Biomedical subjects

T Rowland

Publications and source records attributed to T Rowland.

At least 19 recordsLinked to original sources

PubMed2003

Circulatory responses to progressive exercise: insights from positional differences.

The influence of body position on cardiac responses to progressive exercise was examined in 13 healthy circumpubertal boys. The subjects (mean age 12.5 +/- 1.4 y) performed a progressive cycle test with an identical protocol in the sitting and supine positions. Stroke volume and left ventricular dimensions were assessed with Doppler and two-dimensional echocardiography, respectively. During supine exercise, no changes were seen in stroke volume or left ventricular preload (end-diastolic dimension) with increasing exercise intensity. At rest, mean values for stroke volume and cardiac output were 16.4 % and 27.1 % lower, respectively, with subjects upright compared to supine. With upright exercise these variables rose to become insignificantly different than supine values. Stroke volume while cycling upright rose by 29 % by the second workload but remained stable at higher work intensities. The initial increase in stroke volume observed only when cycling upright presumably reflects mobilization of dependent blood in the lower extremities. The mechanisms governing cardiac responses to exercise when supine and upright are otherwise identical.

Adolescent↗

PubMed2003

Myocardial performance during maximal exercise in adolescents with anorexia nervosa.

AIM: To examine cardiac responses and indicators of myocardial function during maximal exercise in adolescent girls with anorexia nervosa. METHODS: Eight girls (mean age 16.3+/-2.7 years) who satisfied criteria for the diagnosis of anorexia nervosa underwent maximal cycle testing. Cardiac stroke volume and peak aortic velocity and mean acceleration of flow (markers of myocardial contractility) were assessed using Doppler echocardiography and compared to healthy control subjects. Gas exchange variables were measured using open circuit spirometry techniques. RESULTS: Resting and maximal heart rates were less in the patients, and maximal oxygen uptake was significantly lower than controls. Maximal stroke index was greater in the patients than controls, with a normal pattern of response to progressive exercise. Peak aortic velocity and mean acceleration of flow were similar in the two groups when adjusted for heart rate. CONCLUSION: Findings of low heart rate and aerobic fitness previously described in patients with anorexia nervosa were confirmed. However, there was no evidence of abnormal myocardial performance during maximal exercise testing.

Adolescent↗

PubMed2001

Hemodynamic responses to increasing cycle cadence in 11-year old boys: role of the skeletal muscle pump.

Previous studies in adults have indicated a rise in the metabolic cost of increasing cycling cadence at constant work rates. This study examined the metabolic and cardiovascular responses to pedaling rates of 41, 63, and 83 rpm at both zero-load and 50-watts load in 12 prepubertal boys. Increasing cadence from 41 to 83 rpm produced a 52.9% and 23.1% rise in gross energy expenditure in the two work conditions, respectively, despite the constant external work rate. This augmented energy expenditure was accounted for entirely by internal work, as no changes in work metabolic cost (difference between loaded and unloaded cycling) were observed as cadence increased. The rise in energy expenditure with higher pedaling rate during the zero load and 50 watt conditions was accompanied by increases in both heart rate and stroke volume. Arterial venous oxygen difference did not change with increased cadence but was significantly higher with loaded cycling, suggesting that skeletal muscle pump effectiveness is negatively influenced by increased load but not by increased pedaling rate.

Bicycling↗

PubMed2001

Dynamics of left ventricular diastolic filling during exercise: a Doppler echocardiographic study of boys 10 to 14 years old.

STUDY OBJECTIVE: Factors influencing diastolic filling of the left ventricle may serve as critical determinants of both maximal cardiac output and oxygen uptake. This study was conducted to assess diastolic filling dynamics of the left ventricle during progressive upright cycle exercise in children. METHODS: Twelve boys aged 10 to 14 years underwent cycle testing with determination of transmitral flow velocities and pressure gradients as well as cardiac stroke volume using Doppler echocardiography. RESULTS: Estimated diastolic filling period shortened from 0.479 +/- 0.043 s at rest to 0.138 +/- 0.015 s at peak exercise. The peak and mean transmitral pressure gradient rose fourfold from rest to peak exercise. Mitral flow volume per beat rose by only 40% and remained stable beyond mild-to-moderate intensity work. CONCLUSIONS: Increases in transmitral pressure gradient with exercise may serve principally to augment velocity of ventricular filling with the progressively shortening diastolic time period.

