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Biomedical subjects

D Dawson

Publications and source records attributed to D Dawson.

At least 55 records · Page 3Linked to original sources
PubMed2001

The effects of bright light and nighttime melatonin administration on cardiac activity.

Although melatonin has an important physiological role in the facilitation of sleep, its precise mechanism of action is not clear. To investigate the potential contribution of melatonin to influence cardiac autonomic activity in the evening, 16 young healthy subjects participated in a repeated measures design where cardiac autonomic activity, heart rate and blood pressure were examined during three experimental conditions. An initial baseline condition involved dim light exposure (< 10 lux), permitting the normal nocturnal rise in endogenous melatonin. In other sessions, subjects were exposed to bright light (> 3000 lux) to suppress melatonin secretion and administered a placebo or melatonin (5 mg) capsule at the estimated time of increase in endogenous melatonin (wake time + 14 hours). Heart rate, pre-ejection period (a measure of cardiac sympathetic activity) and respiratory sinus arrhythmia (a measure of parasympathetic activity) were not significantly altered in response to the three melatonin levels. While melatonin had no effect on diastolic blood pressure, systolic blood pressure was maximally decreased by 6 +/- 1.93 mmHg (mean +/- SEM, p < 0.005) 150 minutes after exogenous melatonin. The results indicate that melatonin does not directly modulate cardiac autonomic activity, but may rather act directly on the cardiovascular system.

Adolescent↗
PubMed2001

Evaluation of a fatigue model using data from published napping studies.

The authors have previously published the development and empirical validation of a work-related fatigue model. However, published work has not involved data from napping studies. The aim of this paper is to determine how closely the model predicts changes in subjective and objective measures from data published from napping studies. The regression results between the model outputs and logical reasoning, multiple sleep latency test scores, self-rated alertness, profile of mood state fatigue, visual vigilance and reaction time were all strong to very strong (R2 = 0.4-0.9). Only digit symbol substitution revealed moderate (R2 = 0.1-0.2) regression values. The outputs of the model reflect changes due to naps of varying duration and timing measured at varying periods following a nap. Together with the outputs from previous investigations, these results further support the potential use of the fatigue model in operational settings. This appears to be true in settings that utilise napping as well as those that do not.

Circadian Rhythm↗
PubMed2000

Core body temperature is elevated during constant wakefulness in elderly poor sleepers.

STUDY OBJECTIVES: The aim of this study was to test for heightened physiological activity in elderly poor sleeepers compared to good sleepers under ad lib sleep and constant wakeful conditions. DESIGN AND SETTING: Subjects participated in a five-day protocol consisting of four nights of polysomnographic (PSG) and rectal temperature monitoring followed by 26 hours of continuous rectal temperature monitoring under controlled constant wakefulness. PARTICIPANTS: Participants were 16 self-reported sleep maintenance insomniacs and 16 self-reported good sleeping controls over 55 years of age. INTERVENTIONS: NA. MEASUREMENT AND RESULTS: Subjects were grouped according to (1) subjective sleep status and (2) into quartiles according to amount of PSG determined wake after sleep onset (WASO). Significant group differences in temperature were observed when subjects were classified according to PSG but not subjective criteria. In the former case, subjects with the lowest (bottom quartile) compared to the highest (top quartile) amount of PSG determined WASO showed lower sleep and nighttime constant wakeful core body temperatures. CONCLUSIONS: In the elderly, elevated core body temperature is associated with increased nocturnal wakefulness suggesting that physiological activation may underlie sleep maintenance insomnia. This was clearly significant when subjects were compared using objective criteria and temperature was collected under constant wakeful conditions.

Aged↗
PubMed2000

Factors predicting sleep disruption in Type II diabetes.

This study investigated four correlates of diabetes as potential predictors of sleep disruption in people with Type II diabetes. A tentative causal model proposed obesity would lead to more severe diabetes, which would result in increased physical complications, which might in turn affect emotional adjustment, and all of these might combine to cause sleep disruption. It was found that within a diabetic sample, severity of diabetes was related to sleep disruption. Path analysis indicated that the relationship between Type II diabetes and sleep disruption was mediated by physical complications of the disease (pain and nocturia), and not by either obesity or emotional adjustment.

