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PubMed1995

Application of cross-correlation function in the evaluation of objective MLR thresholds in the low and middle frequencies.

In this study, the cross-correlation function was applied in the evaluation of MLR thresholds in the low and middle frequencies. The parameters of the cross-correlation function consist of the correlation coefficient at a lag-time of zero (RO), the maximum correlation coefficient (RM), and the latency delay on the lag-time axis at the point of the maximum correlation coefficient (DL). The normal limits of the parameters of cross-correlation at the MLR threshold level, which was identified by visual detection across frequencies, were obtained in normal-hearing and hearing-impaired subjects. The cross-correlation functions for two traces were also performed below threshold level. All cross-correlation parameters (RO, RM and DL) below threshold level were outside normal limits in 91% of all the subjects. The incidence of the only RM or DL parameter value within normal limits was 6% or 3% of all cases at the subthreshold level. Correlation data allow precise measurements of the MLR threshold and enhance the sensitivity of the definition of the MLR threshold. In addition, our study provides quantifiable information for estimating MLR threshold.

Adult↗

PubMed1992

Physiologic and nonphysiologic determinants of aerobic fitness in mild to moderate asthma.

We studied 27 patients (seven male, 20 female) with stable mild-to-moderate asthma to measure their level of physical fitness and to determine if a relationship existed between aerobic fitness and the degree of airway reactivity, expiratory flow rates, or the amount of habitual leisure-time physical activity. Nonspecific bronchial hyperreactivity (NSBHR) was quantified by methacholine inhalation challenge. On a separate day, exercise capacity was evaluated with incremental exercise testing to exhaustion after bronchodilator pretreatment. The level of physical activity was assessed with a validated written questionnaire. FEV, was 78 +/- 13% predicted prebronchodilator and 92 +/- 14% predicted postbronchodilator. The mean provoking concentration of methacholine that caused a 20% decrease in FEV1 (PC20) was 1.14 +/- 1.38 mg/ml and ranged from 0.019 to 5.71 mg/ml. There was no correlation between PC20 and prebronchodilator FEV1 r = 0.37, p greater than 0.05). Mean maximal oxygen uptake (VO2max) was not significantly different from predicted normal values (36.9 +/- 10.8 versus 38.5 +/- 5.3, p = 0.32). Mean maximal O2pulse (maximal heart rate/VO2max), anaerobic threshold, and dyspnea index were within normal limits. There was no relationship between VO2max and FEV1 when expressed as percentages of predicted values (r = 0.08, p = 0.71) or between VO2max and PC20 (r = 0.23, p = 0.25). There was, however, a significant relationship between VO2max and the level of habitual leisure-time activity (F = 3.64, p less than 0.05). Results from the exercise questionnaire suggested that asthmatics perceive their disease as a limiting factor to improved aerobic fitness and that they lack adequate knowledge about asthma and exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

[Biological effects of microwave radiation of low nonthermal intensity (regarding the maximal admissible values)].

There is still much controversy in scientific approaches to setting limits of exposure to radio-frequency electromagnetic radiation in Russia, Europe and USA. The stumbling stone is recognition or denial of potential risk of biological effects from nonthermal electromagnetic radiation (to 1 mW/cm2). The authors review results of experimental investigations performed in Russia over the years since 1960s to study the direct and delayed effects of ultra-high and microwave frequencies of low non-thermal intensity EMR, and delayed negative effects in employees based on the data of several follow-up epidemiological studies. This evidence was used as a baseline for establishing the Russian limits for chronic exposure to, thresholds of harmful effects and the maximal admissible values of EMR within the above frequencies.

Animals↗

PubMed1980

Effects of d-amphetamine and naloxone on brain stimulation reward.