Adolescent↗

PubMed2000

Role of retinoic acid in lens regeneration.

Prompted by the actions of retinoids and their receptors in gene regulation, in the developing eye and especially in the lens, we have undertaken a detailed study to examine the effects of retinoids on urodele lens regeneration. First, we examined the effects of exogenous retinoids. It was found that exogenous retinoids had no significant effect on lens regeneration. However, when synthesis of retinoic acid was inhibited by disulfiram, or when the function of the retinoid receptors was impaired by using a RAR antagonist, the process of lens regeneration was dramatically affected. In the majority of the cases, lens regeneration was inhibited and lens morphogenesis was disrupted. In a few cases, we were also able to observe ectopic lens regeneration from places other than the normal site, which is from the dorsal iris. The most spectacular case was the regeneration of a lens from the cornea, an event possible only in premetamorphic frogs. These data show that inhibition of retinoid receptors is paramount for the normal course and distribution of lens regeneration. We have also examined expression of RAR-delta during lens regeneration. This receptor was expressed highly in the regenerating lens only. Therefore, it seems that this receptor is specific for the regeneration process and consequently such expression correlates well with the effects of RAR inhibition observed in our studies.

Animals↗

PubMed2000

Cardiovascular fitness in premenarcheal girls and young women.

Maximal oxygen uptake (VO2max) in females, expressed as ml x kg(-1) x min(-1), declines steadily during the first three decades of life. The contribution of diminished cardiovascular function to this apparent fall in aerobic fitness is unknown. Cardiac responses to maximal cycle exercise were compared in 24 premenarcheal females (mean age 11.7 years) and 17 young adult women (mean age 27.4 years) using Doppler echocardiography. Mean VO2max was 40 ml x kg(-1) x min(-1) and 34.7 ml x kg(-1) x min(-1) in the girls and women, respectively (p < 0.05). When VO2max was expressed relative to allometrically-derived mass(0.52), however, no significant difference was observed in aerobic fitness between the two groups. Similar allometric analyses revealed no significant differences in average maximal cardiac output (10.50 vs 10.07 L x min(-1) BSA(-1.11) for girls and women, respectively) nor maximal stroke volume (53 vs 56 ml BSA(-1.13) respectively). These findings suggest that 1) allometric scaling is important in eliminating the effects of body size on VO2max, 2) body dimension differences can account for variations in VO2 in young females, and 3) cardiac functional reserve is similar in premenarcheal girls and young adult women.

Adolescent↗

PubMed2000

Cardiac responses to progressive exercise in normal children: a synthesis.

UNLABELLED: The cardiac responses to exercise are influenced by a complex interplay of changes in diastolic filling, intrinsic myocardial contractility, heart rate, and ventricular afterload. PURPOSE: To characterize these responses in children, findings are reported from two studies utilizing Doppler echocardiographic assessment of stroke volume and cardiac output during maximal upright and semisupine cycle exercise. METHODS: In study 1, stroke volume, heart rate, and peak aortic velocity were assessed during upright cycle exercise to exhaustion in 39 sixth-grade boys. In study 2, similar methods were used to examine cardiac responses to semisupine exercise with measurement of left ventricular dimensions by two-dimensional echocardiography. RESULTS: The findings support patterns similar to that previously described in adults, with an initial rise in stroke volume reaching a plateau at mild-moderate exercise intensities. CONCLUSIONS: The observations in these two studies also suggest 1) peripheral vasodilatation plays an important role in the early rise in stroke volume, 2) increasing heart rate acts to maintain a stable stroke volume and left ventricular diastolic dimension at high workloads, and 3) improvements in contractility serve to maintain stroke volume as the systolic ejection period shortens.

