Probabilistic model of altitude decompression sickness based on mechanistic premises

To develop a predictive equation and to test ideas about the mechanisms involved in hypobaric decompression sickness, we performed statistical analyses on published results of 7,023 exercising O2-breathing men subjected to one-step decompressions in altitude chambers. The dependent variable was signs or symptoms so severe that the person's trial was terminated (forced descent). The three independent variables were 1) duration of 100% O2 breathing at ground level (prebreathing), 2) atmospheric pressure after ascent, and 3) exposure duration. The best model, chosen from trial-and-error combinations of premises about bubble behavior, indicates that decompression sickness outcome depends on 1) prebreathing time, but with an unexpectedly long washout half time for N2; 2) time at altitude, as if bubbles grow; and 3) the estimated difference, raised to the fifth power, between the partial pressure of N2 in tissue before and that in bubbles after decompression, perhaps an index of the number of bubbles generated. We expect the model to provide accurate predictions for decompressions matching those of the bulk of the data; the mechanistic cues should be considered hypotheses for further investigation.     

Incidence of decompression sickness in Navy low-pressure chambers

This study reports the incidence of decompression sickness occurring in U. S. Navy altitude chambers in association with physiological training of aircrews for the period 1 Jan. 1972 to 31 Dec. 1975. There were 79 cases of decompression sickness in 88,520 altitude chamber exposures, an incidence of 0.089%. Among trainees, there were 22 cases in 73,561 exposures, an incidence of 0.029%. Among chamber inside observers, there were 57 cases in 14,959 exposures, an incidence of 0.38%. This 12-fold greater incidence among inside observers over trainees was statistically significant (p less than 0.01). Reasons for the increased incidence of decompression sickness among inside observers are discussed.     

Movement by helicopter of patients with decompression sickness

Rapid movement of a patient with decompression sickness sometimes poses problems when the site of the hyperbaric treatment facility is located a considerable distance away. Six cases of aviator decompression sickness were diagnosed in altitude chamber participants during an 18-month period. Five cases were uncomplicated decompression sickness and the sixth case was of central nervous system decompression sickness. All cases were transferred by low-level helicopter flight. No complications were noted when the helicopter stayed within 200 ft (61 m) AGL of the take-off point. Symptoms of decompression sickness did worsen however, when this altitude was exceeded. This study shows that movement of patients with decompression sickness by low-level helicopter flight is both safe and effective, especially when pressurized aircraft is neither available nor practical.     

Probable decompression sickness in a trainee with atopic dermatitis

Hypobaric chamber training has a potential risk of inducing decompression sickness (DCS). A case of a patient with an atopic dermatitis who complained of paresthesia and numbness in his left arm and shoulder during the altitude exposure is presented here. His symptoms were severe enough for the attending medical officer to diagnose Type II DCS, but it turned out to be a probable case of simple skin bends requiring no treatment. The author can find no better explanation for this discrepancy than the contribution of dermatitis. The possibility of atopic dermatitis confounding the correct diagnosis of the severity of DCS is proposed.     

Hematologic changes in man during decompression: relations to overt decompression sickness and bubble scores

In order to determine whether asymtomatic gas phase separation causes hematologic abnormalities, studies were carried out following two dive series, one to 210 feet of sea water (FSW) for 50 min and the other to 132 FSW for 30 min. Studies included white and red cell count, red cell indices, platelet count, ESR, fibrinogen, fibrin split products, prothrombin time, partial thromboplastin time, coagulation factors II, V, VII, VIII, and X, clot retraction, platelet aggregation and adhesion, euglobulin lysis time, and platelet factor III. Changes were seen in platelet and white cell count, prothrombin time and partial thrombo-plastin time. White cell count was the only variable which correlated with total bubble score. The results are presented and implications of the findings discussed.     