Self-stimulation thresholds were determined in rats by means of a modification of the psychophysical method of limits. Reinforcement values were determined after the administration of d-amphetamine alone, naloxone alone, and naloxone administered concurrently with d-amphetamine. d-Amphetamine yielded dose-related decreases in the threshold (0.25--2.00 mg/kg IP), while naloxone alone (2.0--16 mg/kg IP) caused no consistent changes. For each animal, a dose of d-amphetamine that substantially lowered the threshold was then selected to be administered with varying doses of naloxone. The threshold-lowering effect of d-amphetamine was blocked by naloxone at doses as low as 2.0 or 4.0 mg/kg. This finding suggests the possible involvement of an opiate receptor in the mediation of the enhancement by d-amphetamine of brain stimulation reward.

Animals↗

PubMed1997

When is bone scintigraphy necessary in the assessment of newly diagnosed, untreated prostate cancer?

OBJECTIVE: To evaluate the utility of bone scintigraphy in the assessment of newly diagnosed, untreated prostate cancer. PATIENTS AND METHODS: The probability of a positive bone scan for metastases was analysed for different threshold values of pre-treatment concentrations of prostate specific antigen (PSA), clinical stage, tumour grade based on biopsy, and age in 128 men (mean age 69 years, range 50-90) with newly diagnosed, untreated prostate cancer. The overall survival probabilities estimated from PSA level, extent of bone metastases, tumour grade, clinical stage, and age were calculated using the product-limit method. RESULTS: The positive predictive values of PSA level for bone metastases at thresholds of 10 and 20 ng/mL were poor (27.5 and 47.5%, respectively) whereas similar threshold levels of PSA gave negative predictive values of 100 and 94%, respectively, for a positive bone scan. In a univariate analysis, the overall survival was significantly affected by the extent of bone scan pathology (P < 0.001), the pre-treatment level of PSA (P < 0.001) and tumour grade (P = 0.01), whereas a multivariate analysis identified, in order of significance, tumour grade (P = 0.003), bone scan findings (P = 0.007) and PSA levels (P = 0.03) as independent prognostic factors. CONCLUSIONS: Bone scintigraphy seems to be unnecessary in the evaluation of newly diagnosed, untreated prostate cancer in patients with no clinical signs of bone pathology and serum PSA levels of < or = 10 ng/mL. However, the bone scan accurately assesses bone metastases and the prognostic significance of bone scan findings is superior to that of serum PSA level.

Adenocarcinoma↗

PubMed1999

Modeling of Random Formation of Microporous Material Following Thermodynamic Limitations.

The problem of pore formation in limited (small) volume has been considered. General equations describing the system in the continuous (many particles) and discrete (few particles) cases have been obtained. It has been shown that pore formation is not limited by nucleus genesis because of entropic reasons. Kinetic limitation leads to the auto-acceleration-like form of the dependence of the number of empty cells and the internal area functions. The percolation problem has been solved for 2- and 3-dimensional cases with comparison of systems obtained by traditional Monte Carlo and thermodynamic factors. The 3-dimensional situation leads to reduction of the percolation threshold. However, the difference in the values of percolation thresholds estimated by the ordinary Monte Carlo simulation and with thermodynamic limitation is not significant (less than the eventual error). The change of tortuosity was estimated. At the percolation threshold, the tortuosity decreases rapidly, then very slowly with an increase in microporosity, and only at very high microporosity (close to 1) the decrease in tortuosity is again sharp. The influence of the thermodynamic limitation on the regularity of the micropore cluster has been analyzed based on the consideration of behavior of free energy and surface area of the cluster. It has been found that both of these structural parameters significantly decrease if the thermodynamic limitation is imposed. Copyright 1999 Academic Press.

Journal Article↗

PubMed2005

Heavy metal content in soil reclaimed from a municipal solid waste landfill.

