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PubMed1995

Postural reflexes in Parkinson's disease during 'resist' and 'yield' tasks.

Postural reflexes in leg muscles appear to be set at a fixed gain in Parkinson's disease. To further investigate gain adaptation, we instructed 16 patients with idiopathic Parkinson's disease (studied during the 'off' phase) and 21 healthy controls to either 'resist' or 'yield' in response to 20 serial 4 degrees toe-up perturbations of a supporting platform on which they were standing. We bilaterally recorded destabilizing medium latency (ML) reflexes from stretched gastrocnemius muscles and corrective long latency (LL) reflexes from shortened tibialis anterior muscles. We also assessed changes in center of foot pressure (CFP) and center of gravity (COG). During the 'resist' condition, patients had increased destabilizing ML reflexes, decreased corrective LL reflexes, increased backward displacement of the COG and increased forward (destabilizing) displacement of the CFP. In addition, the backward (corrective) displacement of CFP between 150 and 250 ms was delayed. During the 'yield' condition, reflex gains were modified in controls: LL reflexes were markedly attenuated, whereas ML reflexes were markedly increased. Although this reflex pattern resembled the 'resist' condition in patients, it was not associated with an increased forward displacement of the CFP, but only with a strongly delayed backward displacement of CFP which started after 150 ms. In patients, ML reflex amplitudes remained unchanged during the 'yield' condition, suggesting a fixed reflex gain. LL reflex amplitudes were reduced in patients but significantly less compared to controls, which again suggests a fixed reflex gain. This 'inflexibility' of postural reflexes was reflected by the CFP which showed much smaller changes between 0 and 250 ms in patients than controls. These results could not be ascribed to a different ability to yield because posterior displacement of the COG was identical in patients and controls during the 'yield' condition. We conclude that (1) patients with Parkinson's disease have abnormal and 'inflexible' postural reflexes, associated with delayed corrective movements about the ankle joint and increased body sway; and (2) the increased forward displacement of the CFP in patients likely reflects high stiffness in ankle muscles because reflex changes in controls only affected the CFP more than 150 ms after the perturbation. The increased muscle stiffness and inflexibility of postural reflexes in Parkinson's disease may contribute to balance impairment in daily life.

Adaptation, Physiological↗
PubMed1991

An assessment of the maximum sustainable yield of ivory from African elephant populations.

A general, logistic population model is used to explore the dynamics of harvested elephant populations. The model includes two features peculiar to elephant populations and the harvesting of ivory. First, because of the shape of the growth curve of tusks with age, the conversion factor that relates the number of elephants killed to the ivory yield in weight is not constant, but a function of the population size. Second, tusks from animals that die from natural causes can be retrieved and included in the total yield of ivory. The implications of the relationship between tusk size and age of an animal on the maximum sustainable yield in terms of ivory tonnage and in terms of the number of tusks are explored. The nonequilibrium implications of the tusk growth curve on the population dynamics under different harvesting strategies are also investigated. Results indicate that the maximum sustainable yield is achieved at very low harvest rates with population levels close to the pristine equilibrium. When tusks from animals that die of natural causes are included in the harvest, the maximum yield may, depending on the mortality and recruitment parameters, occur when there is no direct harvest.

Africa↗
PubMed1976

The effect of changes in dose rate on the yield of chromosome aberrations in human lymphocytes exposed to gamma radiation.

The yield of chromosome aberrations was studied in Go human peripheral blood lymphocytes following in vitro exposure to 100, 250 and 500 rad of caesium-137 gamma radiation. The doses were given at various rates up to 400 rad per h with the longest exposures lasting for approx. 50 h. At 500 and 250 rad the dicentric yields fell by 66 and 64% when the dose rate was reduced from 400 to 10 rad per h whereas at 100 rad the reduction was only 29%. Reductions were also noted in frequency of acentric aberrations. At the higher dose rates (greater than 150 R/h) the aberration yield was constant and agreed with data published elsewhere for 3000 R/h. The dose rate at which the decline in aberration yield became apparent was dose dependent and, for dicentrics, occurred at about 150, 100 and 25 rad/h respectively for the 500-, 250- and 100-rad doses. The data are interpreted in terms of the quadratic model of aberration induction in which the dose-squared term represents dose rate dependent two-track aberrations which constitute an increasingly important component of yield as dose increases. The implications of this work for cytogenetic dosimetry are discussed.

Chromosome Aberrations↗
PubMed1977

Dicentric yields induced by gamma-radiation and chromosome arm number in primates.

