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Biomedical subjects

R J Irwin

Publications and source records attributed to R J Irwin.

At least 19 recordsLinked to original sources
PubMed1992

Differential thresholds for limb movement measured using adaptive techniques.

Differential thresholds for limb movement were measured in 10 subjects, using the transformed up-down procedure. Subjects were required to indicate which of two random displacement perturbations delivered to their forearms had the larger standard deviation (SD). The SD of the reference signal was fixed for each experimental condition at one of seven values ranging from 0.05 to 3.2 mm. THe SD of the other signal varied depending on the subject's response. Using this procedure, the differential threshold for limb movement was calculated to be 8%, which is very similar to the thresholds estimated previously for changes in limb position (9%) and force (7%). The sensitivity of the human proprioceptive system to changes in limb displacement was much greater than anticipated, with subjects being able to resolve a 5-microns difference between two perturbations delivered to their arms.

Adult↗
PubMed1992

Amplitude discrimination of sinusoids and narrow-band noise with Rayleigh properties.

The ability of human observers to discriminate differences in the amplitude of sinusoids and narrow-band noises was measured by the rating method of detection theory. Although each sinusoid (always 1000 Hz) was presented at a fixed amplitude, its amplitude on any trial was drawn from one of two Rayleigh probability distributions that differed in mean amplitude: a signal distribution and a noise distribution. Similarly, the amplitudes of the narrow-band noises were distributed as the Rayleigh distribution by virtue of the reciprocal relation between their bandwidth (100 Hz centered on 1000 Hz) and duration (10 msec). The obtained psychometric functions showing the area under the ROC as a function of signal-to-noise ratio were similar for both kinds of signals and were displaced, on average, about 4 dB from an ideal observer's function. The slopes of the obtained functions were similar to those of an ideal observer using 1 degree of freedom--half the number available in Rayleigh noise.

Adult↗
PubMed1992

Salmonella enteritidis and other Salmonella in laying hens and eggs from flocks with Salmonella in their environment.

Seven Canadian layer flocks with Salmonella enteritidis in their environment were investigated to determine the numbers of hens infected with S. enteritidis, the localization of S. enteritidis in organs of infected hens and the numbers of S. enteritidis-infected eggs produced by two affected flocks. By a microagglutination test (MAT) using S. pullorum antigens, these flocks had more seropositive hens (mean 51.9 +/- 16.9%) than two Salmonella-free flocks (mean 13.0 +/- 4.2%). Culture of tissues of 580 hens (433 seropositive) from the seven flocks detected 26 (4.5%) S. enteritidis-infected hens from two flocks. In one flock, 2/150 hens were infected with S. enteritidis phage type (PT) 8, which was confined to the ceca, and no Salmonella spp. were isolated from 2520 eggs (one day's lay). In the second flock, where 24/150 hens were infected with S. enteritidis PT13, extraintestinal infection was found in nine hens and involved the ovaries and/or oviduct in two hens. Salmonella enteritidis PT13 was isolated from one sample of egg contents and from one sample of cracked shells from among 14,040 eggs (one day's lay) from this flock. The overall prevalence of S. enteritidis-contaminated eggs from the two flocks with infected hens was less than 0.06%. Other Salmonella spp. isolated were S. heidelberg from 58 hens (10%), and S. hadar, S. mbandaka and S. typhimurium from one hen (0.2%) each. The MAT with antigens of S. pullorum had a sensitivity of 81% and a specificity of 24% for detecting S. enteritidis-infected hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Agglutination Tests↗
PubMed1991

Habituation to repeated painful and non-painful cutaneous stimuli: a quantitative psychophysical study.

