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Biomedical subjects

H Iyer

Publications and source records attributed to H Iyer.

9 recordsLinked to original sources
PubMed2000

An analysis of the yearly changes in sulfur concentrations at various national parks in the United States, 1980-1996.

An apparent increasing trend in the summer concentrations of particulate sulfur at Shenandoah (for the time period 1982-1995) and at Great Smoky Mountains (for the time period 1984-1995) has been pointed out by some researchers. Others have suggested that these increasing trends may be an analytical artifact resulting from the switch from the Stacked Filter Units (SFU) measurement system to the IMPROVE (Interagency Monitoring of Protected Visual Environments) measurement system that occurred during the winter of 1987. To obtain a better understanding of the effect of the protocol change, we investigate the changes in the seasonal averages of sulfur concentrations for successive pairs of years for the period 1980-1996 for about 20 national park sites in the United States. For the period 1980-1987, we use sulfur data from the old (SFU) database and for the period 1988-1996, we use the IMPROVE database. Changes from one year to the next similar to that between 1987 and 1988 occurred during other years and seasons suggesting that chance causes alone could perhaps explain it, the degree to which chance could have caused the changes was measured using the permutation test for matched. At the very least, additional information such as side by side readings using SFU and IMPROVE measurement methods, may be needed to better understand any systematic effect in the sulfur measurements that may be ascribable to the protocol change.

Air Pollution↗
PubMed2000

Trends in the extremes of sulfur concentration distributions.

Understanding the response of air quality parameters such as visibility to the implementation of new air quality regulations, population growth and redistribution, and federal land managing practices is essential to the evaluation of air quality management plans on air quality in federal Class I areas. For instance, the reduction of SO2 emissions from large single point sources should result in the decrease of extreme sulfate concentrations, while population growth in geographic areas outside of urban centers could cause a slow widespread increase of sulfate and organic concentrations. The change in federal land managing practice of increased prescribed fire on a year-round basis in lieu of large naturally occurring wild fires could have the same effect; that is, the frequency of high sulfur days increase and low sulfur days decrease as the result of the management practice. Therefore, it is of interest to examine the trends associated with the proportion of days during which the concentration of some aerosol species is above or below a certain threshold and decide whether this proportion of days is increasing or decreasing or shows a lack of trend. This is a direct indication of whether the quality of the environment is improving or worsening, or neither.

Aerosols↗
PubMed2000

Sampling duration calculations.

Routine air quality monitoring produces filter samples that, when analyzed, yield the total amount of the aerosol present in the volume of air drawn by the pump in the monitoring device during the given sampling period. From this we obtain an average concentration of the aerosol for the given duration. The samples are therefore really aggregate samples. A natural question then is "what is the effect of the duration of aggregation on the accuracy and precision of the estimate of the quantity of interest?" The answer depends on a number of factors, such as the quantity that is being estimated: a mean, or an extreme value, or some other quantity; the nature of the measurement error--additive versus multiplicative; the costs of laboratory analyses, and so on. In this paper, we investigate these issues when the interest is in estimating the mean concentration of a specified aerosol species over a fixed time period. In particular, we propose a method for determining a sampling duration that will yield the "best estimate" of the mean concentration for a given cost whenever appropriate statistical assumptions hold.

Air Pollution↗
PubMed1987

Distribution of Brucella abortus in infected cattle.

Experimentally and naturally infected cattle were examined bacteriologically to determine the anatomical distribution of specimens yielding Brucella abortus. In 91 experimentally infected pregnant cows, examined 3 to 4.5 months after conjunctival challenge during pregnancy, the most frequently infected specimen was the mammary (syn. supramammary) lymph node. All experimentally infected cows could be identified from cultures of the mammary, mandibular (syn. submaxillary), medial iliac, caudal superficial cervical (syn. prescapular) lymph nodes and uterine caruncles, cotyledons or foetal tissues. Forty-six naturally infected cows were examined and again the most frequently infected specimen was the mammary lymph node. All naturally infected cows could be identified from cultures of the mammary, parotid, mandibular and subiliac (syn. prefemoral) lymph nodes. The distribution of infected specimens was somewhat different in heifers. In 61 naturally infected heifers the most frequently infected specimen was the mandibular lymph node but 8 other specimens would have been required to enable identification of all infected heifers. Specimens from 3 infected bulls were cultured and 11 of the 12 specimens examined were infected in at least one of the bulls. The most frequently infected tissues were the mandibular, caudal superficial cervical, subiliac and scrotal lymph nodes. The results suggest which specimens should be selected for culture, particularly when only a limited amount of effort can be expended.

Animals↗
PubMed1985

Differences between breeds of sheep in their responses to Bacteroides nodosus vaccines.