To evaluate the effect of the chromosome arm number on the yield of dicentric chromosomes, frequencies of gamma-ray-induced chromosome aberrations were examined with peripheral lymphocytes from three different primate species, Saimiri sciureus (arm number, 77), Macaca fascicularis (arm number, 83) and Nycticebus coucang (arm number, 99). Irradiated blood samples were cultured by the same standard technique as that commonly used for human lymphocytes. The yields of dicentrics and dicentrics plus rings at doses of 100, 200 and 300 rad of gamma-irradiation were not significantly different among the three species, in spite of the difference in the chromosome arm number. Furthermore, dose-response relationships for these species were consistent with that for man. Statistical analysis indicated that the expected dicentric yields calculated from the arm number model were significantly different from the observed yields at 200 and 300 rad doses (P less than 0.01). From these results it can be pointed out that there is no correlation between the yield of dicentrics and the effective chromosome arm number, and that the chromosomal radiosensitivity of these primates is essentially the same as that of man, at least in the lymphocyte system.

Animals↗
PubMed1996

Efficacy of fetal echocardiography and yield by risk category.

OBJECTIVE: To determine the efficacy and yield of tertiary center fetal echocardiography for different high-risk groups. METHODS: Between January 1, 1982, and January 1, 1994, scans for anomalies were performed on 3246 women at increased risk for congenital heart disease in their offspring. Gestational age was 16-25 weeks in 83%. Maternal and gestational age as well as prenatal and postnatal diagnosis were recorded, and follow-up was sought for all pregnancies. By comparing prenatal and postnatal diagnoses, sensitivity, specificity, and predictive values were estimated. Multiple logistic regression was applied to establish the relative yield within the high-risk group. RESULTS: Follow-up was available in 3223 cases (99%). In a separate validation study of 777 women for whom a second set of follow-up data was requested, no additional anomalies were revealed. In total, 20 of 47 cases of cardiac malformations were detected (sensitivity 43%). When taking into account cases that remained undetected because of unfavorable scanning conditions (ie, minute size of the anomaly, awkward fetal position, or severe maternal obesity), the sensitivity for congenital heart disease rose to 51%. Specificity and predictive values were high (above 95%). The relative yield across the high-risk group appeared to be high for parental congenital heart disease and maternal diabetes mellitus, whereas a previous infant or other relatives affected, maternal anti-epileptic drug use, maternal drug abuse, and other reasons for referral each had an estimated yield approximately equal to the prevalence of congenital heart disease in the general population (0.8%). CONCLUSION: Fetal echocardiography for known increased risk appears to be moderately effective. Clear differences in yield are present across currently accepted risk categories.

Adult↗
PubMed1989

Relationships between fertility, peak milk yields and lactational persistency in dairy cows.

Peak milk yield, lactational persistency and conception rates were studied using 5928 lactation records of high milk-producing cows at three California dairies. Log-linear analysis was used to study relationships between peak milk yield, lactational persistency, dairy of origin, lactation number and conception rates in 3850 completed lactations. Cows with peak milk yields greater than the median (38.2 kg milk per day) were less likely to have conceived in one or two breedings than cows with peak milk yields lower than or equal to the median. Cows with a higher than median (0.755) lactational persistency were less likely to have conceived in one or two breedings than cows with a lactational persistency lower than or equal to the median. Dairy of origin had a significant effect on the probability of conceiving in one or two breedings. Cows in the first lactation were more likely than those in subsequent lactations to conceive in one or two breedings. This retrospective study demonstrated that subfertility is associated with high peak lactational yields in high milk-producing California cows.

Journal Article↗
PubMed1996

The effect of diet in late pregnancy on progesterone concentration and colostrum yield in ewes.

