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  • 1
    Electronic Resource
    Electronic Resource
    Effects of dissolved electrolytes on the solubility and partial molar volume of helium in water from 50 to 400 atmospheres at 25°C (1983)
    Springer
    Journal of solution chemistry 12 (1983), S. 655-669 
    Details
    ISSN: 1572-8927
    Keywords: Helium solubility ; partial molar volume ; salting-out ; water ; aqueous electrolytes ; high pressure ; Henry's law
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The solubility of helium in water and aqueous CsCl, NaCl and MgCl2 solutions at concentrations up to 3.380 molal has been measured at 50 atm intervals from 50 to 400 atm at 25°C. Setschenow coefficients for helium are practically invariant with pressure in each solution, decrease significantly with increasing electrolyte concentration and vary with the type of electrolyte in a fashion identical to that observed for the low pressure solubilities of other gases. The pressure dependence of the helium solubility in each solution follows a form of Henry's law in which the helium partial molar volume at infinite dilution $$\bar V^{_{He}^o } $$ is independent of pressure. Values of $$\bar V^{_{He}^o } $$ , computed from Henry's law, are smaller for the electrolyte solutions than for water and vary systematically with the type and concentration of dissolved electrolyte. This result is explained qualitatively in terms of ion hydration and its influence on the ability of the intrinsic configurational volume in each liquid to accommodate the relatively small helium molecules. It is concluded that intrinsic solvent structure is an important factor governing the partial molar volume of helium and the pressure dependence of helium solubility in water and aqueous electrolytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648669
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Limits of gas secretion by the salting-out effect in the fish swimbladder rete (1982)
    Springer
    Journal of comparative physiology 146 (1982), S. 129-136 
    Details
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The high dissolved gas tensions required for the secretion of gases into deep-sea fish swimbladders are thought to be produced in the rete mirabile by a countercurrent multiplication mechanism, the capacity of which is theoretically limited by the physical characteristics of the rete and by the magnitudes of minute gas solubility changes in the blood plasma. These gas solubility changes are presumably induced through the salting-out effect following the addition of lactic acid to rete venous blood as it circulates through the gas gland. In order to estimate the maximum swimbladder gas pressures attainable by this mechanism, the effects of lactic acid on N2 and Ar solubilities in water were determined at 5 and 25°C with a new volumetric method. The results show that the salting-out effect with lactic acid is much smaller than with NaCl, and that the agreement between predicted and observed swimbladder gas pressures is more critically dependent on the physical properties of the rete vasculature than indicated by previous theoretical treatments. When augmented by the release of hemoglobin-bound O2, the salting-out effect with lactic acid appears large enough to account for the production of even the highest swimbladder O2 pressures, provided the rete characteristics lie within certain reasonable limits. However, successful theoretical explanation of observed swimbladder N2 pressures in some deep-sea species will require rigorous attention to such theoretically neglected factors as dissolved gas backdiffusion along the rete and the unequal size and number of the rete arterial and venous capillaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00688726
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  • 3
    Electronic Resource
    Electronic Resource
    Patency and blood flow in gas denucleated arterial prostheses (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 493-498 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Biomaterials exposed to blood often fail due to thrombosis. Gas nuclei (air) in the material are thrombogenic and a potential cause of failure. The effects of gas nuclei on patency and blood flow were studied in 4 mm diameter arterial grafts (Gore ePTFE; Johnson and Johnson Vitagraft ePTFE; Bard ACG EXS) in the femoropopliteal position of dogs. Control and denucleated (air-free) grafts were implanted bilaterally. Grafts were denucleated by immersion in degassed saline and exposure to 4 torr vacuum and 3,000-20,000 psig pressure. Graft patency was determined at harvest in 46 dogs. Blood flow was measured with acoustic flow probes in eight dogs. Denucleated graft patency was 60% after 2 days of implant while control patency was 22% (P 〈 .05). Measured blood flow was higher in denucleated grafts than in control grafts (P 〈 .02) in 4 of 5 dogs which had significantly different flows. Patency and flow decreased to zero for both control and denucleated grafts over periods of up to 80 days. Air in the control grafts may have been absorbed within several days, leading to late similarity with the denucleated grafts. Thus, removing the air from 4 mm ePTFE grafts decreased acute thrombosis and increased the patency. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820270410
