Academic literature on the topic 'Threshold increment (fTI)'

Reported differences in neuronal contrast processing between the parallel magnocellular (M) and parvocellular (P) visual pathways invite the hypothesis that contrast discrimination in the human visual system is more sensitive at low contrasts and less sensitive at high contrasts, for stimuli modulated at high compared with low temporal frequencies. In the present study, an edgeless temporally modulated uniform field was selected as the stimulus for psychophysical contrast discrimination, and contrast-increment thresholds for pedestal contrasts ranging from 5.5% to 78.2% were determined with a temporal two-alternative forced-choice staircase procedure. The increment thresholds for five normal subjects were adequately fit by power functions with exponents that shifted continuously from about 0.5 (square-root-law behavior) to about 1.0 (Weber's-law behavior) as stimulus temporal frequency increased from 1 to 30 Hz. A neural simulation, with the use of published contrast-response functions of magnocellular and parvocellular neurons, adjusted with an estimate of response variance, produced two distinct ‘neural increment-threshold functions’ that were similar to the psychophysical results obtained at the highest and the lowest temporal frequencies, respectively. A shift from a relatively more noise-limited neural mechanism to one whose response is predominantly determined by gain is suggested to account for the change of the contrast-increment-threshold function with increasing temporal frequency.

Tilting from supine to upright purportedly enhances both segmental and pulmonary proprioceptive feedback, whereas an expiratory threshold load (ETL) preferentially enhances pulmonary feedback. To test this we studied 13 adults when supine and 60 degrees and 90 degrees head up. We measured tidal volume, inspiratory duration (TI), and expiratory duration (TE) from flow; estimated end-expiratory lung volume from inspiratory capacity; and determined burst amplitudes and durations from abdominal electromyograms (EMGs). ETLs were incremented from 0 (control) to 25 cmH2O in 5-cmH2O steps. Tidal volume was significantly increased by ETL but was unaffected by body position. Every load prolonged TE, whereas TI remained unchanged. When subjects were supine, abdominal EMGs were silent but became tonically active when subjects were upright. During ETL, abdominal activity became rhythmical and phase locked to expiration. Bursts amplitudes were enhanced with each increment in ETL, but burst durations did not change even though TE was prolonged. The altered breathing pattern and active expiration augmented inspiratory flow and decreased end-tidal PCO2. Responses were greatest when subjects were 90 degrees head up. The load-related increments in abdominal recruitment, with no change in burst durations, fit the concept of two central pattern generators: one controlling pattern and the other controlling rhythm of the central respiratory drive.

A new model of visual search is proposed. It is suggested that in searching for a target among distractors, there is some threshold level of similarity between the target and the distractors. When the similarity of the target to a given distractor is below this threshold the distractor can be quickly rejected. When the distractor is above the threshold level of similarity it will take additional time to reject the distractor. Several models of visual search, including threshold and non-threshold models, are simulated on a computer and compared to the results obtained by Geiselman, Landee & Christen (1982) in a visual search task. A threshold search model in which the time to reject distractors over the similarity threshold is a function of the increment above the threshold (where similarity is defined as proposed in Workman & Fisher, 1987), is shown to provide the best fit to the data. Implications for the selection of symbols for graphic displays are briefly discussed.

Eucalytpus dunnii é uma espécie subtropical e tem seu cultivo indicado para regiões onde há ocorrência de geadas. Apesar de ser atualmente utilizada para a produção de papel, carvão e chapas, o uso sólido da madeira para fins mais nobres é conhecido, desde que práticas silviculturais como podas e desbastes sejam consideradas. O presente estudo teve como objetivo analisar o crescimento de indivíduos dominantes de E. dunnii submetidos a diferentes intensidades de poda. Foram testadas quatro diferentes intensidades de poda, mantendo uma copa remanescente de 100, 80, 50 e 20% da altura total de árvores dominantes. Foi utilizado um delineamento inteiramente casualizado com 10 indivíduos por tratamento. Passados 20 meses da realização da poda, a manutenção de até 50% da copa foi suficiente para manter um crescimento em diâmetro considerado normal. Mais importante que a proporção de copa remanescente, é o comprimento absoluto das mesmas. Conclui-se que são necessários, no mínimo, 4 m de copa remanescente para que as árvores mantenham um incremento periódico anual acima de 4 cm (média anual durante o período de 17 a 37 meses). Ao ultrapassar este limite, perdas na ordem de 50% do incremento em diâmetro são esperadas.AbstractOptimum pruning intensity in Eucalytpus dunnii for clear wood producing. Eucalyptus dunnii is a subtropical species, indicated for areas where frosts occur. Besides its current utilization for paper, coal and boards production, the potential for nobler solid-uses are recognized, provided that silvicultural practices such as pruning and thinning are regarded. The objective of this study was to analyze the growth of dominant E. dunnii trees subjected to four different pruning intensities: 100, 80, 50 and 20% of the total tree height of remained canopy. Experimental design was fully randomized, with 10 replications per treatment. After 20 months of pruning, maintaining 50% of canopy was sufficient to allow a normal diameter growth. More important than the proportion, was the absolute length of remained canopy. It was concluded that it is necessary to keep, at least, 4 m of remained canopy in order to maintain a periodic annual increment over 4 cm (average during the 17-37 months period). When this threshold is exceeded, lost in the order of 50% in diameter increment are expected.Keywords: Forest Management; Multiple-uses.

