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Biomedical subjects

D A Brodie

Publications and source records attributed to D A Brodie.

At least 19 recordsLinked to original sources
PubMed2006

The use of heart rate variability measures to assess autonomic control during exercise.

Heart rate variability (HRV) is a non-invasive indicator of cardiac autonomic modulation at rest. During rhythmic exercise, global HRV decreases as a function of exercise intensity. Measures reflecting sympathovagal interactions at rest do not behave as expected during exercise. This makes interpretation of HRV measures difficult, especially at higher exercise intensities. This problem is further confounded by the occurrence of non-neural oscillations in the high-frequency band due to increased respiratory effort. Alternative data treatments, such as coarse graining spectral analysis (CGSA), have demonstrated expected changes in autonomic function during exercise with some success. The separation of harmonic from fractal and/or chaotic components of HRV and study of the latter during exercise have provided further insight into cardioregulatory control. However, more research is needed. Some cross-sectional differences between HRV in athletes and controls during exercise are evident and data suggest longitudinal changes may be possible. Standard spectral HRV analysis should not be applied to exercise conditions. The use of CGSA and non-linear analyses show much promise in this area. Until further validation of these measures is carried out and clarification of the physiological meaning of such measures occurs, HRV data regarding altered autonomic control during exercise should be treated with caution.

Autonomic Pathways↗
PubMed2006

Cardiac pumping capability in patients with peripheral vascular disease.

INTRODUCTION: Peripheral vascular disease (PVD) is a condition characterized by atherosclerotic occlusive disease of the lower extremities, low functional capacity and low exercise tolerance. Less empirical data are available concerning the cardiovascular response to maximum exercise tests in patients with PVD. The purpose of this study was to examine cardiovascular variables in patients with peripheral vascular disease. METHODS: Fifty patients (67 +/- 9 years) completed an incremental exercise test (2 min stages, 3.2 km h(-1), with increases of 2% every 2 min) to maximum claudication pain. Maximal oxygen consumption (VO2) was assessed on a breath-by-breath basis by online expiratory gas analysis (CardiO2, Medical Graphics Co.). Blood pressure was recorded at peak exercise. Following a 30-min rest period, patients exercised at the highest level attained during the first test and cardiac output (QT) was measured using the exponential non-invasive rebreathing method. Cardiac power output peak (CPOpeak) in Watts (W), was then computed. RESULTS: Mean +/- SD values were; 13.85 +/- 4.14 ml kg min(-1); maximal walk time 357 +/- 227 s; peak mean arterial pressure 127 +/- 15 mmHg; 9.8 +/- 2.39 (l min(-1)); CPO 2.86 +/- 0.87 W. CONCLUSION: Patients with peripheral vascular disease demonstrate attenuated levels of cardiovascular capacity. This group of patients should be given exercise therapy in order to improve cardiovascular status and ambulatory function.

Aged↗
PubMed2005

Place(ment) matters: students' clinical experiences and their preferences for first employers.

BACKGROUND: Although a significant volume of nursing research has focused on students' experiences of clinical placements, to date, none has considered these experiences in the context of workforce recruitment and specifically how they may impact upon preferences for working for health care providers. METHODS: In this context, the research used a place-sensitive geographical perspective and a combined questionnaire (n = 650), interview (n = 30) and focus group (n = 7) method to collect data on the complex range of clinical experiences which together impact upon the perceived attractiveness of different health care settings. FINDINGS: The data identified a range of experiential factors associated with mentorship, ward management, learning opportunities and racism. An important finding was that although students' experiences are obtained at the micro ward level, even if they may not necessarily reflect what happens throughout the hospital, they potentially impact, both positively and negatively, upon their broader perceptions of the hospital and the likelihood of seeking work there. IMPLICATIONS: The study highlighted a variety of issues that should be addressed by both higher education institutions and hospitals so that they may be able to provide a more consistent and positive experience for students. In the longer term, this may pay dividends through increased recruitment of new graduates.

Career Choice↗
PubMed2005

Validity and reliability of selected commercially available metabolic analyzer systems.

