Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep
| Autor: | Anne Nicolaysen, Mats J. Johansson, Andreas Wiklund, Gunnar Nicolaysen, Torun Flatebø, Sten Walther |
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| Rok vydání: | 2004 |
| Předmět: |
medicine.medical_specialty
Supine position medicine.medical_treatment Posture Critical Care and Intensive Care Medicine Ventilation/perfusion ratio Fluorescence Positive-Pressure Respiration Intensive care Internal medicine Administration Inhalation medicine Prone Position Supine Position Animals Lung volumes Positive end-expiratory pressure Sodium Pertechnetate Tc 99m Mechanical ventilation Aerosols Lung Sheep business.industry Pulmonary Gas Exchange respiratory system Respiration Artificial Microspheres respiratory tract diseases Prone position medicine.anatomical_structure Anesthesia Models Animal Cardiology business Pulmonary Ventilation |
| Zdroj: | Critical care medicine. 32(10) |
| ISSN: | 0090-3493 |
| Popis: | BACKGROUND: The principal function of the lung is gas exchange requiring adequate ventilation and perfusion at the level of the alveoli. The efficiency of gas exchange is depending on the distributions of regional ventilation (V) and pulmonary blood flow (Q) and their correlation.AIMS: To validate a high-resolution method to quantify regional V and to investigate the combined effect of positive end-expiratory pressure (PEEP) and body position on distributions of regional V and Q in the normal lung with mechanical ventilation. To assess the matching of V and Q by calculating ventilation-perfusion ratio (V/Q) heterogeneity, determining the spatial distribution of V/Q and to investigate the role of nitric oxide (NO) in regional V/Q matching.METHODS: Anesthetized mechanically ventilated sheep were studied in prone or supine position with different levels of PEEP (0, 10 and 20 cmH2O). Measurements of regional V were done by determining the deposition of a wet aerosol of fluorescent microspheres (FMS) with a median mass aerodynamic diameter of 1.1 μm, and validated against Technegas. Radioactive microspheres, 15 μm in diameter, were used for determining regional Q. Nitric oxide synthase (NOS) was inhibited with Nω-nitro-L-arginine methyl ester (L-NAME) to evaluate the role of NO on regional V/Q matching. The right lung was dried at total lung capacity and diced in approx. 1000 regions tracking the spatial location of each region.RESULTS: The deposition of FMS mirrored regional deposition of Technegas and thus regional ventilation well. In prone, with PEEP, only a small dorsal redistribution of V but not of Q was observed. The vertical Q gradient was abolished with PEEP in prone position in conflict with the classical zonal model. In supine position both V and Q were distributed with a unimodal gradient and PEEP displaced the mode further dorsally. V/Q heterogeneity was greater in supine than in prone position with and without PEEP. Furthermore, PEEP generated regions with high V/Q in supine but not in prone position. Inhibition of NOS did not change the V/Q distribution in prone position.CONCLUSION: There were marked differences in redistribution of regional ventilation and regional pulmonary blood flow between prone and supine position when PEEP was applied. NO was not an active mechanism for V/Q matching in normal sheep lungs. |
| Databáze: | OpenAIRE |
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