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PubMed1998

[Evaluation of the Swedish Interactive Thresholding Algorithm, a new thresholding algorithm, of the Humphrey field analyzer in normal subjects].

The Swedish Interactive Thresholding Algorithm (SITA) is a new thresholding algorithm that aims to obtain the same quality of visual fields in a shorter examination time than with the conventional up-and-down method. We investigated the correlation between thresholds measured with the SITA algorithm and those with the conventional up-and-down method in 47 eyes of 47 normal subjects. In each test point, thresholds with the SITA accurate and with the SITA fast showed significant correlation with those of the conventional method (r = 0.693, p < 0.0001 and r = 0.689, p < 0.0001, respectively). The mean deviation (MD) in the conventional method and the difference between MD values of the conventional method and SITA accurate and SITA fast were significantly correlated (r = -0.442, p < 0.006 and r = -0.509, p < 0.00092, respectively). The examination times of the SITA accurate and SITA fast were 48% and 27% of the conventional method. Although the new thresholding algorithm enables us to perform perimetric examination with relatively high accuracy, further investigations should be conducted before we apply it to glaucoma cases.

Algorithms↗
PubMed2004

Colourful orb-weaving spiders, Nephila pilipes, through a bee's eyes.

Many orb-weaving spiders in the tropics forage in open sites during the day and some of them have both bright and dark colourations. The conspicuous UV-reflective colour markings of these spiders have been reported to be attractive to visually oriented prey and thus could increase the spiders' foraging success. Using a combination of field and laboratory studies, we examine whether or not the body colouration of orb-weaving spiders exhibits optical properties that are attractive to insect prey from the viewpoint of insect visual physiology. We compared the prey interception rates and colour contrasts of the typical and melanic morphs of the giant wood spider, Nephila pilipes. Results of the field study showed that the typical morph caught significantly more insects than the melanic morph. Colour contrasts calculated from spectral reflectances of the background and body surface of spiders showed that the brightly coloured body parts of the typical morph exhibited rather high values, but those of the dark body parts were below the discrimination threshold. The differential colour contrasts of body parts generated a visual signal unlike that of a spider but rather like certain forms of food resources. On the other hand, the melanic morphs did not have bright colouration and the colour contrasts of every part of the body were significantly higher than the threshold, making the contour of spiders quite clear to bees.

Animals↗
PubMed1990

Effects of L-carnitine administration on VO2max and the aerobic-anaerobic threshold in normoxia and acute hypoxia.

Seven healthy young male adults were subjected to a total of 56 tests to ascertain the effects of L-carnitine (L-C) and a placebo (P) on ventilation, O2 intake (VO2), CO2 output, heart rate, blood pressure and serum lactic acid, non-esterified fatty acid, glycerol and glucose during strenuous and aerobic/anaerobic threshold-level treadmill exercise. The tests were made in conditions of normoxia (O2 = 20.9%) and hypoxia (O2 = 13.0%, equivalent to 3,500 m above sea level). The only clear difference was in the respiratory quotient (RQ = 0.883, SD 0.025 vs 0.904, SD 0.035) after L-C and P administration respectively (P less than 0.01), under normal oxygenation and 0.861, SD 0.052 following L-C vs 0.926, SD 0.040 after P (P less than 0.01) in acute hypoxia at VO2 levels around the anaerobic threshold. The lower RQ values of the L-C-treated subjects during hypoxia indicate a lower rate of carbohydrate transformation.

Acute Disease↗
PubMed1984

Effect of plasma volume on thermoregulation in the dog.

Panting thresholds, plasma volume (PV) changes and cardiac filling pressure were studied during thermal dehydration in control, water deprived (WD) and hypovolemic (PEG) dogs. WD and PEG dogs showed a delayed panting threshold, apparently due to hypovolevoia. Initiation of heat stress however resulted in a transient plasma expansion in all dogs. Cardiac filling pressure did not change.

Animals↗
PubMed2002

Haptic discrimination of stimuli varying in amplitude and width.

We studied active haptic discrimination of the geometrical features of an object. The geometrical parameters under investigation were the amplitude and width of a gaussian-shaped surface. Haptic discrimination thresholds were measured with regard to three values of these geometrical parameters. We found that humans discriminate up to about 300 shapes when both amplitude and width are extrapolated to the range between 1 micro m and 1 m. Over this range, which covers the span of the arms, the number of discriminations is small compared to the number across the full range of chromaticities in vision. Roughly speaking, humans are far better at discriminating sharp (extensive amplitude and little width) gaussian surfaces from smooth (small amplitude and extensive width) ones than they are at discriminating small (small amplitude and width) surfaces from large (extensive amplitude and width) ones. Our main conclusion is that discrimination in the geometrical domain is poorest when the proportion between amplitude and width is roughly the same for both shapes. Our results are in close agreement with results of earlier experiments on detection thresholds. This indicates that similar, or even the same, neural mechanisms were used for detection and discrimination of the geometrical parameters under investigation.