Automated metabolic gas analysis systems have advanced considerably over the past decade. They provide an abundance of information, which is not possible by using the traditional Douglas bag method and have become an essential tool in both physiological monitoring and in the diagnosis of cardiopulmonary disease. The validity and reliability of the different online metabolic analyzer systems are not well known, with relatively few independent studies being published. The purpose of this review was to examine and evaluate current literature regarding the validity and reliability of commercially available metabolic analyzer systems. This review reveals significant differences between the available systems in the way that they capture and process basic respiratory measurements. Online metabolic analyzer systems were found to vary significantly when compared with Douglas bag methods. These variations have the potential to introduce error into the accuracy with which the health of cardiovascular system can be assessed or training loads can be assigned. Compounding this is the fact that many automated systems are a "black box", which makes it easy to generate data without the user having much understanding of how the data were generated. In conclusion automated metabolic analyser systems are a scientifically robust method for the evaluation of cardiopulmonary function. Individual researchers and clinicians must, however, be able to make their own decisions about the level of error that is tolerable for their individual needs. This presents a significant practical challenge in light of the speed with which technical developments in the field occur and we make some suggestions for the formulation of intersystem comparison studies.

Automation↗
PubMed2004

Agreement between three commercially available instruments for measuring short-term heart rate variability.

Numerous instruments are commercially available to measure heart rate variability, yet little is known regarding the agreement between such instruments. The objective of this study is to assess agreement between measures of heart rate variability in three commercially available instruments. Thirty subjects (20 males) of median age 27.5 (range 19-59 years) underwent simultaneous ECG recordings, under three different resting conditions: supine, standing and supine with controlled breathing, using three commercially available analysers. Intraclass correlation coefficients tended to show excellent agreement (lower 95% C.I., R > 0.75) between all instruments under all conditions. However, further analysis of selected measurements using the limits of agreement method revealed large variation in values generated by all instruments. There was also an evidence of systematic bias between one instrument and the remaining two. The latter finding was due to discrepant ECG recording protocols that were unrelated to consistent operator timing. This study demonstrates that measures of HRV generated by the three instruments did not agree well in all cases. Discrepancies were due to the recording protocols of the systems. This may lead to incomparable results between instruments. It is therefore recommended that: (a) if different instruments are used in the same study or (b) multi-centre study designs are planned or (c) heart rate variability results are discussed with reference to studies using other instruments, levels of agreement need to be reported to ensure comparability.

Adult↗
PubMed2004

Reliability of three commercially available heart rate variability instruments using short-term (5-min) recordings.

AIM: To assess the reliability of heart rate variability (HRV) measures made by three commercially available analysers in healthy subjects. METHODS: Twenty-nine volunteers (20 males, mean age 35 +/- 13 years and nine females, mean age 29 +/- 11 years) underwent repeated HRV measures under three conditions: lying supine, standing, lying supine with controlled breathing. HRV was measured simultaneously by three instruments. Reliability was assessed statistically by calculating coefficient of variation (CV), intraclass correlation coefficient (ICC) and limits of agreement (LoA). RESULTS: A wide range of values were found for CV (1-235%) and ICC (R = 0.16-0.99) dependent on the HRV measure assessed and the position in which the measurement was made. For the most part the analysers gave similar values in each condition. The values for CV and ICC were high but within the range reported in the literature. Values for LoA were also high and showed a wide range of values. CONCLUSIONS: The similarity in measures between systems indicates that biological variation and experimental error play a major role in determining the repeatability of HRV measurements. It is therefore recommended that population-specific reliability coefficients should be published where possible and that authors should take into account the reliability of measures when making sample size calculations.

Adult↗
PubMed2003

Effect of vitamin C supplements on antioxidant defence and stress proteins in human lymphocytes and skeletal muscle.

Oxidative stress induces adaptations in the expression of protective enzymes and heat shock proteins (HSPs) in a variety of tissues. We have examined the possibility that supplementation of subjects with the nutritional antioxidant, vitamin C, influences the ability of lymphocytes to express protective enzymes and HSPs following exposure to an exogenous oxidant and the response of skeletal muscle to the physiological oxidative stress that occurs during exercise in vivo. Our hypothesis was that an elevation of tissue vitamin C content would reduce oxidant-induced expression of protective enzymes and HSP content. Lymphocytes from non-supplemented subjects responded to hydrogen peroxide with increased activity of superoxide dismutase (SOD) and catalase, and HSP60 and HSP70 content over 48 h. Vitamin C supplementation at a dose of 500 mg day-1 for 8 weeks was found to increase the serum vitamin C concentration by ~50 %. Lymphocytes from vitamin C-supplemented subjects had increased baseline SOD and catalase activities and an elevated HSP60 content. The SOD and catalase activities and the HSP60 and HSP70 content of lymphocytes from supplemented subjects did not increase significantly in response to hydrogen peroxide. In non-supplemented subjects, a single period of cycle ergometry was found to significantly increase the HSP70 content of the vastus lateralis. Following vitamin C supplementation, the HSP70 content of the muscle was increased at baseline with no further increase following exercise. We conclude that, in vitamin C-supplemented subjects, adaptive responses to oxidants are attenuated, but that this may reflect an increased baseline expression of potential protective systems against oxidative stress (SOD, catalase and HSPs).

