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E. D. Young 《Bulletin of mathematical biology》1968,30(3):359-385
The arterial system is characterized geometrically as a system of branched elastic fluid lines whose frequency response is
then known in the sense of the Fourier transform. For convenience of visualization the transient response of the individual
tube to an input pressure-flow pair is represented in the time domain by kernel functions indicating the hybrid effect of
viscosity and momentum on the line impedance and damping characteristics. The system as a whole is then divided into a zone
of smaller tubes (below 3 mm) and a zone of larger tubes extending up to the aorta. It is shown that as a system each labyrinth
of tubes below the 3 mm size may be replaced by a single impedance transformation which is dominantly resistive-capacitive.
In the larger tubes, the transformation of the pulse wave at different stations is considered a point of interest. Therefore
hand calculated examples are worked to derive the response of a system involving some of the larger vessels to a pressure
or flow pulse of the typical shape seen near the heart. The result suggests that the dicrotic wave seen in the pressure pulse
of mammals is due to the hybrid viscosity-momentum nature of the longer fluid lines in relation to the gradation of unmatched
terminal impedances with which they are terminated. Damping of the higher frequency components is also accounted for. 相似文献
58.
Ruth C. Steinkamp Clarence L. Young Dolores Nyhus Arnold E. Greenberg 《The Western journal of medicine》1968,109(2):126-133
The amount of sodium ion in water used for ingestion may be critical in effective use of a low sodium dietary regimen. Waters containing not over 20 mg of sodium per liter are provided for in the sodium restricted diets set forth by the American Heart Association. For diets containing more than 500 mg of sodium a day, waters of greater sodium content may be used if proper dietary adjustments are made.While assessment of the long-term average sodium content of a community water supply is difficult, the determined values for sodium lend to classification within range categories. The larger community water supplies in California are presented within several range categories of sodium content.The more commonly used water softeners add sodium to water. The sodium-restricted patient should be cautioned against their use. Similar consideration should probably be given to water supplies of retirement communities where the potential for disorders requiring sodium restriction is greater than in the general population. 相似文献
59.
The ultrastructure of the ejaculated fowl spermatozoon 总被引:1,自引:0,他引:1
60.
Metabolic Processes in Cytoplasmic Particles of the Avocado Fruit. IX. The Oxidation of Pyruvate and Malate during the Climacteric Cycle 总被引:8,自引:7,他引:1 下载免费PDF全文
Mitochondria isolated from preclimacteric avocado fruit oxidize pyruvate at a much lower rate than those separated from climacteric fruit. The external addition of thiamine pyrophosphate (TPP) increased the rate of pyruvate oxidation in both cases.The study of the influence of TPP on the rate of oxidation of malate by mitochondria obtained from both preclimacteric and climacteric fruit indicated that the effect of this cofactor could be understood by assuming that malate was converted to pyruvate. TPP stimulation of malate oxidation was prevented by arsenite, an inhibitor of keto acid oxidation. The addition of glutamate increased the rate of malate oxidation through the transamination of oxaloacetate. This suggests that the rate of oxidation of malate is highly dependent upon mechanisms which remove oxaloacetate efficiently.Incubation of mitochondria from preclimacteric fruit with malate-U-(14)C resulted in the labeling of oxaloacetate and the accumulation of labeled pyruvate. Addition of TPP to this system induced the rapid formation of citrate. This conversion was completely inhibited by arsenite.The results indicate that the ability to carry out the oxidative decarboxylation of alpha-ketoacids improves as the ripening process progresses. The idea was advanced that TPP available to the mitochondria plays an important controlling role. 相似文献