient. Therefore, the delivered flow pattern during PSV might be better synchronised with the patient's demands than during volume-assisted ventilation. In several modern ventilators, inspiration is terminated when the inspiratory flow decreases to 25% of the initial peak value. However, this timing algorithm might cause premature inspiration termination if the initial peak flow is high. This could result not only in an increased risk of dyssynchronization between the patient and the ventilator, but also in reduced ventilatory support. On the other hand, a decreased peak flow might inappropriately increase the patient's inspiratory effort. The aim of our study was to evaluate the influence of the variation of the initial peak-flow rate during PSV on respiratory pattern and mechanical work of breathing. Patients. Six patients with chronic obstructive pulmonary disease (COPD) and six patients with no or minor nonobstructive lung pathology (control) were studied during PSV with different inspiratory flow rates by variations of the pressurisation time (Evita I, Drägerwerke, Lübeck, Germany). During the study period all patients were in stable circulatory conditions and in the weaning phase. Method. Patients were studied in a 45° semirecumbent position. Using the medium pressurization time (1 s) during PSV the inspiratory pressure was individually adjusted to obtain a tidal volume of about 8 ml/kg body weight. Thereafter, measurements were performed during five pressurization times (〈0.1, 0.5, 1, 1.5, 2 s defined as T 0.1, T 0.5, T 1, T 1.5 and T 2) in random order, while maintaining the pressure support setting at the ventilator. Between each measurement steady-state was attained. Positive end-exspiratory pressure (PEEP) and FIO2 were maintained at prestudy levels and remained constant during the study period. Informed consent was obtained from each patient or his next of kin. The study protocol was approved by the ethics committee of our medical faculty. Gas flow was measured at the proximal end of the endotracheal tube with a pneumotachometer (Fleisch no. 2, Fleisch, Lausanne, Switzerland) and a differential pressure transducer. Tracheal pressure (Paw) was determined in the same position with a second differential pressure transducer (Dr. Fenyves & Gut, Basel, Switzerland). Esophageal pressure (Pes) was obtained by a nasogastric balloon-catheter (Mallinckrodt, Argyle, NY, USA) connected to a further differential pressure transducer of the same type as described above. The balloon was positioned 2–3 cm above the dome of the diaphragm. The correct balloon position was verified by an occlusion test as described elsewhere. The data were sampled after A/D conversion with a frequency of 20 Hz and processed on an IBM-compatible PC. Software for data collection and processing was self-programmed using a commercially available software program (Asyst 4.0, Asyst Software Technologies, Rochester, NY, USA). Patient's inspiratory work of breathing Wpi (mJ/l) was calculated from Pes/volume plots according to the modified Campbell's diagram. Dynamic intrinsic PEEP (PEEPidyn) was obtained from esophageal pressure tracings relative to airway pressure as the deflection in Pes before the initiation of inspiratory flow Patient's additive work of breathing (Wadd) against ventilator system resistance was calculated directly from Paw/V tracings when Paw was lower than the pressure on the compliance curve. Two-way analysis of variance (ANOVA) was used for statistical analysis, followed by post hoc testing of the least significant difference between means for multiple comparisons. Probability values less than 0.05 were considered as significant. Results. COPD patients had significantly higher pressure support than control patients. With decreasing inspiratory flow, Wpi increased significantly in COPD patients. Additionally, the duct cycle (Ti/Ttot) significantly increased with decreased flow rates which resulted in a higher PEEPidyn compared to the baseline. At T 1.5 and T 2 with lower flow rates, the pre-set pressure support level was not achieved within inspiration in the COPD patients. Wadd increased significantly at T 1, T 1.5 and T 2 in COPD patients and at T 1.5 and T 2 in the control group. In one patient, premature termination of inspiration owing to high initial peak flow was corrected by adjustment of the inspiratory flow. Conclusion. Our results demonstrate that a decreased peak flow during PSV resulted in increased patient's work of breathing in COPD patients. During lower flow, the pre-set pressure support level was not attained and additional work had to be done on the ventilator system. Furthermore, the higher PEEPidyn during lower flow rates indicates a higher risk of dynamic pulmonary hyperinflation in patients with COPD. We conclude that the use of pressurization times ≥1 s to decrease inspiratory peak flow during PSV is of no benefit and should be avoided, particularly in COPD patients. However, in selected cases, slight decrease of inappropriately high peak flows might be useful for optimization of PSV setting to avoid premature termination of inspiration.