Adult↗
PubMed2005

Effect of CPAP treatment on inspiratory arousal threshold during NREM sleep in OSAS.

The maximal inspiratory effort recorded at the end of apnea has been considered as an index of arousal threshold in obstructive sleep apnea syndrome (OSAS). Previous investigations have shown that the arousal threshold is higher in patients with OSAS than in normal subjects. The aim of the present study was to investigate the effect of continuous positive airway pressure (CPAP) treatment on the inspiratory-effort-related arousal threshold in patients with OSAS. In ten male patients, 40 episodes of apnea during stage 2 non-REM (NREM) sleep were analyzed. Apnea duration (t), esophageal pressure (Pes) at the first occluded breath (Pes1), the minimum of the three initial Pes swings (Pes min), the maximum of the three final Pes swings (Pes Max), DeltaPes (Pes Max-Pes min), RPes (rate of increase of intrathoracic pressure, DeltaPes/t), n (number of occluded breaths during apnea), DeltaPes/n, n/t, and SaO(2) were determined before and after occlusion. These apneic episodes were compared to ten episodes of apnea provoked by a mask occlusion device after 1, 7, 30, and 90 days of CPAP treatment. The therapy resulted in a decrease in the inspiratory-effort-related arousal threshold, as measured by a reduction of Pes Max, without significant changes in apnea duration and apnea-related hypoxemia. Pes1 and DeltaPes/n, which are markers of respiratory drive, significantly decreased between observations. CPAP treatment decreases the inspiratory-effort-related arousal threshold and induces a decrease in ventilatory drive in response to upper airway occlusion.

Arousal↗
PubMed1998

Colour discrimination thresholds in Parkinson's disease: results obtained with a rapid computer-controlled colour vision test.

A dysfunction of dopaminergic retinal neurons is thought to occur in Parkinson's disease, manifesting itself in impaired performance on various visual discrimination tasks. We have investigated whether differences in colour discrimination could readily be detected between a normal group and a Parkinsonian group, using a computer-controlled test of colour vision. Although some individual Parkinsonian patients showed an abnormal elevation of colour discrimination thresholds, there was no significant difference between the normal group and the Parkinsonian group.

Age Factors↗
PubMed2000

Intervention thresholds and ceilings can determine the haemoglobin outcome distribution in a haemodialysis population.

We have explored the consequences of setting different thresholds and ceilings for erythropoietin dose changes in two randomized controlled studies of renal anaemia management based on an established algorithm. STUDY 1: A large (n=236) unselected haemodialysis cohort was randomized to monthly intervention (increased erythropoietin (Epo)) at haemoglobin (Hb) levels falling below either 10.5 g/dl (group A) or 11.5 g/dl (group B) and followed for 6 months. The mean Hb was 0.6 g/dl higher in the 11.5 g/dl threshold group (11.1 g/dl vs 11.7 g/dl) at 6 months (P=0.001++). The Epo dose did not differ between them (median 133 IU/kg/week, Interquartile range (IQR) 86-217 and 140, IQR 74-227 respectively) (P=NS(**)). STUDY 2: A large (n=211) unselected haemodialysis cohort was randomized to a reduction in Epo dose at Hb levels above either 12.0 g/dl (group C) or 13.0 g/dl (group D). The Hb outcome at 8 months differed between group C (mean 11.5 g/dl, SD 1.4) and group D (12.2, SD 2.1) (P=0.03++). The Epo dose did not significantly differ between groups C and D (median 60 IU/kg/week, IQR 32-142 and 71, IQR 38-117 respectively) (P=NS(**)). Study 1 showed that an intervention threshold of 11.0 g/dl with a mean Hb outcome of 11.6 g/dl and SD 1.6 g/dl would produce the desired UK Renal Association Standards outcome of 85% Hb > or =10.0 g/dl. Study 2 demonstrated that a ceiling of 12.0 g/dl narrowed the range of Hb values (P:<0.001##), achieving a SD of 1.37 g/dl, and reduced the number of patients with a Hb >13.0 g/dl from 25 to 12%. This narrowing of the distribution has cost implications for reaching minimum standards in a haemodialysis population. Formal use of threshold and ceiling values for intervention within an anaemia management system enabled the haemodialysis population outcome mean and SD to be literally prescribed.