Repeated stimuli elicit progressively smaller responses and elevated sensory and/or pain thresholds (habituation). The present experiments were designed to determine the rate of habituation of perceptual responses to supraliminal painful and non-painful cutaneous stimuli. Changes in the perceived intensity of electrical stimuli applied to the digital nerves of the index finger were determined by a matching procedure in which subjects set the current applied to the index finger of one hand to match the perceived intensity of a stimulus train (5 pulses at 20 Hz) applied to the other index finger. Twenty-five volunteers took part in 7 experiments in which both non-painful (2.5 times the sensory threshold Ts) and painful (1.2 times the pain threshold Tp) stimulus trains were presented. Subjects were required to match the stimuli at 30 s intervals over a period of 7.5 min. The percentage change in matching current (Y) was fitted by the function Y = -20.7*[1-exp(-0.56*t)] for both painful and non-painful stimuli repeated at 2 Hz. Responses recovered completely within 2 min of cessation of the stimulation. The degree of habituation increased or decreased with the rate of stimulus presentation. These results did not depend on changes in afferent fibre recruitment or fatigue because the afferent volley on the median nerve remained constant throughout the period of stimulation. Thus perceptual responses to the perceived intensity of supraliminal painful and non-painful stimuli delivered to the index finger habituate to the same extent, and the extent of the habituation is a function of the frequency of presentation of the stimulus.

Adult↗
PubMed1991

The prevalence of Salmonella enteritidis and other Salmonella spp. among Canadian registered commercial layer flocks.

A survey was conducted to estimate the prevalence of Salmonella enteritidis and other salmonellas among Canadian commercial egg producing flocks. Environmental (faecal and eggbelt) samples from 152 of 295 (52.9%) randomly selected flocks were contaminated with salmonellas. Thirty-five different salmonella serovars were isolated. Eggbelt samples were more often contaminated with salmonellas than faecal samples (25.7 v. 10.1%). The most prevalent serovars were S. heidelberg, S. infantis, S. hadar, and S. schwarzengrund; they were isolated from samples of 59/295 (20%), 18/295 (6.1%), 17/295 (5.8%), and 15/295 (5.1%) flocks, respectively. Feed samples of 21/295 (7.2%) flocks were contaminated with salmonellas. Salmonella enteritidis was isolated from the environmental samples of 8/295 (2.7%) flocks. Salmonella enteritidis phage type (PT) 8 was isolated from 5 flocks, PT 13a from 2 flocks, and PT 13 from 1 flock.

Animal Feed↗
PubMed1991

The prevalence of Salmonella enteritidis and other Salmonella sp. among Canadian registered commercial chicken broiler flocks.

A nation-wide survey was conducted to estimate the prevalence of Salmonella enteritidis and other salmonellas among Canadian commercial broiler flocks. Environmental (litter and/or water) samples from 226 of 294 (76.9%) randomly selected flocks were contaminated with salmonellas. Litter samples were more often contaminated with salmonellas than water samples (47.4 v. 12.3%). Fifty different salmonella serovars were isolated. The most prevalent serovars were S. hadar, S. infantis, and S. schwarzengrund; they were isolated from samples of 98/294 (33.3%), 26/294 (8.8%), and 21/294 (7.1%) flocks, respectively. Feed samples of 39/290 (13.4%) flocks were contaminated with salmonellas. Salmonella enteritidis was isolated from the environmental samples of 9/294 (3.1%) flocks. Salmonella enteritidis phage type (PT) 8 was isolated from seven flocks, and PT 13a from two flocks.

Animal Feed↗
PubMed1991

Poisoning of Canada geese in Texas by parathion sprayed for control of Russian wheat aphid.

Approximately 200 Canada geese (Branta canadensis) died at a playa lake in the Texas Panhandle shortly after a winter wheat field in the basin adjacent to the lake was treated with parathion to control newly invading Russian wheat aphids (Diuraphis noxia). No evidence of infectious disease was diagnosed during necropsies of geese. Brain ChE activities were depressed up to 77% below normal. Parathion residues in GI tract contents of geese ranged from 4 to 34 ppm. Based on this evidence, parathion was responsible for the goose mortalities. Parathion applications to winter wheat will undoubtedly increase if parathion is applied for control of both Russian wheat aphids and greenbugs (Schizaphis graminum). Geese may potentially be exposed to widespread applications of parathion from fall to spring, essentially their entire wintering period.

