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B Dawson

Publications and source records attributed to B Dawson.

At least 19 recordsLinked to original sources
PubMed1999

Elemental composition of human milk from mothers of premature and full-term infants during the first 3 months of lactation.

To examine longitudinal and gestational effects of mineral content in human milk, we analyzed human milk from lactating mothers of premature (PRT, n = 24, < 2000 g birth weight, < 37 wk gestation) and full-term (FT, n = 19, > 2500 g, 39-41 wk gestation), living in Newfoundland, Canada. Samples were collected once a week for 8 wk with one final sample collected at 3 mo. Milk samples collected in acid-washed containers were wet ashed with concentrated HNO3, and barium, cadmium, calcium, cesium, cobalt, copper, cerium, lanthanum, magnesium, manganese, molybdenum, nickel, lead, rubidium, tin, strontium, and zinc were measured using inductively coupled plasma-mass spectrometry. Data were analyzed using standard multiple-regression procedures with correlated data analyses to take account of the relationship between successive weeks. Results indicated lower Ca and Pb in PRT milk. Calcium was the only nutritionally significant element to differ between groups. Molybdenum in both PRT and FT milk showed a definite decrease with time, suggesting that the Mo content in milk is homeostatically regulated. However, Ce, La, Ba, and Sn did not display any pattern indicative of biological regulation and potential human requirement.

Female↗
PubMed1999

A comparison of skeletal muscle oxygenation and fuel use in sustained continuous and intermittent exercise.

In this study we compared substrate oxidation and muscle oxygen availability during sustained intermittent intense and continuous submaximal exercise with similar overall (i.e. work and recovery) oxygen consumption (VO2). Physically active subjects (n = 7) completed 90 min of an intermittent intense (12 s work:18 s recovery) and a continuous submaximal treadmill running protocol on separate days. In another experiment (n = 5) we compared oxygen availability in the vastus lateralis muscle between these two exercise protocols using near-infrared spectroscopy. Initially, overall VO(2) (i.e. work and recovery) was matched, and from 37.5 min to 67.5 min of exercise was similar, although slightly higher during continuous exercise (8%; P < 0.05). Energy expenditure was constant (22.5-90 min of exercise) and was not different in intermittent intense [0.81 (0.01) kJ x min(-1). kg(-1)] and continuous submaximal [0.85 (0.01) kJ x min(-1) x kg(-1)] exercise. Overall exercise intensity, represented as a proportion of peak aerobic power (VO2(peak)), was 68.1 (2.5)% VO2(peak) and 71.8 (1.8)% VO2(peak) for intermittent and continuous exercise protocols, respectively. Fat oxidation was almost 3 times lower (P < 0.05) and carbohydrate oxidation was approximately 1.2 times higher (P < 0.05) during intermittent compared to continuous exercise, despite the same overall energy expenditure. Capillary plasma lactate was constant from 15 to 90 min of exercise, and pyruvate was constant from 15 to 75 min, although both were higher (P < 0.0001, lactate; P < 0.001, pyruvate) during intermittent [5.05 (0.28) mM, 200 (7) microM, respectively] compared to continuous exercise [2.41 (0.10) mM, 114 (4) microM, respectively]. There was no difference between protocols for either plasma glycerol or non-esterified fatty acids. The decrease in muscle oxygenation during work periods of intermittent exercise resulted in a lower nadir oxygenation [54.62 (0.41)%] compared to continuous exercise [58.82 (0.21)%, P < 0.001]. The decline in oxygenation was correlated with treadmill speed (r = 0.72; P < 0.05). These results show a difference in substrate utilisation and muscle oxygen availability during sustained intermittent intense and continuous submaximal exercise, despite a similar overall VO(2) and identical energy expenditure.

Adult↗
PubMed1999

Effect of work and recovery duration on skeletal muscle oxygenation and fuel use during sustained intermittent exercise.

