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How do changes in exhaled CO₂ measure changes in cardiac output? A numerical analysis model.

Objective: In a previous study in anesthetized animals, the slope of percent decreases in exhaled CO₂ versus percent decreases in cardiac output (Q(T) inflation of vena cava balloons) was 0.73. To examine the mechanisms underlying this exhaled CO₂-Q(T) relationship, an iterative numerical analysis c...

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Published in:Journal of Clinical Monitoring & Computing Vol. 24; no. 6; pp. 413 - 420
Main Authors: Breen PH, Breen, Peter H
Format: research Journal Article
Published: Springer Nature Dec2010
Online Access:View this record in EBSCOhost
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      dt: Dec2010
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      pub: Springer Nature
      place: New York, New York
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        atl: How do changes in exhaled CO₂ measure changes in cardiac output? A numerical analysis model.
      aug:
        au:
          Breen PH
          Breen, Peter H
        affil: Department of Anesthesiology and Perioperative Care, University of California-Irvine, UCI Medical Center, Orange, CA 92868, USA
      sug:
        subj:
          Blood Pressure Physiology
          Carbon Dioxide Metabolism
          Cardiac Output Physiology
          Expiration Physiology
          Models, Biological
          Pulmonary Gas Exchange Physiology
          Animals
          Computer Simulation
          Dogs
      ab: Objective: In a previous study in anesthetized animals, the slope of percent decreases in exhaled CO₂ versus percent decreases in cardiac output (Q(T) inflation of vena cava balloons) was 0.73. To examine the mechanisms underlying this exhaled CO₂-Q(T) relationship, an iterative numerical analysis computer model of non-steady state CO(2) kinetics was developed.Methods: The model consisted of a large peripheral tissue compartment connected by venous return and [Formula: see text] to a small central pulmonary compartment. Equations were developed to describe the movement of CO₂ in this system. Decreases in Q(T) were accompanied by experimentally measured increases in alveolar dead space fraction (VD: (alv)/VT: (alv)), generated by decreased pulmonary vascular pressure during the Q(T) decrease.Results: When the model was perturbed by a 40% decrease in Q(T) and an increase in VD: (alv)/VT: (alv) from 5 to 20.6%, average alveolar expired P(CO₂) (PAE(CO₂)) decreased from 37.5 to 29.4 mm Hg, similar to the animal experiments. Due to the high peripheral tissue compliance for CO₂, the computer model demonstrated that, after a decrease in Q(T), at least 1 h was required for compartment CO₂ stores to approach a new equilibrium state.Conclusions: The numerical analysis computer model helps to delineate the mechanisms underlying how decreased Q(T) resulted in decreased exhaled CO₂. The model permitted deconvolution of the effects of simultaneous variables and the interrogation of parameters that would be difficult to measure in actual experiments.
      pubtype: Academic Journal
      doctype:
        research
        Journal Article
      ougenre: Article
    language: English
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