This research has been sponsored by the Defense Atomic Support Agency NWER Subtask MA 012. r°A BSTRACTTolerance indices were determined, allowing for the effects of body maus, for thirteen mammalian species using the results of experiments in which animals were exposed near a normally reflecting surface to shocked blast waves whose durations ranged from 0. 24 to 400 msec. A general equation wai developed for expressing the interrelations between overpressure, duration c' the blast wave, body mass, and probability of survival. The species % ire divided into high-and :ow-tolerance groups applicable to "large" and "small" mammals, respectively. Since the available evidence indicated that man is more likely to be a member of the high-tolerance group, the tolerance index arbitrarily, but tentatively, assigned to him was the geometric mean of those for the large species. Using criteria developed in experimental studies, the results of the overall analysis were made applicable to free-stream situations in which the long 4 axis of the body is, perpendicular or parallel to the dir'ection of propagation of a s) •cked blast wave.
The cumulative fluxes of radioactive sucrose, sodium, and water across a sheet of cat right ventricle were studied simultaneously to obtain the apparent tissue diffusion coefficients for extravascular diffusion at 37°C. The sucrose data fitted the equations for diffusion in tortuous channels in a plane sheet with a tortuosity factor, λ, of 2.11 ± 0.11 (mean ± SE, n = 10). The fit of the earliest data before attainment of steady state was improved by assuming a Gaussian distribution of diffusion path lengths through the extracellular space, but λ was only changed by a few percent. The sucrose diffusion channel contained 0.27 ± 0.03 ml of total tissue water, which is more than measured by others but still less than the expected sucrose space. The steady-state data for sodium agreed with the model for extracellular diffusion using λ and the area available for diffusion for sucrose when sodium equilibration with a dead-end pore volume (presumed to be intracellular) was taken into account. The cumulative flux data for water were monotonic and lacked secondary inflections. Thus the apparent tissue diffusion coefficients for sucrose, sodium, and water were (in 10 −6 cm 2 /s) 1.77 ± 0.23, 5.13 ± 0.68, and 7.39 ± 0.99, respectively, representing a reduction to 23% of the free diffusion coefficient for sucrose and sodium and 22% for water. Keywords tissue diffusion; cat ventricular myocardium; diffusion models; tracer washout; extracellular fluid; dead-end pores; heterogeneous systems; solute transport Fundamental to the analysis of capillary-tissue exchanges is a knowledge of tissue transfer rates by diffusion outside the capillaries (2,30). The purpose of this work was to determine the apparent tissue diffusion coefficients for sucrose, sodium, and water at body temperature in the cat myocardium. The studies were made in a diffusion cell (32) on a sheet of cat myocardium by a method modified from that described by Page and Bernstein (26). These authors found at 23°C that sodium did not enter the cells and that the steady-state diffusion of water, sodium, and sucrose could be accounted for by fluxes occurring only in the extracellular space. Since cell membrane permeability to water is so high that restriction of water diffusion to the extracellular space seemed unlikely, we felt that a study of the three tracers simultaneously at 37°C was needed.
Eardrum (tympanic membrane) rupture in humans and animals in relation to various blast pressure-time patterns was reviewed.There were few systematic studies on eardrum rupture as a consequence of blast overpressure. Most reports did not describe the area of the eardrum destroyed. The peak overpressures required to produce a 50% incidence of eardrum rupture (Pso) were summarized. Most of the animal data pertained to dogs. The highest Pso for dogs, 296 kPa, was associated with smooth-rising overpressure. For complex wave pat terns occurring inside open shelters subjected to nuclear blasts, the Pso was 205 kPa. For fast-rising blasts in a shock tube it was 78 kPa, and 105 kPa for statically applied pressures. The duration of the overpressure was not a factor unless it was very short. The influence of the ori entation of the head to the oncoming blast was demonstrated. An ear facing the blast may receive reflected overpressures several times that for one side-on to the blast. An ear on the downstream side of the head was exposed to about the same overpressure as the side-on ear. A Pso for humans of 100 kPa and a threshold of 35 kPa has been used widely in blast criteria. A recent study suggests a threshold (Pi) of about 20 kPa, and gives the overpressures required to produce minor, moderate, and major eardrum ruptures. These data were presented in the form of curves showing the overpressures as a function of duration required to inflict a Pi and a Pso of eardrum rupture of the three levels of severity.KEY WORDS -airblast on ears, barotrauma, blast criteria, blast effects, blast pathology, eardrum rupture.
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