The purpose of this study was to compare rates of substrate oxidation in two protocols of intermittent exercise, with identical treadmill speed and total work duration, to reduce the effect of differences in factors such as muscle fibre type activation, hormonal responses, muscle glucose uptake and non-esterified fatty acid (NEFA) availability on the comparison of substrate utilisation. Subjects (n = 7) completed 40 min of intermittent intense running requiring a work:recovery ratio of either 6 s:9 s (short-interval exercise, SE) or 24 s:36 s (long-interval exercise, LE), on separate days. Another experiment compared O(2) availability in the vastus lateralis muscle across SE (10 min) and LE (10 min) exercise using near-infrared spectroscopy (RunMan, NIM. Philadelphia, USA). Overall (i.e. work and recovery) O(2) consumption (VO(2)) and energy expenditure were lower during LE (P < 0.01, P < 0.05, respectively). Overall exercise intensity, represented as a proportion of peak aerobic power (VO2(peak)), was [mean (SEM)] 64.9 (2.7)% VO2(peak) (LE) and 71.4 (2.4)% VO2(peak) (SE). Fat oxidation was three times lower (P < 0.01) and carbohydrate oxidation 1.3 times higher (P < 0. 01) during LE, despite the lower overall exercise intensity. Plasma lactate was constant and was higher throughout exercise in LE [mean (SEM) 5.33 (0.53) mM, LE; 3.28 (0.31) mM, SE; P < 0.001)]. Plasma pyruvate was higher and glycerol was lower in LE [215 (17) microM, 151 (13) microM, P < 0.05, pyruvate; 197 (19) microM, 246 (19) microM, P < 0.05, glycerol]. There was no difference between protocols for plasma NEFA concentration (n = 4) or plasma noradrenaline and adrenaline. Muscle oxygenation declined in both protocols (P < 0.001), but the nadir during LE was lower [52.04 (0. 60)%] compared to SE [61.85 (0.51)%; P < 0.001]. The decline in muscle oxygenation during work was correlated with mean lactate concentration (r = 0.68; P < 0.05; n = 12). Lower levels of fat oxidation occurred concurrent with accelerated carbohydrate metabolism, increases in lactate and pyruvate and reduced muscle O(2) availability. These changes were associated with proportionately longer work and recovery periods, despite identical treadmill speed and total work duration. The proposal that a metabolic regulatory factor within the muscle fibre retards fat oxidation under these conditions is supported by the current findings.

Adult↗
PubMed1999

The iliopubic tract: an important anatomical landmark in surgery.

A band of fascial thickening, termed the iliopubic tract, lies on the posterior aspect of the inguinal region and has been described in the surgical literature as playing an important role during herniorraphy. This study was undertaken to examine the gross and microscopic anatomy of the iliopubic tract in 12 cadavers. The results confirmed that the iliopubic tract can be readily identified as a thickening of the transversalis fascia running deep and parallel to the inguinal ligament. It attaches to the superomedial part of the pubic bone medially, but laterally its fibres fan out within the fascia transversalis and fascia iliaca without bony attachment to the iliac spines. In contrast to the inguinal ligament, the histological analysis of the iliopubic tract shows a high elastin to collagen ratio. The functional significance of this structure merits further study, but there is no doubt that it is important in many approaches to inguinal herniorraphy. For this reason it is considered that the iliopubic tract deserves greater emphasis in the anatomy teaching of the inguinal region.

Aged↗
PubMed1998

Changes in performance, muscle metabolites, enzymes and fibre types after short sprint training.

In contrast to endurance training, little research has been carried out to investigate the effects of short (< 10 s) sprint training on performance, muscle metabolism and fibre types. Nine fit male subjects performed a mean of 16 outdoor sprint running training sessions over 6 weeks. Distances sprinted were 30-80 m at 90-100% maximum speed and between 20 and 40 sprints were performed in each session. Endurance (maximal oxygen consumption; VO2max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 x 40 m sprints, 24 s recovery between each) performance tests were performed before and after training. Muscle biopsy samples (vastus lateralis) were also taken to examine changes in metabolites, enzyme activities and fibre types. After training, significant improvements were seen in 40 m time (P < 0.01), supramaximal treadmill run time (P < 0.05), repeated sprint performance (P < 0.05) and VO2max (P < 0.01). Resting muscle concentrations of ATP and phosphocreatine did not change. Phosphorylase activity increased (P < 0.025), citrate synthase activity decreased (P < 0.01), but no significant changes were recorded in myokinase and phosphofructokinase activities. The proportion of type II muscle fibres increased significantly (P < 0.05). These results demonstrate that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type of training.