Aerosols↗
PubMed1990

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels.

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.

Adult↗
PubMed1989

Psychometric functions for the discrimination of differences in intensity of Gaussian noise.

A new theory of sensory functioning by Laming predicts how the shape of the psychometric function depends on the context in which a signal is presented. The discrimination of intensities of noise was therefore studied with four different stimulus configurations. In one, observers discriminated between two separate noise samples that differed in intensity. In accordance with the theory, a normal probability integral provided a better fit to each observer's data than either of two other functions: a normal integral with respect to the square of the difference, or a normal integral with respect to the fourth power of the difference. In a second task, observers detected an increment in a continuous noise. For eight out of nine sets of data, a square-law function provided a better fit than either a normal integral or fourth-power function. A third task asked observers to decide which of two noises was amplitude modulated. The predicted square-law function provided the best fit for four out of five observers. In a fourth task, one observer detected an interval of amplitude modulation in a continuous noise. As predicted by the theory, a fourth-power function provided the best fit. In addition, Weber fractions for difference discriminations decreased approximately with the square root of sample duration for durations up to 300 msec, whereas Weber fractions for increment detections decreased approximately directly with duration for durations up to 100 msec. The results are usually in qualitative agreement with the theory and often in quantitative agreement as well.

Adult↗
PubMed1989

The prevalence of verocytotoxin-producing Escherichia coli and antimicrobial resistance patterns of nonverocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens.

The prevalence of verocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens was determined by culturing cloacal samples from 500 individual birds selected from 50 poultry farms. Resistance to antimicrobials was determined for each of the isolates. In addition, abattoir and farm-level management data were obtained to evaluate variables that may be considered risk factors for infection. The variables selected included: Percentage of birds condemned at slaughter, percentage of birds dead-on-arrival, bird weight, truck number, farm size, hatchery source, litter source and type, feed source, mortality levels, type of water drinker, water sanitization, down time, barn clean out and history of antibiotic treatment. None of the cloacal samples revealed the presence of verocytotoxin-producing E. coli, though 19/500 (3.8%) contained Salmonella organisms. Nine different Salmonella serotypes were isolated; the most common being S. hadar, S. heidelberg and S. mbandaka. Resistance to tetracycline and streptomycin was common among Salmonella (63%) and E. coli (25.2%) isolates. Resistance to two or more antimicrobials occurred in 420/500 (84%) of the E. coli isolates. No statistically significant associations between abattoir or farm-level management variables and the Salmonella-status of farms were demonstrated.

Abattoirs↗
PubMed1987

Relations among temporal acuity, hearing loss, and the perception of speech distorted by noise and reverberation.

Eight normal listeners and eight listeners with sensorineural hearing losses were compared on a gap-detection task and on a speech perception task. The minimum detectable gap (71% correct) was determined as a function of noise level, and a time constant was computed from these data for each listener. The time constants of the hearing-impaired listeners were significantly longer than those of the normal listeners. The speech consisted of sentences that were mixed with two levels of noise and subjected to two kinds of reverberation (real or simulated). The speech thresholds (minimum signal-to-noise ratio for 50% correct) were significantly higher for the hearing-impaired listeners than for the normal listeners for both kinds of reverberation. The longer reverberation times produced significantly higher thresholds than the shorter times. The time constant was significantly correlated with all the speech threshold measures (r = -0.58 to -0.74) and a measure of hearing threshold loss also correlated significantly with all the speech thresholds (r = 0.53 to 0.95). A principal components analysis yielded two factors that accounted for the intercorrelations. The factor loadings for the time constant were similar to those on the speech thresholds for real reverberation and the loadings for hearing loss were similar to those of the thresholds for simulated reverberation.

Acoustic Stimulation↗
PubMed1986

The width of the auditory filter in children.

