Threshold Determination Method Research Articles

Sensory characterization of polyester-based bottle material inertness using threshold odour number determination

Refillable polyester bottles, for example polyethylene terephthalate (PET) bottles, are known to interact with chemicals. Aroma compounds from a product can be absorbed by the bottle material, remain after washing and remigrate when the bottle is reused, resulting in off-flavour of the new product. A certified reference material has recently been approved with which the chemical and sensory inertness of refillable bottle materials can be tested. In this study a sensory method aimed at characterizing the sensory inertness properties of the reference bottle material was developed. A use–reuse situation was simulated by storing bottle wall strips in a solution of four odour-active compounds (the loading phase) and, after cleaning, immersing them in water (the remigration phase). The remigration water was analysed with both a sensory method, i.e. determination of the threshold odour number, and chemically using gas chromatography–mass spectrometry (GC–MS). Additionally, another PET and a polyethylene naphthalate (PEN) bottle material were also tested. The sensory threshold determination method could differentiate between the PEN materials and the PET materials. Results from chemical analysis showed that the inertness properties of the PET materials were very similar. The PEN material exhibited significantly superior inertness properties, with only 3–24% of the aroma transfer properties of PET.

Limiar de lactato em remadores: comparação entre dois métodos de determinação

O objetivo deste estudo foi comparar os métodos de 4mM (AT4) e Dmáx de limiar de lactato. Dez remadores (23,7 ± 3,33 anos) e quatro remadoras (18 ± 0,81 anos), divididos em três grupos, peso pesado (n = 6), peso leve (n = 4) e feminino (n = 4), (87,23 ± 6,10, 73,22 ± 2,38, 63,27 ± 8,86kg e 187,66 ± 1,63, 183 ± 6,05, 172 ± 5,16cm respectivamente) foram submetidos a uma remoergometria máxima, com cargas iniciais de 130 a 150W e incrementos de 30 a 50W a cada 5min, com pausas de 1min para coleta de sangue. Os valores de potência, freqüência cardíaca e lactato foram determinados a cada carga e utilizados para determinação dos limiares, de acordo com os dois métodos. A concentração de lactato, a produção de potência e freqüência cardíaca, identificadas pelo método Dmáx, foram comparadas com o método AT4 nos grupos peso pesado (3,01 ± 0,73 vs. 4mM, 268,33 ± 29,44 vs. 312 ± 44,02W e 164 ± 4,81 vs. 174 ± 10,09bpm), peso leve (2,51 ± 0,53 vs. 4mM, 232,50 ± 15,00 vs. 277,50 ± 25,98W e 160 ± 8,47 vs. 177 ± 3,79bpm) e feminino (3,21 ± 0,41 vs. 4mM, 160 ± 14,41 vs. 167,50 ± 15,00W e 175 ± 20,42 vs. 185 ± 12,12bpm) através de um teste t de Student para amostras pareadas, sendo significativamente menores (P < 0,05) quando usado o método Dmáx. Os resultados sugerem que o método AT4 superestima as variáveis analisadas no limiar de lactato quando comparado ao método Dmáx.

Gel Formation Analyses by Dynamic Light Scattering

Abstract A novel methodology for non-destructive and real-time determination of the gelation threshold for both chemical and physical systems has been proposed. This method i.e., a time-resolved dynamic light scattering (TRDLS) measurement, allows one not only to determine the gelation threshold but also to investigate critical dynamics near gelation threshold, mechanism of gelation, and architecture of gelling cluster. The gelation threshold was found to be characterized by (1) the appearance of a speckle pattern in the scattering intensity, (2) a power-law in the intensity–time correlation function (ICF), (3) a specific broadening of the distribution function, and (4) a noticeable suppression of the initial amplitude of ICF. All of these features originate from some unique aspects of gels: nonergodicity, frozen inhomogeneities, and divergence of connectivity correlation. As an application of these concepts, we propose four methods for determination of gelation threshold and examine their validity and usefulness for various types of gels; these include chemical gels of N-isopropylacrylamide, a gelling system of silica gel in a reaction batch, thermoreversible physical gels of poly(vinyl alcohol)–Congo Red complex, and biological gels of gelatin and globular protein.

Detection thresholds for intensity increments in a single harmonic of synthetic Japanese macaque (Macaca fuscata) monkey coo calls.

