Direct method for linear equations in branching networks.
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Hemorheology↗
Biomedical subjects
P E Hydon
Publications and source records attributed to P E Hydon.
Gas flow and mixing in the airways.
OBJECTIVE: To survey the current state of scientific knowledge of gas flow and mixing in pulmonary airways, especially at high frequencies. DATA SOURCES: Results from the authors' own laboratory studies and Western bioengineering literature on respiratory fluid mechanics. STUDY SELECTION: This survey concentrates on understanding the principal physical mechanisms that underlie the enhancement of airway gas transport in high-frequency oscillation. The results of experimental, computational, and mathematical studies are described. DATA SYNTHESIS: The topic was covered by seven presenters at the Münster Meeting on High Frequency Ventilation, January 31 to February 2, 1993. Six of these presentations are summarized in the six sections of this paper under the following headings: Introductory Survey; Three-Dimensional Numerical Simulation of Inspiratory and Expiratory Flows in Small Airways; Computational and Experimental Models of High-Frequency Oscillation; Unsteady Gas Mixing in Airways; Gas Dispersion From the Lagrangian Viewpoint; and Soluble Gas Mass Transfer in Tubes and Airways. CONCLUSIONS: The dominant mechanism for the enhancement of gas transport along airways at high frequency is likely to lie in the coupling of the secondary motions caused by airway curvature with the oscillatory longitudinal flow. However, laboratory experiments and theoretical analyses have led only to an accurate simulation of the phenomena in idealized geometries, not in real lungs.
Animals↗
An analysis of the single-pool urea kinetic model and estimation of errors.
The single-pool urea kinetic model assumes that urea is distributed within the body in a volume Vf at a uniform concentration. It may be used to describe the clearance of urea during and following haemodialysis, and to determine the value of the urea concentration at the end of dialysis Cf or the urea generation rate G, and the urea distribution volume Vf. The protein catabolic rate (PCR) is obtained using the ratio G/Vf. The sensitivity of the predictions of the model to small errors in the experimentally estimated model parameters is evaluated and suggests that the model prediction of Cf is relatively insensitive to errors in the estimate of G, but more sensitive to errors in Vf and dialyser clearance K. The determination of G from urea concentration measurements made during dialysis alone is very sensitive to errors. The accurate estimation of G requires the use of concentration measurements made between dialyses. The calculation of the PCR is very sensitive to errors in G and Vf since these are not independent and must be used with caution, particularly when used to compare values between patients.
Humans↗