In a field experiment on irrigated pasture, sheep of several breeds were vaccinated twice, subcutaneously, in the upper neck, with Bacteroides nodosus vaccine containing either depiliated cells (DC vaccine), or whole, piliated cells (WC vaccine) and the responses were measured over the following 14 weeks. DC vaccine was as effective as WC vaccine in protecting against the development of foot-rot under conditions of moderate challenge, although the WC vaccine induced significantly higher pilus agglutinating antibody titres. Foot-rot developed in significantly more vaccinated Merinos (Peppin and Saxon strains) than in Romney Marsh, Dorset Horn or Border Leicester breeds. Agglutinating antibody titres after WC vaccination were significantly lower in the Peppin Merino than in the other sheep for the first 6 weeks, while after DC vaccination the titres remained elevated longer in the Border Leicester and Saxon Merino and were significantly higher from 6 weeks onwards. Reactions at the inoculation sites were generally larger in the British breeds than in the Merinos and among the former the reactions were largest, most numerous and most frequently discharged their contents in the Dorset Horn. Bodyweight gains in all vaccinated sheep were initially reduced, compared with controls, but the differences were no longer significant after the eighth week.

Agglutination Tests↗
PubMed1985

An evaluation of a biphasic medium for the isolation of Brucella abortus from bovine tissues.

The isolation of virulent Brucella abortus from specimens taken from cattle was studied using culture in biphasic medium in which solid and liquid media were contained in the same flask and on solid medium in Petri plates. A total of 8638 specimens from 441 cattle, reactors to one or more of several serological tests or to an allergic test, were used. The specimens consisted of lymph nodes, udder, spleen, uterine caruncles, cotyledons, foetal tissues, foetal stomach contents and mammary secretions. Following maceration each specimen was inoculated into 2 flasks of biphasic medium one with 1 ml (Flask A) and the other with 2 ml (Flask B), and on to solid medium in one Petri plate. The biphasic medium and solid medium were shown to have equal ability to support the growth of B. abortus. The increased rate of detection in the biphasic medium was due to the increased volume of the inoculum used. Brucella were isolated from 1151 specimens. By direct plating on the solid medium 685 specimens were positive whereas Flask A positive for 961 specimens and Flask B for 1031 specimens. The success of the biphasic medium can be judged by the increase in the number of infected animals detected. Of the 150 infected cattle, both techniques identified 126 animals in common, 4 were identified only by the plate technique and 20 only by the biphasic technique. Culture on both solid medium and in biphasic medium is recommended for optimum results.

Animals↗
PubMed1984

Assessment of a complement fixation test to detect Mycoplasma hyopneumoniae infection in pigs.

Serums from pigs slaughtered at abattoirs were tested for evidence of Mycoplasma hyopneumoniae infection using a complement fixation (CF) test which avoids the procomplementary effect of pig serum. To establish a diagnosis of enzootic pneumonia, the lungs from all sampled pigs were examined for pathological and histological changes consistent with the disease and cultures were made for mycoplasmas and bacteria. The study was carried out at Parkville and Bendigo 160 km apart at different times and all serums were tested at both laboratories. The results agreed closely. Thirty-six of 97 pigs at Parkville and 46 of 99 at Bendigo had enzootic pneumonia. About 80% were positive in the CF test. Sixteen per cent of porkers and 36% of baconers gave false negative reactors, that is, a negative test though lesions were present. About 18% to 36% gave false positive reactions but the level in the porkers in the Bendigo group was significantly higher (p less than 0.02). Possible explanations include, for the false negatives, loss of reactivity caused by circulating antigen and for the false positives, cross reacting antibody produced by another infection or failure to appreciate that lesions of EP were present in lungs because either they were not identified as such or they were not detected. The validity of any serological test for this disease cannot be established while there is a possibility that the present methods used for diagnosis, gross and microscopic examination and recovery of M. hyopneumoniae, fail to detect some infected animals. Other criteria may have to be adopted.

Animals↗
PubMed1981

A statistical model and analysis for genetic and environmental effects in responses from twin-family studies.

A statistical model and analysis for genetic and environmental effects in twin-family data are presented. The model is used to derive expressions for phenotypic correlations of 22 essential pair relationships in twin-family units. The analysis proceeds in two steps. First, differential effects of sex, generation, and sex-zygosity of twin-family units and correlations due to cluster sampling are eliminated from correlation data. Then, estimates and tests of model parameters are calculated from the adjusted data. The theory and methods were developed for a Swedish twin-family study of many behaviors possibly related to the smoking habit. There, it is important to screen for behaviors that clearly are under genetic control and to assess relative influences of various biological and social environments on the development of all behaviors. Height data from the Swedish study are used to illustrate concepts and methods presented in this paper.

Body Height↗