An Integrated Physiological Model of the Lung Mechanics and Gas Exchange Using Electrical Impedance Tomography in the Analysis of Ventilation Strategies in ARDS Patients

Mouloud Denai, M. Mahfouf, A. Wang, D. A. Linkens, and G. H. Mills, 'An Integrated Physiological Model of the Lung Mechanics and Gas Exchange Using Electrical Impedance Tomography in the Analysis of Ventilation Strategies in ARDS Patients'. Paper presented at the 3rd International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2010), 20 - 23 January 2010, Valencia, Spain.Peer reviewedFinal Published versio

Simulation of ventilation distribution and gas transport during oscillatory ventilation

High frequency oscillatory ventilation (HFOV) relies on low tidal volumes cycled at supraphysiologic rates, producing fundamentally different mechanisms for gas transport and exchange compared to conventional mechanical ventilation. Despite the appeal of using low tidal volumes to mitigate the risks of ventilator- induced lung injury (VILI), HFOV does not improve mortality in most clinical applications. One possible explanation for this is that HFOV distributes flows throughout the lung in a non-uniform and frequency-dependent manner, especially in the presence of mechanical heterogeneity. This thesis is a systematic investigation of the relationship between carbon dioxide elimination and frequency content during oscillatory ventilation, with emphasis on the frequency- dependent effects of mechanical heterogeneity and various gas transport mechanisms. A computational model consisting of an anatomically-structured airway network was used to simulate ventilation distribution and gas exchange in a canine lung. These simulations were validated against theoretical predictions and experimental data for eucapnic oscillatory ventilation. The model was also used to assess the impact of mechanical heterogeneity on ventilation distribution and gas transport. Simulations demonstrated a critical transition at the resonant frequency, above which the ventilation patterns became spatially clustered and frequency-dependent. Finally, the model demonstrated that pairs of oscillatory frequencies could yield eucapnic conditions with less potential for VILI compared to traditional single frequency HFOV. These results illustrate the importance of frequency selection in managing the distribution of ventilation and gas transport in the heterogeneous lung, and suggest that the frequency content in oscillatory waveforms may be optimized to achieve eucapnic gas exchange using less injurious ventilation.2017-10-27T00:00:00

Inverse problem and multi-compartment lung model for the estimation of lung airway resistance throughout the bronchial tree, An

Includes bibliographical references.2022 Fall.Mechanical ventilation is a vital treatment for patients with respiratory failure, but mechanically ventilated patients are also at risk of ventilator-induced lung injury. Optimal ventilator settings to prevent such injury could be guided by knowledge of the airway resistance throughout the lung. While the ventilator provides a single value estimating the total airway resistance of the patient, in reality the airway resistance varies along the bronchial tree. Multiple literature sources reveal a wide range of clinically used values for airway resistance along the bronchial tree, motivating an investigation to estimate the values of airway resistance in the alveolar tree and the relationship to disease state. In this work, we introduce a multi-compartment asymmetric lung model based on resistor-capacitor circuits by using an analogy between electric circuits and the human lungs. A method for solving the inverse problem of computing the vector of airway resistance values in the alveolar tree is presented. The method uses a linear least squares optimization approach with several constraints. First, a symmetric lung model that makes use of parameters supplied by the mechanical ventilator of patients with acute respiratory distress syndrome (ARDS) is used. We then generalize the model to an asymmetric lung model. The asymmetric model takes regional information data from electrical impedance tomography, a medical imaging technique, and converts them to time dependent lung airway volumes. The linear least squares optimization inverse problem is embedded in an iterative method to update unknown parameters of the forward problem for the asymmetric case

Towards optimal lung volume in high-frequency oscillatory ventilation

Kunstmatige beademing is dikwijls noodzakelijk bij kinderen die op een afdeling voor intensieve zorg worden opgenomen. Deze behandeling is vaak levensreddend, maar kan tekort schieten, leidend tot het ontstaan van chronische beschadiging van de longen of zelfs het overlijden van pati?n. In zijn proefschrift beschrijft Dick Markhorst de eerste ervaringen in Nederland bij grotere kinderen met een alternatieve manier van mechanische beademing; de zogenoemde hoog frequent oscillatoire beademing (HFOV). Deze nieuwe beademingsmethode bleek veilig en effectief te zijn, zelfs in situaties waarin de gebruikelijke beademingsmethode tekort schoot. In het proefschrift worden verder meetmethoden beschreven die de arts kan helpen in het optimaal instellen van de beademingsmachine. In een wiskundig model van de zieke long wordt aannemelijk gemaakt dat bij zeer ernstig zieke longen hoog frequent beademen voordelen heeft boven conventionele beademings technieken. Uit eerder onderzoek is gebleken, dat het longvaat-verwijdende gas stikstof monoxide (NO) beter werkt in combinatie met hoog frequente beademing dan in combinatie met de gebruikelijke beademingsmethoden. In het proefschrift wordt beschreven dat in dat geval wel speciale toedienings en bewakings methoden voor NO moeten worden gebruikt. Hij heeft deze apparatuur ontwikkeld en gevalideerd. Tot slot worden de milieu effecten van de gecombineerde NO - HFOV therapie beschreven en wordt een methode gevalideerd om de omgevings vervuiling met het gas tot acceptabele niveaus te beperkenRoord, J.J. [Promotor]Vught, A.J. van [Promotor]Genderingen, H.R. van [Copromotor

DICOM for EIT

With EIT starting to be used in routine clinical practice [1], it important that the clinically relevant information is portable between hospital data management systems. DICOM formats are widely used clinically and cover many imaging modalities, though not specifically EIT. We describe how existing DICOM specifications, can be repurposed as an interim solution, and basis from which a consensus EIT DICOM ‘Supplement’ (an extension to the standard) can be writte

Mechanical Ventilation

The therapeutic alliance has been found to predict psychotherapy outcome in numerous studies. However, critics maintain that the therapeutic alliance is a by-product of prior symptomatic improvements. Moreover, almost all alliance research to date has used differences between patients in alliance as predictor of outcome, and results of such analyses do not necessarily mean that improving the alliance with a given patient will improve outcome (i.e., a within-patient effect). In a sample of 646 patients (76% women, 24% men) in primary care psychotherapy, the effect of working alliance on next session symptom level was analyzed using multilevel models. The Clinical Outcomes in Routine Evaluation–Outcome Measure was used to measure symptom level, and the patient version of the Working Alliance Inventory–Short form revised (Hatcher & Gillaspy, 2006) was used to measure alliance. There was evidence for a reciprocal causal model, in which the alliance predicted subsequent change in symptoms while prior symptom change also affected the alliance. The alliance effect varied considerably between patients. This variation was partially explained by patients with personality problems showing stronger alliance effect. These results indicate that the alliance is not just a by-product of prior symptomatic improvements, even though improvement in symptoms is likely to enhance the alliance. Results also point to the importance of therapists paying attention to ruptures and repair of the therapy alliance. Generalization of results may be limited to relatively brief primary care psychotherapy