Adult↗
PubMed1997

Cardiovascular autonomic nervous system tests: determination of normative values and effect of confounding variables.

OBJECTIVE: To determine normative values for heart rate variation to deep breathing (VAR) and Valsalva ratio (VAL) as well as the effect of various confounding variables on these measures using data from a large group of normal subjects collected from multiple centers. RESEARCH DESIGN AND METHODS: VAR and VAL were measured on 611 normal subjects, age range 9-79, from 63 centers and was analyzed at a single Autonomic Nervous System Reading Center. Using simple and stepwise logistic regression the effect of age, gender, height, weight, mean arterial blood pressure (MAP) and body mass index (BMI), on VAR and VAL was evaluated. RESULTS: The 95% normative values range (values at 2.5 to 97.5 percentile) for VAR (n = 580) was 12.8-103.5 (mean 49.7) and for VAL (n = 425) was 1.31-2.97 (mean 1.97). No gender effect was found for either VAR or VAL (p > 0.05). VAR correlated inversely with both age and MAP, while VAL correlated inversely with both age and BMI. Since age is the principal confounding variable for both VAR and VAL, normative values are also presented stratified by age. CONCLUSION: Normative values for VAR and VAL based on a large population sample are presented. However, the values presented may not be valid in patients with morbid obesity or malignant hypertension. These data are applicable for either individual patients or for use in multicenter research trials.

Adolescent↗
PubMed1997

Muscle phosphocreatine repletion following single and repeated short sprint efforts.

Phosphocreatine (PCr) repletion following either single (1x6 s, n=7) or repeated (5x6 s, departing every 30 s, n=8) maximal short sprint cycling efforts was measured in separate groups of trained subjects. Muscle biopsies (vastus lateralis) were taken pre-exercise before warming up, and then at 10 s, 30 s and 3 min post-exercise. After the 1 x 6 s sprint PCr concentration was respectively, 55% (10 s; P<0.01), 69% (30 s; P<0.01) and 90% (3 min; NS) of the pre-exercise value (mean+/-SD) (81.1+/-7.4 mmol x kg(-1) DM), whereas after the 5x6 s sprints, PCr concentration was, respectively, 27% (10 s; P<0.01), 45% (30 s; P<0.01) and 84% (3 min; P<0.01) of the pre-exercise value (77.1+/-4.9 mmol x kg(-1) DM). PCr concentration was correlated with muscle lactate at 30 s (r=-0.82; P<0.05) and 3 min of recovery (r=-0.94; P<0.01) for the 1x6 s sprint, but not for the 5x6 s sprints. The extent of PCr repletion was significantly greater after the 5x6 s sprints than the 1x6 s sprint between both 10 s and 30 s and 30 s and 3 min, despite lower PCr levels at 10 s, 30 s and 3 min following the 5x6 s sprints. Full repletion of PCr is likely to take longer after repeated sprints than single short sprints because of a greater degree of PCr depletion, such that replenishment must commence from lower PCr levels rather than because of slower rates of repletion.

Adult↗
PubMed1997

Biochemical and ultrastructural indices of muscle damage after a twenty-one kilometre run.

Increased serum concentrations of intracellular proteins are generally accepted as good indicators of muscle damage. The mechanism of this damage is, however, poorly understood. Twenty male runners completed a 21 km run in as fast a time as possible. Blood samples were obtained from each subject just prior to, immediately after, and 24 hr after the run. Samples were analysed for haemoglobin, haematocrit, creatine kinase (CK), myoglobin (Mb) and malondialdehyde (MDA) concentrations and corrected for percentage change in plasma volume (PV). Percutaneous muscle biopsies were taken from the lateral gastrocnemius muscle of 6 of the subjects 24 hr before and 24 hr after the run and examined by electron microscopy. Mb levels in the serum increased significantly (p < 0.001) immediately post-exercise, while CK levels increased significantly (p < 0.001) at 24 hours post-exercise. The PV corrected serum MDA levels were very close (p = 0.06) to a significant increase immediately post-exercise. Ultrastructural examination of pre-exercise samples revealed evidence of muscle changes consistent with endurance exercise training, but no further damage was evident at 24 hr post-exercise. It is thus suggested that the increased serum levels of CK and Mb after the 21 km run may be a result of free radical induced cell membrane damage and increased permeability, as evidenced by elevated serum MDA levels, and not due to mechanical muscle damage.