ObjectiveThe English Bowel Cancer Screening Programme (BCSP) recommends 3 yearly colonoscopy surveillance for patients at intermediate risk of colorectal cancer (CRC) postpolypectomy (those with three to four small adenomas or one ≥10 mm). We investigated whether faecal immunochemical tests (FITs) could reduce surveillance burden on patients and endoscopy services.DesignIntermediate-risk patients (60–72 years) recommended 3 yearly surveillance were recruited within the BCSP (January 2012–December 2013). FITs were offered at 1, 2 and 3 years postpolypectomy. Invitees consenting and returning a year 1 FIT were included. Participants testing positive (haemoglobin ≥40 µg/g) at years one or two were offered colonoscopy early; all others were offered colonoscopy at 3 years. Diagnostic accuracy for CRC and advanced adenomas (AAs) was estimated considering multiple tests and thresholds. We calculated incremental costs per additional AA and CRC detected by colonoscopy versus FIT surveillance.Results74% (5938/8009) of invitees were included in our study having participated at year 1. Of these, 97% returned FITs at years 2 and 3. Three-year cumulative positivity was 13% at the 40 µg/g haemoglobin threshold and 29% at 10 µg/g. 29 participants were diagnosed with CRC and 446 with AAs. Three-year programme sensitivities for CRC and AAs were, respectively, 59% and 33% at 40 µg/g, and 72% and 57% at 10 µg/g. Incremental costs per additional AA and CRC detected by colonoscopy versus FIT (40 µg/g) surveillance were £7354 and £180 778, respectively.ConclusionsReplacing 3 yearly colonoscopy surveillance in intermediate-risk patients with annual FIT could reduce colonoscopies by 71%, significantly cut costs but could miss 30%–40% of CRCs and 40%–70% of AAs.Trial registration numberISRCTN18040196; Results.

Background and aims: Current guidelines recommend colonoscopy every 3–5 years for colorectal cancer (CRC) screening of individuals with a familial history of CRC. The objective of this study was to compare the cost effectiveness of screening alternatives in this population. Methods: Eight screening strategies were compared with no screening: fecal immunochemical test (FIT), Stool DNA and blood-based screening every 2 years, colonoscopy, computed tomography colonography, colon capsules, and sigmoidoscopy every 5 years, and colonoscopy at 45 years followed, if negative, by FIT every 2 years. Screening test and procedures performance were obtained from the literature. A microsimulation model reproducing the natural history of CRC was used to estimate the cost (€2018) and effectiveness [quality-adjusted life-years (QALYs)] of each strategy. A lifetime horizon was used. Costs and effectiveness were discounted at 3.5% annually. Results: Compared with no screening, colonoscopy and sigmoidoscopy at a 30% uptake were the most effective strategy (46.3 and 43.9 QALY/1000). FIT at a 30 µg/g threshold with 30% uptake was only half as effective (25.7 QALY). Colonoscopy was associated with a cost of €484,000 per 1000 individuals whereas sigmoidoscopy and FIT were associated with much lower costs (€123,610 and €66,860). Incremental cost-effectiveness rate for FIT and sigmoidoscopy were €2600/QALY ( versus no screening) and €3100/QALY ( versus FIT), respectively, whereas it was €150,000/QALY for colonoscopy ( versus sigmoidoscopy). With a lower threshold (10 µg/g) and a higher uptake of 45%, FIT was more effective and less costly than colonoscopy at a 30% uptake and was associated with an incremental cost–effectiveness ratio (ICER) of €4240/QALY versus no screening. Conclusion: At 30% uptake, current screening is the most effective screening strategy for high-risk individuals but is associated with a high ICER. Sigmoidoscopy and FIT at lower thresholds (10 µg/g) and a higher uptake should be given consideration as cost-effective alternatives. Plain Language Summary Cost-effectiveness analysis of colorectal cancer screening strategies in high-risk individuals Fecal occult blood testing with an immunochemical test (FIT) is generally considered as the most cost-effective alternative in colorectal cancer screening programs for average risk individuals without family history. Current screening guidelines for high-risk individuals with familial history recommend colonoscopy every 3–5 years. Colonoscopy every 3–5 years for individuals with familial history is the most effective strategy but is associated with a high incremental cost–effectiveness ratio. Compared with colonoscopy, if screening based on FIT is associated with a higher participation rate, it can achieve a similar effectiveness at a lower cost.