There is evidence that Japanese macaques (Macaca fuscata) are extremely sensitive to dynamic changes in the relative amplitudes of coo call harmonics during discrimination tests. To verify this evidence using more controlled stimulus configurations, the authors examined threshold sensitivity of macaque monkeys to amplitude increments added to the standard level of coo call harmonics. Psychophysical threshold determination methods paralleled those used previously to determine macaque sensitivity to amplitude increments added to vowel-like stimuli. Variation was detectable although thresholds were elevated relative to those obtained with vowel-like stimuli in another investigation (C. G. Le Prell, A. J. Niemiec, & D. B. Moody, 2001). This elevation was probably a function of natural amplitude modulation in the standard stimuli.

Psychometrics of odor quality discrimination: method for threshold determination.

There is no natural physical continuum for odor quality along which an odor quality discrimination (OQD) threshold can be measured. In an attempt to overcome this problem, the substitution-reciprocity (SURE) method defines a framework for the measurement of an OQD threshold. More specifically, it (i) defines a threshold concept for OQD, including the quantification of qualitative change of the stimulus, and (ii) suggests how to avoid perceived intensity as an unwanted cue for discrimination. In doing this, the psychometric properties of odor quality in the case of eugenol and citral are investigated using both discrimination (experiment 1) and scaling (experiment 2). Based on discriminatory responses, a change of approximately one-third in stimulus content was needed to reach the OQD threshold for eugenol and citral.

Seizure threshold estimation by formula method: a prospective study in unilateral ECT.

Formula methods of estimating seizure threshold in bilateral electroconvulsive therapy (ECT) have been successful in 75% (at the first ECT) and 80% (at the sixth ECT) of treatments (Gangadhar et al., 1998). This study showed the same results for unilateral (UL) ECT patients. Its aim was to compare formula and titration methods for threshold determination. The seizure threshold (dependent variable) was determined by the titration method used at the first ECT in consecutive consenting patients (n = 80) prescribed UL ECT under general anesthesia. The independent variables were age, gender, diagnosis, illness severity, concurrent drugs, head circumference, and inion-nasion distance. Forward, step-wise, linear regression analysis showed age as the only significant predictor of seizure threshold (15% of variance). A formula based on regression analysis was prospectively applied in an independent sample (n = 30) of patients receiving UL ECT using the titration method for threshold determination. The results calculated a higher threshold than the actual threshold used in 14 patients, a threshold level in 8 patients, and below threshold in 8 patients. Formula-based estimates would have been successful in 22 (73%) patients, but the majority of them would have received higher than the recommended stimulus dose. Titration is the method preferred for clinical use. However, if a patient's doctor wishes to use the formula-based method, he or she should do so with specific considerations.

Electromyographic Response to Exercise in Cardiac Transplant Patients: A New Method for Anaerobic Threshold Determination?

The purpose of this study was to investigate the possible use of integrated surface electromyography (iEMG) in cardiac transplant patients (CTPs) as a new noninvasive determinant of the metabolic response to exercise by studying the relationship between the iEMG threshold (iEMGT) and other more conventional methods for anaerobic threshold (AT) determination, such as the lactate threshold (LT) and the ventilatory threshold (VT). Thirteen patients (age: 57+/-7 years, mean+/-SD; height: 163+/-7 cm; body mass: 70.5+/-8.6 kg; posttransplant time: 87+/-49 weeks) were selected as subjects. Each of them performed a ramp protocol on a cycle ergometer (starting at 0 W, the workload was increased in 10 W/min). During the tests, gas exchange data, blood lactate levels, and iEMG of the vastus lateralis were collected to determine VT, LT, and iEMGT, respectively. The results evidenced no significant difference between mean values of VT, LT, or iEMGT, when expressed either as oxygen uptake (11.1+/-2.4, 11.7+/-2.3, and 11.0+/-2.8 mL/kg/min, respectively) or as percent maximum oxygen uptake (61.6+/-7.5, 62.2+/-7.7, and 59.6+/-8.2%, respectively). In conclusion, our findings suggest that iEMG might be used as a complementary, noninvasive method for AT determination in CTPs. In addition, since the aerobic impairment of these patients is largely due to peripheral limitation, determination of iEMGT could be used to assess the effectiveness of an exercise rehabilitation program to improve muscle aerobic capacity in CTPs.

