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At least 1,495 records · Page 83Linked to original sources
PubMed1977

The importance of the intestinal countercurrent exchanger for 85Kr absorption from the feline gut.

The rate of 85Kr absorption from the feline gut was studied at varying intestinal blood flows induced by i.a. infusions of a vasodilator drug or by lowering arterial inflow pressure. The effects on rate of absorption of distending the intestine by increasing intraluminal pressure from 0-1 to 5-7 cm H2O as well as of augmenting the rate of luminal perfusion of the 85Kr solution were also investigated. Distending the small bowel increased rate of 85Kr absorption at all levels of intestinal blood flow except at the very low and the very high blood flow rates. Decreasing blood flow by lowering of arterial perfusion pressure decreased the rate of absorption from the distended gut while it had no effect in the collapsed small intestine. Increasing the rate of luminal perfusion enhanced the rate of 85Kr absorption at all blood flow levels except at the lowest ones. The results are discussed with regard to villous hemodynamics, intestinal countercurrent exchange and intraluminal concentration gradients in the lumen. It is concluded that the countercurrent exchanger represents, under physiological conditions, the major limiting factor for the absorption of lipophilic solutes such as 85Kr.

Animals↗
PubMed1983

Intramural blood flow distribution in the small intestine of the cat studied by carbon monoxide uptake and 85krypton elimination.

Carbon monoxide (CO) uptake from the feline small intestine was measured to investigate if it could be used to determine blood flow in the superficial parts of the intestinal mucosa. Several observations were made that substantiated this proposal: 1) Lowering PCO in the intestinal lumen from 100 to 70 kPa did not influence the rate of CO absorption during "resting" blood flow conditions, while the same reduction of lumen PCO resulted in a decreased rate of CO uptake during isoprenaline induced vasodilatation. These observations suggest that CO uptake was flow limited during "rest" and diffusion limited during vasodilation. 2) Lowering perfusion pressure or totally occluding the intestinal vascular supply markedly reduced the rate of CO uptake. 3) The diffusion distance for CO into the tissue was calculated to be 75-225 micron, i.e. CO mainly diffused into the villous tissue. 4) The flow values calculated from the CO measurements were of the same order of magnitude as earlier reported with other techniques (microspheres, indicator dilution method). It was concluded that CO absorption mainly reflected villous blood flow during "resting" and low intestinal blood flow. Total blood flow (venous drop recorder) and muscle layer blood flow (85Kr elimination) were measured simultaneously to CO uptake. From these determinations "resting" blood flow distribution in the small intestine was calculated.

Animals↗
PubMed1994

Fractionated martian atmosphere in the nakhlites?

Considerable evidence points to a martian origin of the SNC meteorites. Noble gas isotopic compositions have been measured in most SNC meteorites. The 129Xe/132Xe vs, 84Kr/132Xe ratios in Chassigny, most shergottites, and lithology C of EETA 79001 define a linear array. This array is thought to be a mixing line between martian mantle and martian atmosphere. One of the SNC meteorites, Nakhla, contains a leachable component that has an elevated 129Xe/132Xe ratio relative to its 84Kr/132Xe ratio when compared to this approximately linear array. The leachable component probably consists in part of iddingsite, an alteration product produced by interaction of olivine with aqueous fluid at temperatures lower than 150 degrees C. The elevated Xe isotopic ratio may represent a distinct reservoir in the martian crust or mantle. More plausibly, it is elementally fractionated martian atmosphere. Formation of sediments fractionates the noble gases in the correct direction. The range of sediment/atmosphere fractionation factors is consistent with the elevated 129Xe/132Xe component in Nakhla being contained in iddingsite, a low temperature weathering product. The crystallization age of Nakhla is 1.3 Ga. Its low-shock state suggests that it was ejected from near the surface of Mars. As liquid water is required for the formation of iddingsite, these observations provide further evidence for the near surface existence of aqueous fluids on Mars more recently than 1.3 Ga.

Atmosphere↗
PubMed1992

Stomach outline visualization in gastrointestinal transit studies using scintigraphy.

A major disadvantage of gamma scintigraphy in gastrointestinal transit studies is the inability to provide adequate delineation of anatomical details. As an aid to the important requirement of outlining the stomach to ensure accurate quantification of the time at which material empties from this organ, a new technique is described, using short half-life 81mKr gas to provide clearer identification of the stomach outline and position.

Gastrointestinal Transit↗
PubMedDate not supplied

Theoretical analysis of regional blood flow studies.

Regional blood flow measurements were analyzed using a two-compartment model. The distribution of injected tracer between blood and tissue was assumed to be in equilibrium only at the beginning of the experiment. Equations for the determination of the partition coefficient of injected radionuclides from in vivo measurements were derived. These equations can also be used for estimation of the relative blood content of a tumor or an organ. The results were applied to experiments, where three diffusible radionuclides were injected simultaneously into patients with diagnosed tumors.

Argon↗
PubMed2003

Non-invasive diagnosis of tracheobronchomalacia using a modified ventilation radioisotope lung scan.

The use of radionuclide ventilation lung scan to characterise the physiological effects of tracheobronchomalacia is a novel application of this non-invasive technique. In the reported case the right upper lobe was found to be not ventilated below a pressure of 20 cm H2O despite evidence from a dynamic tracheobronchogram of the right upper lobe bronchus opening at the lower pressure of 15 cm H2O.

Bronchial Diseases↗