Adaptation, Psychological↗
PubMed2000

Double-strand breaks on artificial chromosomes in yeast.

Yeast artificial chromosomes composed primarily of bacteriophage gamma DNA exhibit very low levels of meiotic crossing over compared with similarly sized intervals of natural yeast DNA. When these recombinationally quiet chromosomes were augmented with a 12.5 kb insert of sequences from yeast chromosome VIII, genetic studies demonstrated that the artificial chromosomes had acquired recombination properties characteristic of this region of chromosome VIII. On authentic yeast chromosomes, most meiotic recombination events are initiated at sites where the DNA is cleaved to create a double-strand break (DSB). This report describes physical analyses that were carried out to examine the relationship between DSB sites and the recombination behavior of the artificial chromosomes. The results show that DSBs are rare on these artificial chromosomes, except for the 12.5 kb insert. Mapping of the DSB sites shows that their positions correlate with the previously determined positions of DSB sites on chromosome VIII. Deletion of two characterized chromosome VIII DSB sites from the 12.5 kb insert on the artificial chromosome resulted in the loss of the predicted DSB fragments and a reduction in crossing over between artificial chromosomes.

Bacteriophage lambda↗
PubMed2000

Assessment of strategic self-regulation in traumatic brain injury: its relationship to injury severity and psychosocial outcome.

Standard neuropsychological tests administered in a constrained and artificial laboratory environment are often insensitive to the real-life deficits faced by patients with traumatic brain injury (TBI). The Revised Strategy Application Test (R-SAT) creates an unstructured environment in the laboratory in which environmental cues and internal habits oppose the most efficient strategy, thus mimicking the real-life situations that are problematic for patients with TBI. In this study, R-SAT performance was related both to severity of TBI (i.e., depth of coma) sustained 2-3 years earlier and to quality of life outcome as assessed by the Sickness Impact Profile. This relationship held after accounting for variance attributable to TBI-related slowing and inattention. These findings support the validity of the R-SAT and suggest that behavioral correlates of quality of life outcome in TBI can be assessed in the laboratory with unstructured tasks.

Acute Disease↗
PubMed2000

The ability to self-monitor performance when fatigued.

The present study aimed to systematically investigate the effects of elevated fatigue levels on the ability to self-monitor performance. Eighteen participants, aged 19-26 y, remained awake for a period of 28 h. Neurobehavioural performance was measured at hourly intervals using four tests from a standardized computer test battery. From these four tests, six measures of performance were obtained: grammatical reasoning (accuracy and response latency); vigilance (accuracy and response latency); simple sensory comparison and tracking. In addition, before and after each test, participants completed visual analogue scales which required them to rate their alertness level and the speed and accuracy of their performance. Individual test results for both self-ratings and neurobehavioural performance were converted to z-scores. Planned comparison analysis indicated that scores on four of the six performance measures decreased significantly as hours of wakefulness increased. Similarly, predicted performance scores for all six measures of performance decreased significantly. Analysis revealed moderate correlations between predicted and actual performance for the four parameters affected by fatigue. Furthermore, moderate to high correlations were found between all six performance parameters and their respective post-test self-ratings. In addition, moderate to high correlations were found between predicted performance and alertness. Taken together, these findings suggest that as fatigue levels increase, subjects globally assess performance decrements. Results suggest that subjective alertness may in part mediate an individual's global assessment of performance.

Adult↗
PubMed2000

The BCSH guideline on addressograph labels: experience at a cardiothoracic unit and findings of a telephone survey.

