Biomedical subjects

Ellen Dawson

Publications and source records attributed to Ellen Dawson.

11 recordsLinked to original sources

PubMed2006

Beta-adrenergic receptor desensitization in man: insight into post-exercise attenuation of cardiac function.

Desensitization of the beta-adrenoreceptors (beta-AR) may contribute to a post-exercise reduction in left ventricular (LV) function. However, attenuation of the chronotropic and inotropic responses to a beta-AR agonist may depend upon alterations in parasympathetic tone. Furthermore, changes in cardiac output and LV diastolic function in response to a beta-AR agonist, pre- to post-prolonged exercise, remain unclear. Seven trained males (mean+/-s.d., age 27+/-6 years) performed 4 h of ergometer rowing. Peak heart rate (HR) and LV systolic and diastolic functional responses to incremental isoproterenol (isoprenaline) infusion (2, 4 and 6 microg kg min-1) were assessed after vagal blockade (glycopyrrolate, 1.2 mg). LV systolic function was assessed by the pressure/volume ratio (systolic blood pressure/end systolic volume) and , whilst diastolic function was evaluated as peak early and late transmitral filling velocities. Following exercise, the pressure/volume ratio decreased by 25% (P<0.05), whereas was unchanged (P>0.05). The early/late filling ratio was reduced by 36% after exercise, due to an elevation in late LV filling (P<0.01). The increase in HR response to isoproterenol infusion was blunted post-exercise at both 4 and 6 microg kg min-1 (127+/-7 and 132+/-6 beats min-1) compared with pre-exercise (138+/-8 and 141+/-12 beats min-1, P<0.05). Additionally, the pressure/volume ratio and were blunted post-exercise in response to isoproterenol (P<0.05). In contrast, diastolic function was similar before and after exercise during isoproterenol infusion (P>0.05). Desensitization of the beta-AR contributes to an attenuated left ventricular systolic but not diastolic function following prolonged exercise.

Adrenergic beta-Agonists↗

PubMed2006

Longitudinal and radial systolic myocardial tissue velocities after prolonged exercise.

We assessed segmental and global left ventricular (LV) systolic function using tissue Doppler imaging (TDI) in 30 subjects (age: 18-62 y) before and after a marathon race. Longitudinal plane systolic (S') TDI velocities were assessed at 5 sites on the mitral annulus and radial plane S' velocities were assessed at the LV septal and free wall in a subsample (n = 9). Heart rate (HR) and LV diastolic internal dimension were also assessed before (pre) and immediately after (post) the race. Pre-post changes in all variables were analysed by repeated measures analysis of variance (ANOVA). Delta scores for TDI data were correlated with alterations in indices of LV loading, as well as with age and finishing time. Segmental longitudinal and radial TDI velocities were not significantly different pre to post race (p > 0.05), which resulted in no change in mean S' velocities (longitudinal: pre 17.0 +/- 3.4 cm x s(-1), post 17.4 +/- 4.0 cm x s(-)1; radial: pre 13.0 +/- 5.4 cm x s(-1), post 14.2 +/- 7.1 cm x s(-1); p > 0.05). Any pre-post changes in TDI data were not related to an elevated post race HR (r = 0.15, p > 0.05), a decreased post race LV internal dimension in diastole (r = 0.10, p > 0.05), age (r = -0.25, p > 0.05), or finishing time (r = -0.13, p > 0.05). Our data suggest that marathon running does not induce any segmental or global depression in LV systolic function.

Adolescent↗

PubMed2005

Mitral annular myocardial velocity assessment of segmental left ventricular diastolic function after prolonged exercise in humans.