In the ewe, high level feeding is associated with low levels of circulating progesterone and that progesterone withdrawal is a prerequisite for lactogenesis and the onset of copious milk secretion. A total of 108 ewes was allocated to a 3 x 2 factorial experiment to determine the effect of diet on serum progesterone (P4) concentration and colostrum yield. On D 96 of pregnancy, the ewes were offered either grass silage, molassed sugar beet pulp (beet pulp) silage or grass silage supplemented with beet pulp. All ewes were given ad libitum access to silage. From D 126 of pregnancy, half the diets were supplemented with soybean meal with the aim of achieving a total crude protein intake of 220 g/ewe/day. Blood samples were taken on D 142 of pregnancy and at 1, 10 and 18 h post lambing for P4 determination. Metabolizable energy intakes (Mega Joules/ewe/day) of 9.1, 11.2 and 12.1 (SEM 0.37) and crude protein intakes (g/ewe/day) of 142.8, 167.4 and 162.0 (SEM 3.46) were recorded for grass silage, beet pulp ensiled and beet pulp supplemented silages, respectively, from D 126 to D 147 of pregnancy. Soybean meal supplementation increased the crude protein intake from 97.1 to 217.0 g/ewe/day (SEM 2.86) and Metabolisable Energy intake from 9.0 to 12.6 Mega Joules/ewe/day (SEM 0.31). Supplementation with soybean meal decreased P4 concentration (ng/ml) on D 142 (P < 0.05) and at 1 h (P < 0.01), 10 h (P < 0.01) and 18 h post lambing (P < 0.01). Ewes offered grass silage had higher P4 concentrations on D 142 (P < 0.01) and at 1 h after lambing (P < 0.05) than the beet pulp-supplemented ewes. There were negative linear relationships between P4 concentration at D 142 and colostrum yield at 1 h (P < 0.01) and between P4 concentration at 1 h and colostrum yield at 1 h (P < 0.001) and total yield at 18 h (P < 0.001). In conclusion, ewes which were underfed had higher P4 concentrations at all times, and there were negative linear relationships between colostrum yield and P4 concentrations on D 142 of pregnancy and at 1 h post lambing.

Journal Article↗
PubMed1980

Quantitative measures of mutagenicity and mutability based on mutant yield data.

We described how mutant yield data (mutants per cell treated) can be used both to compare the mutagenicity of different mutagens, and to characterize the mutability of different cell types. Yield curves reveal the net effect of the lethal and genetic actions of mutagens on cells. Normally, yields are the quantities measured in assays for mutagenesis, and rectilinear plots of such data baldly reveal the amount of experimental error and the extent of actual mutant induction above the background level. Plots of yield versus lethal hits can be used to quantify the relative mutagenic efficiency (RME) of agents whose physical exposure doses otherwise would be incommensurable, as well as the relative mutability (Rmt) of different strains to the same mutagen. Plots of yield versus log dose provide an unambiguous way of assessing the relative mutational sensitivities (Rms) and mutational resolutions (Rmr) of different strains against a given mutagen. Such analysis is important for evaluation of the relative merits of excision-proficient and excision-deficient strains of the same organism as mutagen-testing systems. The mathematical approach outlined here is applied, by way of example, to measurements of UV and 4-NQO induced mutagenesis in both repair-deficient and repair-proficient haploid strains of the yeast Saccharomyces cerevisiae.

4-Nitroquinoline-1-oxide↗
PubMed1988

Selecting ozone exposure statistics for determining crop yield loss from air pollutants.

Numerous ozone exposure statistics were calculated using hourly ozone data from crop yield loss experiments previously conducted for alfalfa, fresh market and processing tomatoes, cotton, and dry beans in an ambient ozone gradient near Los Angeles, California. Exposure statistics examined included peak (maximum daily hourly) and mean concentrations above specific threshold levels, and concentrations during specific time periods of the day. Peak and mean statistics weighted for ozone concentration and time period statistics weighted for hour of the day were also determined. Polynomial regression analysis was used to relate each of 163 ozone statistics to crop yield. Performance of the various statistics was rated by comparing residual mean square (RMS) values. The analyses demonstrated that no single statistic was best for all crop species. Ozone statistics with a threshold level performed well for most crops, but optimum threshold level was dependent upon crop species and varied with the particular statistics calculated. The data indicated that daily hours of exposure above a critical high-concentration threshold related well to crop yield for alfalfa, market tomatoes, and dry beans. The best statistic for cotton yield was an average of all daily peak ozone concentrations. Several different types of ozone statistics performed similarly for processing tomatoes. These analyses suggest that several ozone summary statistics should be examined in assessing the relationship of ambient ozone exposure to crop yield. Where no clear statistical preference is indicated among several statistics, those most biologically relevant should be selected.

Journal Article↗
PubMed1994

Exposure of oats, Avena sativa L., to filtered and unfiltered air in open-top chambers: effects on grain yield and quality.

Field grown oats, Avena sativa L. cv Vital, were exposed to filtered and unfiltered air from anthesis until harvest in open-top chambers at a site in south-west Sweden. Ambient plots were used to study the influence of the chamber itself. With the exception of the number of grains per panicle, which was significantly higher in the charcoal-filtered treatment, no significant filtration effects were obtained for any of the plant growth parameters studied), i.e. grain yield, number of panicles per square metre, 1000-grain weight, straw yield and harvest index.) The chamber had a significant negative effect on grain yield, 1000-grain weight and straw yield. None of the yield quality parameters that were measured, such as crude protein content, crude fibre content, fat content, volume weight of the grain and water content of the grain at harvest, were significantly influenced by either air filtration, or the presence of the chamber. The chlorophyll content of the flag leaves was higher in the charcoal-filtered treatment than in the non-filtered and ambient air treatments towards the end of the experiment, indicating that filtering of the air delayed senescence. The decline of the shoot area after the onset of plant senescence proceeded faster in both chamber treatments. The faster development in the chamber was explained by the faster accumulation of thermal time in the chamber.

