Document Detail


The dependence of measured alveolar deadspace on anatomical deadspace volume.
MedLine Citation:
PMID:  15980045     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
BACKGROUND: Changes in pulmonary deadspace are indicators of disease status (e.g. pulmonary embolus, acute respiratory distress syndrome) and they have prognostic usefulness in the intensive care unit. The components of pulmonary deadspace, the alveolar and anatomical deadspaces (VDalv and VDanat), are commonly considered to be independent (i.e. the addition of airway equipment should not alter the measured VDalv). However, VDanat has been shown to affect VDalv in the absence of changes in alveolar ventilation or perfusion. We sought to quantify the variability in measured VDalv induced by changes in VDanat using a cardiorespiratory computational model. METHODS: Using the Nottingham Physiology Simulator, we examined three simulated ventilated patients with small, moderate and large ventilation-perfusion (VQ) defects. Each patient received 12.5 bpm x 500 ml. We varied VDanat between 50 and 250 ml, keeping the VQ ratio of each alveolus constant. We calculated VDalv by subtracting VDanat (measured using Fowler's technique) from the physiological deadspace (measured using the Bohr-Enghoff equation). We calculated fresh-gas tidal volume (VTfresh) by subtracting VDanat from the exhaled tidal volume and calculated VDalv/VTfresh. In the simulated patient with the large VQ defect, we performed the same protocol with tidal volumes of 750 and 1000 ml. RESULTS: When VDanat increased from 50 to 250 ml (500 ml tidal volume) VDalv decreased by 48.3% (mean value across the three VQ defects) and VDalv/VTfresh decreased by 15.1%. These relationships were similar at each tidal volume studied. CONCLUSIONS: Measured VDalv is altered by changes in VDanat despite constant VQ ratios in each alveolus. This has implications for the interpretation of deadspace measured in the clinical setting. The variability is less for the ratio VDalv/VTfresh.
Authors:
I K Moppett; C B Gornall; J G Hardman
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Publication Detail:
Type:  Journal Article; Validation Studies     Date:  2005-06-24
Journal Detail:
Title:  British journal of anaesthesia     Volume:  95     ISSN:  0007-0912     ISO Abbreviation:  Br J Anaesth     Publication Date:  2005 Sep 
Date Detail:
Created Date:  2005-08-03     Completed Date:  2005-09-23     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0372541     Medline TA:  Br J Anaesth     Country:  England    
Other Details:
Languages:  eng     Pagination:  400-5     Citation Subset:  IM    
Affiliation:
University Department of Anaesthesia, University Hospital, Nottingham NG7 2UH, UK.
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MeSH Terms
Descriptor/Qualifier:
Computer Simulation*
Humans
Models, Biological*
Patient Simulation
Pulmonary Gas Exchange / physiology
Respiration Disorders / physiopathology
Respiratory Dead Space / physiology*
Tidal Volume / physiology

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