Adult↗
PubMed1995

Impact of trophoblast penetration through the basal membrane on the efficacy of drug therapy in tubal pregnancies.

Concentrations of beta-human chorionic gonadotrophin (HCG) of 2500 IU/l are generally considered to be maximal for successful drug therapy of tubal pregnancies [instillation of prostaglandin-F2 alpha (PGF2 alpha) or hyperosmolar glucose]. The purpose of our study was to ascertain if there was an association between the significantly higher failure rates above this threshold value and the histologically determined anatomopathological substratum. We therefore evaluated the impact of trophoblast penetration through the basal membrane of the Fallopian tube on the efficacy of drug therapy. Pre-operative serum beta-HCG concentrations were compared with the histologically determined trophoblast penetration, distinguishing between ectopic pregnancies with intra-luminal growths up to the myosalpinx, and those with extra-luminal growths going beyond the basal membrane and penetrating the myosalpinx. Basic data were obtained from a group of patients who received primary surgical treatment but it had never been the intention for them to receive drug therapy (independently of their initial beta-HCG values; group I, n = 43). These reference data were compared with the findings in preparations from another group of patients obtained during secondary surgical intervention, performed to achieve final cure of tubal pregnancy after failure of primary PGF2 alpha instillation (group II, n = 30). Group I patients showed a significantly higher rate of intra-luminal trophoblast growths (P = 0.0001) at beta-HCG values < 2500 IU/l; above this threshold value, extra-lumina spread was found significantly more often (P = 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Chorionic Gonadotropin↗
PubMed2002

Form and motion coherence processing in dyspraxia: evidence of a global spatial processing deficit.

Form and motion coherence was tested in children with dyspraxia and matched controls to assess their global spatial and global motion processing abilities. Thresholds for detecting form coherence patterns were significantly higher in the dyspraxic group than in the control group. No corresponding difference was found on the motion coherence task. We tested eight children with dyspraxic disorder (mean age 8.2 years) and 50 verbal-mental-age matched controls (mean age 8.4 years) to test for a neural basis to the perceptual abnormalities observed in dyspraxia. The results provide evidence that children with dyspraxia have a specific impairment in the global processing of spatial information. This finding contrasts with other developmental disorders such as Williams syndrome, autism and dyslexia where deficits have been found in global motion processing and not global form processing. We conclude that children with dyspraxia may have a specific occipitotemporal deficit and we argue that testing form and motion coherence thresholds might be a useful diagnostic tool for the often coexistent disorders of dyspraxia and dyslexia.

Analysis of Variance↗
PubMed1982

Spatial frequency thresholds versus border enhancement: sensitivity to retinal defocus.

Two psychophysical methods for monitoring retinal defocus are compared. One methods, spatial frequency thresholds with sine wave grids, is well known. The second methods is relatively new: it uses the effect of defocus on the width of the perceptually enhanced region of brightness or darkness generated next to a luminance edge. Both methods produce characteristic functions as the retinal image is thrown out of focus. However, spatial frequency thresholds appear relatively unchanged until a certain level of defocus has been introduced, whereas border enhancement spread is affected even by very small deviations from focus. It is suggested that variations in the frequency threshold are dampened in the near-focus range by aberrations and by the nonlinear relation between contrast and defocus, but chiefly by the resolution limit of the retina and visual pathways. However, it is found that the apparent lack of response to small deviations from focus is due to a drastic compression rather than absence of threshold changes. If responses through this region are shown on a greatly expanded scale in relation to the rest of the function. fluctuations appear that often match those generated by border enhancement.

Differential Threshold↗
PubMed2002

Effects of pulse amplitude, pulse frequency, and stimulus duration on seizure threshold: a laboratory investigation.