Journal Article↗
PubMed1981

Contrast effects in photoelectron microscopy; UV dose-dependent quantum yields of biological surface components.

The relative brightness of photoelectron microscopy images as a function of exposure to UV light has been determined from model systems representative of biological cell surface components. Quantitative data for amino acid homopolymers, yields. The photoelectron quantum yields, increase substantially over the initial values. For example, the quantum yields fo poly-L-tyrosine at 200 nm is initially about 5 X 10(-8) electron/incident photon. The quantum yield increases with 254 nm irradiation, leveling off at about 5 X 10(-4) electrons/incident photon after a dose of 3 X 10(21) quanta cm-2. Pre-irradiation of poly-L-tyrosine in the presence of certain chemical agents, for example, the Lewis base diborane (B2H6), results in a substantial reduction of the dose-dependent increase in quantum yield. Exposure to the reducing agent stannane (SnH4) essentially eliminates the effect. These chemical treatments provide methods of controlling the UV dose-dependent effects in the photoelectron images.

Amino Acids↗
PubMedDate not supplied

Photoelectron microscopy and photoelectron quantum yields of the fluorescent dyes fluorescein and rhodamine.

Photoelectric properties of the dyes fluorescein and rhodamine were determined with the aim of assessing the usefulness of these compounds as labels in photoelectron microscopy. The photoelectron quantum yields were measured over the wavelength range 180-230 nm. At 230 nm the quantum yields for fluorescein disodium salt, rhodamine B free base and rhodamine B HCl salt are approximately 10(-5) electrons per incident photon. At 180 nm these values rise to approximately 10(-3) electrons per incident photon. All forms of fluorescein do not have the same quantum yield. The neutral form of fluorescein has a quantum yield an order of magnitude lower than the disodium salt. Beam current measurements were performed on labeled and unlabeled proteins to determine the effect of the high light intensity employed in the photoelectron microscope. The initial beam current measurements and the quantum yield curves are consistent and demonstrate that there is significant contrast between labeled and unlabeled proteins. However, after several minutes in the photoelectron microscope, the proteins become more photoemissive and the contrast diminishes. This change in contrast explains several puzzling observations in the literature.

Electrons↗
PubMed1983

Cigarette smoking as a risk for cardiovascular disease III: Biochemical effects with higher nicotine yield cigarettes.

Subjects who smoked a medium range nicotine yield cigarette were given a higher nicotine yield cigarette (an increase of 0.34 mg nicotine) to smoke ad libitum for two weeks. Plasma nicotine, cotinine, thiocyanate and blood carboxyhemoglobin levels were determined as well as various physiological parameters including heart rate and blood pressure. Increases in plasma nicotine were most directly correlated to heart rate when smokers were first challenged with a higher nicotine yield cigarette (r = 0.85); less directly correlated after a two-week acclimatization period (r = 0.42) and poorly related to their customary product (r = 0.23). Interestingly, it was noted that subjects did not compensate for higher nicotine yield by smoking fewer cigarettes per day when incremental nicotine changes were realistic. They did, however, show higher plasma nicotine, thiocyanate and an upward trend in plasma cotinine with the stronger cigarettes. These increases in cigarette constituents present in plasma, coupled with increasing correlation of heart rate and nicotine uptake, lead us to suggest that uptitration of smokers might cause them to establish new baseline levels. These findings have important health implications in light of recent suggestions to increase the nicotine yet decrease the tar of cigarettes in an attempt to overcome smoker compensation phenomena observed with low yield products.

Adult↗
PubMed1993

Evaluation of the quantum yield for E-->Z isomerization of bilirubin bound to human serum albumin. Evidence of internal conversion processes competing with configurational photoisomerization.

The quantum yield (phi zz) for the E--> photoisomerization of bilirubin (BR) bound to human serum albumin (HSA) under laser light irradiation has been evaluated with absorbance spectroscopy implemented by the high-performance liquid chromatography technique. The value at 458 nm is about 0.2, four times smaller than the value previously reported in the literature. As for the Z-->E configurational and the structural photoisomerization processes, the quantum yield varies with excitation wavelength, from 0.23 in the blue to 0.16 in the green. The sum of the quantum yields of the Z<-->E configurational photoisomerization reactions is 0.2-0.3 in the blue-green spectral region, thus giving direct evidence of the existence of internal conversion processes of the BR-HSA complex which compete with configurational photoisomerization. An evaluation of the quantum yields of the Z<-->E reactions for filtered broad-band light excitation in the 390-530 nm spectral region from data already published in the literature is also reported. Good agreement with our data of the quantum yields phi ZZ and phi ZE is found, despite the diversity of the experimental procedures in the two cases.