Testing of hypotheses about altitude decompression sickness by statistical analyses

Human prostate cancers frequently show loss of heterozygosity (LOH) at loci on the long arm of chromosome 16 (16q). In this study, we analyzed prostate cancer specimens from 48 patients (Stage B, 20 cases; Stage C, 10 cases; cancer death, 18 cases) for allelic loss on 16q, using either restriction fragment length polymorphism (RFLP)- or polymerase chain reaction (PCR)-based methods. Allelic losses were observed in 20 (42%) of 48 cases, all of which were informative with at least one locus. Detailed deletion mapping identified three distinct commonly deleted regions on this chromosome arm: q22.1-q22.3, q23.2-q24.1, and q24.3-qter. On the basis of a published sex-averaged framework map, the estimated sizes of the commonly deleted regions were 4.7 (16q22.1-q22.3), 17.2 (16q23.2-q24.1) and 8.4 cM (16q24.3-qter). Allelic losses on 16q were observed more frequently in the cancer-death cases (11 of 18; 61%) than in early-stage tumor cases (9 of 30; 30%; P < 0.05). In 7 of 11 patients from whom DNA was available from metastatic cancers as well as from normal tissues and primary tumors, the primary cancer foci had no detectable abnormality of 16q, but the metastatic tumors showed LOH. These results suggest that inactivation of tumor suppressor genes on 16q plays an important role in the progression of prostate cancer. We also analyzed exons 5-8 of the E-cadherin gene, located at 16q22.1, in tumor DNA by means of PCR-single strand conformation polymorphism and direct sequencing, but we detected no somatic mutations in this candidate gene.     

The role of oxygen radicals in the physiology and pathology of human sperm

Reactive oxygen species in low doses are necessary compound of sperm capacitation and hyperactivation. Superoxide anion, hydroxyl radical and hydrogen peroxide initiate sperm capacitation. The edding of antioxidant enzymes inhibits the spontaneous and induced sperm hyperactivation. The process of capacitation is accompanied with the superoxide anion production output by spermatozoa. High doses of reactive oxygen species block the sperm motility through the inhibition of ATP synthesis by the mitochondrial enzymes and cell membrane compounds injury.     

Hypertension and sickness absence: the role of perceived symptoms

The association between perceived symptoms and absenteeism was examined in five groups of employed adults: normotensives, unaware hypertensives, aware and untreated hypertensives, aware and treated hypertensives, and falsely aware normotensives. Aware hypertensives (untreated and treated) and falsely aware normotensives had a higher average of perceived symptoms than normotensives, whereas unaware hypertensives had lower. The absenteeism rate across the groups showed a similar pattern. A significant interaction of perceived symptoms by study group on absenteeism was uncovered. Hypertensives and falsely aware normotensives who reported a low level of symptoms were not absent more than their normotensive counterparts. However, aware hypertensives and falsely aware normotensives who perceived a high symptoms level showed higher absenteeism than unaware hypertensives and normotensives with a similar level. This suggests that aware hypertensives have a greater tendency than both normotensives and unaware hypertensives to equate their symptoms with ill health and to act accordingly. Special attention should be directed to aware hypertensives who perceive a threat to their health.     

Probabilistic models for sequential taste effects in triadic choice.

Sequential effects and positional response bias are accounted for in new models for triadic choice. These models were applied to data on distilled water and dilute NaCl solutions by use of the triangular and 3-alternative forced-choice methods with 4 participants. The concept of a "conditional stimulus" is introduced to describe stimuli that are created partially by prior oral environmental effects. The effects of 1 or 2 prior stimuli on triadic choice were evaluated. The triad models used were based on a Thurstonian variant of M. W. Richardson's (1938) method of triads and a Thurstonian model for 1st choice among 3 possibly different stimuli. Maximum likelihood estimates of the scale values for conditional stimuli and bias parameters showed that it was necessary only to consider 1 prior stimulus. It was also shown that salt concentration differences are not the physical analog of the mental representations for the conditional stimuli. The results strongly suggest a water taste to salt taste continuum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in human monosynaptic H-reflex during altitude decompression

Test subjects exposed to altitude decompression without preliminary denitrogenization showed in 65-75% of cases stability or reduction of the amplitude of the H-response of a leg with subsequent painful sensations and in increase of the amplitude of the H-response in the other leg as long as they were raised to an altitude of 11,000 m. When bends developed in a leg the amplitude of the H-response in that leg decreased and in the opposite leg increased. During the descent and disappearance of painful sensations changes in the amplitude of the H-response were just the opposite. It is assumed that a decrease of the amplitude of the H-response during altitude decompression was associated with oxygen deficiency of nerve afferents and an increase--with the descending activating supraspinal effect.     