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  • 4
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    Heterogeneous nucleation of bubbles at solid surfaces in gas-supersaturated aqueous solutions (1980)
    Elsevier
    Details
    Publication Date: 1980-03-01
    Print ISSN: 0021-9797
    Electronic ISSN: 1095-7103
    Topics: Chemistry and Pharmacology , Physics
    Published by Elsevier
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    PAPER CURRENT
  • 5
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    Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue (2003)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Models of gas bubble dynamics employed in probabilistic analyses of decompression sickness incidence in man must be theoretically consistent and simple, if they are to yield useful results without requiring excessive computations. They are generally formulated in terms of ordinary differential equations that describe diffusion-limited gas exchange between a gas bubble and the extravascular tissue surrounding it. In our previous model (Ann. Biomed. Eng. 30: 232-246, 2002), we showed that with appropriate representation of sink pressures to account for gas loss or gain due to heterogeneous blood perfusion in the unstirred diffusion region around the bubble, diffusion-limited bubble growth in a tissue of finite volume can be simulated without postulating a boundary layer across which gas flux is discontinuous. However, interactions between two or more bubbles caused by competition for available gas cannot be considered in this model, because the diffusion region has a fixed volume with zero gas flux at its outer boundary. The present work extends the previous model to accommodate interactions among multiple bubbles by allowing the diffusion region volume of each bubble to vary during bubble evolution. For given decompression and tissue volume, bubble growth is sustained only if the bubble number density is below a certain maximum.
    Keywords: Life Sciences (General)
    Type: Annals of biomedical engineering (ISSN 0090-6964); Volume 31; 4; 471-81
    Format: text
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  • 6
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    Mathematical model of diffusion-limited gas bubble dynamics in unstirred tissue with finite volume (2002)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Models of gas bubble dynamics for studying decompression sickness have been developed by considering the bubble to be immersed in an extravascular tissue with diffusion-limited gas exchange between the bubble and the surrounding unstirred tissue. In previous versions of this two-region model, the tissue volume must be theoretically infinite, which renders the model inapplicable to analysis of bubble growth in a finite-sized tissue. We herein present a new two-region model that is applicable to problems involving finite tissue volumes. By introducing radial deviations to gas tension in the diffusion region surrounding the bubble, the concentration gradient can be zero at a finite distance from the bubble, thus limiting the tissue volume that participates in bubble-tissue gas exchange. It is shown that these deviations account for the effects of heterogeneous perfusion on gas bubble dynamics, and are required for the tissue volume to be finite. The bubble growth results from a difference between the bubble gas pressure and an average gas tension in the surrounding diffusion region that explicitly depends on gas uptake and release by the bubble. For any given decompression, the diffusion region volume must stay above a certain minimum in order to sustain bubble growth.
    Keywords: Aerospace Medicine
    Type: Annals of biomedical engineering (ISSN 0090-6964); Volume 30; 2; 232-46
    Format: text
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  • 7
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    Statistical Analysis of Risk Factors in the Prebreathe Reduction Protocol (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The 165 exposures from four 2-hour protocols were analyzed for correlations or trends between decompression sickness (DCS) or venous gas emboli (VGE), and variables that affect risk in the subject and astronaut populations. The assumption in this global survey is that the distributions of gender, age, body mass index, etc., are equally represented in all four tested procedures. We used Student t-test for comparisons between means and chi-square test between comparisons of proportions with p〈0.05 defining a significant level. The type and distribution of the 19 cases of DCS were similar to historical cases. There was no correlation of age, gender, body mass index or fitness level with greater incidence of DCS or VGE. However increased age was associated with more Grade IV VGE in males. The duration and quantity of exercise during prebreathe is inversely related to risk of DCS and VGE. The latency time for VGE was longer (103 min +/- 56 SD, n = 15) when the ergometry was done approximately 15 min into the prebreathe than when done at the start of the prebreathe (53 min +/- 31, n = 13). The order of the ergometry did not influence the overall DCS and VGE incidence. We identified variables other than those of the prebreathe procedures that influence the DCS and VGE outcome. The analysis suggests that males over 40 years have a high incidence of Grade IV VGE.