Bilirubin↗
PubMed2006

High-yielding plasmid extraction method from acidophilic heterotrophic bacteria of the genus Acidiphilium.

Plasmid yield from Acidiphilium strains always had been poor following various standard methods. We adopted some simple modifications in the alkaline lysis procedure to get a better yield of plasmid from these bacteria. An approximately 10- to 20-fold increase in the plasmid yield was achieved when harvested Acidiphilium cells were preincubated 16-20 h at pH 6 in nitrogen-free medium. Another independent approach showed that freezing (-18 to -20 degrees C) of the harvested cells initially and at two subsequent steps in the alkaline lysis procedure of plasmid DNA extraction improved the yield further by 1.5- to 3-fold. The combination of these changes yielded at least 15- to 30-fold more plasmid from various Acidiphilium strains as compared with standard methods.

Acidiphilium↗
PubMed2006

Effect of clinical phenotype on yield of long QT syndrome genetic testing.

OBJECTIVES: The purpose of this study was to examine the effect of clinical phenotype on the yield of genetic testing for congenital long QT syndrome (LQTS). BACKGROUND: Since the discovery of the first LQTS susceptibility genes in 1995, numerous genotype-phenotype relationships have emerged during the past decade of research genetic testing. In May 2004, LQTS genetic testing became a clinically available molecular diagnostic test. METHODS: Blinded to genetic test results, analysis of the clinical phenotype was performed in 541 consecutive unrelated patients referred to Mayo Clinic's Sudden Death Genomics Laboratory for LQTS genetic testing from August 1997 to July 2004. RESULTS: The yield of genetic testing correlated significantly with the corrected QT interval (QTc) and clinical diagnostic score ranging from 0% when QTc was <400 ms to 62% when QTc was >480 ms (p < 0.0001). Among those with the highest clinical probability, the yield was 72% (89 of 123). The yield fluctuated substantially depending on age at diagnosis in males. Among physicians who referred > or =5 patients, the yield ranged from 0% to 80% (p < 0.0001). CONCLUSIONS: In this large cohort of unrelated patients referred for LQTS genetic testing, the clinical phenotype strongly correlated with the likelihood of elucidating a pathogenic mutation with the cardiac channel gene screen.

Adolescent↗
PubMed2005

Tensile and compressive stress yield criteria for cancellous bone.

Experimentally based isotropic tensile and compressive strain yield criteria for cancellous bone are shown to imply tensile and compressive stress yield criteria, respectively. In particular, it is deduced that the directional variation of uniaxial yield stress is proportional to the one of Young's modulus. The obtained tensile and compressive stress yield criteria, in turn, imply information about the total stress yield criterion for cancellous bone.

Bone and Bones↗
PubMed2006

Cervical facet capsular ligament yield defines the threshold for injury and persistent joint-mediated neck pain.

The cervical facet joint has been identified as a source of neck pain, and its capsular ligament is a likely candidate for injury during whiplash. Many studies have shown that the mechanical properties of ligaments can be altered by subfailure injury. However, the subfailure mechanical response of the facet capsular ligament has not been well defined, particularly in the context of physiology and pain. Therefore, the goal of this study was to quantify the structural mechanics of the cervical facet capsule and define the threshold for altered structural responses in this ligament during distraction. Tensile failure tests were preformed using isolated C6/C7 rat facet capsular ligaments (n=8); gross ligament failure, the occurrence of minor ruptures and ligament yield were measured. Gross failure occurred at 2.45+/-0.60 N and 0.92+/-0.17 mm. However, the yield point occurred at 1.68+/-0.56 N and 0.57+/-0.08 mm, which was significantly less than gross failure (p<0.001 for both measurements). Maximum principal strain in the capsule at yield was 80+/-24%. Energy to yield was 14.3+/-3.4% of the total energy for a complete tear of the ligament. Ligament yield point occurred at a distraction magnitude in which pain symptoms begin to appear in vivo in the rat. These mechanical findings provide insight into the relationship between gross structural failure and painful loading for the facet capsular ligament, which has not been previously defined for such neck injuries. Findings also present a framework for more in-depth methods to define the threshold for persistent pain and could enable extrapolation to the human response.

Animals↗