In 1998 we implemented a BCSH recommendation that addressograph labels should not be used on blood transfusion specimen tubes. Over a 12-month period before the ban was introduced our laboratory received 5964 red cell transfusion requests, 182 (3.1%) of which contained an error in the identification details (ID) supplied on the request form and/or specimen. Three of these errors were of the 'wrong patient' type, i.e. the sample belonged to a different patient from the one whose ID appeared on the specimen tube and request form. Over the 12 months after the ban was introduced 511 (8. 1%) of 6326 requests contained a labelling error, an increase in error rate of 165%; no wrong-patient errors were identified, however. In a survey, seven (29.2%) of 24 transfusion laboratories in the UK accepted specimens labelled with addressograph stickers; in four of these cases a local blood transfusion committee had agreed that the BCSH guideline should not be followed. We believe the BCSH guideline is valid; its implementation, however, has major financial and workload implications, which probably explains why many hospitals apparently do not comply with it.

Blood Banks↗
PubMed2000

Infection of the subcutis and skin of cats with rapidly growing mycobacteria: a review of microbiological and clinical findings.

Mycobacteria were isolated and characterised from 49 cats with extensive infections of the subcutis and skin. Cats were generally between 3 and 10 years of age, and female cats were markedly over-represented. All isolates were rapid-growers and identified as either Mycobacteria smegmatis (40 strains) or M fortuitum (nine strains). On the basis of Etest for minimum inhibitory concentration and/or disc diffusion susceptibility testing, all strains of M smegmatis were susceptible to trimethoprim while all strains of M fortuitum were resistant. M smegmatis strains were typically susceptible to doxycycline, gentamicin and fluoroquinolones but not clarithromycin. All M fortuitum strains were susceptible to fluoroquinolones, and often also susceptible to gentamicin, doxycycline and clarithromycin. Generally, M smegmatis strains were more susceptible to antimicrobial agents than M fortuitum strains. Treatment of mycobacterial panniculitis involves long courses of antimicrobial agents, typically of 3-6 months, chosen on the basis of in vitro susceptibility testing and often combined with extensive surgical debridement and wound reconstruction. These therapies will result in effective cure of the disease. One or a combination of doxycycline, ciprofloxacin/enrofloxacin or clarithromycin are the drugs of choice for long-term oral therapy.

Animals↗
PubMed2000

Behavior and neurocognitive performance in children aged 5-10 years who snore compared to controls.

Sleep disordered breathing in children is a common but largely underdiagnosed problem. It ranges in severity from primary snoring to obstructive sleep apnea syndrome (OSAS). Preliminary evidence suggests that children with severe OSAS show reduced neurocognitive performance, however, less is known about children who snore but do not have severe upper airway obstruction. Participants included 16 children referred to the Ear, Nose and Throat/Respiratory departments of a Children's Hospital for evaluation of snoring and 16 non-snoring controls aged 5-10 years. Overnight polysomnography (PSG) was carried out in 13 children who snored and 13 controls. The PSG confirmed the presence of primary snoring in seven and very mild OSAS (as evidenced by chest wall paradox) in eight children referred for snoring while controls showed a normal sleep pattern. To test for group differences in neurocognitive functioning and behavior, children underwent one day of testing during which measures of intelligence, memory, attention, social competency, and problematic behavior were collected. Compared to controls, children who snored showed significantly impaired attention and, although within the normal range, lower memory and intelligence scores. No significant group differences were observed for social competency and problematic behavior. These findings suggest that neurocognitive performance is reduced in children who snore but are otherwise healthy and who do not have severe OSAS. They further imply that the impact of mild sleep disordered breathing on daytime functioning may be more significant than previously realized with subsequent implications for successful academic and developmental progress.

Analysis of Variance↗
PubMed2000

Attenuation of sleep propensity, core hypothermia, and peripheral heat loss after temazepam tolerance.

If changes in thermoregulation mediate sleepiness induced by sedative/hypnotics, then a reduction in the soporific efficacy (tolerance) of these agents may be accompanied by a concomitant reduction in their thermoregulatory effects. We compared the thermoregulatory and soporific effects of acute temazepam (30 mg at 1400) in 11 young male subjects before and immediately after 7 consecutive days of temazepam (30 mg). Subjects lay supine (0800-2030), while foot (T(ft)) and rectal (T(c)) temperatures were recorded. Sleep onset latency (SOL) was measured hourly using 20-min multiple sleep latency tests. Relative to placebo, temazepam significantly reduced both T(c) and SOL (-0.31 degrees C and 14.1 min) while increasing T(ft) (3.39 degrees C). A significant tolerance developed after the week of temazepam, with a mean reduction in soporific efficacy of 4.0 +/- 0.8 min. This was accompanied by a concomitant attenuation in both T(c) (-0.16 degrees C) and T(ft) (1.44 degrees C). Furthermore, SOL was temporally related to T(ft) and the maximum rate of decline in T(c) before and after tolerance. Together, these results indicate that the thermoregulatory system may be functionally involved in the regulation of sleepiness.