Comparison of different oxygen exchange models

A functional distribution of coronary volume can be estimated from the response of arterio-venous O2 content difference (AVO2) to a flow step. However, the results depend on the assumed O2 exchange model. The previously used model consisted of a single mixed compartment with O2 exchange (reference model). The purpose of this study is to provide an estimate of the errors made in the volume estimations by not taking into account factors as flow heterogeneity, different mixing sites or Krogh-like O2 exchange. The approach is indirect: the response of the AVO2 to a flow step has been calculated with alternative O2 exchange models in which factors mentioned are incorporated. These transients are fitted with the reference model. The resulting estimated volumes are different from the volumes assumed in the alternative models. Large differences are obtained with some of the alternative models, e.g. the model with Krogh characteristics. However, these models seem unrealistic because capillary pO2 is higher than venous pO2. Only small differences in volume are obtained with the more realistic models. Therefore, these results indicate that the coronary volumes are approximated well by the estimations obtained with the reference model. These volume estimations were 9.9 and 3.8 ml 100 g-1 for the O2 exchange vessels and the distal venous volume, respectively.     

The role of oxygen in thymocyte apoptosis

Signals generated by T cell receptor (TCR) cross-linking (or phorbol 12-myristate-13-acetate + Ca2+ ionophore), glucocorticoids or ionizing radiation all stimulate apoptotic cell death in thymocytes by signals that are initially distinct from each other. However, when these stimuli were administered to thymocyte cultures that were maintained under an atmosphere containing less than 20 ppm oxygen as opposed to one that contained 18.5% molecular oxygen, cell death was inhibited or abrogated, suggesting that the induction of death by all three different stimuli depend on the presence of molecular oxygen. Studies of the effects of the cysteine analog N-acetyl cysteine (NAC) with normal thymocytes demonstrated that this antioxidant inhibited the induction of death by each of the different stimuli in a manner the paralleled anaerobiosis. Furthermore, studies with thymocytes demonstrated that the induction of nur77, a gene shown to be involved in thymocyte apoptosis signaled through the TCR or its surrogates, is not inhibited by NAC or dependent upon molecular oxygen. The possible implications for negative selection of NAC-mediated inhibition of TCR-signaled thymocyte cell death was examined in thymic organ culture. Treatment of these cultures with NAC provided significant protection against staphylococcal enterotoxin B-mediated deletion of V beta 8-expressing thymocytes.     

Method of computing positive pressure in the human lung following space cabin decompression

The paper presents a mathematical model and differential equations to be used in computer-aided estimations of the positive pressure in human lugs upon space cabin blast decompression. The paper gives a simplified method of computing the pressure which utilizes a special diagram of decompression of a rigid container communicating with the cabin through a hole of a constant area. The characteristic feature of the method is a simultaneous computation of the air outflowing from the lungs and their expansion during decompression. The paper illustrates the advantage of the simultaneous computation of the processes and specifies the pulmonary regions of positive pressure at given blast decompressions. The paper compares theoretical and experimental (data by foreign researchers) peak values of the positive pressure in human lungs during blast decompression, indicating good agreement of the results.     

The role of reactive oxygen species in atherosclerosis

Reactive oxygen species (ROS) are probably not only unintended, toxic side-products of oxygen metabolism in mammalian cells, they also have several important physiologic functions including antimicrobial killing, regulation of cellular proliferation and growth, and regulation of vascular tone. ROS are generated within the vessel wall by several mechanisms, including a vascular type of a NAD(P)H oxidase. ROS formation can be stimulated by mechanical stress, environmental factors, the peptide angiotensin II, cytokines, native low-density lipoproteins (LDL), and in the presence of catalytic metal ions. Their ability to modify LDL, react with endothelial-derived nitric oxide subsequently forming peroxynitrite, and amplify the expression of various genes important for leukocyte recruitment within the arterial wall are the basis of the oxidant injury theory of atherosclerosis. In animal studies, antioxidant therapy (probucol, butylated hydroxytoluene, N', N'-diphenylenediamide, vitamin E, superoxide dismutase) have been successfully used to prevent fatty streak formation, and to restore impaired nitric oxide-dependent vasorelaxation. In man, antioxidant therapy (e.g., supplementation with vitamin E) clearly increased the resistance of LDL to oxidative modification. Case-controlled and prospective clinical studies suggest a relation between baseline antioxidant plasma levels and/or antioxidant supplementation and risk of cardiovascular events. In one secondary prevention trial (randomized, blinded, placebo-controlled), vitamin E supplementation reduced significantly the risk for non-fatal myocardial infarctions. Before general recommendations can be made, results of further large-scale trials should be awaited.     