In an effort to explore why CO2 output (VCO2) at peak exercise is lower during pregnancy than postpartum despite little change in the peak O2 uptake (VO2), we determined the VCO2/VO2 relationship during rapidly incremental exercise and estimated the anaerobic threshold (AT) and the respiratory compensation (RC) point. We measured heart rate, VO2, VCO2, and minute ventilation (VE) at rest and during cycle exercise tests with rapidly increasing exercise intensities until maximal effort in 33 volunteers at 16-, 25-, and 35-wk gestation and postpartum. Through modification of the V-slope method, we estimated the AT and RC point for each test by nonlinear regression analysis in a three-dimensional space (defined by VE, VO2, and VCO2) for a line assumed to have two breakpoints; we found a good fit for all tests. The AT and RC points were found at exercise intensities of approximately 50 and 80% peak VO2, respectively, with no significant differences between test periods. VE was significantly higher during pregnancy than during postpartum at rest and throughout incremental exercise. A lower peak VCO2 relative to peak VO2 during pregnancy compared with postpartum was reflected by a more shallow slope of VCO2 vs. VO2 above the AT point. This suggests that during pregnancy the buffering of lactic acid is reduced.

Background In the UK, patients with one or two adenomas, of which at least one is ≥ 10 mm in size, or three or four small adenomas, are deemed to be at intermediate risk of colorectal cancer (CRC) and referred for surveillance colonoscopy 3 years post polypectomy. However, colonoscopy is costly, can cause discomfort and carries a small risk of complications. Objectives To determine whether or not annual faecal immunochemical tests (FITs) are effective, acceptable and cost saving compared with colonoscopy surveillance for detecting CRC and advanced adenomas (AAs). Design Diagnostic accuracy study with health psychology assessment and economic evaluation. Setting Participants were recruited from 30 January 2012 to 30 December 2013 within the Bowel Cancer Screening Programme in England. Participants Men and women, aged 60–72 years, deemed to be at intermediate risk of CRC following adenoma removal after a positive guaiac faecal occult blood test were invited to participate. Invitees who consented and returned an analysable FIT were included. Intervention We offered participants quantitative FITs at 1, 2 and 3 years post polypectomy. Participants testing positive with any FIT were referred for colonoscopy and not offered further FITs. Participants testing negative were offered colonoscopy at 3 years post polypectomy. Acceptibility of FIT was assessed using discussion groups, questionnaires and interviews. Main outcome measures The primary outcome was 3-year sensitivity of an annual FIT versus colonoscopy at 3 years for detecting advanced colorectal neoplasia (ACN) (CRC and/or AA). Secondary outcomes included participants’ surveillance preferences, and the incremental costs and cost-effectiveness of FIT versus colonoscopy surveillance. Results Of 8008 invitees, 5946 (74.3%) consented and returned a round 1 FIT. FIT uptake in rounds 2 and 3 was 97.2% and 96.9%, respectively. With a threshold of 40 µg of haemoglobin (Hb)/g faeces (hereafter referred to as µg/g), positivity was 5.8% in round 1, declining to 4.1% in round 3. Over three rounds, 69.2% (18/26) of participants with CRC, 34.3% (152/443) with AAs and 35.6% (165/463) with ACN tested positive at 40 µg/g. Sensitivity for CRC and AAs increased, whereas specificity decreased, with lower thresholds and multiple rounds. At 40 µg/g, sensitivity and specificity of the first FIT for CRC were 30.8% and 93.9%, respectively. The programme sensitivity and specificity of three rounds at 10 µg/g were 84.6% and 70.8%, respectively. Participants’ preferred surveillance strategy was 3-yearly colonoscopy plus annual FITs (57.9%), followed by annual FITs with colonoscopy in positive cases (31.5%). FIT with colonoscopy in positive cases was cheaper than 3-yearly colonoscopy (£2,633,382), varying from £485,236 (40 µg/g) to £956,602 (10 µg/g). Over 3 years, FIT surveillance could miss 291 AAs and eight CRCs using a threshold of 40 µg/g, or 189 AAs and four CRCs using a threshold of 10 µg/g. Conclusions Annual low-threshold FIT with colonoscopy in positive cases achieved high sensitivity for CRC and would be cost saving compared with 3-yearly colonoscopy. However, at higher thresholds, this strategy could miss 15–30% of CRCs and 40–70% of AAs. Most participants preferred annual FITs plus 3-yearly colonoscopy. Further research is needed to define a clear role for FITs in surveillance. Future work Evaluate the impact of ACN missed by FITs on quality-adjusted life-years. Trial registration Current Controlled Trials ISRCTN18040196. Funding National Institute for Health Research (NIHR) Health Technology Assessment programme, NIHR Imperial Biomedical Research Centre and the Bobby Moore Fund for Cancer Research UK. MAST Group Ltd provided FIT kits.