Residues reclaimed from a municipal solid waste (MSW) landfill were characterized for the concentrations of a number of heavy metals. The residue fractions analyzed included a fine fraction (<0.425 mm), an intermediate fraction (>0.425 and <6.3 mm) and a fraction consisting of paper products that could ultimately degrade to a smaller size. The intermediate fraction appeared to be organic in nature, while the fine fraction was more soil-like. In general, the metal concentrations were greatest in the intermediate fraction and lowest in the fine fraction. The effect of sample age on the elemental content was also investigated. The concentrations of several elements were greater in older samples (sample approximately 8 years in age) when compared to newer samples (sample approximately 3 years in age). Limitations associated with the land application of residual soil (composed of the fine and intermediate fractions) were assessed by comparing measured concentrations to regulatory threshold values. In general, most metal concentrations were below regulatory thresholds for use in unrestricted settings. At the concentrations measured, however, several elements might limit reuse options, depending on which regulatory threshold serves as a benchmark. Elevated concentrations of arsenic presented the greatest limitation with respect to common US thresholds while elevated cadmium concentrations presented the greatest limitation when compared to UK thresholds. The source of the arsenic was determined to be the waste, not the cover soil.

Environmental Monitoring↗

PubMed1995

Upper limit of plasma alanine amino transferase during phase I studies.

In Phase I clinical studies, the maximum tolerated dose has to be determined by a case by case analysis sometimes using a laboratory adverse effect, e.g. an increase in alanine amino transferase (ALT). For this reason a threshold to discriminate between significant or non significant adverse changes in ALT is required particularly in Phase I studies, in order to deal with the very common "close to the limit values". Previous methods (limit of normal range or normal range plus an arbitrary margin) do not solve this problem. The authors propose a new method taking into account the threshold used as inclusion criteria for ALT (R) and the range of spontaneous variations measured under identical Phase I study conditions (V). The (R) and (V) thresholds, respectively, are defined as 50 IU.l-1 and a 50% increase, from baseline. Thus an ALT value is recognized as a "significant adverse experience" if it exceeds 50 IU.l-1 above an increase from baseline exceeding 50% of the baseline value. To highlight the value of the method, it was implemented in a one year period including 8 studies and 134 subjects. The sensitivity, specificity and positive predictive value of various methods were compared. The results showed the following: Six out of 134 subjects had significant adverse changes in ALT (4%); and all these 6 subjects were detected by the proposed new method without error. Eight subjects including two false positives, were detected by an use of the normal range limit, and only 4 were detected using, the 10% margin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Progesterone in diagnosis of ectopic pregnancy.

Previous reports suggest that serum progesterone value may be useful in the diagnosis of ectopic pregnancy. These studies have based discriminatory thresholds on a limited number of patients without using statistical correction for biologic variability in an infinitely large population. This study was designed to determine the ability of a single progesterone value to discriminate between normal, ectopic and blighted pregnancies. Sera were obtained from all positive beta HCG tests at Shands Hospital, University of Florida. All samples were assayed simultaneously with a solid phase RIA for progesterone and the results compared with pregnancy outcome. The mean progesterone for normal pregnancies was 32.8 +/- 4.25 ng/ml (n = 49), for ectopic pregnancies 7.8 +/- 0.79 ng/ml (n = 51), and pregnancies which spontaneously aborted 8.1 +/- 0.91 ng/ml (n = 74). Using individual prediction limits progesterone greater than 24 ng/ml would exclude an ectopic pregnancy in 99% of patients. Thus, this test may be useful in selected patients when the diagnosis is unsure after beta HCG and transvaginal ultrasound have been performed.

Abortion, Spontaneous↗

PubMed1991

Warm and cold specific somatosensory systems. Psychophysical thresholds, reaction times and peripheral conduction velocities.

Perception thresholds for warm and cold sensation were measured by two methods, the method of levels and the method of limits, at various rates of temperature change. The following findings were obtained. (1) The threshold value is critically dependent upon the method through which it is obtained, being higher for the method that includes reaction time in the measurement. (2) When using a method that includes participation of reaction time, threshold increases with increasing rate of temperature change. (3) The artefactual threshold elevation recorded through the method of limits corresponds precisely to the reaction time. (4) Conduction velocities for the primary afferents mediating the sensations of warm and cold, calculated on the basis of reaction time and conduction distance are in keeping with the mediation of warm sensation by unmyelinated primary afferents and of cold sensation by small myelinated afferents. (5) Measurement of threshold by the method of levels and direct measurement of reaction time enables calculation of conduction velocity for the specific sensory submodality tested from a single stimulation site.

