Document Detail

Within-breath arterial PO2 oscillations in an experimental model of acute respiratory distress syndrome.
MedLine Citation:
PMID:  11103189     Owner:  NLM     Status:  MEDLINE    
Tidal ventilation causes within-breath oscillations in alveolar oxygen concentration, with an amplitude which depends on the prevailing ventilator settings. These alveolar oxygen oscillations are transmitted to arterial oxygen tension, PaO2, but with an amplitude which now depends upon the magnitude of venous admixture or true shunt, QS/QT. We investigated the effect of positive end-expiratory pressure (PEEP) on the amplitude of the PaO2 oscillations, using an atelectasis model of shunt. Blood PaO2 was measured on-line with an intravascular PaO2 sensor, which had a 2-4 s response time (10-90%). The magnitude of the time-varying PaO2 oscillation was titrated against applied PEEP while tidal volume, respiratory rate and inspired oxygen concentration were kept constant. The amplitude of the PaO2 oscillation, delta PaO2, and the mean PaO2 value varied with the level of PEEP applied. At zero PEEP, both the amplitude and the mean were at their lowest values. As PEEP was increased to 1.5 kPa, both delta PaO2 and the mean PaO2 increased to a maximum. Thereafter, the mean PaO2 increased but delta PaO2 decreased. Clear oscillations of PaO2 were seen even at the lowest mean PaO2, 9.5 kPa. Conventional respiratory models of venous admixture predict that these PaO2 oscillations will be reduced by the steep part of the oxyhaemoglobin dissociation curve if a constant pulmonary shunt exists throughout the whole respiratory cycle. The facts that the PaO2 oscillations occurred at all mean PaO2 values and that their amplitude increased with increasing PEEP suggest that QS/QT, in the atelectasis model, varies between end-expiration and end-inspiration, having a much lower value during inspiration than during expiration.
E M Williams; J P Viale; R M Hamilton; H McPeak; L Sutton; C E Hahn
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  British journal of anaesthesia     Volume:  85     ISSN:  0007-0912     ISO Abbreviation:  Br J Anaesth     Publication Date:  2000 Sep 
Date Detail:
Created Date:  2000-12-07     Completed Date:  2000-12-07     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0372541     Medline TA:  Br J Anaesth     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  456-9     Citation Subset:  IM    
Nuffield Department of Anaesthetics, University of Oxford, Radcliffe Infirmary, UK.
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MeSH Terms
Blood Pressure / physiology
Cardiac Output / physiology
Models, Animal
Oxygen / blood
Positive-Pressure Respiration / adverse effects*
Pulmonary Atelectasis / blood,  physiopathology*
Respiratory Distress Syndrome, Adult / blood,  physiopathology*
Respiratory Physiological Phenomena*
Reg. No./Substance:

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