Measurement of Ventilatory Threshold in the Patients with Chronic Airway Obstruction

BACKGROUND: There are many suggested methods for the indirect determination of anaerobic threshold(AT) using the changes of ventilatory parameters in respones to ventilatory load accompanying the increase of blood lactic acid level during exercise and the threshold derived from them is called ventilatory threshold( VT). They include ventilatory equivalent method(VEM), End-tidal PO2 method(PETO2), V-slope method(VSM), and respiratory quotient method(RQ). But in the patients with chronic airway ohstruction(CAO), the AT determined by ventilatory methods may not reflect true AT because the patients with GAO show inadequate ventilatory response to the increase of blood lactic acid level during excercise. METHODS: For the investigation of detection rate and reliability of above four VT determination methods in the patients with GAO, we performed the symptom-limited and maximal incremental exercise test in 17 patients with GAO and 12 normal controls. The incremental workload was 10 W/min in GAO group and 25 W/min in control group. The reliability of VT in each group was investigated by the calculation of Spearman correlation coefficient. RESULTS: The detection rates of VT were 100% by RQ, 91.7% by both VEM and POETO2, and 83.3% by VSM in normal control group, while 94.1% by RQ, 64.7% by VEM and PETO2, and 83.3% by VSM in GAO group. Good correlations were noted among VEM, PETO2, and VSM except RQ in normal control group. But there was no significant correlation except between VEM and PETO2 in GAO group. CONCLUSIONS: RQ is very sensitive but crude and VEM is near similar to PETO2. The clinical usefulness of VT determined by ventilatory method might be limited in patients with severe GAO.

Evaluation of a new E-optotype chart for measuring contrast sensitivity.

Clinical examinations of the contrast sensitivity (CS) are currently made by one-trial measurements of a restricted number of spatial frequencies around the peak of the CS function (CSF). These methods do not allow calculation of the confidence intervals of the single measurements, thus preventing examiners from evaluating the reliability of their data. We elaborated a new method of CS measurement at the peak of the CSF, aiming at economical clinical applicability together with enhanced reliability. Moreover, we tried to establish lower limits of normal CS that would allow classification of low test results as pathological. A chart containing six columns of E optotypes of constant size and decreasing contrast (from about 16% to 0.5%) was used to perform six-fold contrast threshold determination (method of descending limits, forced choice). Optotype dimensions are intended to measure the CS at spatial frequencies corresponding to 3 and 6 cycles per degree (c/deg). The reference values were defined by testing 61 normal subjects: 31 "young" (16-35 years) and 30 "old" (56-81 years). The mean logCS found in the young group was 2.07 +/- 0.086 SD for 3 c/deg and 1.94 +/- 0.154 SD for 6 c/deg, while in the old group the mean logCS was 1.88 +/- 0.095 SD and 1.74 +/- 0.118 SD respectively. This simple method of measuring CS can provide a single CS value together with a confidence interval for the individual patient, thus allowing evaluation of measurement reliability.

Blood lactate, plasma catecholamines and ventilatory parameters during incremental treadmill running. - Reproducibility and relation of different methods for threshold determination.

Blood lactate, plasma catecholamines and ventilatory parameters during incremental treadmill running. - Reproducibility and relation of different methods for threshold determination.

Anaerobic threshold determination and its importance in chronic heart failure patients

The goal of this study was to compare various methods of anaerobic threshold (AT) determination and to estimate its importance for both the prescription of appropriate physical activity and long‐term follow‐up evaluation in patients with chronic heart failure (CHF). Twenty‐eight persons (New York Heart Association Classification II, III) passed a symptom‐limited spiroergometrical test; some of them were serially measured. The incremental work rate was graded by 0.25 W‐kg‐1 every 4 minutes. AT was determined from ventilatory parameters (VT), on the one hand, and from base excess changes (—BET), on the other. VT was determined in 79% and —BET in 50% of patients. The correlation between other functional parameters and both VT and ‐BET parameters was close (r = 0.94 for heart rate, for example). The possibility of making an AT determination decreased in Weber's class C patients. AT determination was also possible in persons showing a change in acid‐base balance at rest. Basic functional parameters (heart rate...

Anaerobic threshold in children: determination from saliva analysis in field tests

The purpose of this study was to determine the anaerobic threshold of children by the analysis of saliva collected during field tests. A group of 25 children (mean age, 10.5 years) performed an incremental exercise test on a track, consisting of 4-min stages at increasing running velocities. Before each test (at rest) and at the end of each stage, both blood (via finger pricks) and saliva samples (for measurement of salivary concentrations of Na+ and Cl-) were collected to determine lactate threshold (Thla-) and saliva threshold (Thsa), respectively. There were no significant differences between values of Thla- and Thsa when expressed either as running velocity [mean Thla-, 10.73 (SD 1.96) km.h-1; mean Thsa, 10.89 (SD 1.69) km.h-1)] or heart rate [Thla-, 182(SD 14) beats. min-1 Thsa 183 (SD 11) beats.min-1]. In addition, correlations between Thsa and Thla were high, when both values were expressed as running velocity in kilometres per hour (r = 0.89; P < 0.001), or heart rate in beats per minute (r = 0.90; p < 0.001). In conclusion, these findings suggested that saliva analysis would be a valid method for anaerobic threshold determination in field tests.