Because young children have poorer auditory temporal resolution than older children, they ought to have, according to the inverse relation between temporal and frequency resolution, narrower auditory filters than older children. Therefore, the auditory filters of two 6-year-olds, two 10-year-olds, and two adults were measured by having them detect a 400-ms sinusoid (500, 1000, or 3000 Hz) centered in a spectral notch in a band of noise. The signal power for 71% correct was determined as a function of notch width with the two-alternative, forced-choice procedure. The principal results showed a significant decrease in signal power with age and a significant interaction between age and notch width. The best-fitting parameters of a model of the auditory filter showed that the filter was significantly wider for the 6-year-olds than for the 10-year-olds or the adults.

Adult↗
PubMed1985

The development of auditory temporal acuity in children.

The development of auditory temporal acuity was studied in 56 children aged 6-12 years and compared with that of 8 adults. Acuity was measured by determining the minimum detectable duration of a brief cessation in a noise band with the 2-alternative forced-choice method. For detection of gaps in a broadband noise, acuity improved significantly with age and reached adult values by 11 years. The minimum detectable duration was significantly shorter at higher levels of the noise. For narrow-band noises, acuity also improved significantly with age and depended on the center frequency of the band. The improvement in temporal acuity with age was attributed to the development of sensory processes and not to age-related changes in nonsensory factors.

Adult↗
PubMed1979

Intravesical thio-tepa: a study of 3H-thymidine uptake in normal urothelium and FANFT-induced tumors in rats.

Treatment of superficial low-grade bladder cancer often incorporates intravesical instillations of the alkylating agent thio-TEPA. Current dosages and administration schedules are empiric inasmuch as cytokinetic data are sparse. The FANFT-induced bladder rat tumor model closely approximates human bladder cancer. This study measuring 3H-thymidine uptake identified peaks of maximal synthetic activity at 3 and 9 days after thio-TEPA exposure in both normal and neoplastic urothelium. Thus, repeat instillation at these intervals may improve cytotoxicity and overall response rate.

Animals↗
PubMed1978

Ileal conduit hemorrhage secondary to portal hypertension.

The clinical features and management of 3 patients who presented with the triad of massive hemorrhage from the ileal conduit, portal hypertension due to liver disease, and portosystemic varices related to the conduits are described. One patient, a class C cirrhotic, was treated conservatively and died of blood loss and hepatic coma. Two patients were managed with splenorenal shunts initially, followed by creation of colon conduits, and are currently doing well. Surgical approximation of areas draining in the portal and systemic circulation with subsequent development or adhesion-related varices probably explains the predilection for involvement of the ileal conduit and may explain the presence of varices in mild to moderate portal hypertension before other signs of hepatic decompensation are evident. Superior mesenteric angiography with special attention directed at the venous phase is necessary to document this entity.

Adult↗
PubMed1978

Changes of cell cycle affecting cidal effect of triethylene thiophosphoramide on cultured human bladder carcinoma cells.

The cell cycle of the human bladder carcinoma cell line (MGH-U1 cells) was prolonged immediately after low dose of triethylene thiophosphoramide (Thio Tepa). Although the elongated cell cycle time seemed to return to the control level 48 hr following the treatment, there still remained postsynthetic accumulation and postmitotic diminution in the cell population and the cells were insensitive to high dose of the agent. The present results suggest that Thio Tepa is less effective for G2 cells, but more effective for G1 or S cells.

Cell Cycle↗
PubMed1978

[32P] diphosphonate dose determination in patients with bone metastases from prostatic carcinoma.

In an initial safety study, phosphorus-32 (as diphosphonate) was administered intravenously to five patients with painful bone metastases from prostatic carcinoma; two patients received 9 mCi and three were given 3 mCi. Hematological, biochemical, ECG, x-ray, bone-scan data, and clinical observation, were followed for 2 mo. At both dose levels, bone-marrow depression was noted. One of the patients, who received 9 mCi, had only a slight dip in the levels of circulating white blood cells and platelets. The other 9-mCi patient was the only one with discrete metastases by bone scan; he had bone-marrow depression, from which he recovered, and was the only one of the five who had relief of bone pain.

Adenocarcinoma↗