Classification of decompression sickness.
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Decompression Sickness↗
Biomedical subjects
K V Kumar
Publications and source records attributed to K V Kumar.
Patent foramen ovale and hypobaric decompression.
Gas microbubbles were detected in the left ventricle of a supine subject being screened for an atrial septal defect as a participant of a hypobaric decompression study. This determination was made using the saline echocontrast procedure. We found provocation by a Valsalva maneuver not to be necessary in this individual for right-to-left passage of contrast microbubbles into the left heart and middle cerebral artery. When this same individual underwent hypobaric decompression to a simulated altitude of 21,000 ft, numerous gas microbubbles were detected in the right heart, but no gas bubbles were detected in either the left ventricular outflow tract or in the middle cerebral artery. This observation appears to be a novel finding, not previously reported.
Cerebral Arteries↗
Early stopping of aerospace medical trials: application of sequential principles.
A two-period, crossover trial was conducted in the hypobaric chamber on human subjects to compare the influence of inflight exercise (experimental) and restricted activity (control) on altitude decompression sickness (DCS) during simulated extravehicular activities. Out of 39 pairs (total of 78 exposures), 4 cases of DCS occurred under control and 5 occurred under experimental conditions. Analysis of the crossover results showed that the P values for differences in DCS occurrence was 0.56. Under these circumstances, it was necessary to decide whether additional information would be obtained by accruing more subjects. This problem was examined by using a skew sequential design in which the "stopping rule" was based on an alpha of 0.05 (one-sided) and power of 80%. The result of this analysis was in favor of the null hypothesis, and the trial was terminated. The authors recommend the use of similar stopping rules in aerospace trials to optimize sample size without compromising statistical validity.
Adult↗
Essential fatty acid metabolism in south Indians.
Coronary artery disease (CAD), hypertension and diabetes mellitus are more common in Indians compared to their incidence in the Western population. The exact reason for this is not known. One of the risk factors for the development of and complications due to CAD, hypertension and diabetes mellitus could be hyperinsulinemia and insulin resistance and low plasma levels of arachidonic acid and eicosapentaenoic acid, metabolites of dietary essential fatty acids (EFAs), cis-linoleic and alpha-linolenic acids. Fatty acid analysis of the plasma phospholipid (PL) fraction of normal Indians showed that they have low concentrations of arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid in comparison to those seen in Canadian and Minnesota (USA) normals. Since insulin can activate EFA metabolism, this alteration in the EFA metabolism may, at least, in part explain the high incidence of CAD, hypertension and diabetes mellitus and insulin resistance and hyperinsulinemia that are common in Indians.
Adult↗
Health of the elderly in a community in transition: a survey in Thiruvananthapuram City, Kerala, India.
Results of a survey to assess the health and functional status of the elderly (defined as those who are 60 years or older) in Thiruvananthapuram city, the capital of Kerala state, India, are discussed. As the process of development results in longevity without concomitant economic success, traditional support systems break down. The differences in status of the elderly dependent on gender and socioeconomic class are highlighted. Women are poorer and generally suffer more morbidity than men in old age, even though their death rates are lower. The better-off among the elderly enjoy a quality of life much superior to their poor brethren. Thus, in transitional societies such as Kerala, socioeconomic status and gender play a significant role in determining the quality of life of the elderly, a finding which may have some policy implications.
Aged↗
Survivorship models for estimating the risk of decompression sickness.
Several approaches have been used for modeling the incidence of decompression sickness (DCS) such as Hill's dose-response and logistic regression. Most of these methods do not include the time-to-onset information in the model. Survival analysis (failure time analysis) is appropriate when the time to onset of an event is of interest. The applicability of survival analysis for modeling the risk of DCS is illustrated by using data obtained from hypobaric chamber exposures simulating extravehicular activities (n = 426). Univariate analysis of incidence-free survival proportions were obtained for Doppler-detectable circulating microbubbles (CMB), symptoms of DCS and test aborts. A log-linear failure time regression model with 360-min half-time tissue ratio (TR) as covariate was constructed, and estimated probabilities for various TR values were calculated. Further regression analysis by including CMB status in this model showed significant improvement (p < 0.05) in the estimation of DCS over the previous model. Since DCS is dependent on the exposure pressure as well as the duration of exposure, we recommend the use of survival analysis for modeling the risk of DCS.