Adult↗
PubMed2001

Time course of responses of human skeletal muscle to oxidative stress induced by nondamaging exercise.

Previous studies in animals have demonstrated that a single period of aerobic exercise induces a rise in the skeletal muscle activity of the antioxidant enzymes superoxide dismutase and catalase and an increase in the muscle content of heat shock proteins (HSPs). The purpose of this study was to examine the time course of response of human skeletal muscle superoxide dismutase and catalase activities and the content of HSP60 and HSP70 after a period of exhaustive, nondamaging aerobic exercise. Seven volunteers undertook one-legged cycle ergometry at 70% maximal oxygen uptake for 45 min. Biopsies were obtained from the vastus lateralis muscle 7 days before and at 1, 2, 3, and 6 days after exercise. Muscle superoxide dismutase activity increased to a peak at 3 days postexercise, muscle catalase activities were unchanged, and muscle content of HSP60 and the inducible HSP70 increased by variable amounts to reach means of 190% and 3,100% of preexercise values, respectively, by 6 days postexercise. These data indicate that human skeletal muscle responds to a single bout of nondamaging exercise by increasing superoxide dismutase activity and provide the first evidence of an increase in HSP content of human skeletal muscle after a submaximal exercise bout.

Adult↗
PubMed2000

Estimation of body composition in muscular dystrophy by MRI and stereology.

We have applied the Cavalieri method of modern design stereology with magnetic resonance imaging for estimating the volume of whole-body muscle and fat compartments in four patients with muscular dystrophy, a patient with myopathy, five controls, an anorexic subject, and a body builder. Detailed systematic series (ie, 50) of axial MR images (T1-weighted, TR/TE 400/10 msec) were obtained throughout the whole body of each subject. The results showed that 15, 20, and 35 axial sections through the body are sufficient to secure coefficients of error (CEs) on the estimates of total muscle and fat volume of around 10%, 5%, and 3% respectively in muscular dystrophy patients and controls. The mean normalized volumes of muscle in four muscular dystrophy patients were decreased by 27% (t-test: P < 0.05), and those of total fat were increased by 12% (t-test: P > 0.05) relative to controls. The Cavalieri method provides a direct, efficient, and mathematically unbiased approach for studying human body compartments and may have application in assessing treatment efficacy in patients with muscular dystrophy. J. Magn. Reson. Imaging 2000;12:467-475.

Adipose Tissue↗
PubMed2000

Review article: alginate-raft formulations in the treatment of heartburn and acid reflux.

Alginate-based raft-forming formulations have been marketed word-wide for over 30 years under various brand names, including Gaviscon. They are used for the symptomatic treatment of heartburn and oesophagitis, and appear to act by a unique mechanism which differs from that of traditional antacids. In the presence of gastric acid, alginates precipitate, forming a gel. Alginate-based raft-forming formulations usually contain sodium or potassium bicarbonate; in the presence of gastric acid, the bicarbonate is converted to carbon dioxide which becomes entrapped within the gel precipitate, converting it into a foam which floats on the surface of the gastric contents, much like a raft on water. Both in vitro and in vivo studies have demonstrated that alginate-based rafts can entrap carbon dioxide, as well as antacid components contained in some formulations, thus providing a relatively pH-neutral barrier. Several studies have demonstrated that the alginate raft can preferentially move into the oesophagus in place, or ahead, of acidic gastric contents during episodes of gastro-oesophageal reflux; some studies further suggest that the raft can act as a physical barrier to reduce reflux episodes. Although some alginate-based formulations also contain antacid components which can provide significant acid neutralization capacity, the efficacy of these formulations to reduce heartburn symptoms does not appear to be totally dependent on the neutralization of bulk gastric contents. The strength of the alginate raft is dependant on several factors, including the amount of carbon dioxide generated and entrapped in the raft, the molecular properties of the alginate, and the presence of aluminium or calcium in the antacid components of the formulation. Raft formation occurs rapidly, often within a few seconds of dosing; hence alginate-containing antacids are comparable to traditional antacids for speed of onset of relief. Since the raft can be retained in the stomach for several hours, alginate-based raft-forming formulations can additionally provide longer-lasting relief than that of traditional antacids. Indeed, clinical studies have shown Gaviscon is superior to placebo, and equal to or significantly better than traditional antacids for relieving heartburn symptoms. Alginate-based, raft-forming formulations have been used to treat reflux symptoms in infants and children, and in the management of heartburn and reflux during pregnancy. While Gaviscon is effective when used alone, it is compatible with, and does not interfere with the activity of antisecretory agents such as cimetidine. Even with the introduction of new antisecretory and promotility agents, alginate-rafting formulations will continue to have a role in the treatment of heartburn and reflux symptoms. Their unique non-systemic mechanism of action provides rapid and long-duration relief of heartburn and acid reflux symptoms.

