Human Decompression Modelling

At present, no decompression algorithm is able to predict safe decompression for all dive scenarios. In practice, empirical adjustments are made by experienced organisations or divers in order to improve decompression profiles for the range of depths and durations needed on any particular dive. Bubble formation and growth in the human body are the fundamental causes of decompression sickness, and it is believed that there is significant scope for incorporating better modelling of these processes into the design of decompression algorithms. VR Technology is a leading supplier of technical dive computers. The company is interested in expanding upon an existing algorithm (the Variable Gradient Model - VGM), which is used to design ascent profiles/decompression schedules and thereby mitigate the risk of decompression sickness in divers. The Study Group took the approach of trying to extend the existing Haldane model to account more explicitly for the formation of bubbles. By extending the model to include bubble dynamics it was expected that some physical understanding could be gained for the existing modifications to some of the parameters. The modelling that occurred consisted of first looking at the Haldane model and then considering a single small isolated bubble in each of the compartments and interpreting the predictions of the model in terms of decompression profiles

What general practitioners need to know about patent foramen ovale

A patent foramen ovale (PFO) consists of a hole between the right and left atriums of the heart that did not close the way it should after birth. Twenty five percent of the population have a PFO, but this usually does not cause problems, because the opening is functionally closed by the difference in pressure between the heart and the chest. This study is a literature review about the clinical significance of PFO and its management in three clinical situations: cryptogenic strokes, migraine with aura and scuba divers who sustained a decompression sickness. PFOs had been linked with various medical conditions such as strokes, migraine, and with certain types of decompression sickness (DCS). In general, this association is not very well established. Young patients who sustain a cardiovascular event without a known cause (cryptogenic stroke) have resulted in the tendency to screen these patents becoming the norm and more PFOs are being closed using standard methods and devices. The association of PFOs and migraine attacks is less clear. In the case of scuba divers the risk of suffering from a decompression accident is increased if one has a PFO. The management of these patients remains difficult.peer-reviewe

Relative Decompression Risks of Spacecraft Cabin Atmospheres - Comparision of Gases Using Miniature Pigs Final Report

Using miniature pigs for analysis of altitude decompression sickness and relative decompression hazards of various cabin atmospheres of inert gase

Environmental health discipline science plan

The purpose of this plan is to provide a conceptual strategy for NASA's Life Sciences Division research and development activities in environmental health. It covers the significant research areas critical to NASA's programmatic requirements for the Extended Duration Orbiter, Space Station Freedom, and exploration mission science activities. These science activities include ground-based and flight; basic, applied, and operational; animal and human subjects; and research and development. This document summarizes the history and current status of the program elements, outlines available knowledge, establishes goals and objectives, identifies scientific priorities, and defines critical questions in the three disciplines: (1) Barophysiology, (2) Toxicology, and (3) Microbiology. This document contains a general plan that will be used by both NASA Headquarters Program Officers and the field centers to review and plan basic, applied, and operational research and development activities, both intramural and extramural, in this area. The document is divided into sections addressing these three disciplines

Gas bubble dynamics in soft materials

Epstein and Plesset's seminal work on the rate of gas bubble dissolution and growth in a simple liquid is generalized to render it applicable to a gas bubble embedded in a soft elastic medium. Both the underlying diffusion equation and the expression for the gas bubble pressure were modified to allow for the non-zero shear modulus of the elastic medium. The extension of the diffusion equation results in a trivial shift (by an additive constant) in the value of the diffusion coefficient, and does not change the form of the rate equations. But the use of a Generalized Young-Laplace equation for the bubble pressure resulted in significant differences on the dynamics of bubble dissolution and growth, relative to a simple liquid medium. Depending on whether the salient parameters (solute concentration, initial bubble radius, surface tension, and shear modulus) lead to bubble growth or dissolution, the effect of allowing for a non-zero shear modulus in the Generalized Young-Laplace equation is to speed up the rate of bubble growth, or to reduce the rate of bubble dissolution, respectively. The relation to previous work on visco-elastic materials is discussed, as is the connection of this work to the problem of Decompression Sickness (specifically, "the bends"). Examples of tissues to which our expressions can be applied are provided. Also, a new phenomenon is predicted whereby, for some parameter values, a bubble can be metastable and persist for long times, or it may grow, when embedded in a homogeneous under-saturated soft elastic medium.Comment: 18 pages, 4 figures, 1 table, (Included also "Supplementary information": 2 pages, 1 table

Hazards of high altitude decompression sickness during falls in barometric pressure from 1 atm to a fraction thereof

Various tests related to studies concerning the effects of decompression sicknesses at varying pressure levels and physical activity are described. The tests indicate that there are no guarantees of freedom from decompression sicknesses when man transitions from a normally oxygenated normobaric nitrogen-oxygen atmosphere into an environment having a 0.4 atm or lower pressure and he is performing physical work

A review of the influence of physical condition parameters on a typical aerospace stress effect: Decompression sickness

The study examines data on episodes of decompression sickness, particularly from recent Navy work in which the event occurred under multiple stress conditions, to determine the extent to which decompression sickness might be predicted on the basis of personal characteristics such as age, weight, and physical condition. Such information should ultimately be useful for establishing medical selection criteria to screen individuals prior to participation inactivities involving extensive changes in ambient pressure, including those encountered in space operations. The main conclusions were as follows. There is a definite and positive relationship between increasing age and weight and the likelihood of decompression sickness. However, for predictive purposes, the relationship is low. To reduce the risk of bends, particularly for older individuals, strenuous exercise should be avoided immediately after ambient pressure changes. Temperatures should be kept at the low end of the comfort zone. For space activities, pressure changes of over 6-7 psi should be avoided. Prospective participants in future missions such as the Space Shuttle should not be excluded on the basis of age, certainly to age 60, if their general condition is reasonably good and they are not grossly obese. (Modified author abstract