Saliva electrolytes as a useful tool for anaerobic threshold determination.

The purpose of the present study was to determine the anaerobic threshold by analysis of changes in saliva composition during an incremental exercise test on a cycle ergometer. Thirteen healthy males underwent a submaximal test with an initial load of 50 W and load increases of 50 W per 3 min, until capillary blood lactate exceeded 4 mmol.l-1. A maximal test for maximum O2 uptake (VO2max) determination (initial load of 100 W and load increases of 50 W per 2 min) was also performed. Saliva and blood samples were obtained only in the submaximal test. Saliva threshold (Thsa) was defined as the point at which the first increase in either Cl- or Na+ occurred. Catecholamine threshold (Thca) was defined as the point at which a nonlinear increase occurred in either adrenaline or noradrenaline. The lactate (Thla) and ventilatory (Thve) thresholds were determined according to published criteria. No significant differences were found between Thsa values and the other methods of threshold determination. A high correlation was found between Thsa and Thla (r = 0.82, P < 0.01), and Thsa and Thca (r = 0.75, P < 0.05). These results support the validity of Thsa as a new method for noninvasive determination of the anaerobic threshold.

Noninvasive Determinations of the Anaerobic Threshold: Reliability and Validity in Patients with COPD

We compared the intraobserver and interobserver agreement of blood (BGT) and gas exchange (GET) methods for determination of the anaerobic threshold (AT) in patients with COPD. In addition, we determined the sensitivity and specificity of the gas exchange methods for determination of the AT. Two noninvasive methods, the V-slope (VS) and the ventilatory equivalents method (VEM) were compared with two blood sampling methods, the log standard HCO3 (SB) vs log VO2 (SBT) and base excess (BE) vs VO2 (BET). Twenty-nine patients with COPD (FEV1 < 60%) performed incremental exercise tests to exhaustion while breath-by-breath gas exchange measurements were made. Blood samples were drawn at the end of each minute for SB and BE. Two trained observers determined the VO2 at the threshold for each of the four indices on two separate occasions two weeks apart. Our results demonstrated the following: only modest interobserver and intraobserver agreement was noted by Spearman rank correlations; the VEM was as sensitive as the VS in COPD patients; and the presence of a true metabolic acidosis was not reliably predicted by GET methods. Moreover, although the blood methods accurately identified the presence of metabolic acidosis, there was disagreement on the actual point of the BGT. We conclude that gas exchange indices were not helpful for the determination of metabolic acidosis in patients with COPD.

Experimental methods for reaction threshold determination using molecular beam and laser techniques

An overview of of currently available experimental methods for determining chemical reaction thresholds is presented. Two main categories are discussed depending on whether or not lasers are involved in the experimental setup. The presentation outlines the state-of-the-art in this area of the molecular reaction dynamics field with different examples of what can be learned from chemical reaction threshold measurements. A discussion about the limiting factors on the collision energy resolution in either beam-beam or gas cel experiments is also presented

A new approach for the determination of ventilatory and lactate thresholds.

In order to determine the ventilatory threshold (VT) and the lactate threshold (LT) in a reliable way, a new method is proposed and compared with conventional methods. The new method consists of calculating the point that yields the maximal distance from a curve representing ventilatory and metabolic variables as a function of oxygen uptake (VO2) to the line formed by the two end points of the curve (Dmax method). Male cyclists (n = 8) performed two incremental exercise tests a week apart. Ventilatory/metabolic variables were measured and blood was sampled for later lactate measurement during each workload and immediately after exercise. No statistical differences were observed in the threshold values (expressed as absolute oxygen uptake; VO2) determined by the Dmax method and the conventional linear regression method (according to O2 equivalent; EqO2) and venous blood at the onset of blood lactate (OBLA), while VT assessed with the conventional linear method (according to the slope of CO2 output; Vslope) yielded significantly lower threshold values. Similar results were obtained from the reproducibility test. Thus, the Dmax method appears to be an objective and reliable method for threshold determination, which can be applied to various ventilatory or metabolic variables yet yield similar results. The results also showed that breathing frequency can be used to determine VT.