Adult↗
PubMed2000

Effects of short-term psychological stress on the time and frequency domains of heart-rate variability.

The purpose of this study was to test the hypothesis that short-term psychological stress produces significant changes in sympathovagal activity. A simple, noninvasive method was used measuring the timing and frequency of heart-rate variability (HRV). 30 normal healthy subjects were assigned into two age- and sex matched groups. In the experimental condition a 5-min. psychological stress test, predominantly based on the Stroop Word Color Conflict Test, was employed in a competitive setting and included a financial inducement to produce psychological strain. Analysis showed that during psychological stress a significant reduction in the timing and frequency of heart rate variability was observed. The standard deviation of interbeat intervals decreased. A significant increase in heart rate was also observed. Within the frequency domain, a significant reduction in the high frequency component of HRV and a significant increase in the low frequency component were observed. There was also a significant increase in the low frequency to high frequency ratio. Self-evaluation of physical tension and emotional state measured by visual analog scales also showed significant increases following psychological stress. No significant differences were observed on any variables within the control group. The results indicate a shift towards sympathetic predominance as a result of parasympathetic withdrawal and demonstrates that this psychological stress test is effective in provoking a characteristic defence-arousal reaction. This simple, cost-effective method of analysing heart rate variability is suitable for detection of short-term changes in sympathovagal balance.

Adolescent↗
PubMed1997

Dental erosion, oral hygiene, and nutrition in eating disorders.

OBJECTIVE: To determine the influence of oral hygiene practices and additional fluoride on erosive tooth wear in eating disorders. The proportional dietary intake of carbohydrates, fats, and proteins was also investigated. METHOD: Tooth wear was measured with the use of the tooth wear index (TWI). All subjects completed a questionnaire on past dental history as well as a 1-week diet sheet. A total of 33 subjects participated in the study, 20 of whom were follow-ups, allowing the progress of dental erosion to be made. All subjects were referred from the Department of Clinical Psychology. RESULTS: Oral hygiene practices between subjects with and without severe erosion were not significantly different. Only 8 bulimics spent more time brushing after vomiting than at other times. The pH of vomitus from 6 subjects ranged between 2.9 and 5.0, with a mean of 3.8, well below the critical pH for enamel demineralization to occur. Of the 20 follow-up subjects, 12 (60%) exhibited worsening tooth wear. The mean values for daily carbohydrate, protein, and fat intake were not significantly different at baseline and at recall, and the proportional dietary intake was similar to recommended energy provision at 47%, 40%, and 13%, respectively. DISCUSSION: The contribution by toothbrush abrasion to the overall wear in the eroded dentition of bulimics is not significant. Therefore, immediate post-vomiting oral hygiene practices can be recommended. The proportional nutritional intake values of carbohydrates, fats, and proteins in this group of bulimics are acceptable.

Adult↗
PubMed1996

Influence of preconception on body image.

The purpose of this study was to establish whether preconceived body images influence quantitative perceptions of body shape. 59 healthy female subjects were subdivided into four groups by amount of activity and body mass index. The body shape of the same person, dressed differently to appear like a model, a student, and a cook, was classified by reference to an adiposity scale based on line drawings. A significant difference was shown between the representations of the types of occupation, with the model viewed consistently as the slimmest and the cook as the fattest. The obese women classified all three occupational groups as slimmer than the nonobese, and the active groups as slimmer than the inactive. The implications of this work relate to a better understanding of body-image distortion, to treatment for eating disorders, and a recognition that people retain preconceived perceptions developed on the basis of experience.

Adult↗
PubMed1994

Body-image perception in pre- and postadolescent females.

The purpose of this study was to examine both perceived and ideal body-image to establish if the process of adolescence was a contributory factor. A distorting mirror and silhouette pictures were used to examine the image in two groups of 59 pre- and 41 postadolescent girls. The girls' perception of themselves was reasonably accurate yet both groups had a significantly slimmer mean ideal image, irrespective of adolescent status. The differences between the two groups were nonsignificant whether using the distorting mirror or the pictures. The only difference to be observed was when using a body-satisfaction scale. The postadolescents were significantly less satisfied about their nonhead body parts. Scores from the mirror and the pictures question the assumption that body-image dissatisfaction is a postadolescent phenomenon. This should be a cause for concern as eating disorders, which appear to be linked to body-image, are being observed in younger children. The comparability between scores for the pictures and the distorting mirror opens the possibility of home-based therapy in the treatment of perceptual and eating disorders.