Computer Simulation↗
Oxy-radicals, lipid peroxides and essential fatty acids in patients with glomerular disorders.
It is now believed that free radicals and eicosanoids participate in the pathogenesis of immune mediated mesangial cell injury and renal tissue damage including glomerulonephritis. But relatively little information is available about the role of essential fatty acids, (EFAs), the precursors of eicosanoids, in renal diseases. We studied the levels of superoxide anion, hydrogen peroxide, lipid peroxides and the concentrations of various metabolites of EFAs in the plasma phospholipid fraction of patients with glomerular disorders. A significant increase in the production of superoxide anion and hydrogen peroxide both by unstimulated and phorbol-myristate acetate (PMA)-stimulated leukocytes, increase in the plasma lipid peroxide levels and a marked reduction in the levels of arachidonic acid (AA) and eicosapentaenoic acid, the precursors of 2 and 3 series prostaglandins (PGs) respectively, were observed in these patients. Since eicosapentaenoic acid and prostacyclin, which is derived from AA, are believed to be of benefit in the prevention of progression of renal disease, and as free radicals can cause renal dysfunction, our results suggest that free radicals and the metabolites of EFAs play a significant role in the pathogenesis of glomerular disorders.
Adolescent↗
Are free radicals involved in the pathobiology of human essential hypertension?
Possible involvement of reactive oxygen species and nitric oxide in the pathogenesis of human essential hypertension was investigated. It was observed that both superoxide anion and hydrogen peroxide production by polymorphonuclear leukocytes and the plasma levels of lipid peroxides are higher in uncontrolled essential hypertension compared with normal controls. Nitric oxide levels measured as its stable metabolite nitrite, as an index of nitric oxide synthesis, revealed its levels to be low in hypertensive patients. Superoxide anion, hydrogen peroxide, lipid peroxides and nitric oxide levels reverted to normal values after the control of hypertension by drugs. The concentrations of anti-oxidants such as vitamin E and superoxide dismutase were found to be decreased in patients with uncontrolled hypertension. Several anti-hypertensive drugs inhibited lipid peroxidation in vitro. Angiotensin-II, a potent vasoconstrictor, stimulated free radical generation in normal leukocytes which could be blocked by calmodulin antagonists. These results suggest that an increase in free radical generation and a simultaneous decrease in the production of nitric oxide and anti-oxidants such as SOD and vitamin E occurs in essential hypertension. This increase in free radical generation can inactivate prostacyclin and nitric oxide and decrease their half life which can lead to an increase in peripheral vascular resistance and hypertension.
Adult↗
Epidemiology of decompression sickness under simulated space extravehicular activities.
Several ground-based trials were conducted by NASA at the Lyndon B. Johnson Space Center, Houston, TX, during 1982-90 to examine the risk of altitude decompression sickness (DCS) during space extravehicular activities. There were 22 different pressure profiles involving single and staged decompression procedures, each lasting from 180 to 360 min at the final altitude. A total of 164 healthy subjects participated in 426 exposures to altitude. Symptoms of DCS occurred in 17% (74/426) and circulating microbubbles by precordial Doppler ultrasound were detected in 42% (179/426) of all exposures. About 27% (20/74) of exposures with symptoms resulted in test abort, and one-third of all test aborts required treatment in the hyperbaric chamber. There was about 3.20 times (95% Confidence Interval [95% CI] = 1.56-6.66) higher risk of symptoms in the presence of Doppler-detectable microbubbles. Examination of individual risk factors showed that there was about 4.3 times (95% CI = 1.62-11.50) higher risk of symptoms with increasing number of exposures. These findings emphasize the importance of evaluating risk factors from ground-based trials for application in operational decision-making and treatment strategies.