    Keywords: Aerospace Medicine
    Type: May 14, 2000 - May 18, 2000; Houston, TX; United States
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    NASA TECHNICAL REPORTS
  • 8
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    A Mathematical Model of Diffusion-Limited Gas Bubble Dynamics in Tissue with Varying Diffusion Region Thickness (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: A three-region mathematical model of gas bubble dynamics has been shown suitable for describing diffusion-limited dynamics of more than one bubble in a given volume of extravascular tissue. The model is based on the dynamics of gas exchange between a bubble and a well-stirred tissue region through an intervening unperfused diffusion region previously assumed to have constant thickness and uniform gas diffusivity. As a result, the gas content of the diffusion region remains constant as the volume of the region increases with bubble growth, causing dissolved gas in the region to violate Henry's law. Earlier work also neglected the relationship between the varying diffusion region volume and the fixed total tissue volume, because only cases in which the diffusion region volume is a small fraction of the overall tissue volume were considered. We herein extend the three-region model to correct these theoretical inconsistencies by allowing both the thickness and gas content of the diffusion region to vary during bubble evolution. A postulated difference in gas diffusivity between an infinitesimally thin layer at the bubble surface and the remainder of the diffusion region leads to variation in diffusion region gas content and thickness during bubble growth and resolution. This variable thickness, differential diffusivity (VTDD) model can yield bubble lifetimes considerably longer than those yielded by earlier three-region models for given model and decompression parameters, and meets a need for theoretically consistent but relatively simple bubble dynamics models for use in studies of decompression sickness (DCS) in human subjects, Keywords: decompression sickness, gas diffusion in tissue, diffusivity
    Keywords: Aerospace Medicine
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  • 9
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    Bioimpedance Measurement of Segmental Fluid Volumes and Hemodynamics (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Bioimpedance has become a useful tool to measure changes in body fluid compartment volumes. An Electrical Impedance Spectroscopic (EIS) system is described that extends the capabilities of conventional fixed frequency impedance plethysmographic (IPG) methods to allow examination of the redistribution of fluids between the intracellular and extracellular compartments of body segments. The combination of EIS and IPG techniques was evaluated in the human calf, thigh, and torso segments of eight healthy men during 90 minutes of six degree head-down tilt (HDT). After 90 minutes HDT the calf and thigh segments significantly (P 〈 0.05) lost conductive volume (eight and four percent, respectively) while the torso significantly (P 〈 0.05) gained volume (approximately three percent). Hemodynamic responses calculated from pulsatile IPG data also showed a segmental pattern consistent with vascular fluid loss from the lower extremities and vascular engorgement in the torso. Lumped-parameter equivalent circuit analyses of EIS data for the calf and thigh indicated that the overall volume decreases in these segments arose from reduced extracellular volume that was not completely balanced by increased intracellular volume. The combined use of IPG and EIS techniques enables noninvasive tracking of multi-segment volumetric and hemodynamic responses to environmental and physiological stresses.
    Keywords: Aerospace Medicine
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Effects of microgravity on tissue perfusion and the efficacy of astronaut denitrogenation for EVA (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A potentially flight-applicable, breath-by-breath method for measuring N2 elimination from human subjects breathing 100 percent O2 for 2-3 hr periods has been developed. The present report describes this development with particular emphasis on required methodological accuracy and its achievement in view of certain properties of mass spectrometer performance. A method for the breath-by-breath analysis of errors in measured N2 elimination profiles is also described.
    Keywords: AEROSPACE MEDICINE
    Type: Aviation, Space, and Environmental Medicine (ISSN 0095-6562); 58; A100-A10
    Format: text
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