Adult↗
PubMed1996

Extent of intellectual, cognitive, and academic decline in adolescent traumatic brain injury.

Pre-injury cognitive data are rarely available for review for individuals suffering from traumatic brain injury (TBI). Although pre-injury intelligence and academic scores may be available, particularly if an individual is learning-disabled (LD), data on specific cognitive abilities are unlikely to exist. We present neuropsychological data for a 15-year-old Caucasian female with a learning disability who was administered IQ testing 2 weeks prior to a significant TBI, as well as other measures of specific cognitive abilities (e.g. memory and perceptual-motor skills) throughout her education. Comparison of pre- and post-TBI data showed: (1) global and generally consistent decline in all cognitive areas and (2) relatively stable performance on tests of academic ability, supporting the validity of such test scores as estimates of premorbid intelligence.

Adolescent↗
PubMed1996

Oxygen consumption during recovery from prolonged submaximal cycling below the anaerobic threshold.

The purpose of this study was to compare the magnitude and duration of excess post-exercise O2 consumption (EPOC) measured after submaximal cycling at three different intensities of equivalent energy cost but all performed below the anaerobic threshold (AT). Eight healthy young women performed the three cycling sessions after an initial determination of VO2max (M +/- SD) (41.8 +/- 7.0 ml.kg-1.min-1) and AT (73 +/- 5% VO2max). The high intensity (HI) exercise was performed at 65% VO2max (90% of AT workload) for 30 minutes, while the moderate (MI) and low intensity (LI) exercise sessions were performed at approximately 55% VO2max (75% AT) and -45% VO2max (60% AT) respectively, until the energy cost matched that expended in the HI condition. Prior to each exercise session baseline resting VO2 and respiratory exchange ratio (RER) were measured by open circuit spirometry at the end of a 35 min period of supine rest. These measures were also made during the exercise and recovery periods. Post-exercise VO2 was measured continuously until baseline VO2 (within 1 SD of resting value for 2 consecutive min) was reached. The duration of EPOC (13-14 min) was similar following all three exercise sessions. The gross EPOC energy expenditure and VO2 were both significantly greater (p < 0.01) following the HI (137.0 +/- 6.3 kJ and 6.63 +/- 0.30 1) condition than the MI condition (116.6 +/- 8.7 kJ and 5.69 +/- 0.42 1) but no significant differences existed between the MI and LI (107.4 +/- 5.8 kJ and 5.24 +/- 0.29 1) conditions for either of these variables. It was concluded that the magnitude of EPOC following submaximal exercise of equivalent energy cost but below the AT, is determined more by the intensity of exercise rather that the exercise energy cost.

Adult↗
PubMed1995

The P1A alloantigen system is a sensitive indicator of the structural integrity of the amino-terminal domain of the human integrin beta 3 subunit.