BACKGROUND: Stimulus intensity during electroconvulsive therapy (ECT) is reckoned in units of charge (mC). The values of pulse amplitude, pulse width, pulse frequency, and stimulus duration can be varied to yield different composite stimuli, all of which have the same charge. There is little information on the extent to which variations in these stimulus parameters influence the seizure threshold at constant charge in the context of ECT. METHODS: We administered once daily electroconvulsive shocks (ECS) to two groups of rats, starting with a stimulus intensity of 1 mC and increasing in 1 mC steps until the thresholds of each of three different types of seizure were identified. In one group (n = 10), the charge was raised first by increasing pulse amplitude and later by increasing pulse frequency. In the other group (n = 10), the charge was raised by increasing the stimulus duration only. RESULTS: The mean seizure threshold ranged from 8.4 to 11.4 mC, depending on the type of seizure described, in the group in which pulse amplitude and frequency were manipulated; this range was 2.5 to 5.5 mC in the group in which the stimulus duration was manipulated (p < 0.001 for each of three types of seizures). Rats (n = 7) that did not convulse with an 8-mC stimulus in the amplitude and frequency group all convulsed with a 5-mC stimulus from the stimulus duration schedule. The first manifestation of seizure activity was significantly less likely to be generalized with amplitude and frequency titration than with stimulus duration titration (20% vs. 90%, respectively). The mean motor seizure durations (at different thresholds) were comparable with the two methods of stimulus titration. CONCLUSIONS: Seizure thresholds are lower when stimulus duration is the parameter that is increased during dose titration. The many clinical implications of this finding require study.

Animals↗
PubMed1975

The effect of vagus nerve stimulation upon vulnerability of the canine ventricle: role of sympathetic-parasympathetic interactions.

The effect of vagus nerve stimulation (VNS) upon ventricular vulnerability was studied in 30 mongrel dogs subjected to varying levels of adrenergic stimulation. Vulnerability was assessed both by determining the minimum current required to produce ventricular fibrillation (VF threshold) and by plotting VF threshold throughout the vulnerable period (VF zone). Chloralose-anesthetized animals were studied by means of sequential pulses applied to the apex of the right ventricular endocardium. Testing was carried out in closed-chest dogs, in open-chest dogs with and without left stellate ganglion stimulation (LSGS), and in open- and closed-chest dogs pretreated with propranolol. In the absence of adrenergic stimulation. VNS was without significant effect on either the VF threshold or the VF zone under closed- or open-chest conditions. During LSGS, however, VNS was associated with a 93 +/- 22% (mean +/- SE) increase in VF threshold (P less than 0.01) and constriction of the VF zone. Vagus nerve stimulation combined with LSGS raised VF threshold to the control value, but not beyond. After beta-adrenergic blockade with propranolol, VNS was without effect on VF threshold in either open- or closed-chest animals. It is concluded that augmented sympathetic tone is a precondition for a VNS-induced elevation in VF threshold. The vagal effect is indirect and is expressed by opposing the effects of heightened adrenergic tone on ventricular vulnerability.

Acetylcholine↗
PubMed1977

Clinical assessment of analgesics using ultrasonic stimulation. A new method.

A quantitative method for measuring pain threshold by the use of ultrasonic stimulation in man was designed and the possibility of clinical application in assessing analgesics was investigated. Ultrasonic stimulus was given to Japanese subjects on the palmer distal part of the 2nd, 3rd and 4th fingers of both hands. The latent time between start of the stimulation and withdrawal of the hand when perceiving pain was considered the pain threshold. The ultrasonic evoked pain was a sharp pin-prick type, without sensations such as thermal and mechanical. The pain threshold lowered with increasing either stimulus intensity or water bath temperature when the hand of the subject was immersed during measurement. Normal threshold to ultrasonic stimulation measured in both 50 men and 50 women gave nearly normal distribution curves; women being more sensitive to ultrasonics than men. Analgesia with codeine phosphate (20 mg p.o.), aspirin (1.5, 1.0, 0.5 g p.o.), aminopyrine (100 mg p.o.) and mefenamic acid (500 mg p.o.) in volunteers of both sexes was demonstrated significantly using this method under double blind circumstances. Pentobarbital, diazepam, butylscopolamine, bromelain and placebo each in the usual dose used clinically failed to alter the pain threshold. Humans were at least 25 fold more sensitive than mice to the analgesics used herein.

Adolescent↗
PubMed1988

Spatial waveform discrimination following higher-harmonic adaptation.

Campbell and Robson [J. Physiol. (London) 197, 551 (1968)] proposed that a near-threshold square-wave grating can be distinguished from a sine-wave grating of the same spatial frequency and fundamental amplitude when the channel tuned to the third-harmonic component of the square wave reaches its own threshold. To test this hypothesis, we measured waveform discrimination thresholds with two-interval forced-choice methods before and after 4-min adaptation to a high-contrast sine-wave grating, the spatial frequency of which equaled that of the square wave's third harmonic. The results indicate that 3f adaptation has only a negligible effect on discrimination thresholds. In a further experiment, we adapted observers to both 3f and 5f harmonic frequencies of the square-wave test grating presented sequentially over 4 min. Although substantial threshold elevations occurred at the 3f and 5f frequencies, the elevation in waveform discrimination threshold was small. These results suggest that the independent-channel hypothesis alone cannot account for the visibility of complex features (edges) following harmonic adaptation.

