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Biomedical subjects

C Drake

Publications and source records attributed to C Drake.

At least 55 records · Page 3Linked to original sources
PubMed1997

Perceptual attenuation of nonfocused auditory streams.

The aim of this study was to measure the perceptual attenuation, measured in decibels, resulting from the focusing of attention on one stream within a multistream auditory sequence. The intensity of a nonfocused stream was increased until the accuracy of detecting a temporal irregularity in this stream was the same as in a focused stream. Eight subjects were required to detect a temporal irregularity created by delaying or advancing one tone which could be situated in one of three temporally regular streams played simultaneously to create a multistream sequence. The three streams differed in tempo and frequency. Subjects' attention was focused on one of the streams by preceding the multistream sequence with one of the single streams (a cue). We first established the size of temporal irregularity detected at a 90% level in cued streams, confirming that subjects were able to focus on one particular stream. Second, an irregularity of this size was not detected above chance level in noncued streams, demonstrating that listeners focus only on the cued stream. Third, for 5 subjects, a 15-dB increase in the level of one of the noncued streams was necessary to bring detection up to that found in the cued streams. This gain provides an equivalent measure of the perceptual attenuation of nonfocused streams. For 3 other subjects, detection in the noncued stream remained at chance performance whatever the level. For all subjects, detection in the cued stream decreased slightly as the level of the noncued stream increased. We conclude that the attenuation of nonfocused auditory streams can attain as much as 15 dB, at least for some subjects.

Attention↗
PubMed1996

Surgical treatment for colic in the foal (67 cases): 1980-1992.

Sixty-seven foals age < 150 days underwent a ventral celiotomy for colic. Of the 67 foals, 51 foals (82%) recovered from anaesthesia and 42 (63%) were subsequently released from the hospital. Three (6%) of the 51 foals were subjected to a repeat celiotomy. Long term follow-up was available on 36 foals. Twenty-nine (57%) of the 51 foals recovered from anaesthesia, were alive at least 2 years following surgery. Adhesions were identified in 8 (17%) of the foals which recovered from general anaesthesia but were subsequently subjected to euthanasia due to recurrent colic. Strangulating lesions were associated with a lower survival rate. Nineteen per cent of foals with strangulating intestinal lesions survived > 2 years following surgery, compared to 69% of foals with nonstrangulating lesions. The age of foals on admission had a significant effect on survival. Only 10% of foals less than 14 days of age survived, compared to 45.8% of foals between age 15 and 150 days.

Aging↗
PubMed1996

Recovery of Histoplasma capsulatum from BACTEC TB media.

From 1990 through 1994, we fortuitously isolated Histoplasma capsulatum from six patients with AIDS whose specimens of blood were processed by the BACTEC system using Middlebrook broth selective for acid-fast bacilli (13A medium). Growth indices became positive after an average of 17 days of incubation (range, 11 to 20 days). No acid-fast bacilli were seen, but small budding yeasts characteristic of H. capsulatum were present.

AIDS-Related Opportunistic Infections↗
PubMed1996

Effects of U-74389G, a novel 21-aminosteroid, on small intestinal ischemia and reperfusion injury in horses.