Adolescent↗

PubMed2002

Acquisition and expression of proximal and distal upper limb stimulus-response curves to transcranial magnetic stimulation.

Motor cortex stimulus-response (S/R) curves are an indication of cortical excitability and are of relevance to topographical mapping. The aims of this study were to compare two different methods of collecting data to construct a S/R curve for transcranial magnetic stimulation (TMS) in the upper limbs, to identify reliable summary statistics for the S/R curve, and to determine whether S/R curves predicted motor threshold. Motor evoked potentials (MEP) were obtained from biceps brachii (BB) and abductor pollicis brevis (APB) muscles at rest with a circular coil centered at the vertex. Motor threshold was determined using a validated protocol. MEPs were obtained with 1% increments in intensity or from the average of five trials at 5% increments. The S/R relationships were fitted to linear, S-shaped, and Boltzmann functions. A linear function determined from the average of five trials accurately summarized our data (r2 from 0.6 to 0.9, P < 0.05, n = 8, for right APB and from 0.6 to 0.9, P < 0.05, n = 8 for right BB). The X-axis intercept of the line determined using these methods fell between the upper and lower limits of motor threshold in all eight subjects. We propose that MEP values obtained at intervals of 5% averaged over five trials, fitted to a linear function provides a practical means of assessing the S/R characteristics of TMS for proximal and distal upper limb muscles.

Adolescent↗

PubMed2002

Statistical processing for gastric slow-wave identification.

Successful identification of gastric slow waves in canine gastric electrical activity (GEA) data was achieved using a statistical data-processing procedure based on the multiple linear regression (MLR) curve fitting technique. Both distal and proximal waveforms were identified, first by construction of separate orthonormal bases from pre-selected sets of representative distal and proximal gastric slow waves (GSWs). Respective basis matrices were used to fit proximal and distal data to an MLR data model. Residual waveforms were computed from the original and 'fitted' waveforms and used in identifying GSWs in the data. Canine GEA data were split into 1,800-point blocks, and each 245-point data segment in a block was processed to identify the GSWs. Gastric slow waves were located in the data using a residual mean-squared error (MSE) threshold and, for distal GEA data, the minimum value of the main distal waveform peak. All threshold values were determined empirically and were set to detect GSWs while limiting false matches. Identification rates of 95% and 99% for proximal and distal GSWs, respectively, represent a significant improvement over those obtained in a previous study in which the same data were analysed using linear signal-processing methods. The use of the method presented in this paper for real-time identification of GSWs in conjunction with an implantable gastric pacer unit appears promising. Because the technique is inherently customisable, results obtained in this study should also be applicable to human subjects.

Algorithms↗

PubMed2006

A prospective study on radiation-induced changes in hearing function.

PURPOSE: To quantitate changes in hearing function after radiotherapy for head-and-neck tumors. METHODS AND MATERIALS: At the Department of Radiotherapy and Radiation Oncology, 32 patients were irradiated for head-and-neck tumors. Three-dimensional treatment planning was applied. Total tumor doses were 30.0-77.6 Gy, local doses to the inner ear (n = 64) ranged from 1.7 to 64.3 Gy. Audiometry was performed before the onset of radiotherapy (RT), at a tumor dose of 40 Gy or at the end of palliative treatment, at the end of curative RT, and 2-6 months post-RT. Assays applied were frequency-specific threshold measurements for air and bone conduction, measurements according to Weber and Rinne, tympanometry and assessment of the stapedius reflex. RESULTS: Age and prior disease significantly decreased, whereas previous or concurrent alcohol consumption significantly increased hearing ability. A significant reduction in hearing ability during RT was found for high frequencies (at 40 Gy) and low frequencies (at end of RT), which persisted after RT. No differences were observed for air or bone conduction. None of the other assays displayed time- or dose-dependent changes. Dose-effect analyses revealed an ED50 (dose at which a 50% incidence is expected) for significant changes in hearing thresholds (15 dB) in the range of 20-25 Gy, with large confidence limits. CONCLUSIONS: Radiation effects on hearing ability were confined to threshold audiogram values, which started during the treatment without reversibility during 6 months postradiotherapy.

