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Biomedical subjects

D B Clark

Publications and source records attributed to D B Clark.

At least 55 records · Page 3Linked to original sources
PubMed1989

Comparative analysis of photosynthetic light environments within the crowns of juvenile rain forest trees.

Irradiances within the crowns of saplings of two tropical tree species were simultaneously compared in primary rain forest in Costa Rica. The species examined, Minquartia guianensis Aubl., a relatively slow-growing, canopy species, and Pithecellobium pedicellare (DC) Benth., a less-tolerant, emergent species, have different crown and leaf display patterns. Crown light environments were assessed by placing arrays of quantum sensors among leaves and recording at 5-s intervals for seven days with microloggers. Median total daily quantum flux densities for saplings of both species were less than 2% of full sun and did not differ significantly. More than 90% of the measurements within the crowns of these saplings were less than 25 micromol m(-2) s(-1). Spatial variability of photon flux densities within sapling crowns was similar for the two species despite differences in leaf display patterns. In saplings of both species, photon flux densities varied significantly over the relatively short distances within crowns and from day to day. Height growth of both species was significantly correlated with total daily photon flux densities and with percentage of full sun. However, only the tolerant species, Minquartia, showed a significant correlation between diameter growth and crown light environment.

Journal Article↗
PubMed1989

A semi-continuous method for purification of factor IX complex from human plasma.

We report the development of a semi-continuous method for preparation of factor IX complex from human plasma using ion exchange resins. Traditionally, stirred batch adsorption has been used due to the high pressure drops and low flow rates associated with soft gels in packed columns. Batch methods, however, typically involve higher labor costs and are more cumbersome in process environments. In the semi-continuous process, cryo-supernatant plasma is pumped through a 'stirred column' containing the resin. At both lab and pilot scale, higher recoveries of factor IX (FIX) were obtained at decreased total process times, compared to batch adsorption. A residence time of 15 min was found to be sufficient for capture of 95% of the FIX in the starting plasma. In the pilot plant, 550 liters of plasma was passed through a 50-liter column containing 8.5 liters of resin, yielding a 68% recovery of FIX. The results suggest that the recovery of FIX depends on the mode of contact (batch, continuous or packed column) between plasma and resin.

Blood Coagulation Factors↗
PubMed1988

Tonic arousal and activity: relationships to personality and personality disorder traits in panic patients.

Personality theorists have long predicted a relationship between personality traits and autonomic activation. In this study, 48 patients with panic disorder underwent personality assessment by questionnaire (Eysenck Personality Inventory: 48 patients) and by interview (Personality Disorders Examination: 35 patients). Ambulatory heart rate and activity were measured by the Vitalog method and were used as measures of activation and autonomic arousal. There was a significant positive correlation between histrionic traits and activity level and a significant negative correlation between sociability and heart rate. The findings are consistent with previous studies showing a negative relationship between sensation-seeking personality traits and cerebrospinal fluid levels of norepinephrine and a positive relationship between extroversion and cerebrospinal fluid levels of dopamine.

Adult↗
PubMed1988

Dentin in chronic renal failure: an ultrastructural study.

Disturbances in the mineralization of hard tissues in patients suffering from chronic renal failure and in patients undergoing chronic hemodialysis are a well-established phenomenon. These disturbances are the result of complex pathophysiologic alterations in calcium and phosphorus metabolism. Disturbances in the dentin of teeth, analagous to those occurring in bone, were not recognized until 1983 when it was reported that a significantly thicker predentin layer was present in the teeth of patients with chronic renal failure and in patients being treated with chronic hemodialysis (1). The aim of the present study was to conduct a comparative ultrastructural (SEM) analysis of dentin in this group of patients. A wide spectrum of changes was detected, ranging from mild disturbances with increasing tubule irregularity and focal obliteration of tubule lumens, to widespread formation of dysplastic dentin exhibiting numerous mineralized, largely atubular globules with only occasional large, irregular tubules. In general, these changes appeared to reflect the type and effectiveness of treatment rendered (renal transplant or hemodialysis therapy). The findings suggest that dentin exhibits significant ultrastructural alterations when the underlying homeostatic regulation of calcium and phosphorus metabolism is disturbed in systemic disorders such as chronic renal failure.

Adolescent↗
PubMed1987

Iodine-123 HIPDM brain imaging findings in subacute spongiform encephalopathy (Creutzfeldt-Jakob disease).

Decreased perfusion of the left frontal and left temporoparietal cortex has been shown in [123I] HIPDM planar and single photon emission computed tomographic images of a patient with Creutzfeldt-Jakob disease (CJD) that was proven by brain biopsy and subsequent autopsy. An EEG showed diffuse, periodic discharges most prominent to the left hemisphere. Concurrent head computed tomography (CT), nuclear magnetic resonance (NMR), and cerebral angiographic studies were negative. Abnormalities demonstrated by [123I]HPDM imaging and by EEG may represent changes in neurophysiological and neurochemical status while cerebral angiography, CT, and possibly NMR register only anatomic or structural lesions. Premortem diagnosis of CJD depends on brain biopsy; the availability of the [123I] HIPDM study may provide regional cerebral neurochemical and neurophysiological information, guiding or avoiding brain biopsy in the appropriate clinical setting.