We assessed segmental and global left ventricular (LV) diastolic function via tissue-Doppler imaging (TDI) as well as Doppler flow variables before and after a marathon race to extend our knowledge of exercise-induced changes in cardiac function. Twenty-nine subjects (age 18-62 year) volunteered to participate and were assessed pre- and post-race. Measurements of longitudinal plane TDI myocardial diastolic velocities at five sites on the mitral annulus included peak early myocardial tissue velocity (E'), peak late (or atrial) myocardial tissue velocity (A') and the ratio E'/A'. Standard pulsed-wave Doppler transmitral and pulmonary vein flow indices were also recorded along with measurements of body mass, heart rate, blood pressures and cardiac troponin T (cTnT), a biomarker of myocyte damage. Pre- to post-race changes in LV diastolic function were analysed by repeated measures ANOVA. Delta scores for LV diastolic function were correlated with each other and alterations in indices of LV loading. Diastolic longitudinal segmental and mean TDI data were altered post-race such that the mean E'/A' ratio was significantly depressed (1.51 +/- 0.34 to 1.16 +/- 0.35, P < 0.05). Changes in segmental and global TDI data were not related to an elevated post-race HR, a decreased post-race pre-load or an elevated cTnT. The pulsed wave Doppler ratio of peak early transmitral flow velocity (E)/peak late (or atrial) flow velocity (A) was also significantly reduced post-race (1.75 +/- 0.46 to 1.05 +/- 0.30, P < 0.05); however, it was significantly correlated with post-race changes in heart rate. The lack of change in E/E' from pre- to post-race (3.4 +/- 0.8 and 3.3 +/- 0.7, respectively) suggests that the depression in diastolic function is likely to be due to altered relaxation of the left ventricle; however, the exact aetiology of this change remains to be determined.

Adolescent↗

PubMed2005

Impact of marathon running on cardiac structure and function in recreational runners.

The present study examined the relationship between LV (left ventricular) function, markers of cardiac-specific damage and markers of oxidative stress in recreational runners following a marathon. Runners (n=52; 43 male and nine female; age, 35+/-10 years; height, 1.74+/-0.08 m; body mass, 75.9+/-8.9 kg) were assessed pre- and immediately post-marathon. LV function was assessed using standard M-mode two-dimensional Doppler echocardiography and TDI (tissue-Doppler imaging) echocardiography. Serum was analysed for cTnT (cardiac troponin-T), TEAC (Trolox equivalent antioxidant capacity; a measure of total antioxidant capacity), MDA (malondealdehyde) and 4-HNE (4-hydroxynonenal). A strong relationship was observed between standard and TDI echocardiography for all functional measures. Diastolic function was altered post-marathon characterized by a reduction in E (peak early diastolic filling: 0.79+/-0.11 compared with 0.64+/-0.16 cm/s; P<0.001), an increase in A (peak late diastolic filling: 0.48+/-0.11 compared with 0.60+/-0.12 cm/s; P<0.001) and a resultant decrease in E/A (ratio of E to A; 1.71+/-0.48 compared with 1.10+/-0.31; P<0.001). Ejection fraction remained unchanged post-marathon. Thirty-two runners presented with cTnT values above the lower limit of detection for the assay (0.01 microg/l), and 20 runners presented post-marathon with cTnT values above the acute myocardial infarction cut-off value (0.05 microg/l). No significant correlations were observed between cTnT and any functional measurements. MDA (2.90+/-1.58 compared with 3.59+/-1.47 micromol/l) and TEAC (1.80+/-0.12 compared with 1.89+/-0.21 mmol/l) were significantly increased post-marathon, but were unrelated to changes in function or cTnT. In conclusion, the present study demonstrated a reduction in diastolic function and widespread evidence of minimal cardiac damage following a marathon in recreational runners. The mechanism(s) underpinning the altered function and appearance of cTnT appear unrelated to reactive oxygen species.

Adolescent↗

PubMed2004

Altered cardiac function and minimal cardiac damage during prolonged exercise.

