2 results for Anderson, JC

  • A mathematical model of alveolar gas exchange in partial liquid ventilation

    Suresh, Vinod; Anderson, JC; Hirschl, RB; Grotberg, JB (2006)

    Journal article
    The University of Auckland Library

    In partial liquid ventilation (PLV), perfluorocarbon (PFC) acts as a diffusion barrier to gas transport in the alveolar space since the diffusivities of oxygen and carbon dioxide in this medium are four orders of magnitude lower than in air. Therefore convection in the PFC layer resulting from the oscillatory motions of the alveolar sac during ventilation can significantly affect gas transport. For example, a typical value of the P├ęclet number in air ventilation is Pe~0.01, whereas in PLV it is Pe~20. To study the importance of convection, a single terminal alveolar sac is modeled as an oscillating spherical shell with gas, PFC, tissue and capillary blood compartments. Differential equations describing mass conservation within each compartment are derived and solved to obtain time periodic partial pressures. Significant partial pressure gradients in the PFC layer and partial pressure differences between the capillary and gas compartments (PC-Pg) are found to exist. Because Pe1, temporal phase differences are found to exist between PC-Pg and the ventilatory cycle that cannot be adequately described by existing non-convective models of gas exchange in PLV. The mass transfer rate is nearly constant throughout the breath when Pe1, but when Pe1 nearly 100% of the transport occurs during inspiration. A range of respiratory rates (RR), including those relevant to high frequency oscillation (HFO)+PLV, tidal volumes (VT) and perfusion rates are studied to determine the effect of heterogeneous distributions of ventilation and perfusion on gas exchange. The largest changes in PCO2 and PCCO2 occur at normal and low perfusion rates respectively as RR and VT are varied. At a given ventilation rate, a low RR-high VT combination results in higher PCO2, lower PCCO2 and lower (PC-Pg) than a high RR-low VT one.

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  • Effect of gravity on liquid plug transport through an airway bifurcation model

    Zheng, Y; Anderson, JC; Suresh, Vinod; Grotberg, JB (2005)

    Journal article
    The University of Auckland Library

    In this study, gravitational and surface mechanisms determining the distribution of instilled liquids are examined experimentally using a bench top model of a symmetrically bifurcating airway. A liquid plug was instilled into the parent tube and driven through the bifurcation by a syringe pump. The effect of gravity was adjusted by changing the roll angle (phi) and pitch angle (gamma) of the bifurcation (phi = gamma = 0) deg was isogravitational). phi determines the relative gravitational orientation of the two daughter tubes: when phi not equal 0 deg, one daughter tube was lower (gravitationally favored) compared to the other gamma determines the component of gravity acting along the axial direction of the parent tube when gamma not equal 0 deg, a nonzero component of gravity acts along the axial direction of the parent tube. A splitting ratio R-S, is defined as the ratio of the liquid volume in the upper daughter to the lower just after plug splitting. We measured the splitting ratio, R-S, as a function of the parent-tube capillary number (Ca-p); the Bond number (Bo); phi; gamma; and the presence of pre-existing plugs initially blocking either daughter tube. A critical capillary number (Ca-c) was found to exist below which no liquid entered the upper daughter (R-S = 0), and above which R-S increased and leveled off with Ca-p. Ca-c increased while R-S decreased with increasing phi, gamma, and Bo for blocked and unblocked cases at a given Ca-p > Ca-c. Compared to the nonblockage cases, R-S decreased (increased) at a given Ca-p while Ca-c increased (decreased) with an upper (lower) liquid blockage. More liquid entered the unblocked daughter with a blockage in one daughter tube, and this effect was larger with larger gravity effect. A simple theoretical model that predicts R-s and Ca-c is in qualitative agreement with the experiments over a wide range of parameters.

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