Sam Bayat

Sam Bayat
Centre Hospitalier Universitaire de Grenoble | CHU Grenoble · Laboratoire d'explorations fonctionnelles respiratoires, Clinique de physiologie, sommeil et exercice

MD, PhD

About

131
Publications
8,912
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1,140
Citations
Citations since 2016
73 Research Items
631 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
Additional affiliations
September 2006 - August 2016
Université de Picardie Jules Verne
Position
  • Professor

Publications

Publications (131)
Article
Full-text available
Background PEEP selection in severe COVID-19 patients under extracorporeal membrane oxygenation (ECMO) is challenging as no study has assessed the alveolar recruitability in this setting. The aim of the study was to compare lung recruitability and the impact of PEEP on lung aeration in moderate and severe ARDS patients with or without ECMO, using c...
Article
Full-text available
Background Although high-frequency percussive ventilation (HFPV) improves gas exchange, concerns remain about tissue overdistension caused by the oscillations and consequent lung damage. We compared a modified percussive ventilation modality created by superimposing high-frequency oscillations to the conventional ventilation waveform during expirat...
Article
Full-text available
CT registration-derived indices provide data on regional lung functional changes in COPD. However, because unlike spirometry which involves dynamic maximal breathing maneuvers, CT-based functional parameters are assessed between two static breath-holds, it is not clear how regional and global lung function parameters relate to each other. We assess...
Article
Introduction The high potential of Microbeam Radiation Therapy (MRT) in improving tumor control whilst reducing side effects has been shown by numerous preclinical studies. MRT offers a widened therapeutic window by using the periodical spatial fractionation of synchrotron generated x-rays into an array of intense parallel microbeams. MRT now enter...
Article
Full-text available
The magnitude and distribution of strain imposed on the peripheral airspaces by mechanical ventilation at the microscopic level and the consequent deformations are unknown despite their importance for understanding the mechanisms occurring at the onset of ventilator-induced lung injury. Here a 4-Dimensional (3D + time) image acquisition and process...
Article
Full-text available
Synchrotron radiation offers unique properties of coherence, utilized in phase-contrast imaging, and high flux as well as a wide energy spectrum which allow the selection of very narrow energy bands of radiation, used in K-edge subtraction imaging (KES) imaging. These properties extend X-ray computed tomography (CT) capabilities to quantitatively a...
Article
Full-text available
COVID-19 has negatively affected the delivery of respiratory diagnostic services across the world due to the potential risk of disease transmission during lung function testing. Community prevalence, reoccurrence of COVID-19 surges, and the emergence of different variants of the SARS-CoV-2 virus have impeded attempts to restore services. Finding co...
Preprint
Full-text available
The magnitude and distribution of strain imposed on the peripheral airspaces by mechanical ventilation at the microscopic level and the consequent deformations are unknown despite their importance for understanding the mechanisms occurring at the onset of ventilator-induced lung injury. Here a 4-Dimensional (3D + time) image acquisition and process...
Article
Key points: Gas ventilation is inhomogeneous in the lung of many species. However, it is not known down to what length scales this inhomogeneity persists. It is generally assumed that ventilation becomes homogenous at subacinar length scales, beyond the spatial resolution of available imaging techniques. Here we imaged the distribution of inhaled...
Article
Full-text available
Background Nasal high flow (NHF) is a non-invasive breathing therapy that is based on the delivery via a large-caliber nasal cannula of heated and humidified air at flow rates that exceed peak inspiratory flow. It is thought that positive airway pressure generated by NHF can help reduce gas trapping and improve regional lung ventilation. There are...
Article
Regional viscoelastic properties of thoracic tissues in acute respiratory distress syndrome (ARDS) and their change with position and positive end-expiratory pressure (PEEP) are unknown. In an experimental porcine ARDS, dorsal and ventral lung (R 2 ,L and E 2 ,L) and chest wall (R 2 ,cw and E 2 ,cw) viscoelastic resistive(R) and elastic(E) paramete...
Article