OBJECTIVE: To determine the effects of the 21-aminosteroid, U-74389G, on reperfusion of the equine jejunum, using total (TVO) and partial (PVO) vascular occlusion during the ischemic period. DESIGN: TVO: 16 healthy horses were randomly allotted to 3 groups-4 horses received the vehicle alone, 6 horses received a low dosage (3 mg/kg o body weight), and 6 horses a high dosage (10 mg/kg) of U-7438G. PVO: 10 healthy horses were randomly allotted to 2 groups--5 horses received the vehicle alone, and 5 horses received the low dosage (3 mg/kg) of U-74389G. PROCEDURES: TVO was induced for 1 hour followed by 2 hours of reperfusion. During PVO, blood flow was reduced to 20% of baseline for 2 hours, followed by 2 hours of reperfusion. For both models, either the vehicle alone or the drug was given 15 minutes prior to reperfusion. Samples were obtained before, during, and after ischemia for determination of myeloperoxidase (MPO) activity, malondealdehyde (MDA) concentration, concentration of conjugated dienes (PVO experiment only), and morphometric analysis. RESULTS: TVO: tissue concentration of MDA and MPO activity were not altered in any group by ischemia or reperfusion. During ischemia, mucosal volume and surface area were reduced. After reperfusion, no further reduction occurred. After initial decrease in submucosal volume during ischemia, there was a significant increase after reperfusion in the vehicle-only group (P < 0.05). PVO: there were no alterations in the concentration of either MDA or conjugated dienes. There was significant increase in the activity of MPO during ischemia and reperfusion (P < 0.05). These effects were similar for the vehicle-only and drug groups. During ischemia, there was a significant decrease in mucosal surface area and volume (P < 0.05), that was continued during reperfusion for the vehicle-only (P < 0.05). Submucosal volume increased during ischemia and reperfusion. CONCLUSIONS AND CLINICAL RELEVANCE: Reduced blood flow during ischemia (PVO group) caused continued loss in mucosal volume and surface area during reperfusion. At the dosage given, the 21-aminosteroid, U-74389G, was not effective in preventing continued reduction in mucosal volume and surface area after restoration of blood supply in the horses subjected to reduced blood flow.

Animals↗
PubMed1996

In vitro biomechanical comparison of the strength of the linea alba of the llama, using two suture patterns.

OBJECTIVE: To compare the strength of the sutured linea alba, in vitro, using 2 suture patterns. ANIMALS: 12 clinically normal llamas. PROCEDURE: 2 incisions in the linea alba of 12 llamas were closed with a simple continuous or inverted cruciate pattern, and tissue was harvested after 10 days. In 6 llamas the simple continuous line was intact; the inverted cruciate specimens contained 6 sutures. In 6 llamas, 1 knot was excised in the simple continuous pattern to simulate a failed line; the cruciate pattern contained 5 knots. Tissue sections were taken from cranial, between, and caudal to the linea alba incisions to compare fascial thickness. The sutured specimens were mounted in a mechanical testing system and tested to failure. A mixed-model ANOVA was used to evaluate the effects of suture pattern and incisional position on mechanical properties. RESULTS: Significant differences were not found between suture patterns or between location for yield force, failure force, or yield strain, whereas failure strain was lower for the intact simple continuous pattern than the inverted cruciate pattern (P = 0.003). From histomorphometric analysis, the caudal tissue specimens were significantly thinner than the middle tissue specimen cranial to the umbilicus (P = 0.006). CONCLUSION: There was no significant difference in monotonic breaking strength of the linea alba sutured with the simple continuous or inverted cruciate pattern. CLINICAL RELEVANCE: These results justify the use of the simple continuous pattern over the cruciate pattern for ventral midline closure in llamas because of the ease of placement and speed.

Abdominal Muscles↗
PubMed1995

Preclinical evaluation of manganese carbonate particles for magnetic resonance imaging of the liver.

RATIONALE AND OBJECTIVES: We characterized the physical, biological, and imaging properties of a manganese (Mn) carbonate particle suspension, a contrast agent for hepatic magnetic resonance (MR) imaging. METHODS: Mn carbonate suspensions were produced by controlled precipitation and characterized using light microscopy, transmission electron microscopy, and in vitro relaxivity studies. Efficacy of the agent was studied in normal and tumor-bearing rats using T1-weighted MR imaging. RESULTS: Following intravenous injection of Mn carbonate particles at doses ranging from 10 to 100 mumol Mn/kg, peak hepatic contrast enhancement of approximately 35% occurred from about 125 min until the termination of the MR imaging studies that varied from 125 to 305 min. Lesion conspicuity was increased because of relative intensity differences between normal liver and tumor. Data also showed that Mn carbonate particles dissolved on delivery to the liver, allowing Mn to interact with intrahepatic macromolecular complexes to provide positive contrast enhancement. CONCLUSION: Mn carbonate particles produce significant and sustained hepatic enhancement and should improve detection of small or isointense liver lesions.

Analysis of Variance↗
PubMed1995

Evaluation of meniscal tears: fast spin-echo versus conventional spin-echo magnetic resonance imaging.