PURPOSE: The purpose of the present study was to examine markers of cardiac function and cardiac damage during a simulated half-ironman triathlon in highly trained athletes. METHODS: Nine highly trained male triathletes volunteered for the study (mean +/- SD; age: 33 +/- 3 yr; height: 1.8 +/- 0.1 m; body mass: 77.7 +/- 3.2 kg). The subjects completed a half-ironman triathlon; 1.9-km swim in an indoor 20-m pool, followed by a laboratory-based 90-km cycle and 21.1-km run. Venous blood samples were drawn and echocardiographic assessment completed before the start of exercise, immediately after each stage, and 24 h postexercise. Serum was analyzed for total creatine kinase activity (CK), creatine kinase isoenzyme MB(mass) (CK-MB(mass)), and cardiac troponin T (cTnT). Left ventricular systolic (stroke volume, and systolic blood pressure/end systolic volume ratio (SBP/ESV)) and diastolic (ratio of early [E] to late [A], ventricular filling E:A) measurements were derived from echocardiographic assessment. RESULTS: The mean completion time of the half-ironman triathlon was 301 +/- 28 min. Left ventricular contractility (SBP/ESV) was significantly reduced after the half-ironman triathlon (P < 0.05). A significant reduction in E:A was observed after the run phase of the half-ironman triathlon (P < 0.05). Significant increases in CK and CK-MB(mass) were observed during and after the half-ironman triathlon (P < 0.05), and cTnT was elevated in four subjects over the course of the half-ironman triathlon. CONCLUSIONS: The physiologic stress imposed by the half-ironman triathlon resulted in a reduced left ventricular contractility and altered diastolic filling, coupled with minimal cardiac damage in a number of highly trained male triathletes. The mechanisms behind such altered cardiac function and cardiac damage after prolonged exercise are yet to be elucidated.

Adult↗

PubMed2004

Effects of massage on limb and skin blood flow after quadriceps exercise.

PURPOSE: At present, there is little scientific evidence that postexercise manual massage has any effect on the factors associated with the recovery process. The purpose of this study was to compare the effects of massage against a resting control condition upon femoral artery blood flow (FABF), skin blood flow (SKBF), skin (SKT), and muscle (MT) temperature after dynamic quadriceps exercise. METHODS: Thirteen male volunteers participated in 3 x 2-min bouts of concentric quadriceps exercise followed by 2 x 6-min bouts of deep effleurage and pétrissage massage or a control (rest) period of similar duration in a counterbalanced fashion. Measures of FABF, SKBF, SKT, MT, blood lactate concentration (BLa), heart rate (HR), and blood pressure (BP) were taken at baseline, immediately after exercise, as well as at the midpoint and end of the massage/rest periods. Data were analyzed by two-way ANOVA. RESULTS: Significant main effects were found for all variables over time due to effects of exercise. Massage to the quadriceps did not significantly elevate FABF (end-massage 760 +/- 256 vs end-control 733 +/- 161 mL x min(-1)), MT, BL, HR, and BP over control values (P < 0.05). SKBF (end-massage 150 +/- 49 vs end control 6 +/- 4 au) SKT (end-massage 32.2 +/- 0.9 vs end-control 31.1 +/- 1.3degreesC) were elevated after the application of massage compared with the control trial (P < 0.05). CONCLUSION: From these data it is proposed that without an increase in arterial blood flow, any increase in SKBF is potentially diverting flow away from recovering muscle. Such a response would question the efficacy of massage as an aid to recovery in postexercise settings.

Adult↗

PubMed2004

The impact of prolonged exercise in a cold environment upon cardiac function.

PURPOSE: The purpose of the present study was to examine the impact of cold exposure coupled with prolonged exercise upon postexercise left ventricular (LV) function and markers of myocardial damage. METHODS: colon; Eight highly trained male athletes (mean +/- SD; age: 28.2 +/- 8.8 yr; height: 1.78 +/- 0.07 m; body mass: 74.9 +/- 7.6 kg; VO2max: 65.6 +/- 7.0 mL x kg(-1) x min(-1)) performed two 100-mile cycle trials, the first in an ambient temperature of 0 degrees C, the second in an ambient temperature of 19 degrees C. Echocardiographic assessment was completed and blood samples drawn before, immediately postexercise, and 24-h postexercise. Left ventricular systolic (stroke volume [SV], ejection fraction [EF], and systolic blood pressure/end systolic volume ratio [SBP/ESV]) and diastolic (early [E] to late [A] filling ratio [E:A]) parameters were calculated. Serum was analyzed for creatine kinase isoenzyme MB (CK-MBmass) and cardiac troponin T (cTnT). cTnT was analyzed descriptively whereas other variables were assessed using two-way repeated-measures ANOVA. RESULTS: No significant change was observed in systolic function across time or between trials. A significant difference between trials was observed in E:A immediately after exercise (1.4 +/- 0.4 [19 degrees C] vs 1.8 +/- 0.3 [0 degrees C]) (P < 0.05). CK-MBmass was significantly elevated immediately after exercise in both trials (P < 0.05). Positive cTnT concentrations were observed in two subjects immediately after the 19 degrees C trial (0.012 microg x L(-1) and 0.034 microg x L(-1)). CONCLUSIONS: Cycling 100 miles in an ambient temperature of 19 degrees C is associated with an acute change in diastolic filling that is not observed after prolonged exercise at 0 degrees C. Prolonged exercise is associated with minimal cardiac damage in some individuals; it appears that this is a separate phenomenon to the change in diastolic filling.

