Guo-Fan Ye

A compartmental model for oxygen-carbon dioxide coupled transport in the microcirculation

We present a multicompartmental model for an oxygen-carbon dioxide transport system. The compartmental equations and their lumped parameters are derived through space averaging of the corresponding distributed model. The model can predict compartmental distributions of oxygen and carbon dioxide partial pressures, oxygen-hemoglobin saturation, and pH. Other unique features include the effects of the radial distribution of partial pressures and the difference in metabolic rates between vessel wall and tissue. A model for the cat brain, based on this formulation, is compared with results of experiments and with two types of earlier models: one without space averaging and one without carbon dioxide transport. The results suggest that space averaging the convective terms significantly affects the behavior of the model. This is consistent with conclusions from our earlier oxygen-only model. Our observations also demonstrate, however, significant differences between the results from the oxygen-carbon dioxide model and the oxygen-only model. For instance, at low blood flow rates or at low level of oxygen input, predicted oxygen partial pressures can differ by as much as 30% between the two models. Results obtained from the present model are supported by available experimental findings.

O2–Hb Reaction Kinetics and the Fåhraeus Effect during Stagnant, Hypoxic, and Anemic Supply Deficit

AbstractWe modified our previous computer model of O2 and CO2 transport in the cerebral microcirculation to include nonequilibrium O2–Hb kinetics and the Fåhraeus effect (reduced tube hematocrit in small microvessels). The model is a steady-state multicompartmental simulation which includes three arteriolar compartments, three venular compartments, and one capillary compartment. Three different types of oxygen deficits (stagnant, hypoxic, and anemic conditions) were simulated by respectively reducing blood flow, arterial O2 saturation, and systemic hematocrit to one half of normal. Microcirculatory distributions for

A compartmental model of oxygen transport derived from a distributed model: treatment of convective and oxygen dissociation properties

P_{{\text{O}}_{\text{2}} } ,{\text{ }}P_{{\text{CO}}_{\text{2}} } ,

Computer - Modeling of Oxygen Supply to Cartilage: Addition of a Compartmental Model

O2 saturation and deviations from equilibrium, and the O2 and CO2 fluxes for each compartment were predicted for the three O2 supply deficits. Differences were found for O2 extraction ratios and relative contributions of arteriolar, venular, and capillary gas fluxes for each type of deficit. The Fåhraeus effect and O2–Hb kinetics reduced O2 extraction in all cases and altered microcirculatory gas distributions depending on the specific type of O2 supply deficits. The modified model continues to predict that capillaries are the major site where gas exchange takes place, and demonstrates that the Fåhraeus effect and nonequilibrium O2–Hb kinetics are important mechanisms that should not be neglected in O2 and CO2 transport modeling. While this model provides useful insight regarding the influence of the Fåhraeus effect and O2–Hb kinetics under steady state, the addition of a distributed and dynamic simulation should further elucidate the effects of the brains heterogeneous properties and transient behavior.

Formulation and Realization of a Multicompartmental Model for O2-CO2 Coupled Transport in the Microcirculation

A popular and useful technique used to model blood flow in cardiovascular simulations is to divide each blood vessel into a series of segments, each with its own lumped resistance, intertance, and compliance parameters. The values of these parameters are usually obtained through a simplification of the Navier-Stokes equations for fluid flow. However, the simplification often ignores the nonlinear and convective terms of the equations, resulting in errors in the parameter values, especially in the value found for resistance per unit length. We report a new method for the calculation of vessel resistance per unit length which takes into account the effects of vessel taper and wall compliance. It is shown that these effects can be addressed by the addition of two time-varying terms to the calculation of resistance per unit length. One term, due to vessel taper, is proportional to volumetric flow rateQ. The other term, due to vessel compliance, is proportional to ∂p/∂t. These variables are readily available in computer simulations of blood flow in lumped parameter systems. Using data for the descending aorta, the new parameter values, when averaged over a cardiac cycle, compare favorably with results in the literature.

Equal Oxygen Delivery May Not Result in Equal Oxygen Consumption

The authors derive a compartmental model for oxygen transport in vascular blood which is suitable for both steady and time-varying analysis, and which can be used with any kind of oxygen dissociation function. The derivation focuses on the establishment of expressions for the lumped convective term and the lumped oxygen dissociation function. Results of the simulation show that the value of the lumped convective term in the present model is significantly larger than that found in previously published models, and that the value computed from the present lumped oxygen dissociation function, while not significantly different under normal or mildly hypoxic conditions from that used in the other models, becomes significantly larger under severe hypoxia.<<ETX>>

Extension of a multielement compartmental model for O/sub 2/-CO/sub 2/ transport to time-varying applications

A partial pressure dependent metabolic mechanism was incorporated into our previous multicompartmental model for O/sub 2/-CO/sub 2/ coupled transport in the cat cerebral microcirculation-tissue system. The refined model predicts the distribution of O/sub 2/ and CO/sub 2/ concentrations and regional flux along the microcirculation under various hemodynamic and metabolic conditions. Our simulation indicates that capillaries are the main site for O/sub 2/ as well as CO/sub 2/ exchange in the microcirculation. This is in contrast with results from the Roth and Wade model suggesting precapillary preponderance of CO/sub 2/ exchange.

Influence of O2-Hb Kinetics and the Fähraeus Effect on the Arteriolar Role in Gas Exchange

Our previous studies have focussed on the architecture of the avian growth plate and the oxygen consumption of growth plate chondrocytes in order to develop an appropriate computer model for estimating chondrocyte anoxia (Haselgrove et al., 1993). Initially, we used two models: the Krogh cylinder (Silverton et al., 1989), and a second model with similar geometry utilizing a complex oxygen consumption as a function of oxygen concentration (Silverton et al., 1990). For this purpose, we divided the growth plate into two anatomical regions; the region of resting-proliferating chondrocytes and the region of hypertrophic chondrocytes. We modeled the two growth plate regions separately and ignored the transition zone. We also used a two dimensional analysis assuming that the major flow of oxygen was radial rather than axial. To extend our model, we have now used a compartmental model originally developed for modeling the oxygen and carbon dioxide distribution in the microvasculature of the brain (Ye et al., 1993). With this model we have been able to evaluate the contribution of the microvacular structure to oxygen supply of the resting and hypertrophic regions of the growth cartilage and to estimate oxygen and carbon dioxide partial pressure variations in the growth plate.