Biomedical subjects

R J Irwin

Publications and source records attributed to R J Irwin.

At least 37 records · Page 2Linked to original sources

PubMed1999

Are there critical bands in kinesthesia?

The effect of changing the bandwidth of noise on the ability of human subjects to detect a 10-Hz sinusoidal movement signal was measured in two experiments. The objective of these studies was to investigate whether critical bands exist for the kinesthetic system, as has been demonstrated for the auditory and tactile systems. It was found that subjects' ability to detect a 10-Hz sinusoidal movement stimulus embedded in noise was not influenced by the bandwidth of the noise over a range of 4-10 Hz. These findings suggest that, if a critical filter does exist for this system, it would have to be greater than 10 Hz.

Auditory Perception↗

PubMed1998

Stability of memory for colour in context.

Memory for colours presented in isolation was compared with that for colours presented as part of a clip-art image or as part of a non-meaningful, Mondrian-like image. The area under the Receiver Operating Characteristic for deciding that two colours, presented at different delay intervals, were the same or different provided an index of memory for colour. The provision of a context reduced the decay of memory, regardless of whether the context was meaningful (clip-art images) or non-meaningful (Mondrian-like images). The result was seen as a generalisation of the auditory phenomenon of profile analysis, in which memory for the amplitude of a single component of a complex sound is more stable than that for the component in isolation.

Color↗

PubMed1998

Placement of metallic stents in ureters obstructed by carcinoma of the cervix to maintain renal function in patients undergoing long-term chemotherapy.

OBJECTIVE: Metallic stents, sometimes augmented by "J" endostents, were placed in ureters obstructed by advanced carcinoma of the cervix to improve or maintain renal function in these patients at a level necessary to pursue long-term chemotherapy and radiation therapy. SUBJECTS AND METHODS: Seventeen ureters in 11 patients were treated with metallic stents, which were placed by an anterograde approach in 10 patients and by a retrograde approach in one. An anterograde ureteroneocystostomy was necessary in two of the 11 patients. J endostents were placed for I month in all patients. In 10 ureters, J endostents were reintroduced during follow-up 1-48 months later. RESULTS: In 17 ureters, metallic stents were successfully placed; in the remaining three ureters, the procedures were aborted because of technical difficulties. The goal of improving and maintaining renal function was met in 10 patients. Serum creatinine levels returned to normal in four patients and stabilized at a range of 2.7-3.2 mg/dl in six more patients, permitting treatment with chemotherapy, radiation therapy, or both. Four of the 11 patients died within 4 months after treatment, and three more died within 2 years. At the time of death or last follow-up, seven metallic stents and eight combinations of metallic stents and J endostents were patent. Complications were minor. CONCLUSION: Placement of metallic stents is recommended as an effective method to ensure patency and to facilitate cystoscopic replacement of J endostents in ureters compromised by carcinoma of the cervix. Renal function can be maintained, allowing chemotherapy. Survival is governed by the effectiveness of chemotherapy and radiation therapy.

Adult↗

PubMed1998

Discriminability in length of lines in the Müller-Lyer figure.

Receiver-operating characteristics for the discriminability in the length of the lines of the Müller-Lyer figure were obtained by the rating method of detection theory. Six observers judged the shaft length of the lines of the figure with reference to the same standard line. Maximum-likelihood estimates of the index of discriminability, d', were linear function of the difference in the length of the lines, but the functions did not pass through the origin because of a constant error of judgment. Because discriminability was determined by ROC analysis, the constant error could not be attributed solely to changes in criterion placement; instead, it showed that the Müller-Lyer figure induced a change in the discriminability of the lines.

Female↗

PubMed1998

Global primary blast injury: a rat model.

Blast wave injury from bombs cause a unique but poorly understood spectrum of injuries. Previous blast wave models involved high energy explosives detonated in an open field without the sophisticated monitoring of laboratory equipment. We characterized a rodent model that produces a global blast injury in a safe laboratory environment. Male rats, prospectively randomized to four groups of ten, were anesthetized and subjected to a blast at 2.0 cm, 2.5 cm, or 3.5 cm from the blast nozzle. The control group received no blast. Intensity of the blast (80-120 psi peak pressure, 1-2 msec duration) was controlled by varying the distance of the blast wave generator to the rat. The rats were monitored for three hours following the blast and then euthanized. Bradycardia was an immediate but transient response to blast injury. Mean arterial pressure was bimodal with severe hypotension occurring immediately after the blast and, again, two to three hours later. The characteristic injuries from a blast wave, such as pulmonary hemorrhage with increased lung weight, intestinal serosal hemorrhage, and hemoperitoneum, were found in the rats subjected to the blast pressure wave. In conclusion, our rodent model accurately reproduces the clinical spectrum of injuries seen in blast victims and will provide a powerful tool for studying the pathophysiology and potential treatments of bomb blast victims.