RATIONALE AND OBJECTIVES: We compared the performance of fast spin-echo (FSE) with conventional spin-echo (CSE) magnetic resonance (MR) imaging sequences in the detection of meniscal tears. METHODS: Seventy-three patients underwent MR examination of the knee for suspected internal derangement. Each patient was scanned with a CSE sequence and one of two FSE sequences. The primary difference between the two FSE sequences consisted of the echo train length (ETL). Thirty-seven patients (group 1) were scanned with the FSE I sequence (ETL = 8), and 36 patients (group 2) were scanned with the FSE II sequence (ETL = 4). Menisci were graded as torn or not torn on the basis of their MR appearance. The sequences were compared with each other and with the surgical findings in 31 patients who underwent arthroscopy. RESULTS: In group 1, there was a significant discrepancy between the CSE and FSE I techniques (p = .006). The FSE I sequence detected only 11 of 19 surgically proven torn menisci as opposed to 18 of 19 detected with the CSE sequence. The FSE II sequence performed significantly better in group 2, with an accuracy equal to that of the CSE sequence. CONCLUSION: FSE sequences are extremely technique dependent with regard to detecting meniscal tears and should not replace CSE sequences in this setting until further studies are performed to optimize the technique.

Adolescent↗
PubMed1995

Prognostic models and the propensity score.

Subjects in observational studies of exposure effects have not been randomized to exposure groups and may therefore differ systematically with regard to variables related to exposure and/or outcome. To obtain unbiased estimates and tests of exposure effects one needs to adjust for these variables. A common method is adjustment via a parametric model incorporating all known prognostic variables. Rosenbaum and Rubin propose adjustment by the conditional exposure probability given a set of covariates which they call the propensity score. They show that, at any value of the propensity score, covariates are on average balanced between exposure groups. Thus matching on the propensity score leads to unbiased estimators and tests of exposure effect. However, the validity of the method depends on knowing the exposure probability. This quantity is usually not known in observational studies and needs to be estimated.

Bias↗
PubMed1994

Iodinated nanoparticles for indirect computed tomography lymphography of the craniocervical and thoracic lymph nodes in normal dogs.

RATIONALE AND OBJECTIVES: We evaluated the imaging characteristics of an interstitially or intraperitoneally delivered iodinated particulate contrast agent for computed tomography (CT) lymphography of the craniocervical and thoracic lymph nodes. METHODS: We injected 2-4 ml of 15% wt/vol iodinated nanoparticle suspension subcutaneously, submucosally, or intraperitoneally in eight normal dogs. CT and plain radiographic images were obtained prior to contrast administration and 4 hr, 24 hr, and 7 days after injection. Correlation was made to detailed postmortem assessment. RESULTS: CT images showed enhancement of regional nodes draining injection sites. Mean attenuation of opacified nodes was 313 +/- 297 (mean +/- standard deviation), 536 +/- 453, and 492 +/- 372 Hounsfield units at 4 hr, 24 hr, and 7 days postinjection, respectively. Lymph node opacification on CT images correlated well with node location found at postmortem. CONCLUSION: Craniocervical and thoracic lymph nodes can be effectively opacified from interstitial or intraperitoneal delivery of this iodinated nanoparticulate contrast agent.

Animals↗
PubMed1994

Neuropathology of intracranial arteriovenous malformations following conventional radiation therapy.

Conventional fractionated radiation therapy was used in 15 patients to treat arteriovenous malformations (AVMs) of the brain deemed inoperable or incompletely obliterated using endovascular or surgical techniques. The AVMs measured from 0.8 to 85 cm3 (mean 28.2 cm3; median 24 cm3). Angiography in 12 patients 1-21 years following radiation therapy demonstrated no significant change in 7, slight reduction in 2, near complete obliteration in 1, and complete obliteration in 2. Magnetic resonance imaging further demonstrated apparent obliteration in one other case. Three irradiated AVMs were available for pathological examination following fatal recurrent hemorrhage after 21 years in case 1 and following surgery after 5 years in cases 2 and 3. Doses of 20 and 45 Gy were delivered to the area of the AVM in 10 and 15 fractions with a 6-MV linear accelerator in case 1 and in cases 2 and 3, respectively. A blinded histopathological comparison was made of the latter cases and three AVMs removed at surgery that were not previously irradiated and that were comparable in size, number of arterial feeders, and location within the brain. Segmental hyalinization of some blood vessels was seen in both irradiated and nonirradiated cases. The single postmortem specimen showed extensive thrombosis but a patent nidus. The findings are in keeping with the clinical impression that conventional fractionated radiation therapy fails to alter the natural history of cerebral AVMs. The favorable outcome of radiosurgery on small- to medium-sized AVMs appears attributable to the shorter duration of therapy using relatively high-dose prescriptions to the nidus.