Comparison of two methods of noninvasive anaerobic threshold determination in middle‐aged men

The anaerobic threshold (AT) was determined noninvasively during incremental exercise on a bicycle ergometer in two groups (N, = 22, N2 = 16) of healthy, untrained middle‐aged men (mean age, 31.5 ± 4.8, and 51.8 ± 5.4 years; maximal rate of oxygen consumption (VO2max)was 43.3 ± 7–9, and 34.4 ±8.0 ml‐kg‐1.‐min‐l) using two testing methods simultaneously: ventilatory threshold and heart rate response (the modified Conconi test). The value of selected functional parameters at AT determined by either method showed no significant difference between the two determinations either in absolute or relative terms. A high correlation was found between the value of the functional parameters at the AT estimated by the two methods (p =3 0.005 in all cases). The two methods of AT determination are interchangeable and may be used under the following conditions: The initial exercise intensity is between 40 and 60% of VO2max; the duration of each exercise increment ranges from 30 to 90 seconds; the increments cause a heart ...

Metabolic Acidosis during Exercise in Patients with Chronic Obstructive Pulmonary Disease: Use of the V-slope Method for Anaerobic Threshold Determination

Patients with chronic obstructive pulmonary disease (COPD) usually have limited exercise tolerance owing to low ventilatory capacity. Because metabolic acidosis induced by exercise increases ventilatory drive, decreasing the hydrogen ion stimulus may improve exercise capacity. However, in those with mechanical limitation to ventilation or chemoreceptor insensitivity, identifying metabolic acidosis may be difficult using gas exchange methods that depend on the ventilatory response to the acidosis. We compared a modification of a gas exchange method (V-slope) for determining the lactate (anaerobic) threshold (AT), which is independent of ventilatory response with a method using the change in blood standard bicarbonate (HCO3-) level in COPD and normal subjects during cycle incremental exercise. In 43 normal subjects, the VO2 at which metabolic acidosis was identified using the two method correlated (r = 0.75), although mean values differed. In 22 patients with moderately severe to severe COPD, eight who had a change in standard HCO3- less than 2.0 mEq/L between rest and 2 min of recovery from exercise (group 1) were contrasted with 14 whose blood standard HCO3- fell by greater than 2.5 mEq/L (group 2). Mean VC was higher and FEV1/VC was lower in group 2, but mean FEV1, maximal voluntary ventilation, and diffusing capacity for carbon monoxide were not different. The degree of obstruction did not correlate strongly with the degree of exercise metabolic acidosis. The AT determined by the V-slope method was compared with that from standard HCO3-; good correlation between these methods was found (r = 0.98), although mean values were different. The V-slope method predicted metabolic acidosis in 10/14 who had a fall in HCO3- more than 2.5 mEq/L. A significant proportion of patients with COPD seem to develop metabolic acidosis during exercise. The V-slope gas exchange method may be useful in selecting those patients with COPD who develop exercise metabolic acidosis and might therefore benefit from exercise training.

A Model to Evaluate Alternative Methods of Defibrillation Threshold Determination

The voltage (or, equivalently, energy) at which defibrillation occurs for a specific episode of fibrillation can be represented by specifying or estimating the probability of successful defibrillation for each voltage or energy. This relation of voltage to probability is the probability function. For a series of attempts, the probability function predicts the frequency with which defibrillation will occur at a given voltage. By defining the defibrillation threshold (DFT) as the voltage at which the probability function takes on a specific value, say 50%, a method of defibrillation threshold determination can be evaluated by how accurately and precisely it estimates the "true" defibrillation threshold. By utilizing estimated probability functions from animals and humans, the relative performance of different methods of defibrillation threshold determination can be evaluated. Three methods were evaluated using published animal data and human clinical data: (1) stepping down to the first voltage that fails; (2) stepping up to the first voltage that succeeds; and (3) doing both 1 and 2 and averaging. In all cases, Method 3 has lower total error. Definitions of defibrillation threshold other than the 50% level can also be evaluated in this fashion.

Towards fully objective evoked response audiometry.

The amplitude spectra of the auditory brainstem potentials evoked by free-field stimuli revealed significant differences from the corresponding spectra of pre-stimulus records. This was most marked for low order harmonics and in response to high intensity stimuli. In general, however, the shape of the amplitude spectrum for pre-stimulus and post-stimulus epochs was similar and the magnitude of the differences between corresponding harmonics became progressively smaller as stimulus intensity was reduced. Given that the spectrum of each coherent grand average is a function of the amplitude and phase spectra of the response ensemble, these were separately examined. Ensemble mean amplitude of individual harmonics diminished with stimulus intensity while their phases became progressively less aggregated. Phase standard deviation, used as a parameter of this aggregation, was found to change more systemically with stimulus intensity than ensemble mean amplitude. Phase standard deviation values for threshold responses were generally significantly smaller than corresponding harmonics obtained from sub-threshold responses. By contrast the amplitude differences between populations of threshold and sub-threshold responses were generally non-significant. These findings suggested that fully objective methods of threshold determination might more successfully be based on ensemble phase measures rather than amplitude measures.