    Notes: Zusammenfassung Bei einigen Respiratoren kann unter Pressure Support Ventilation (PSV) der Inspirationsfluß (V˙ i ) durch Veränderung der Druckanstiegszeit variiert werden. Über den Einfluß des Inspirationsflußprofils unter PSV auf die Atemarbeit ist besonders bei Patienten mit chronischer Atemwegsobstruktion (COPD) kaum etwas bekannt. Wir untersuchten an 6 COPD-Patienten und 6 Patienten ohne Lungenerkrankung (Kontrollgruppe) die Effekte einer Variation von V˙ i unter PSV auf atemmechanische Variablen und die mechanische Atemarbeit. Unter individuell eingestellter Druckunterstützung wurde die Druckanstiegszeit in 5 Stufen verändert. Die Verlängerung der Druckanstiegszeit verminderte den initialen V˙ i in beiden Patientengruppen. Gleichzeitig stieg die Atemarbeit in der COPD-Gruppe bei verringertem V˙ i signifikant an. Eine Ursache hierfür war, daß bei den COPD-Patienten bei langsamen Druckanstiegszeiten die eingestellte Druckunterstützung nicht mehr erreicht wurde. Der langsamere V˙ i führte zu einer Verlängerung der Inspiration auf Kosten der Exspirationszeit. Dies verursachte bei COPD-Patienten eine unerwünschte Erhöhung des intrinsischen PEEP. Die Auswirkungen eines niedrigeren V˙ i unter PSV in der Kontrollgruppe waren klinisch nur wenig relevant. Unsere Ergebnisse zeigen, daß besonders bei Patienten mit COPD unter PSV hohe initiale Inspirationsflüsse zu bevorzugen sind, da ein niedriger Fluß die Patientenatemarbeit erhöht und eine dynamische Lungenüberblähung verstärkt. Allerdings konnte bei einem Patienten ein vorzeitiger Inspirationsabbruch aufgrund eines hohen Initialflusses durch Anpassung des Flußprofils korrigiert werden. In Einzelfällen kann daher eine Verlängerung der Druckanstiegszeit bis auf maximal 1 s sinnvoll sein.
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Analytical Biochemistry 65 (1975), S. 507-524 
    ISSN: 0003-2697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Molecular Spectroscopy 59 (1976), S. 86-95 
    ISSN: 0022-2852
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0022-4073
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0930-9225
    Keywords: Schlüsselwörter Postoperative Nachbeatmung – Haemodynamik – pulmonaler Gasaustausch – aortokoronare Bypassoperation ; Key words Postoperative short-term ventilation – hemodynamics – pulmonary gas exchange – coronary artery bypass grafting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The beneficial effects of biphasic positive airway pressure (BIPAP) ventilation in the case of long-term mechanical ventilation of patients with ARDS are well known. The aim of the present study was to compare the hemodynamic and ventilatory effects of BIPAP with synchronized intermittent mandatory ventilation combined with pressure support ventilation (S-IMV/PSV) in short-term ventilated patients after CABG surgery. After approval by the local ethics committee eighteen male patients were investigated. The patients were randomly assigned to one of two groups representing the respective ventilation mode. Hemodynamic measurements and blood gas analyses were performed during sedation with propofol, in awake patients having reached extubation criteria and after extubation. Statistical analysis of data was performed using non-parametric tests.¶   During the first set of measurements only inspiratory peak pressure was increased significantly by 20% in S-IMV/PSV ventilated patients compared to the BIPAP ventilated patients. In this study design the increased inspiratory peak pressure did not adversely affect hemodynamic parameters and blood gas analyses, as they did not vary with the ventilatory mode. After extubation the arterial oxygen partial pressure showed only a significant decrease by 19% in the S-IMV/PSV ventilated patients.¶   Our results demonstrate that both investigated ventilatory modes have comparable effects on hemodynamics when used for short-term ventilatory support in patients after cardiac surgery. The patient’s ability to breathe independently from the mechanical respiratory cycle during BIPAP ventilation improves the patient’s comfort and may reduce the risk of myocardial ischemia in the early postoperative period by minimizing the stress due to inadequate adaptation to the ventilator.