Adult↗
PubMed1993

Enantioselective enzymatic biotransformation of 2'-deoxy-3'-thiacytidine (BCH 189) monitored by capillary electrophoresis.

Concentrations of the enantiomers of 2'-deoxy-3'-thiacytidine (BCH 189) have been monitored during enantiospecific biotransformation catalyzed by cytidine deaminase. This enzymatic reaction is monitored by capillary electrophoresis (CE) over a 51-h time period. The use of dimethyl-beta-cyclodextrin as a chiral electrolyte additive in a pH 2.3 phosphate buffer system gives enantiomeric separation with results for peak efficiencies, resolution, and analysis time of the order of 25,000 plates, > 1.5 and 30 min, respectively. The features of the CE method are compared with those of the previously favored chiral HPLC method.

Antiviral Agents↗
PubMed1993

Tempo sensitivity in auditory sequences: evidence for a multiple-look model.

Differential thresholds for tempi (with interonset intervals ranging from 100 to 1,500 msec) were measured using an adaptive 2IFC paradigm for several types of auditory sequences. In Experiment 1, the number of intervals in an isochronous sequence was varied to compare the sensitivity for single intervals with that for sequences of two to six intervals. Mean relative just noticeable differences (JNDs) decreased as the number of intervals increased (single intervals = 6%, two intervals = 4%, four intervals = 3.2%, six intervals = 3%) and were optimal at intermediate tempi for both sequences and single intervals (as low as 1.5% in the range between 300 and 800 msec). In Experiment 2, the sensitivity for different types of irregular sequences was studied. Globally, JNDs for irregular sequences were of an intermediate level between that observed for single intervals and that observed for regular sequences. However, the closer a sequence was to regularity, the lower its relative JND. Experiment 3 demonstrated that musicians were more sensitive than nonmusicians to changes in tempo, and this was true for single intervals and for regular and irregular sequences, demonstrating the role of training on these abilities. The results are discussed in terms of possible underlying mechanisms, in particular those providing a mental representation of the mean and dispersion of successive interval durations.

Acoustic Stimulation↗
PubMed1993

Reproduction of musical rhythms by children, adult musicians, and adult nonmusicians.

Many sequential events, musical rhythms in particular, can be described by a hierarchical structure, with lower order events recursively combining to form higher levels. This study investigated factors influencing the ease of reproduction of short musical rhythms that reflect various organizational principles. For adults and children, reproduction was better for rhythms with the following characteristics: (1) binary rather than ternary subdivision, (2) two rather than three different durations, (3) the ability to be segmented into two shorter rhythms of identical duration, and (4) intensity accents on important hierarchical positions. These findings suggest that a prototypical temporal structure--that is, a regular beat with binary subdivisions--is functional in childhood. The ability to process complex hierarchical structure appeared to be influenced more by musical training than by passive acculturation.

Adult↗
PubMed1993

Effects of the 21-aminosteroid U-74389G on ischemia and reperfusion injury of the ascending colon in horses.