Within the native integrin alpha pi b beta 3, the conformation of the amino-terminal domain of the beta 3 subunit has a significant influence on the availability of the Leu33/Pro33 polymorphism that defines the A1 and A2 alleles, respectively, of the P1A alloantigen system. The majority of anti-P1A1 IgG antibodies, affinity-purified by adsorption to either (A1/A1)-platelets or purified alpha pi b(A1) beta 3, fail to bind to the Leu33 polymorphic loop within Cys26-Cys38 in native beta 3 unless this sequence is maintained in a proper orientation by two noncontiguous human beta 3 sequences. By comparing IgG binding to recombinant beta 3 molecules composed of segments of human, Xenopus and avian sequences expressed by Spodoptera frugiperda cell lines, we have found that neither region alone is sufficient for full expression of the epitope. One sequence, that most proximal to Leu33/Pro33, lies within beta 3[54-133], and a second distal sequence is located within beta 3[435-490]. Proximity of the distal sequence to the Cys26-Cys38 loop in native beta 3 is confirmed by the fact that both anti-P1A1 IgG and the murine monoclonal antibody SZ21, specific for beta 3[28-35], completely inhibit the binding of rabbit polyclonal IgG specific for the sequence beta 3[479-485]. Anti-P1A1 IgG antibodies from all of the 7 donors selectively bind to the epitope within the native conformation of beta 3. However, in one of the seven donors, roughly 60% of the anti-P1A1IgG binds exclusively to denatured (A1) beta 3, and not to either denatured (A2) beta 3 or nondenatured (native) (A1) beta 3. This IgG subpopulation cannot be purified by adsorption to intact (A1/A1)-platelets or to native alpha pi b(A1) beta 3 integrin. The physiologic relevance of this exceptional type of anti-P1A1 antibody is debatable, but the presence of IgG with this specificity only in an immunized subject suggests that the epitope may well be presented on a "denatured" form of beta 3 in vivo. Regardless, our results indicate that the amino-terminal domain of the native beta 3 molecule associates with noncontiguous beta 3 sequences, and the epitope recognized by a majority of anti-P1A1 antibodies is a sensitive indicator of correct tertiary structure within this region of beta 3.

Amino Acid Sequence↗
PubMed1995

Station gender bias in a multiple-station test of clinical skills.

PURPOSE: To apply differential item functioning (DIF) procedures to investigate station gender bias in multiple-station tests of clinical skills, and to compare these results with those obtained by comparing the station-score distributions of men and women examinees. METHOD: The data were from 23 stations used in the selection of seven successive cohorts (1987-1993) of candidates to the Ontario Pre-Internship Program for graduates of foreign medical schools. The stations had been used on at least three occasions, with a minimum sample of about 210 candidates per station. Each station's score was expressed as both a binary score and a continuous score, and DIF was assessed using the Mantel-Haenszel procedure with the binary scores and analysis of covariance with the continuous scores. For each station, DIF effect sizes were calculated and compared with the gender-group mean differences. RESULTS: Using the binary scores, significant DIF was observed for three stations; using the continuous scores, significant DIF was observed for five stations. Significant gender differences were observed in the scores of nine stations. In eight, these differences favored women. Overall, in more stations the direction of DIF favored the men, while the women demonstrated higher levels of ability. CONCLUSION: The results suggest the importance of using a DIF approach for controlling the "ability factor" in studies of this kind: although significant gender differences were observed in the continuous score distributions of nine stations, generally these differences were not indicative of station gender bias.

Analysis of Variance↗
PubMed1995

Effects of oral creatine loading on single and repeated maximal short sprints.

This investigation determined whether oral creatine (Cr) loading could enhance single and repeated short sprint performance. A 1 x 10 s cycle sprint (Study One) and 6 x 6 s (departing every 30 s) repeated cycle sprints (Study two) were the performance tests used. Separate groups of subjects, randomly assigned to either a Cr or placebo (P) group, were used in each study in a double blind design. After performing a familiarization and two baseline tests subjects loaded with 5g of Cr or P four times per day for five days before repeating the tests one and three days post-loading. In Study One (n = 9 in each group), work completed (kJ) at 2, 4, 6, 8 and 10 s and peak power (W) were greater than baseline values in each of the post-loading trials in both the Cr and P groups. There were no between group performance differences. In Study Two (n = 11 in each group) after loading, the Cr group recorded significantly greater scores than the P group in total work (kJ) completed over the 6 sprints, work completed in sprint 1, and peak power (W). Post-exercise blood lactate and pH responses were not different between the Cr and P groups after loading in either study. Although Study One results are equivocal, Study Two results suggest that Cr supplementation can enhance both single (if sprint 1 results are considered in isolation) and repeated short sprint performance.

Administration, Oral↗
PubMed1994

Performance on the National Board of Medical Examiners. Part I Examination by men and women of different race and ethnicity.