À travers le monde, les équipes sanitaires ont été en première ligne pour lutter contre la propagation du virus SARS-CoV-2, responsable de la pandémie de Covid-19. Au-delà du traitement de l’urgence médicale, des recherches sont nécessaires pour mieux comprendre comment inhiber les mécanismes d’action du virus. On peut, entre autres, imager par dif...
Article
Full-text available
Mechanical ventilation can damage the lungs, a condition called Ventilator-Induced Lung Injury (VILI). However, the mechanisms leading to VILI at the microscopic scale remain poorly understood. Here we investigated the within-tidal dynamics of cyclic recruitment/derecruitment (R/D) using synchrotron radiation phase-contrast imaging (PCI), and the r...
Article
Full-text available
In this article, we present an X-ray tomographic imaging method that is well suited for pulmonary disease studies in animal models to resolve the full pathway from gas intake to gas exchange. Current state-of-the-art synchrotron-based tomographic phase-contrast imaging methods allow for three-dimensional microscopic imaging data to be acquired non-...
Article
Full-text available
Purpose Radiotherapy is an important treatment component for patients with lung cancer. However, the survival time gained with clinical radiotherapy techniques is relatively short. Data from pre-clinical experiments suggest that synchrotron microbeam radiotherapy (MRT) could be much better suited to control malignant brain tumours than current clin...
Article
Full-text available
Many lung disease processes are characterized by structural and functional heterogeneity that is not directly appreciable with traditional physiological measurements. Experimental methods and lung function modeling to study regional lung function are crucial for better understanding of disease mechanisms and for targeting treatment. Synchrotron rad...
Article
Full-text available
Background Benefits of variable mechanical ventilation based on the physiological breathing pattern have been observed both in healthy and injured lungs. These benefits have not been characterized in pediatric models and the effect of this ventilation mode on regional distribution of lung inflammation also remains controversial. Here, we compare st...
Preprint
Full-text available
Background: Nasal high flow (NHF) is a non-invasive breathing therapy that is based on the delivery via a large-caliber nasal cannula of heated and humidified air at flow rates that exceed peak inspiratory flow. It is thought that positive airway pressure generated by NHF can help reduce gas trapping and improve regional lung ventilation. There are...
Article
Recent trends in hard X-ray micro-computed tomography (microCT) aim at increasing both spatial and temporal resolutions. These challenges require intense photon beams. Filtered synchrotron radiation beams, also referred to as `pink beams', which are emitted by wigglers or bending magnets, meet this need, owing to their broad energy range. In this w...
Article
Oscillometric measurements of respiratory system resistance (R rs ) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R rs , but also introduce marked flow (V')-dependent changes. We employed intrabreath oscillometry in casts of the upper airways constructed from head CT images of 46 infants. We...
Article
Patients with moderate-to-severe acute respiratory distress syndrome (ARDS) benefit from prone positioning. Although the accuracy of esophageal pressure (Pes) to estimate regional pleural pressure (Ppl) has previously been assessed in supine position, such data are not available in prone position in ARDS. In 6 anesthetized, paralyzed and mechanical...
Preprint
Full-text available
The following is a recommendation for healthcare professionals performing lung function testing during the COVID-19 pandemic. Since transmission of Corona virus is mostly by contact, during lung function procedures transmission can occur also via aerosolised respiratory secretions (during cough and sneezing). Since the safety of our patients and st...
Article
Full-text available
In humans, studies based on Developmental Origins of Health and Disease (DOHaD) concept and targeting short half-lived chemicals, including many endocrine disruptors, generally assessed exposures from spot biospecimens. Effects of early-life exposure to atmospheric pollutants were reported, based on outdoor air pollution levels. For both exposure f...
Article
Full-text available
Modern ventilatory strategies are based on the assumption that lung terminal airspaces act as isotropic balloons that progressively accommodate gas. Phase contrast synchrotron radiation computed tomography (PCSRCT) has recently challenged this concept, showing that in healthy lungs, deflation mechanisms are based on the sequential de-recruitment of...
Article