Adult↗
The influence of prior exercise at anaerobic threshold on decompression sickness.
This study was conducted to examine the effects of exercise prior to decompression on the incidence of altitude decompression sickness (DCS). In a balanced, two-period, crossover trial, 39 healthy individuals (29 males, 10 females) of mean (S.D.) age 32.5 (7.7) years and body mass index 23.7 (3.4) were each exposed twice, without denitrogenation, to an altitude of 6,400 m (21,000 ft) in a hypobaric chamber. Under the experimental condition, subjects exercised at their predetermined anaerobic threshold levels for 30 min each day for 3 d prior to altitude exposure; the other condition was a non-exercise control. Under both conditions, subjects performed exercise simulating space extravehicular activities at altitude for a period of 3 h, while breathing 100% oxygen. There were nine preferences (untied responses) for DCS, four under control and five under experimental conditions; all were Type I, pain-only bends. No carryover effect between exposures was detected, and the test for treatment differences showed p = 0.56 (95% confidence interval = 0.34-0.58) for symptoms. No significant difference in DCS preferences was found after subjects exercised up to their anaerobic threshold levels during the days prior to decompression.
Adult↗
Time to detection of circulating microbubbles as a risk factor for symptoms of altitude decompression sickness.
This study investigated the association between time at onset of circulating microbubbles (CMB) and symptoms of altitude decompression sickness (DCS), using Cox proportional hazard regression models. The study population consisted of 125 individuals who participated in direct ascent, simulated extravehicular activities profiles. Using individual CMB status as a time-dependent variable, we found that the hazard for symptoms increased significantly (at the end of 180 min at altitude) in the presence of CMB (Hazard Ratio = 29.59; 95% confidence interval [95% CI] = 7.66-114.27), compared to no CMB. Further examination was conducted on the subgroup of individuals who developed microbubbles during the test (n = 49), by using Cox regression. Individuals with late onset of CMB (> 60 min at altitude) showed a significantly reduced risk of symptoms (hazard ratio = 0.92; 95% CI = 0.89-0.95), compared to those with early onset (< or = 60 min), while controlling for other risk factors. We conclude that time to detection of circulating microbubbles is an independent determinant of symptoms of DCS.
Adult↗
Informed consent: a study of experiences and opinion of utilizers of health services from India.
One hundred and forty-eight subjects drawn from urban and rural settings who had been hospitalized for any medical problem within the previous three years were interviewed using a semi structured interview schedule to understand their opinion and experiences of informed consent. Sixty medical officers providing primary care in both urban and rural areas were concurrently interviewed to gather their opinion. Results revealed that respondents were dissatisfied with the information they had received about the different aspects of their illness. Both the doctors and the patients felt the need for providing adequate information to utilizers of health services. The two groups identified certain constraints, like illiteracy, in obtaining informed consent. Doctors compared to patients more often thought that illiterates could not understand the information. Patients more often felt that information about nature of investigations and about prognosis need not be routinely revealed.
Adolescent↗
Reactive oxygen species, lipid peroxides and essential fatty acids in patients with rheumatoid arthritis and systemic lupus erythematosus.
We studied free radical generation, lipid peroxidation and the levels of essential fatty acids and of their metabolites in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Both superoxide and hydrogen peroxide generation by peripheral leukocytes but not malondialdehyde levels, as measured by thiobarbituric acid assay, were found to be significantly enhanced both in RA and SLE. Fatty acid analysis of the plasma PL fraction revealed that both LA and ALA metabolites are significantly decreased in RA and SLE compared to controls. These results suggest that essential fatty acid metabolism is altered in RA and SLE.