OBJECTIVE: To investigate the performance of men and women from various racial and ethnic backgrounds on the National Board of Medical Examiners Part I examination, controlling for any differences in measures of educational background and academic performance before entering medical school. DESIGN: A retrospective analysis of existing records from the National Board of Medical Examiners and the Association of American Medical Colleges. SETTING: National Board of Medical Examiners. PARTICIPANTS: All students taking the June administration of Part I for the first time in 1986, 1987, or 1988 and who were 2 years from graduation from an accredited medical school. METHODS: Multiple regression methods were used to estimate Part I examination group differences in performance that would be expected if all students entered medical school with similar Medical College Admission Test scores, undergraduate grade point averages, and other prematriculation measures. MAIN OUTCOME MEASURE: Performance on the Part I examination. RESULTS: There were substantial differences in performance, with white students scoring highest, followed by Asian/Pacific Islanders, Hispanics, and blacks; within all racial and ethnic categories, women scored lower than men. Controlling for dissimilarities in academic background greatly reduced Part I differences among most racial and ethnic groups, except Asian/Pacific Islander men; unexplained differences remained between men and women. Results were consistent for the 3 years examined. CONCLUSIONS: The results of this study do not imply that physician performance varies among racial and ethnic groups or between men and women; no written examination can measure all the abilities that may be desirable to assess. Validity research investigating reasons for the reported gender and racial and ethnic differences in performance on the National Board examinations should be continued.

Achievement↗
PubMed1994

Mouse hepatic metabolites of ketoconazole: isolation and structure elucidation.

Oxidation, cleavage and degradation of the imidazole and piperazine rings, O-dealkylation, and aromatic hydroxylation are the reported pathways of ketoconazole (KC) metabolism. Metabolites were examined in hepatic extracts from male Swiss Webster mice treated with KC (350 mg kg-1 po x 7 days) in a 0.25% gum tragacanth suspension at 10 ml kg-1. Livers were collected 24 h after the last dose and stored at -70 degrees C. A mixture of chloroform/methanol extracts of liver homogenates were dried under vacuum and methanol extracts of the residue were chromatographed by a series of preparative and analytical HPLC techniques. Structure assignments were made by NMR and MS/MS techniques. It was demonstrated that KC was biotransformed to a number of products. Nine were isolated and seven identified as exclusive products of the biotransformation of the 1-acetylpiperazine moiety of KC. This substituent was biotransformed to the following: piperazine (de-N-acetyl ketoconazole, DAKC), N-carbamylpiperazine, N-formylpiperazine, 2,3-piperazinedione, 2-formamidoethylamine, ethylenediamine and amine. The 1H-NMR and MS data suggested that the remaining two metabolites were products resulting from the oxidation of the imidazole ring.

Animals↗
PubMed1994

Thermoregulation of paraplegic and able bodied men during prolonged exercise in hot and cool climates.

The purpose of this study was to compare the thermoregulatory responses of trained paraplegics (TP) and able bodied subjects (AB) performing submaximal exercise of the same relative intensity in both hot and cool conditions. Five TP (lesion range T12 to L3) and five AB subjects experienced in wheelchair use performed 60 minutes of constant load (55-60% of VO2 max) arm ergometry exercise in 37 degrees C and 15 degrees C climatic conditions. Heart rate (HR), sweat rate and rectal (Tr) and skin (Tsk) temperatures were recorded. In the hot climate the TP subjects recorded a significantly greater change in Tsk (delta Tsk) from 0 to 60 minutes of exercise than the AB subjects, because of greater thigh and calf temperatures, but no other significant differences were found between these groups. In the cool climate no significant differences were observed between the TP and AB groups. It was concluded that TP have a similar thermoregulatory ability to AB subjects who perform identical prolonged exercise in hot and cool conditions, although their lower limb skin temperatures are greater, probably because of venous pooling in the legs. While these results are a promising indication of the ability of TP to thermoregulate effectively while exercising in the, heat caution regarding their participation in endurance competitions in hot conditions should be expressed until data collected during wheelchair exercise (rather than arm ergometry) in the heat is available.

Adult↗