Adult↗

PubMed2005

Maximum angle of ocular duction during visual fixation as a function of age.

PURPOSE: To measure and compare the maximum angle of ocular duction in healthy individuals as a function of age. METHODS: A calibrated arc perimeter was modified to display one of six randomly presented targets (high contrast Snellen equivalent letters), in both vertical (supra/infraduction) and horizontal (ab/adduction) gaze to the dominant eye of 204 healthy volunteers with best-corrected visual acuity. A bite-bar and headrest were employed to prevent head movement. Using a modified method of limits for discrimination threshold, a maximum mean angle of ocular duction was determined by stepping a target out in 5 degrees steps until an error was reported and thereafter bracketing around the limits of the target identification in 1 degrees steps. A mean threshold value was determined as the angle at which a subject obtained a correct response 75% of the time in two and as many as the trails in each of the four randomly presented directions of gaze (abduction, adduction, supraduction and infraduction). RESULTS: A decrease in mean maximum duction angle was found over all age groups in al four directions (p < 0.001), with a step decline beginning in the sixth decade and almost doubling in the oldest age group tested (80-95 years-olds). The percent change in mean maximum angle of duction due to age from the 14-19 to the 80-95 year-olds was: abduction 21%, adduction 24%, supraduction 35%, infraduction 26%. CONCLUSION: Baseline data are useful to differentiate normal changes occurring with age from early signs of disease. AdditIonally, disease progression and effects of treatment can be monitored.

Adolescent↗

PubMed1987

Muscle fibre type composition, motoneuron firing properties, axonal conduction velocity and refractory period for foot extensor motor units in dystrophia myotonica.

Seven patients with dystrophia myotonica were investigated using neurophysiological combined with histochemical techniques to elucidate motor unit properties in foot extensor muscles, which are often involved in the early stages of this disorder. For the 25 extensor digitorum brevis motor units studied the axonal conduction velocity, the axonal refractory period and the voluntary firing properties were within normal limits. However, high threshold motor units were not observed and the mean value of the axonal conduction velocities was lower (p less than 0.02) for the dystrophia myotonica motor units when compared with corresponding data from healthy subjects. There were also signs of impaired impulse propagation in the terminal part of the motor unit. In muscle biopsy specimens from the anterior tibial muscle, fibre type composition and structure were demonstrated using enzyme histochemical techniques for adenosine-triphosphate and immunohistochemical techniques for identification of the types of myosin isoform present. The histochemical findings indicated a type I fibre dominance, which was most obvious in the more seriously affected muscles. Neonatal myosin was observed preferentially in small but also in some normal sized fibres. Furthermore, some ring fibres were present and these showed staining with antineonatal myosin in their superficial portion. This indicates that an abnormal regeneration is one cause of the myopathic appearance of the muscle fibres in dystrophia myotonica. These investigations show that there is a reduced proportion of type II motor units in foot extensor muscles involved in the myopathy in dystrophia myotonica although it cannot definitely be established whether this is due to a loss of high threshold type II motor units or type II to type I transformation.

Action Potentials↗

PubMed1980

[Toxic heavy metals in foodstuffs (author's transl)].