Analysis of Variance↗

PubMed1997

Cardiopulmonary physiology of primary blast injury.

OBJECTIVE: Bomb blast survivors are occasionally found in profound shock and hypoxic without external signs of injury. We investigated the cardiovascular and pulmonary responses of rats subjected to a blast pressure wave. DESIGN: Prospectively randomized, controlled animal study. MATERIALS AND METHODS: Rats were instrumented and subjected to a blast pressure wave of different intensities from a blast wave generator. Cardiopulmonary parameters were recorded for 3 hours or until death. MEASUREMENTS AND MAIN RESULTS: The cardiovascular response to a blast pressure wave was immediate bradycardia, hypotension, and low cardiac index. Three hours later, the rats developed hypotension, low cardiac index, and low stroke volume. Interestingly, systemic vascular resistance remained unchanged. The pulmonary response was a decreased PaO2 and stable PacO2, suggesting a ventilation-perfusion mismatch from massive pulmonary hemorrhage. CONCLUSIONS: Blast-induced circulatory shock resulted from immediate myocardial depression without a compensatory vasoconstriction. Hypoxia presumably resulted from a ventilation-perfusion mismatch caused by pulmonary hemorrhage.

Animals↗

PubMed1997

Androgen modulation of the messenger ribonucleic acid of retinoic acid receptors in the prostate, seminal vesicles, and kidney in the rat.

Previously, we reported that the steady state level of messenger RNA (mRNA) transcripts of retinoic acid receptors (RAR) alpha and gamma in the testes of 20-day-old rats can be modulated by exogenous testosterone. These results suggest that androgen regulation of Sertoli cell functions may involve biochemical events mediated by RAR genes. In this study, we examined the effects of castration and testosterone replacement on the steady state level of mRNA transcripts for RAR alpha and gamma in the prostate, seminal vesicles, and kidney of the rat. Northern blot analysis revealed that in intact adult rats, the relative steady state levels of the 3.4- and 2.7-kilobase (kb) mRNA transcripts for RAR alpha and the 3.4-kb transcript for RAR gamma in the prostate were at least 20-fold higher than those in the seminal vesicles and kidney. The relatively high abundance of RAR mRNA transcripts in the prostate suggests the physiological importance of RAR-mediated processes in this organ. Castration resulted in an increase in the level of RAR mRNA transcripts in the prostate and seminal vesicles, reaching a maximum of 2- to 4-fold in the prostate and 15- to 23-fold in the seminal vesicles within 6 days. On the other hand, the levels of mRNA transcripts of RAR alpha and -gamma in the kidney were reduced by 40-50% 1 day after castration. The effects of castration on RAR mRNA levels in all three organs were prevented by implantation of 3-cm testosterone capsules at the time of castration, a regimen that provides physiological levels of serum testosterone. In a subsequent experiment, adult male rats were given a single sc injection of 2 mg testosterone 3 days after castration. This treatment resulted in an acute suppression of the level of RAR mRNA transcripts in all three organs within 30 min. Thereafter, the levels of RAR alpha and -gamma mRNA transcripts in the prostate continued to decrease, whereas those in the seminal vesicles returned to the castrated levels within 6 h. On the other hand, RAR mRNA levels in the kidney rebounded by 1 h and remained at the level found in the untreated castrated rats. These results demonstrate that the steady state level of mRNA transcripts for RAR alpha and -gamma in the prostate, seminal vesicles, and kidney can be modulated by testosterone in organ-specific manners, thus suggesting that the RAR-mediated processes may be involved in the effects of androgen in these organs. Furthermore, the relatively low increment in prostatic RAR mRNA levels after castration compared to that in the seminal vesicles demonstrates a difference in androgen responses between these two organs. This difference could dictate the efficacy of the effects of androgen on cellular function and may contribute to the disparate vulnerabilities to androgen-related uncontrolled cell proliferation and/or malignancy in the prostate and seminal vesicles.

Animals↗

PubMed1997

Likelihood-ratio decision strategy for independent observations in the same-different task: an approximation to the detection-theoretic model.

An optimal decision strategy for deciding whether two things are the same or different is to adopt a likelihood-ratio criterion. The parametric equations for the receiver operating characteristic (ROC) based on the likelihood-ratio strategy when observations are independent are complicated; they require the numerical evaluation of a double integral. An approximation to the parametric equations for the likelihood-ratio strategy was developed. This approximation takes the form of a pair of equations that describe ROCs virtually indistinguishable from those of the full model.

Decision Making↗

PubMed1995

Perception of simple and complex visual stimuli: decision strategies and hemispheric differences in same-different judgments.