Biochemical mechanisms of evolution and the role of oxygen

The concept formulated here presumes the existence of specific mechanisms of evolution that save intermediate (and therefore imperfect) forms of organisms from elimination by natural selection. A change in the life strategy made in situations when the appearance of a new trait worsens, rather than improves, adaptation of the organism to the changing environment can be one of these mechanisms. The concept postulates that, in such cases, K-strategy (relatively low rates of reproduction and activity in general but long life span) is replaced by r-strategy (high activity and reproduction but short life span). A decrease in the life span upon the K --> r transition is suggested to be an unavoidable consequence of an elevation of formation of toxic reactive oxygen species under conditions of increased rates of aerobic metabolism required for the increased life activity. The phenomenon of giantism of transgenic tobacco plants that overproduce a mitochondrial heat shock protein (experiments done by A. Moore) is assumed to be explained by an r --> K transition. On the other hand, a decrease in the life activity and a considerable increase in life span occurring in a nematode upon mutations inhibiting the CoQ biosynthesis (S. Hekimi) might serve as an example of a K --> r transition.     

Probabilistic retroactive interference: The role of accessibility bias in interference effects.

Probabilistic retroactive interference (RI) refers to the interfering effects of intermixing presentations of an earlier studied response (A-B) with presentations of a competing response (A-D). As an example, for a 2/3 condition, a cue word was presented with its earlier studied response twice and its competing response once during the interference phase. Performance on direct and indirect tests of memory for earlier studied responses was combined to reveal dissociations between effects on recollection and accessibility bias. Manipulating probabilistic RI influenced accessibility bias but left recollection unchanged. Effects of probabilistic RI were compared with effects of traditional, nonprobabilistic RI. The authors contrast their dual-process model with traditional accounts of RI and discuss the importance of distinguishing between recollection and accessibility bias for understanding interference effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of oxygen in thiosulphate leaching of gold

The role of oxygen in thiosulphate leaching of gold has been investigated in both pure gold and ore systems. The gold dissolution decreased in the presence of oxygen in the pure gold system. Air or oxygen bubbling caused higher consumption of thiosulphate and leaching passivation. Nitrogen bubbling largely increased gold dissolution and this beneficial effect appeared to be more noticeable at a higher nitrogen flowrate. Nitrogen bubbling stabilised thiosulphate and prevented the passivation of gold. The use of oxygen pre-saturated water had little effect on gold dissolution. The counter current leaching tests showed that both gold passivation and the products due to thiosulphate decomposition affected the gold dissolution. The leaching solutions could be re-used without any impact on gold dissolution under a nitrogen atmosphere.Mineralogy affected the thiosulphate leaching system under different atmospheres. The leaching behaviour of a sulphide ore with only a small amount of sulphides was determined by the leaching behaviour of gold. However, air bubbling gave a higher overall recovery in the leaching of a pyrite concentrate, while nitrogen bubbling only marginally increased the overall gold recovery. Oxygen injection enhanced the dissolution of sulphides, releasing more gold from the sulphide matrices. Nitrogen injection hindered the corrosion process of the sulphides, affecting the overall gold recovery. Nitrogen bubbling decreased the thiosulphate consumption in the leaching of the pyrite concentrate, while air bubbling increased the thiosulphate consumption. It is suggested that high sulphide containing ores should be pre-treated to fully or partially break down the sulphide matrices to liberate gold, followed by gold leaching under a nitrogen atmosphere.