The relationship between blood lactate concentration ([La]) and O2 uptake (VO2) during incremental exercise remains controversial: does [La] increase smoothly as a function of VO2 (continuous model), or does it begin to increase abruptly above a particular metabolic rate (threshold model)? The dynamic characteristics of the underlying physiological system are investigated using system identification analysis techniques. A multivariate deterministic time series model of the [La] and VO2 response to incremental changes in work rate was fitted to simulated and experimental data. Time-varying system response parameters were determined through the application of a weighted recursive least squares algorithm. The model, using the identified time-varying parameters, provided a good fit to the data. The variation of these parameters over time was then examined. Two major transitions in the parameters were found to occur at intensity levels equivalent to 53 +/- 8% and 77 +/- 9% maximal VO2 (experimental data). These changes in the model parameters indicate that the best linear dynamic model that fits the observed system behavior has changed. This implies that the system has changed its operation in some way, by altering its structure or by moving to a different operating region. The identified parameter changes over time suggest that the exercise intensity range (from rest to maximal VO2) is divided into three main intensity domains, each with distinct dynamics. Further study of this three-phase system may help in the understanding of the underlying physiological mechanisms that affect the dynamics of [La] and VO2 during exercise.

This study was conducted to assess whether respiratory frequency can be used as a valid parameter for estimating ventilatory threshold and for examining differences in exercise modes such as a cycle ergometer and a treadmill. 24 men and 12 women performed an incremental exercise test to exhaustion on a cycle ergometer and on a treadmill. Oxygen uptake, carbon dioxide output, pulmonary ventilation, ventilatory frequency, and heart rate were measured continuously every 30 sec. during the test. Three different and independent reviewers detected the ventilatory threshold point and break point of respiratory rate, which were then compared. Analysis indicated that (1) ventilatory threshold was well correlated with break point of respiratory rate for both cycle ( r = .88, p<.001) and treadmill exercise ( r = .96, p<.001). However, on the average, ventilatory threshold was only 71% (cycle) or 88% (treadmill) of break point of respiratory rare. (2) The regression equation for treadmill exercise was more accurate than that for cycling, but the detected data samples were smaller. The break point of respiratory rate was more easily detected for the cycle ergometer test (33 of 36 subjects) than for the treadmill test (only 15 of 36). The cycle ergometer test identified the break point of respiratory rate more easily than did the treadmill test. (3) There was an association between physical fitness and whether the break point of respiratory rate was detectable, and the more fit the subject (above average), the more likely the break point was to be undetected. Our study demonstrates that the break point of respiratory rate is closely associated with ventilatory threshold and that the cycle ergometer test is more conducive than the treadmill test to the detectability of break point of respiratory rate.

Glare is an important, but often overlooked parameter in lighting systems design. This parameter can significantly affect human biorhythm, causing a discomfort or in the worst cases it can dazzle drivers, which can lead to car accidents. Therefore, it´s necessary for lighting designers to consider glare in their designs, specifically threshold increment value. This thesis focuses on glare measurement caused by exterior lighting systems and comparison of usage different types of camera lens for threshold increment measurements with luminance analyser. For a better understanding of the whole issue, there is a part describing how human eye perceives light, which is followed by definition and division of the glare. Afterwards, there is part describing calculation procedure of the threshold increment, which serves as a basis for the practical part of the thesis. Practical part of the thesis is dedicated to experimental measurement of glare from exterior lighting system on Technická street, right behind VUT FEKT T12 building. The measurement is done using luminance analyser and the LumiDISP program, while 3 lenses are used for the measurements. The output of this thesis are values of threshold increment obtained by using 4 different methods (3 lenses) and subsequent comparison of the suitability of the lenses for the glare measurements. To supplement, a simulation of the measured lighting system in the Relux program and a subsequent comparison of the results with the measured values are performed.