    Notes: Zusammenfassung Die Vorteile einer Biphasic positive airway pressure (BIPAP) Beatmung in bezug auf den pulmonalen Gasaustausch bei Patienten mit ARDS sind hinreichend bekannt. Ziel dieser Studie war es, die haemodynamischen und pulmonalen Effekte von BIPAP und synchronized intermittent mandatory ventilation/pressure support ventilation (S-IMV/PSV) bei Patienten nach kardiochirurgischen Eingriffen zu vergleichen.¶   Insgesamt wurden 18 männliche Patienten nach einer aortokoronaren Bypassoperation randomisiert einem der beiden Beatmungsmodi zugeordnet. Haemodynamische Messungen und arterielle Blutgasanalysen erfolgten nach Ankunft auf der Intensivstation unter Sedierung, sowie vor und nach Extubation. Die statistische Auswertung der Daten erfolgte mit nicht-parametrischen Testverfahren.¶   Während der ersten Messphase lag der maximale inspiratorische Druck bei Patienten mit S-IMV/PSV-Beatmung 20% über den Werten der Patienten mit BIPAP-Beatmung. Dieses zeigte keinen Einfluss auf die erhobenen haemodynamischen Parameter, welche während der gesamten Messphase nicht signifikant unterschiedlich zwischen den Gruppen waren. Nach Extubation fiel lediglich in der Gruppe mit S-IMV/PSV-Beatmung der arterielle Sauerstoffpartialdruck signifikant um 19% ab.¶   Die Ergebnisse zeigen, dass unter den Studienbedingungen die Effekte von BIPAP und S-IMV/PSV auf die Haemodynamik vergleichbar sind. Der bessere Patientenkomfort aufgrund der Möglichkeit der Spontanatmung unabhängig vom Beatmungszyklus ist allerdings ein Vorteil der BIPAP-Beatmung gegenüber anderen Beatmungsverfahren, welcher durch Stressreduktion zur Minimierung des postoperativen Risikos einer Myokardischaemie beitragen kann.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 69 (1991), S. 731-735 
    ISSN: 1432-1440
    Keywords: Medical expert systems ; Artificial intelligence ; Medical diagnosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The rapid expansion of computer-based systems for problem solving or decision making in medicine, the so-called medical expert systems, emphasize the need for reappraisal of their indication and value. Where specialist knowledge is required, in particular where medical dicisions are susceptible to error these systems will probably serve as a valuable support. In the near future computer-based systems should be able to aid the interpretation of findings of technical investigations and the control of treatment, especially where rapid reactions are necessary despite the need of complex analysis of investigated parameters. In the distant future complete support of diagnostic procedures from the history to final diagnosis is possible. It promises to be particularly attractive for the diagnosis of seldom diseases, for difficult differential diagnoses, and in the decision making in the case of expensive, risky or new diagnostic or therapeutic methods. The physician needs to be aware of certain dangers, ranging from misleading information up to abuse. Patient information depends often on subjective reports and error-prone observations. Although basing on problematic knowledge computer-born decisions may have an imperative effect on medical decision making. Also it must be born in mind that medical decisions should always combine the rational with a consideration of human motives.
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  • 9
    ISSN: 1432-1238
    Keywords: Key words Phrenic nerve stimulation ; Work of breathing ; Oesophageal pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: Five commercially available oesophageal balloon catheters (OBCs) were tested to evaluate the accuracy in transmitting fast-changing pressure signals which can be observed, for example, during phrenic nerve stimulation.¶Setting: Research laboratory of a university hospital.¶Method: The OBCs tested varied in length (900–1390 mm) and inner diameter (0.9–1.5 mm) as well as in balloon material [latex or polyvinyl-chloride (PVC)]. A 180-cm tube served as a control. A sudden pressure drop was generated by the explosion of a pressurized latex balloon. The time between the pressure drop and 75, 50, 25 and 10 % of the maximal pressure was measured.¶Results: The time intervals required to transduce a pressure drop of 90 % varied between the different OBCs from 85 to 476 ms(control 32 ms). Transmission time was lower in OBCs with a larger inner diameter. Shortening the OBCs resulted in a further decrease in transmission time.¶Conclusion: The type of OBC used has an impact on signal processing. An OBCs with a short transmission time should be chosen, especially if fast pressure changes are to be evaluated such as during phrenic nerve stimulation.
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  • 10
    ISSN: 1432-1335
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Es wurden die Einwirkung des Kanzerogens 3H-3,4-Benzpyren und des Nichtkanzerogens 3H-1,2-Benzpyren auf die Schweinehaut mit Hilfe von Kryostatschnitten autoradiographisch untersucht. Es fanden sich weder im Verteilungsmuster noch in der Verweildauer signifikante Unterschiede zwischen dem Karzinogen und dem Nichtkarzinogen. Die zelligen Bestandteile (Histiocyten, Fibroblasten und Capillarendothelien) wurden stark markiert, schwach dagegen die intercelluläre Grundsubstanz und kaum die kollagenen Fasern. Die Markierung hängt mit der hauptsächlich stattfindenden Bindung an lösliche Zellbestandteile, vor allem wahrscheinlich an lösliche Proteine zusammen. Die gleich nach Karzinogenapplikation auftretende starke Silberkornbelegung nimmt nach 1–2 Tagen stark ab, die rad. akt. Substanzen sind nach 5 Tagen weitgehend aus der löslichen Gewebsfraktion verschwunden.
    Notes: Summary The action of the carcinogen 3H 3,4-Benzpyrene and of the non-carcinogenic 3H 1,2-Benzpyrene on the skin of the pig was studied autoradiographically using cryostat sections. There was no significant difference between the carcinogen and non-carcinogen in either the distribution pattern or the duration of attachment of the substance. The cellular components (histiocytes, fibroblasts and capillary endothelial cells) were strongly labelled, the intercellular ground substance comparatively weakly and the collagen fibres hardly at all. The labelling principally marks the attachment to the soluble cell components, probably to the soluble proteins in particular. The intense deposition of silver grains which appears immediately after the application of carcinogen is greatly reduced after one to two days, and after a further five days the radioactive substances disappeared almost entirely from the soluble tissue fraction.
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