Sixteen horses were allotted at random to 3 groups: vehicle only; low dosage (vehicle and 3 mg of U-74389G/kg of body weight); high dosage (vehicle and 10 mg of U-74389G/kg). These solutions were given prior to reperfusion. The ascending colon was subjected to 2 hours of ischemia followed by 2 hours of reperfusion. Before, during, and after ischemia, full-thickness colonic tissue biopsy specimens were obtained for measurement of malondealdehyde (MDA) concentration and myeloperoxidase activity and for morphologic evaluation. Although increases were not significant, MDA concentration and myeloperoxidase activity increased during ischemia and reperfusion. Administration of U-74389G did not have significant effects on MDA concentration and myeloperoxidase activity. However, the lower dosage tended (P = 0.08) to reduce myeloperoxidase activity at 30 and 60 minutes of reperfusion. In horses of the vehicle-only group, ischemia induced a decrease in mucosal surface area that was continued into the reperfusion period (P < or = 0.05). Administration of U-74389G at both dosages (3 and 10 mg/kg) prevented the reperfusion-induced reduction in mucosal surface area, which was significant at 60 minutes (high dosage; P = 0.05) and 90 minutes (low and high dosages; P = 0.02). After initial reduction in horses of all groups, mucosal volume increased for the initial 60 minutes of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1991

Immersion events in residential swimming pools. Evidence for an experience effect.

BACKGROUND: --Drowning and near-drowning in residential swimming pools are leading causes of morbidity and mortality for young children. We tested the hypothesis that the period immediately after a pool is acquired is a time of high risk for these events. This study was also designed to provide population-based data on swimming pool immersion events, regardless of severity. METHODS: --We conducted a mail survey of a probability sample of Sacramento County, California, households with in-ground swimming pools in January 1988; 80% of eligible subjects responded. Onset of exposure to a pool was defined as the month in which (1) the responding household had a pool installed, or (2) the responding household first occupied a residence with a pool. Exposures began in 1959 through 1987. RESULTS: --The home swimming pool immersion event rate was 11 per 1000 pool-years. The rate per 1000 pool-years was higher for the first 6 months of exposure than thereafter (0 to 6 months, 44; 7 to 24 months, 14; greater than 24 months, seven), but 77% of events occurred outside the high-risk period. For households whose exposures began in 1984 through 1987, the immersion event rate was 51 per 1000 pool-years overall and 123 per 1000 pool-years for the first 6 months of pool exposure; these increases probably represent underreporting of earlier events. In this group, 48% of events occurred outside the high-risk period. The family swimming pool accounted for 91% of immersion events at the respondents' homes. CONCLUSIONS: --The residential swimming pool is an important hazard for pool-owning households. The first 6 months of exposure constitute a high-risk period, but many immersion events occur later. Pool drowning prevention programs may focus on newly acquired swimming pools and their owners but should be as broad as possible to maximize their effectiveness.

California↗
PubMed1991

The epidemiology of seatbelt-associated injuries.

This study examined the frequency of spine and abdominal injuries to motor vehicle occupant crash victims, the relationship between the two types of injuries, and the association with restraint use. There were 303 motor vehicle occupants treated at a regional trauma center for spine and/or abdominal injuries over a 5-year period. Patients with Chance-type fractures of the lumbar spine were much more likely to be rear seat passengers and to be using a lap belt than were patients with other types of spinal injuries. Similarly, patients with hollow viscus injuries were more likely to be rear seat passengers and to be lap belted than were patients with injuries to the spleen, liver, pancreas, or kidneys. Nearly two thirds of the lumbar Chance-type fractures were associated with hollow viscus injuries, including six of seven children. This increased risk of Chance-type fractures and hollow viscus injuries was associated with increased use of lap-belt seat restraints in the population.

Abdominal Injuries↗
PubMed1990

The inability of young children to reproduce intensity differences in musical rhythms.

A musical rhythm can be described in terms of both its temporal and its dynamic structure. However, although 6-year-old children are able to perceive and reproduce simple temporal structures, even 8-year-olds rarely reproduce intensity differences. Four experiments on the perception and reproduction of musical rhythms by 5- to 8-year-old children demonstrate that even though dynamic structure is clearly dominated by its temporal support, intensity differences play a role in reinforcing the temporal structure. The inability of children to reproduce intensity differences appears to be due neither to an inability to control the intensity of their tap responses nor to the fact that they cannot perceive such changes in intensity. Rather, the results seem best interpreted in terms of the allocation of attentional resources. With simple stimulus material (Experiments 1-3), the children focused on temporal information, and only when the processing of temporal information was mastered did they have "enough attention left" to direct it to intensity differences (Experiment 2). With more complex orchestral music (Experiment 4), attention was primarily allocated to the dynamic structure.

Attention↗