Adult↗
Free radical generation, lipid peroxidation and essential fatty acids in patients with septicemia.
Infections due to gram-negative bacteria and other organisms can lead to septicemia and shock in some patients. Endotoxins, which cause these pathophysiological events, stimulate macrophages to elaborate tumor necrosis factor and other lymphokines. These lymphokines can augment free radical generation by polymorphonuclear leukocytes, macrophages and other cells, which may ultimately produce respiratory distress syndrome, multiorgan failure and irreversible shock seen in septicemia. This is supported by our results presented here that there is indeed an increase in free radical generation and lipid peroxidation in patients with septicemia. In addition, analysis of plasma lipid profile in these patients showed that gamma-linolenic, dihomogamma-linolenic and arachidonic acids of n-6 series and alpha-linolenic and eicosapentaenoic acids of the n-3 series are decreased in their plasma phospholipid fraction. These results suggest that free radicals, lipid peroxides, and alteration in essential fatty acid metabolism may have a role in the pathogenesis of septicemia.
Adolescent↗
Threshold altitude resulting in decompression sickness.
A review of case reports, hypobaric chamber training data, and experimental evidence indicated that the threshold for incidence of Altitude Decompression Sickness (DCS) was influenced by various factors such as prior denitrogenation, exercise or rest and period of exposure, in addition to individual susceptibility. Fitting these data with appropriate statistical models has the potential for estimating the frequency of occurrence of DCS at various altitudes under different experimental conditions and allows us to examine the influence of various factors on the threshold for DCS. This approach was illustrated by logistic regression analysis on the incidence of DCS below 9,144 m (30,000 ft). Estimations using these regressions showed that under a noprebreathe, 6-h exposure, simulated extravehicular activity profile, the threshold for symptoms occurred at approximately 3,353 m (11,000 ft); while under a no-prebreathe, 2-h exposure profile with knee-bends exercise, the threshold occurred at 7,925 m (26,000 ft). These examples showed that definition of threshold altitude should be qualified by the particular combination of experimental variables under which it was observed.
Aerospace Medicine↗
Binaural speech discrimination under noise in hearing-impaired listeners.
This study was undertaken to assess speech discrimination under binaural listening with background noise in hearing-impaired subjects. Subjects (58 sensori-neural, 23 conductive, and 19 mixed) were administered an indigenous version of W-22 PB words under: Condition I--Quiet--chamber noise below 28 dB with speech at 60 dB; and at a constant signal-to-noise (S/N) ratio of +10 dB with background white noise at 70 dB in Condition II and 80 dB in Condition III. The scores were a) 81 +/- 16%, b) 77 +/- 9%, and c) 79 +/- 13%. Mean scores decreased significantly (p less than 0.001) with noise in all groups while the score was more (p less than 0.001) at the higher noise level only in the sensori-neural group. The decrease in scores with advancing hearing impairment was less in noise than in quiet, probably due to binaural and satisfactory S/N ratio. The scores did not fall below 70% unless the handicap was marked. The need for suitable standards of binaural speech discrimination under noise in aircrew assessment is emphasized.
Adolescent↗
Decompression sickness and the role of exercise during decompression.
The risk of decompression sickness (DCS) is greatly increased with exercise at altitude. Bends is the commonest symptom in altitude DCS. Though the adverse effect of exercise at altitude is well known, the role of exercise during decompression is not clear. In this paper, a case of bends occurring with exercise during accidental decompression is presented. The event occurred while exercising on a treadmill at an altitude of approximately 4,572 m (15,000 ft) in the hypobaric chamber. No oxygen pre-breathe was done and ambient air was breathed throughout. The role of hypoxia and exercise during decompression, as well as individual susceptibility, are discussed. Even moderately severe exercise at low altitude may predispose healthy individuals breathing ambient air to DCS, especially when exercise is undertaken during decompression.
Adult↗
Initiation of DNA synthesis in HeLa cell-free system.
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Cell Fractionation↗