The accuracy with which observers could judge whether two visual stimuli were the same or different was measured with the rating method of detection theory. For judgments of whether two pictures referred to natural or manufactured things, the shape of the obtained receiver operating characteristic (ROC) was consistent with the observers adopting an optimal decision strategy. A similar result was found for judgments of complex but meaningless visual patterns. For judgments of whether two colours that differed along a simple sensory dimension were the same or different, however, the resulting ROC was consistent with the observers adopting a suboptimal differencing strategy. The accuracy of the judgments did not depend on the visual field to which the stimuli were presented.

Brain↗

PubMed1995

Decision strategies and visual-field asymmetries in same-different judgments of word meaning.

The accuracy with which observers judged whether two words belonged to the same semantic category was determined from a detection-theoretic analysis of same-different judgments. In Experiment 1, one word was presented centrally and the other word in either the left visual field (LVF) or the right visual field (RVF); in Experiment 2, both words were presented to either the LVF or the RVF. In order to obtain receiver-operating characteristics (ROCs) of performance, observers were asked to rate their confidence that the two words belonged to the same semantic category. Two models of the decision strategy were fitted to the obtained characteristics: a differencing model, in which the decision variable was the difference between the two observations; and an optimal model, in which each observation was judged in relation to a criterion. In both experiments, the optimal model provided a better fit than the differencing model to the obtained characteristics. Maximum-likelihood estimates of both the criterion-free parameter, d', and the area under the operating characteristic, p(A), were greater for words presented in the RVF than for those presented in the LVF.

Adult↗

PubMed1994

A comparison of two methods for isolation of Salmonella from poultry litter samples.

Two methods were compared to determine their ability and efficiency in detecting Salmonella in poultry litter samples. Method 1 consisted of pre-enrichment in buffered peptone water (BPW), selective motility enrichment in Modified Semisolid Rappaport Vassiliadis (MSRV) agar, and plating onto MacConkey (MC) agar. Method 2 employed tetrathionate brilliant green (TBG) broth and plating on brilliant green agar with novobiocin (BGAN) and on xylose lysine tergitol 4 (XLT4) agar. Method 1 resulted in a significantly higher isolation rate, was cheaper, and was less labor intensive.

Animals↗

PubMed1994

Discriminability of electrocutaneous stimuli after topical anesthesia: detection-theory measurement of sensitivity to painful stimuli.

In three experiments on the psychophysical measurement of pain, electrocutaneous currents were applied to the volar surface of the forearm. In the first experiment, a conventional category scaling method was compared with the rating method of signal detection. The results of both methods were analyzed in detection-theory terms to derive receiver operating characteristic curves and measures of the discriminability of adjacent currents. The rating method yielded larger discriminability values than the category scale did, and that method was therefore used in the subsequent experiments to examine the effect of a topical anesthetic on discriminability. When the stimuli were applied through surface electrodes, no effect of the topical anesthetic on discriminability was found, but when the stimuli were applied to a more localized area by intradermal needle electrodes, a dose-dependent effect of the anesthetic on discriminability occurred. For this experiment, the slope of the cumulative sensitivity function increased with increasing elapsed time since the removal of the anesthetic. This result is congruent with the theory that discriminability can serve as a measure of sensitivity to painful stimuli.

Anesthesia↗

PubMed1994

A national survey to estimate the prevalence of Salmonella species among Canadian registered commercial turkey flocks.

In 1990-1991, a national survey was conducted to estimate the prevalence of Salmonella species among Canadian commercial turkey flocks. Two hundred and seventy flocks were randomly selected across Canada. The proportion sampled from each province was selected according to each province's share of the national turkey market. Samples, consisting of 12 pooled litter and four pooled dust samples, were used to determine the Salmonella status of the environment of each flock. Additionally, a one kilogram sample of feed was taken from each flock premise. Salmonella was recovered from environmental samples in 234/270 (86.7%) of flocks and from feed samples in 26/266 (9.8%) of flocks. Forty-eight different Salmonella serovars were isolated from flock environmental samples. The most prevalent serovars were S. anatum, S. hadar, S. agona, S. heidelberg and S. saintpaul which were isolated from 53/270 (19.6%), 49/270 (18.1%), 49/270 (18.1%), 42/270 (15.6%) and 34/270 (12.6%) flocks, respectively.

Animals↗

PubMed1993

Perinephric panniculitis.

Panniculitis is an inflammatory condition of adipose tissue that is mainly seen subcutaneously or intra-abdominally. There have been rare case reports of retroperitoneal involvement but no reported cases of perinephric panniculitis. To our knowledge we report the first documented case of perinephric panniculitis.

Humans↗

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↗