Adolescent↗

PubMed2000

Cardiac responses to exercise in competitive child cyclists.

PURPOSE: Cardiovascular responses to exercise in highly trained child endurance athletes have not been well-defined. This study compared hemodynamic responses with progressive cycle exercise in seven competitive child cyclists (mean age 11.9 yr) compared with 39 age-matched untrained boys. METHODS: Doppler echocardiography and gas exchange variables were utilized to assess cardiovascular changes during submaximal and maximal exercise. RESULTS: Mean VO2max was 60.0 (+/-6.0) and 47.0 (+/-5.8) mL x kg(-1) x min(-1) in the cyclists and nonathletes, respectively. At rest and maximal exercise, the cyclists demonstrated greater stroke index than the untrained subjects (resting mean 59 (+/-6) vs 44 (+/-9) mL x m(-2); maximal mean 76 (+/-6) vs 60 (+/-11) mL x m(-2)), but the ratio of maximal:rest stroke index was similar in both groups (1.31 for cyclists, 1.41 for nonathletes). Both groups showed a plateau in stroke volume beyond low-intensity work levels. No significant difference was observed in maximal arteriovenous oxygen difference. CONCLUSIONS: These findings indicate that 1) maximal stroke volume is the critical determinant of the high VO2max in child cyclists and 2) factors that influence resting stroke volume are important in defining VO2max differences between child endurance athletes and untrained boys.

Bicycling↗

PubMed2000

Influence of cardiac functional capacity on gender differences in maximal oxygen uptake in children.

OBJECTIVE: To examine the role of gender differences in cardiac functional capacity in explaining higher mean values for maximal oxygen uptake (VO(2)max) in boys than in girls. DESIGN: Comparative group exercise testing. SETTING: Pediatric exercise testing laboratory. SUBJECTS: Twenty-five prepubertal boys (mean [+/- SD] age, 12 +/- 0.4 years) and 24 premenarcheal girls (mean age, 11.7 +/- 0.5 years). INTERVENTIONS: Maximal incremental upright cycle exercise. MEASUREMENTS AND RESULTS: Mean values for VO(2)max were the following: boys, 47.2 +/- 6.1 mL/kg/min; and girls, 40.4 +/- 5.8 mL/kg/min (16.8% difference; p < 0.05). The average maximal stroke index with Doppler echocardiography was 62 +/- 9 mL/m(2) for boys and 55 +/- 9 mL/m(2) for girls (12.7% difference; p < 0.05). No significant gender differences were seen in maximal heart rate or arterial venous oxygen difference. When VO(2)max and maximal stroke volume (SV) were expressed relative to lean body mass, gender differences declined but persisted, falling to 6.2% and 5.2%, respectively. CONCLUSIONS: These findings indicate that differences in SV as well as in body composition contribute to gender-related variations in VO(2)max during childhood. Whether this reflects small gender differences in relative heart size or dynamic factors influencing ventricular preload and contractility during exercise is unknown.

Body Composition↗

PubMed1999

One-mile run performance and cardiovascular fitness in children.

BACKGROUND: Endurance run tests are administered in schools to assess cardiovascular fitness, defined in the laboratory as maximum oxygen consumption. OBJECTIVE: To examine the validity of this concept, assessing the influences of body fat and maximum values of oxygen consumption per unit time, stroke volume, heart rate, and arteriovenous oxygen difference on 1-mile (1.6-km) run time in healthy sixth-grade boys. STUDY DESIGN: Subjects were 36 boys with a mean (SD) age of 12.2 (0.5) years. The relationship was examined between body fat content (estimated by skinfold measurements) and maximum oxygen consumption per kilogram and cardiac variables (during maximum cycle testing) with 1-mile run velocity. RESULTS: Body fat content and maximum oxygen consumption per kilogram (independent of body fat) accounted for 31% and 28% of the variance in run velocity, respectively. Stroke volume was the only component of maximum oxygen consumption that related to run performance. CONCLUSIONS: These findings suggest that cardiovascular fitness and body fat content contribute equally to 1-mile run time in healthy boys and together account for only 60% of the variance in performance on this endurance fitness test. Consequently, 1-mile run performance in children may not serve as a strong indicator of cardiovascular fitness.