Aged↗
PubMed1982

Effectiveness of alternative parent training formats.

Alternative formats were compared for training parents of retarded children to teach self-help skills and manage problem behaviors. Sixty-six families with moderately to severely retarded children ages 3-13 were assigned for 3 months to group parent training (n = 37), individual parent training (n = 16), or delayed training control (n = 13). Measures administered before and after training evaluated: (1) parent knowledge of behavior modification, (2) a behavior sample of parent teaching, and (3) child self-help skills and behavior problems. Trained families gained significantly more than control families on parent measures but not on the child self-help skill measure. Group and individually trained families demonstrated almost identical gains. At a 6-month follow-up, group and individually trained families continued to show equal performance. Group training requires about half the professional time per family as individual training, and therefore seems a more cost-effective approach.

Adolescent↗
PubMed1982

Behavioral training for parents of mentally retarded children: prediction of outcome.

Prediction models for outcome of behavioral parent training were developed. Forty-nine families completed a training program for parents of mentally retarded children and were followed-up 14 months later. The outcome variables were the mother's posttraining knowledge of behavioral principles and follow-through programming. Predictor variables included parents' socioeconomic status, education, pretraining experience, performance during training, and child characteristics. The relationships between predictor and outcome variables were utilized in discriminant analyses to yield prediction formulae. The accuracy of predictions and their clinical implications were discussed.

Adolescent↗
PubMed1981

Twins with Alzheimer's disease.

Twins of identical appearance were both affected by Alzheimer's senile dementia. In one, dementia began in her late 60s. She died at age 74. In the other, onset was at age 83. She died of ovarian carcinoma at age 85. The histopathologic findings of Alzheimer's disease were confirmed in both twin sisters.

Aged↗
PubMed1980

Review of 38 cases of subacute sclerosing panencephalitis: effect of amantadine on the natural course of the disease.

Thirty-eight cases of subacute sclerosing panencephalitis (SSPE) were reviewed. Deterioration in school performance, personality changes, and seizures were common early symptoms. Initial examination frequently showed myoclonus, spasticity, and extrapyramidal dysfunction, and in two-thirds of patients these findings were asymmetrical or focal. Retinitis or papilledema was present on initial examination in 50% of the patients. At last follow-up 24 children had died, with a mean survival of 42 months. Most patients reached a state of severe neurological impairment within 13 months. Subsequent evidence of improvement was noted in 10 children and was sustained in 4. Fifteen patients received antiviral treatment. Ten treated patients died from 5 to 133 months (mean, 58) from onset of their illness, while 15 untreated patients survived a mean of 33 months. Duration of survival appeared to be affected most by treatment with amantadine. Three patients treated with the drug were alive 97 to 139 months after onset of SSPE, and 5 died with a mean survival of 78 months. Five of 6 individuals treated with rifampin died after a mean survival of 27 months. Prolonged remissions occurred only in patients treated with amantadine. Although the number of treated individuals was small, our data suggest that amantadine may affect the natural course of SSPE.

Amantadine↗
PubMed1976

A comparison of the key-peck and treadle-press operants in the pigeon: differential-reinforcement-of-low-rate schedule of reinforcement.

Key pecking and treadle pressing in pigeons were compared under concurrent (key-treadle) and single-operant differential-reinforcement-of-low-rate schedules of food reinforcement ranging from 5 to 60 sec (concurrent procedure) or 5 to 120 sec (single-operant procedure). Under both procedures, the two operants followed the same general law: decreasing response rate and reinforcement rate and increasing number of responses per reinforcement as a function of increasing schedule interval. High correlations were found between key pecking and treadle pressing for the measures of response rate, reinforcement rate, and responses per reinforcement. Regression equations allowed the prediction of treadle pressing from key pecking. More bursting occurred in responding to the key, and key pecking showed a more precise temporal discrimination than treadle pressing. A test for sequential dependencies between key and treadle responses showed significant dependencies not only under the concurrent procedure but also in data created artificially by merging key and treadle sequences from different pigeons under the concurrent procedure and from the same pigeon under the single-operant procedure. It seems likely that the sequential dependencies found were due to the independent action of the schedule on each operant and that behavioral dependencies did not occur with the concurrent training procedure. The key-peck operant does not appear to have any special qualities that preclude its use in discovering general laws of behavior, at least under the differential-reinforcement-of-low-rate schedule. The usefulness of the key peck in other situations requires direct experimental study.

Journal Article↗
PubMed1975

Spinal cord infarction due to minor trauma in children.

In two children, ages 22 months and 4 years, after slight trauma, flaccid weakness of both arms developed, followed by flaccid quadriplegia with sphincter involvement. No vertebral fracture or dislocation was found, myelograms were negative, and diagnosis was made only after the full clinical syndrome developed. Pathologic studies revealed ischemic infarction involving the cervical cord and low medulla in one patient, and central gray matter of low cervical cord in the other, without hematomyelia or external compressive lesions. The pattern of infarction may be related to spasm of distal branches of the central sulcal arteries in a terminal arterial bed.

Arteries↗