Adolescent↗
PubMed1993

Unbiased estimation of human body composition by the Cavalieri method using magnetic resonance imaging.

The classical methods for estimating the volume of human body compartments in vivo (e.g. skin-fold thickness for fat, radioisotope counting for different compartments, etc.) are generally indirect and rely on essentially empirical relationships--hence they are biased to unknown degrees. The advent of modern non-invasive scanning techniques, such as X-ray computed tomography (CT) and magnetic resonance imaging (MRI) is now widening the scope of volume quantification, especially in combination with stereological methods. Apart from its superior soft tissue contrast, MRI enjoys the distinct advantage of not using ionizing radiations. By a proper landmarking and control of the scanner couch, an adult male volunteer was scanned exhaustively into parallel systematic MR 'sections'. Four compartments were defined, namely bone, muscle, organs and fat (which included the skin), and their corresponding volumes were easily and efficiently estimated by the Cavalieri method: the total section area of a compartment times the section interval estimates the volume of the compartment without bias. Formulae and nomograms are given to predict the errors and to optimize the design. To estimate an individual's muscle volume with a 5% coefficient of error, 10 sections and less than 10 min point counting (to estimate the relevant section areas) are required. Bone and fat require about twice as much work. To estimate the mean muscle volume of a population with the same error contribution, from a random sample of six subjects, the workload per subject can be divided by square root of 6, namely 4 min per subject. For a given number of sections planimetry would be as accurate but far more time consuming than point counting.

Body Composition↗
PubMed1992

Effect of very low calorie diet on body composition and exercise response in sedentary women.

The effect of very low calorie diet (VLCD) on fat-free mass (FFM) and physiological response to exercise is a topic of current interest. Ten moderately obese women (aged 23-57 years) received VLCD (1695 kJ.day-1) for 6 weeks. FFM, estimated by four conventional techniques, and heart rate (fc), blood lactate (la(b)), mean arterial pressure (MAP), respiratory exchange ratio (R) and rating of perceived exertion (RPE) were measured during a submaximal cycle ergometry test 1 week before, in the 2nd and 6th week, and 1 week after VLCD treatment. Strength and muscular endurance of the quadriceps and hamstrings were tested by isokinetic dynamometry. The 11.5-kg reduction in body mass was approximately 63% fat and 37% FFM. The latter was attributed largely to the loss of water associated with glycogen. Whilst exercise fc increased by 9-14 beats.min-1 (P < 0.01), there were substantial decreases (P < 0.01) in submaximal MAP (1.07-1.73 kPa), la(b) (0.75-1.00 mmol.l-1 and R (0.07-0.09) during VLCD. R and fc returned to normal levels after VLCD. Gross strength decreased (P < 0.01) by 9 and 13% at 1.05 rad.s-1 and 3.14 rad.s-1, respectively. Strength expressed relative to body mass (Nm.kg-1) increased (P < 0.01) at the lower contraction velocity, but there was no change at the faster velocity. Muscular endurance also decreased (P < 0.01) by 62 and 82% for the hamstrings and quadriceps, respectively. We concluded that the strength decrease was a natural adaptation to the reduction in body mass as the ratio of strength to FFM was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Body fat estimations by electrical impedance and infra-red interactance.

The purpose of this study was to examine body fat estimation using three methods of electrical impedance (the BIA-103 Body Composition Analyser--RJL Systems, Detroit; the BMR 2000 Body Composition Analyzer--Berkeley Medical Research, San Leandro; the BC300 Body Composition Analyzer--Spacelabs, Dallas) and an infra-red interactance method (Futrex 5000 Analyzer--Futrex Inc. Gaithersburg) as an alternative to hydrodensitometry. Five different groups were examined using at least one of the electrical systems and in all cases utilising hydrodensitometry as the criterion method. The results produced highly significant correlations between all methods, but caution is recommended due to the limited common variance in some cases. The individual electrical methods differed from hydrodensitometry by a maximum of 1.1% in obese women, by 21.6% in athletic adults, by 6.2% in the slightly obese group, by 8.1% in normal women and by 56.0% in normal children. Significant mean differences between one of the impedance methods and hydrodensitometry were only noted in two of the groups tested. This suggests, allowing for the limitations of hydrodensitometry itself, that the other three electrical methods appear to be reasonably valid alternatives to underwater weighing, especially for field work of an epidemiological nature.

Adipose Tissue↗