Full-text available
Background Introducing mathematically derived variability (MVV) into the otherwise monotonous conventional mechanical ventilation has been suggested to improve lung recruitment and gas exchange. Although the application of a ventilation pattern based on variations in physiological breathing (PVV) is beneficial for healthy lungs, its value in the pr...
Article
Full-text available
Background: Although PEEP and inversed I:E ratio have been shown to improve gas exchange in ARDS, both can adversely affect systemic hemodynamics and cerebral perfusion. The goal of this study was to assess how changes in PEEP and I:E ratio affect systemic and cerebral oxygenation and perfusion in normal and injured lung. Methods: Eight anesthet...
Article
Full-text available
Introduction: The mechanisms of lung inflation and deflation are only partially known. Ventilatory strategies to support lung function rely upon the idea that lung alveoli are isotropic balloons that progressively inflate or deflate and that lung pressure/volume curves derive only by the interplay of critical opening pressures, critical closing pr...
Article
Objectives: Airway closure is involved in adverse effects of mechanical ventilation under both general anesthesia and in acute respiratory distress syndrome patients. However, direct evidence and characterization of individual airway closure is lacking. Here, we studied the same individual peripheral airways in intact lungs of anesthetized and mec...
Article
Background: Although a high inspired oxygen fraction (FiO2) is commonly used in paediatric anaesthesia, the impact on postoperative lung function is unclear. We compared lung volume, ventilation heterogeneity, and respiratory mechanics in anaesthetised children randomised to receive low or high FiO2 intraoperatively. Methods: In a double-blind r...
Article
Background Airway hyper‐reactivity, inflammation and remodeling contribute to inhomogeneity of ventilation‐perfusion ratio in asthma. Short‐term variations in can cause changes in expired capnographic indices. Objectives To measure acute changes in the phase 3 slope of the volumetric capnogram after β2‐agonist inhalation (ΔSIII), for comparison wi...
Article
The interpretation of pulmonary function tests (PFTs) to diagnose respiratory diseases is built on expert opinion that relies on the recognition of patterns and the clinical context for detection of specific diseases. In this study, we aimed to explore the accuracy and interrater variability of pulmonologists when interpreting PFTs compared with ar...
Article
Full-text available
Whereas time capnography (Tcap) is routinely displayed during mechanical ventilation, the volumetric representation (Vcap) is seldom used. We compared the diagnostic value of indices derived from Tcap and Vcap following ventilation to perfusion ratio () mismatch subsequent to experimentally induced acute respiratory distress syndrome (ARDS), and al...
Article
Background: The ability of inotropic agents to alter airway reactivity and lung tissue mechanics has not been compared in a well-controlled experimental model. Therefore, we compared the potential to alter lung tissue viscoelasticity and bronchodilator effects of commonly used inotropic agents in an isolated perfused rat lung model. Methods: Aft...
Chapter
Lung diseases are a major burden of public health especially in developed countries and therefore continue to be an active interest in preclinical and clinical research. Due to the complex structure and motion of the lung, an in vivo or in situ analysis would be very beneficial. However, this is very challenging for virtually all imaging technologi...
Article
Ovalbumin (OVA) sensitization has limitations in modelling asthma. Thus, we examined the value of allergic sensitization using a purified natural allergen, house dust mite (HDM), over the sensitization performed with OVA. Mice were sham-treated, or sensitized with OVA- or HDM with identical chronology. Airway resistance, tissue damping and elastanc...
Article
Rationale: Despite the importance of dynamic changes in the regional distributions of gas and blood during the breathing cycle for lung function in the mechanically ventilated patient, no quantitative data on such cyclic changes is currently available. Methods: We used a novel gated synchrotron CT-imaging to quantitatively image regional lung ga...
Article
Objectives: Positive pressure ventilation exposes the lung to mechanical stresses that can exacerbate injury. The exact mechanism of this pathologic process remains elusive. The goal of this study was to describe recruitment/derecruitment at acinar length scales over short-time frames and test the hypothesis that mechanical interdependence between...