Redouane Fodil

Interaction between steady flow and individualised compliant segments: Application to upper airways

To describe upper airway obstruction in patients with sleep apnea syndrome, the steady state solutions of a simple model of local pharyngeal obstruction were studied. Importantly, the present model embodies a series of two individualised elements, each having its own compliance, which enables the consideration, from a conceptual point of view, of local differences in anatomical and physiological properties between pharyngeal regions. The evolution of inspiratory flow and area variations were predicted using the transmural pressure at the downstream element as the controlled variable. Derivation and normalisation of fundamental governing equations, written for non-viscous and viscous fluids, reveal very different kinds of behaviour, depending on values of the speed index defined from the local distensibility, or its modulation by a friction factor for viscous fluid. The two-element model is able to describe a considerably rich mechanical behaviour, including the occurrence of critical conditions when area becomes very high or small, i.e. when the distensibility-dependent speed index at the upstream element tends toward unity. In spite of its simplicity, not only does the present model describe steady state behaviours that resemble the well-known phenomenon of choking in an elastic tube, but the viscous fluid conditions also reveal (i) an area evolution following a typical doubly folded shape, (ii) the occurrence of a close succession maximum and minimum flows which can be seen as a physiological ‘flow plateau’. It is concluded that the concept of interaction behind the two-element model must be considered as soon as flow interacts in a compliant structure characterised by anatomical and/or functional singularities.

Description and microbiology of endotracheal tube biofilm in mechanically ventilated subjects.

BACKGROUND: A biofilm is found on the inner side of endotracheal tubes (ETT) in mechanically ventilated patients, but its features and role in pneumonia remain unclear. METHODS: This prospective, observational, monocentric study included critically ill ventilated subjects. Measurement of the ETT inner volume was first performed before extubation using the acoustic reflection method. After extubation, the biofilm was studied by means of optical and atomic force microscopy. Bacteriological analysis was then performed and compared with clinical documentation. RESULTS: Twenty-four subjects were included. Duration of intubation lasted from 2 to 79 d (mean ± SD: 11 ± 15 d). The mean percentage of ETT volume loss evaluated in situ (n = 21) was 7.1% and was not linked with the duration of intubation. Analyses with atomic force microscopy (n = 6) showed a full coverage of the inner part of the tube with biofilm, even after saline rinse. Its thickness ranged from 0.8 to 5 μm. Bacteriological cultures of the biofilm (n = 22) often showed the same bacteria as in tracheal secretions, especially for pathogenic organisms. Pseudomonas aeruginosa and Candida albicans were among the most frequent microorganisms. In subjects who had experienced a successfully treated episode of ventilator-associated pneumonia (n = 5), the responsible bacteria were still present in the biofilm. CONCLUSIONS: ETT biofilm is always present in intubated patients whatever the duration of intubation and appears quickly after intubation. Even after soft rinse, a small but measurable part of biofilm remains always present, and seems strongly adherent to the ETT lumen. It contains potentially pathogenic bacteria for the lung.

Airflow modeling of steady inspiration in two realistic proximal airway trees reconstructed from human thoracic tomodensitometric images

Detailed description of the flow field in human airways is highly important to better understand human breathing and provide a patients customized diagnosis. An integrated numerical simulation platform is presently proposed in order to incorporate medical images into a numerical software to calculate flow field and to analyze it in terms of fluid dynamics. The platform was set up to compute steady inspiratory airflow in realistic human airways reconstructed from tomodensitometric medical images at resting breathing conditions. This morpho-functional simulation platform has been tested retrospectively with two CT-scanned patient airway morphological models: (i) a normal airway model (subject A) with no evidence of morphological alteration and (ii) a highly altered airway model (subject B) exhibiting a severe stenosis in the right main bronchus. First, various morphological aspects proper to each airway model are provided to show the performance and interest of the reconstruction method. Second, we describe the three-dimensional flow patterns associated to the global morphological features, which are mainly shared by the present realistic models and previous idealistic airway models. Finally, the flow characteristics associated to local morphological features specific to realistic airway models are discussed. The results demonstrate that the morpho-functional simulation platform is able to capture the main features of airway velocity patterns but also more specific airflow patterns which are related to customized patient morphological features such as laminar vortex formation. The present results suggest that the proposed airway functional imaging platform is adequate to provide most of functional information related to airflow and enable a patient to patient diagnosis.

Using hidden Markov models for sleep disordered breathing identification

Abstract In this work, an automatic diagnosis system based on hidden Markov models (HMMs) is proposed to help clinicians in the diagnosis of sleep apnea syndrome. Our system offers the advantage of being based on solid probabilistic principles rather than a predefined set of rules. Conventional and new simulated annealing based methods for the training of HMMs are incorporated. The inference method of this system translates parameter values into interpretations of physiological and pathophysiological states. The interpretation is extended to sequences of states in time to obtain a state-space trajectory. Some of the measurements of the respiratory activity issued by the technique of polysomnography (brain activity, respiratory activity, oxygen levels, and cardiac activity) are considered for off-line and on-line detection of the different sleep apnea syndromes: obstructive, central and hypopnea. Experimental results using respiratory clinical data and some future perspectives of our work are presented.

Upper airway calibre and impedance in patients with steinert's myotonic dystrophy

Myotonic dystrophy (MD) can be responsible for increased inspiratory muscle loading, the origin of which is debated, with some authors incriminating distal lesions and others central abnormalities. Using a recent non-invasive method based on single transient pressure-wave reflection analysis, we measured central airway calibre from the mouth to the carina and respiratory impedance in a group of adults with MD, a group of patients with sleep apnoea syndrome (SAS) but no neuromuscular disease, and a group of normal controls. All participants were awake during the measurements. We found no reduction in central airway calibre in the patients with the adult form of MD, as compared to the normal controls. These data suggest that MD may be associated with peripheral airway obstruction related to alterations in the elastic properties of the lung.

Phase-contrast helium-3 MRI of aerosol deposition in human airways.

One of the key challenges in the study of health‐related aerosols is predicting and monitoring sites of particle deposition in the respiratory tract. The potential health risks of ambient exposure to environmental or workplace aerosols and the beneficial effects of medical aerosols are strongly influenced by the site of aerosol deposition along the respiratory tract. Nuclear medicine is the only current modality that combines quantification and regional localization of aerosol deposition, and this technique remains limited by its spatial and temporal resolutions and by patient exposure to radiation. Recent work in MRI has shed light on techniques to quantify micro‐sized magnetic particles in living bodies by the measurement of associated static magnetic field variations. With regard to lung MRI, hyperpolarized helium‐3 may be used as a tracer gas to compensate for the lack of MR signal in the airways, so as to allow assessment of pulmonary function and morphology. The extrathoracic region of the human respiratory system plays a critical role in determining aerosol deposition patterns, as it acts as a filter upstream from the lungs. In the present work, aerosol deposition in a mouth–throat phantom was measured using helium‐3 MRI and compared with single‐photon emission computed tomography. By providing high sensitivity with high spatial and temporal resolutions, phase‐contrast helium‐3 MRI offers new insights for the study of particle transport and deposition. Copyright