Adipose Tissue↗

PubMed1999

Cardiovascular responses to exercise in children and adolescents with myocardial dysfunction.

OBJECTIVES: The objective of this study was to understand the expected hemodynamic responses to exercise in children and adolescents with myocardial dysfunction. METHODS AND RESULTS: With the use of Doppler and M-mode echocardiography, cardiovascular changes during maximal semisupine exercise in 11 patients (7 to 17 years old) with myocardial dysfunction were compared with those of a healthy control group (n = 11). Endurance fitness and mean values for maximal cardiac index, stroke index, heart rate, peak aortic velocity, and left ventricular shortening fraction were all significantly lower in the patients (P <.05). Stroke volume rose at the onset of exercise in both groups; whereas values were subsequently stable in the control subjects, stroke volume declined at high-intensity exercise in the patients. CONCLUSIONS: These findings imply that augmented myocardial contractility is necessary to sustain stroke volume during exercise. Moreover, the results suggest that pattern of stroke volume response to exercise may serve as a useful marker of myocardial function in children with heart disease.

Adolescent↗

PubMed1998

Cardiac responses to exercise in child distance runners.

Cardiovascular responses to exercise in trained endurance child athletes have been largely unexplored. Doppler echocardiography was utilized to compare cardiac variables during progressive upright cycle exercise to exhaustion in trained male prepubertal distance runners (n = 8) and untrained control boys (n = 14). Athletes demonstrated a greater maximal stroke index and cardiac index. Stroke volume rose progressively with increasing workloads in the runners but remained stable beyond low intensities in the non-athletes. No significant differences in stroke volume were observed between the two groups at rest. This contrasts with the greater resting stroke volumes typically seen in adult endurance athletes compared to non-athletes. Likewise, values for maximal stroke index were less in the child runners than those typically seen in trained adults. This study demonstrated that the stroke volume response to exercise differs in boy runners compared to non-athletes. The findings also suggest quantitative differences in such responses between prepubertal and young adult athletes.

Adolescent↗

PubMed1998

Comparison of multiple prediction models for ambulation following spinal cord injury.

Few studies have properly compared predictive performance of different models using the same medical data set. We developed and compared 3 models (logistic regression, neural networks, and rough sets) in the in prediction of ambulation at hospital discharge following spinal cord injury. We used the multi-center Spinal Cord Injury Model System database. All models performed well and had areas under the receiver operating characteristic curve in the 0.88-0.91 range. All models had sensitivity, specificity, and accuracy greater than 80% at ideal thresholds. The performance of neural network and logistic regression methods was not statistically different (p = 0.48). The rough sets classifier performed statistically worse than either the neural network or logistic regression models (p-values 0.002 and 0.015 respectively).

Acute Disease↗

PubMed1998

Building manageable rough set classifiers.

An interesting aspect of techniques for data mining and knowledge discovery is their potential for generating hypotheses by discovering underlying relationships buried in the data. However, the set of possible hypotheses is often very large and the extracted models may become prohibitively complex. It is therefore typically desirable to only consider the "strongest" hypotheses, so that smaller models can be obtained that also retain good classificatory capabilities. This paper outlines how rule-based classifiers based on rough set theory and Boolean reasoning that are both small and perform well can be developed. Applied to a real-world medical dataset, the final models are shown to exhibit good performance using only a subset of the available information. Furthermore, the number of resulting rules is low and enables practical a posteriori inspection and interpretation of the models.

Classification↗

PubMed1997

Gender effects on submaximal energy expenditure in children.