Adult↗
PubMed1999

Tuberculosis in Australia: bacteriologically confirmed cases and drug resistance, 1997. Report of the Australian Mycobacterium Reference Laboratory Network.

The Australian Mycobacterium Reference Laboratory Network collected and analysed laboratory data on new diagnoses of infection with Mycobacterium tuberculosis complex during 1997. A total of 722 cases were identified, representing an annual incidence of 3.9 cases of laboratory culture-confirmed tuberculosis (TB) per 100,000 population. Historical data shows that Australia's TB incidence rates of culture-confirmed TB have varied little in recent years, ranging from 3.9 to 4.1 cases per 100,000 population. The incidence rate continues to vary between States, reflecting differences in the distribution of persons belonging to high-risk categories for TB. The male to female ratio showed a slight increase to almost 1.3:1, but in keeping with previous years, males with culture-confirmed TB were older (median age group 45-49 years) than females (median age group 35-39 years), and approximately half of all pulmonary diagnoses involved positive microscopy. Lymphatic disease again accounted for almost 20% of the total cases, with 66% of cases being recorded in females. Approximately 9% of isolates, a decrease from 11% in 1996, had in vitro resistance to at least one of the four standard anti-tuberculosis drugs. Fourteen isolates were multi-drug resistant in 1997 compared with 15 in 1996. Overall, the data indicates a remarkably stable picture for TB in Australia.

AIDS-Related Opportunistic Infections↗
PubMed1999

A population-based study of children with cerebral tuberculosis in New South Wales.

OBJECTIVE: To determine the incidence of childhood cerebral tuberculosis (tuberculous meningitis [TBM] and tuberculoma) in a defined population. DESIGN: Retrospective, population-based study. SETTING AND PARTICIPANTS: All resident children aged up to 14 years in New South Wales diagnosed with cerebral tuberculosis, from 1982 to 1996. MAIN OUTCOME MEASURE: Population-based incidence of childhood TBM. RESULTS: 10 children with TBM and one with tuberculoma were identified in the 15 years. The incidence of TBM was 0.053 (95% CI, 0.025-0.097) per 100,000. Eight of the 10 TBM patients were born in Australia and five were of white European origin. Only one had been vaccinated with BCG vaccine. Three of the children died. CONCLUSIONS: The incidence of childhood TBM in New South Wales is low, and comparable with that in other First World countries.

Adolescent↗
PubMed1999

Sleeping with an electric blanket: effects on core temperature, sleep, and melatonin in young adults.

Previous studies have inferred a relationship between core temperature and sleep disruption from manipulations of core temperature such as heating prior to sleep or administration of hyperthermic substances. To examine the relationship more directly, this study aimed to produce a direct increase in core temperature during the sleep period. Following an adaptation night, 16 subjects underwent counter-balanced baseline and experimental conditions, on non-consecutive nights between 1900 and 0800h. In the experimental condition, subjects were heated between 0230h and wake up, which significantly increased mean core temperature from baseline levels between 0400 and 0700h by 0.18 +/- 0.03 degree C (mean +/- SEM, p < 0.05). This increase in core temperature was associated with a significant decrease in sleep efficiency between 0330 and 0730h of 5.5 +/- 0.9% (mean +/- SD, p < 0.05). Polysomnographic measures indicated a significant increase in the number of stage changes and the amounts of stage 0 and stage 1 sleep (p < 0.05). Other stages of sleep and the number and duration of arousals were not significantly effected by heating. There was a strong trend toward and increase in the number of arousals (p = 0.054), however, core body temperature did not increase across arousals. Also, melatonin output was not effected by heating. Taken together, these results suggest that increased nocturnal core temperature alone may disrupt sleep. Additionally, the results support evidence suggesting that the circadian regulation of the sleep/wake cycle may be mediated via core temperature.