1. In the Federal Republic of Germany two staple foodstuffs, cereals and milk, are regularly checked by means of monitoring programmes for their content of heavy metals, this check being representative for the whole country. Other foodstuffs are analysed in the laboratories of the Food Control Authorities, but these inspections are carried out rather sporadically and are not yet of a "monitoring" nature. 2. The measured values from a number of laboratories are fed into a central data bank (Datenbank-ZEBS) at the Federal Health Office and are thus available for statistical and hygienic evaluation. 3. At present, information is available on the lead, cadmium and mercury content of foodstuffs which represent roughly 70 to 80 per cent of the food consumed by an average adult. The intake of lead, cadmium and mercury due to the consumption of these foodstuffs has been calculated and extrapolated to the complete food consumption. It was found that the value ascertained are clearly lower than the toxicological threshold values published by FAO/WHO. 4. Nevertheless, the intake needs to be limited, because the average heavy metal content of some foodstuffs has increased, probably because of anthropogenic reasons. This is especially likely to apply to the cadmium content of wheat. To attempt a restriction by regulation, is at present not considered in Germany to be the optimal solution. Instead, the Federal Health Office has published guidance values which contain an appeal to the foodstuff industry and food control authorities to investigate the causes, whenever these guidance values are approached or exceeded, with the objective of avoiding high levels.

Cadmium↗

PubMed2000

Impaired fasting glucose: how low should it go?

OBJECTIVE: Impaired fasting glucose (IFG) has been recently introduced as a stage of abnormal carbohydrate metabolism, but the evidence on which its glucose limits (fasting plasma glucose [FPG] 6.1-6.9 mmol/l) are based is not strong. The aim of this study was to determine if 6.1 mmol/l represents a clear cutoff in terms of the risk of future diabetes and in terms of elevated cardiovascular risk factor levels, and to examine the use of other lower limits of IFG. RESEARCH DESIGN AND METHODS: A population-based survey of the island of Mauritius was undertaken in 1987, with a follow-up survey 5 years later. On both occasions, an oral glucose tolerance test was performed and cardiovascular risk factors were measured. RESULTS: Data were available from 4,721 nondiabetic people at baseline, and from 3,542 at follow-up. At baseline, blood pressure, lipids, and obesity increased in a linear fashion with increasing FPG, with no evidence of a threshold effect. The risk of developing hypertension at follow-up was greater for those people with baseline FPG > or =6.1 mmol/l (P<0.001). The risk of developing diabetes at follow-up increased with increasing baseline FPG, but there was little evidence of a threshold near 6.1 mmol/l. CONCLUSIONS: Cardiovascular risk and risk of future diabetes increase continually with increasing FPG, and there is no threshold value on which to base a definition of IFG. If a lower limit of approximately 5.8 mmol/l is used, the category defines a group more similar to the group with impaired glucose tolerance, with regard to total prevalence and the risk of subsequent diabetes.

Adult↗

PubMed2004

Home-based self-measurement of blood pressure: a proposal using new reference values (the PURAS study).

OBJECTIVES: To establish reference values for blood pressure by means of self-measurement of blood pressure (BP) conducted at home. DESIGN: Descriptive study of the distribution of self-measured BP at home and its correspondence with clinic-based measurements of BP. METHODS: The aim of this study is to define the home BP levels that correspond to clinic BP thresholds 140/90 mmHg (hypertension) and 130/85 mmHg (normality). The sample consisting of 1411 randomly selected adults stratified by age and gender. A pre-calibrated electronic device (Omron 705CP) was used for BP and heart rate (HR) measurements and a trained nurse performed clinic-based sphygmomanometer measurements. The same nurse provided tutorials for the subjects on how to obtain 12 self-measured BP values at home using the Omron device in a single day. RESULTS: Of the 1184 volunteers that attended the appointment, 195 were known as hypertensives and were excluded from the study. The average age of the remaining 989 subjects (50.4% females) was 44.3 years. Clinic BP values were significantly higher than self-measured BP at home regardless of age and gender. Both had good correlations (systolic BP, r=0.84 and diastolic BP, r=0.77). Using linear regression, the self-measured BP at home hypertension threshold would be 131/82 mmHg and the limit of normality 123/78 mmHg. Using corresponding percentiles, these values would be 134/85 and 124/80 mmHg, respectively. CONCLUSIONS: The self-measured BP at home values found in this study, when defining hypertension, are lower than values currently accepted (135/85 mmHg). Long-term studies are necessary to confirm these results.

Adult↗