Previous studies have suggested that submaximal energy expenditure relative to body mass during weight-bearing exercise may be greater in boys compared to girls. This two-part study examined a) gender-related five-year longitudinal changes in submaximal walking economy and b) gross, net, and delta muscle work efficiency during submaximal cycle exercise in a cross-sectional analysis of boys and girls. In the longitudinal study, the influence of pre-exercise metabolic expenditure, stride frequency, and substrate utilization (by RER) on changes in economy were examined. During the five years, mean VO2 per kg during submaximal treadmill walking (measured at 8% slope, 3.25 mph) decreased 16% in girls and 13% in boys (p > 0.05 for gender). Likewise, no significant gender differences were observed in decline of stride frequency over time. RER values were similar between sexes except in the final two years when girls had significantly greater values than the boys. No gender-related differences were observed in any measure of muscle work efficiency. This study failed to reveal significant gender differences in utilization of energy during submaximal exercise in children.

Child↗

PubMed1997

Cardiac responses to maximal upright cycle exercise in healthy boys and men.

Previous investigations have indicated that children demonstrate a lower cardiac output at a given oxygen uptake during exercise compared with adults. This study compared cardiac responses with maximal upright cycle exercise in 15 boys (mean age 10.9 yr) and 16 men (mean age 30.7 yr) to determine whether this observation reflects differences in size or age-related influences on myocardial function. Stroke volume, aortic peak velocity, and systolic ejection time were measured to peak exercise in all subjects using Doppler ultrasound techniques. No significant differences were observed in resting, submaximal, or peak mean values for these variables relative to body size between the boys and men. Average values for peak stroke index, cardiac index, and peak aortic velocity were 59 (+/-11) mL.m-2, 11.33 (+/-2.32) L.min-1.m-2, and 152 (+/-30) cm.s-1, respectively, for the boys. Respective values for the men were 61 (+/-14) mL.m-2, 11.08 (+/-2.52) L.min-1.m-2, and 144 (+/-24) cm.s-1 (P > 0.05). This study failed to demonstrate evidence of impaired cardiac responses to maximal exercise in prepubertal boys compared with that in adult males.

Adult↗

PubMed1997

Cardiac effects of a competitive road race in trained child runners.

BACKGROUND: Animal studies and investigations of adult endurance athletes indicate a transient depression of myocardial function after prolonged high-intensity exercise. PURPOSE: To determine whether a similar decrease is observed in child distance runners after a 4-km competitive road race. METHODS: Anthropometric measures, resting M-mode echocardiograms, maximal cycle exercise tests with estimation of cardiac output, and electrocardiograms were performed before a 4-km road race in nine run-trained boys (mean age, 12.2 years). Weight and resting echocardiogram and electrocardiogram were assessed immediately after the race. The entire test battery was repeated 24 hours later. RESULTS: Small but significant decreases in mean body weight and left ventricular end-diastolic dimension were observed immediately after the race, but there were no changes in shortening fraction. These findings are consistent with the effects of dehydration. Measurements returned to prerace values by 24 hours of recovery. Peak work capacity, maximal stroke volume, and maximal cardiac output were similar on prerace and 24-hour-postrace testing. No electrocardiographic abnormalities were observed. CONCLUSIONS: No adverse cardiac effects were observed from a competitive 4-km road race in male child distance runners.

Adolescent↗

PubMed1991

Autoantibody to heat-shock protein 90 can mediate protection against systemic candidosis.

Epitope mapping shows that patients recovering from systemic infection with Candida albicans produce antibodies against both fungal-specific and conserved epitopes of the heat-shock protein (hsp) 90. In a mouse model of systemic candidosis, mortality was halved by prior administration of sera from two infected patients containing antibodies to hsp 90. One of these patients had no other candidal antibodies detectable on immunoblotting. The protective effect was mediated by the immunoglobulin fraction of the immune serum. It was not observed with a normal human serum. A mouse monoclonal antibody raised against one of the conserved peptide epitopes suggested that an autoantibody to hsp 90 could mediate protection against systemic candidosis in the animal model.

Animals↗