Adaptation, Physiological↗
PubMed2003

Monitoring of brain tissue oxygenation during aneurysm surgery: prediction of procedure-related ischemic events.

OBJECT: The aim of this study was to evaluate the feasibility of monitoring brain tissue oxygenation (PO2) during aneurysm surgery for the detection of procedure-related ischemia. METHODS: Between 1997 and 1998, PO2 was monitored prospectively in a cohort of 40 patients (42 recordings) during aneurysm surgery in the anterior circulation within the vascular territory of the aneurysm-bearing artery. The position of the probe used to measure oxygenation levels was verified on computerized tomography (CT) scanning on the 1st postoperative day. Because of the mislocation of one probe and the malfunction of another, data from only 38 patients (40 recordings) were suitable for analysis. Relative changes from baseline to absolute nadir values of intraoperative PO2 were correlated with simultaneously recorded somatosensory evoked potentials (SSEPs), and cardiovascular and ventilatory parameters. The frequency of ischemic events was evaluated with the aid of CT on the 1st postoperative day as a substitute parameter for intraoperative ischemia. Clinical outcome was evaluated 30 days postoperatively based on the Glasgow Outcome Scale. Except for three, all patients underwent surgery for treatment of a symptomatic aneurysm. Mean baseline PO2 was 23.9 mm Hg (range 2-67.2 mm Hg) before clip application. A relative decrease in PO2 (20% decrease in value compared with baseline) occurred in 12 patients and was a sensitive indicator for the risk of ischemia during temporary arterial occlusion, but was less predictive of nonocclusive ischemia (sensitivity 0.5; positive predictive value [PPV] 0.42; p > 0.05). Results of receiver operating characteristic analysis demonstrated a postclipping PO2 nadir of 15 mm Hg as a dichotomizing threshold for the prediction of ischemia. This threshold rendered an improved sensitivity (0.9) and PPV (0.56) for procedure-related ischemia (p = 0.0003). The results of utility analysis revealed this monitoring parameter to be clinically diagnostic. Only PO2 monitoring, and not SSEP at the tibial nerve, was predictive of ischemia within the anterior cerebral artery territory. CONCLUSIONS: Using 15 mm Hg as a dichotomizing threshold, intraoperative PO2 monitoring enables one to identify patients at risk for procedure-related ischemia during aneurysm surgery and surpasses SSEP monitoring. This newly defined threshold based on intraoperative PO2 monitoring provides a basis for studies on treatments for procedure-related ischemia during aneurysm surgery.

Adult↗
PubMed1989

Nasal provocation with histamine: a comparison of the determination of the threshold of reactivity by three methods of rhinomanometry.

Three methods of rhinomanometry were compared with each other with respect to their ability to determine the histamine threshold (histamine concentration for a 100% increase of the initial total nasal resistance): the active anterior rhinomanometry (P.A.R.). Nasal challenge and consecutive measurement by the three methods of rhinomanometry were conducted in a group of 11 volunteers. The three methods gave significantly different histamine concentration thresholds (p = 0.002). Unilateral histamine thresholds as available from A.A.R. and P.A.R. (at a flow of 250 cm3/sec) did not differ significantly (p = 0.299). For A.A.R. and A.P.R., histamine thresholds were assessed at five different pressure values as well as at five different flow values. The thresholds did not appear to be significantly different at any one of those pressure gradients (p = 0.690) or flow values (p = 0.357).

Clinical Trials as Topic↗
PubMed1975

Application of visually evoked response near the threshold of vision to objective measurement of dark adaptation.

The visually evoked response (VER) to dim lights with intensities within the scotopic or lower mesopic range increased in amplitude during the progressive dark adaptation. The VER amplitude vs. time curve resembled the psychophysical dark adaptation curve. The spectral sensitivity curve of the dark-adapted VER matched the C.I.E. scotopic sensitivity curve. The dark-adapted VER was abnormal in patients with retinitis pigmentosa and with congenital stationary night blindness and recordable in a patient with cone dysfunction. There was a close correlation between the VER threshold and subjective threshold of visual perception. The dark-adapted VER may be useful as an objective index of dark adaptation.

Adaptation, Ocular↗