Adult↗
PubMed1999

Correlation between wrist activity monitor and electrophysiological measures of sleep in a simulated shiftwork environment for younger and older subjects.

Although several studies have examined the correlation between nocturnal PSG and activity measurement, validation studies of actigraphically measured sleep in shiftworking populations have not been reported. This study investigates the correlation between sleep recorded using EEG and actigraphic techniques during a simulated 12-hour shift rotation. Thirty-two subjects were allocated to groups according to age. Group (1) included sixteen subjects mean (+/- s.d.) age of 21.2 +/- 2.7 years, and Group (2) included sixteen subjects mean (+/- s.d.) age of 43.9 +/- 6.8 years. An adaptation night was followed by two 12-hour day shifts (7 am-7 pm), 24 hours off and then two 12-hour night shifts (7 pm-7 am). For the entire study subjects wore an activity monitor, and while in bed, sleep was recorded using polysomnography; both techniques were collected in 30-second epochs. A high epoch for epoch agreement between wrist activity monitoring and EEG measures of sleep was recorded for daytime and nighttime sleep periods (80-90%). There was a high correlation between EEG and actigraphically recorded sleep duration in young (0.98-0.77) and older (0.78-0.96) subjects for all sleep periods. Sleep efficiency correlations were extremely variable for both the young (0.72-0.15) and older (-0.18-0.58) subjects for daytime and nighttime sleep periods. Taken together these results suggest that wrist activity monitoring is a valid measure of sleep/wake activity and sleep duration, in a simulated shiftwork environment. However, some caution should be used for more specific measures, such as sleep efficiency particularly in older subjects.

Adult↗
PubMed1999

Targeting of marrow-derived astrocytes to the ischemic brain.

Bone marrow progenitor cells have been shown to contribute to a small proportion of cells in nonhematopoietic tissues including the brain. In the acute unilateral middle cerebral artery occlusion model in spontaneously hypertensive rats following male-to-female bone marrow transplantation, we present data suggesting that 55% more marrow-derived cells, in general, and 161% more GFAP-positive astrocytes, in particular, migrate preferentially to the ischemic cortex than to the contralateral non-ischemic hemisphere. In addition to their biological significance, our findings could have therapeutic implications. Marrow-derived progenitor cells could potentially be used as vehicles for ex vivo gene transfer to the brain.

Animals↗
PubMed1999

Daytime melatonin and temazepam in young adult humans: equivalent effects on sleep latency and body temperatures.

1. As changes in core body temperature are generally associated with concomitant changes in sleep propensity, it is possible that the effects of hypnotic/soporific agents may be related to changes in thermoregulation. Therefore, to increase our knowledge of the mechanisms by which these agents exert their soporific effects, we compared the thermoregulatory and soporific effects of temazepam (20 mg per os (p.o.)) with those of melatonin (5 mg p.o.) when administered at 14.00 h to 20 young healthy adults (13 male, 7 female; age, 23.5 +/- 0.4 years). 2. From 08.00 to 20.30 h, subjects lay in bed, and foot and rectal (Tc) temperatures were recorded. Sleep onset latency (SOL) was measured using 20 min multiple sleep latency tests, performed hourly from 11.00 to 20.00 h, during which time heart rate was recorded. 3. Compared with placebo, both melatonin and temazepam significantly reduced Tc (-0.17 +/- 0.02 and -0.15 +/- 0.03 C, respectively) and SOL (by 4.8 +/- 1.49 and 6.5 +/- 1.62 min, respectively). Although both treatments significantly increased heat loss, only melatonin demonstrated cardiac effects. Importantly, there was a temporal relationship between minimum SOL and the maximum rate of decline in Tc for both melatonin (r = 0.48) and temazepam (r = 0.44). 4. A possible role of thermoregulation in sleep initiation is suggested by the similar temporal relationship between Tc and SOL for two different classes of soporific agents.

Adolescent↗