Adult↗

PubMed2004

Postexercise left ventricular function and cTnT in recreational marathon runners.

PURPOSE: To assess the impact of prolonged exercise on left ventricular (LV) function and the appearance of cardiac troponin T (cTnT) in older and recreational athletes. METHODS: Heart rate (HR), blood pressures, and cTnT were recorded in 35 subjects (age range 22-57 yr, finishing time 157-341 min) pre- and postrace. Echocardiograms (N = 26) assessed stroke volume (SV), ejection fraction (EF), sBP/LV end-systolic volume (sBP/ESV), diastolic filling (E:A ratio) as well as preload (LV internal dimension at end-diastole [LVIDd]) and afterload (LV wall stress). HR and core temperature were recorded in-event. Prepost changes in LV function were analyzed by repeated measures t-test. Delta scores for LV function and cTnT data were correlated with each other, age, finishing time, alterations in loading, and in-event data. RESULTS: SV was significantly decreased postrace (109 +/- 31 vs 85 +/- 25 mL, P < 0.05) likely due to a significant decrease in LVIDd (5.3 +/- 0.4 vs 4.9 +/- 0.5 cm, P < 0.05; r = 0.80, P < 0.05). LV wall stress was unchanged postrace (90 +/- 25 vs 89 +/- 27 g x cm(-2), P > 0.05). EF (70 +/- 12 vs.70 +/- 10%, P > 0.05) and sBP/ESV (3.7 +/- 2.9 vs 4.0 +/- 2.0, P > 0.05) did not change prepost race and were not related to age or finishing time (P > 0.05). E:A ratio was significantly reduced postrace (1.73 +/- 0.38 vs 1.41 +/- 0.25, P < 0.05) and could not be explained by an increased HR (56 +/- 9 vs 84 +/- 10, P < 0.05; r = 0.08, P > 0.05), a reduced LVIDd (r = 0.11, P > 0.05), age, finishing time, or in-event data. Postrace 26/33 subjects presented cTnT values in the range 0.024-0.080 microg x L(-1) that were not related to changes in LV function, loading, age, finishing time, or in-event data. CONCLUSION: No evidence of load-independent depression in LV systolic function was reported. Changes in cTnT and E:A were not related, and their etiology is uncertain.

Adult↗

PubMed2003

Does the human heart fatigue subsequent to prolonged exercise?

A reduction in left ventricular systolic and diastolic function subsequent to prolonged exercise in healthy humans, often called exercise-induced cardiac fatigue (EICF), has recently been reported in the literature. However, our current understanding of the exact nature and magnitude of EICF is limited. To date, there is no consensus as to the clinical relevance of such findings and whether such alterations in function are likely to impact upon performance. Much of the existing literature has employed field-based competitions. Whilst ecologically valid, this approach has made it difficult to control many factors such as the duration and intensity of effort, fitness and training status of subjects and environmental conditions. The impact of such variables on EICF has not been fully evaluated and is worthy of further research. To date, most EICF studies have been descriptive, with limited success in elucidating mechanisms. To this end, the assessment of humoral markers of cardiac myocyte or membrane disruption has produced contradictory findings partially due to controversy over the validity of specific assays. It is, therefore, important that future research utilises reliable and valid biochemical techniques to address these aetiological factors as well as develop work on other potential contributors to EICF such as elevated free fatty acid concentrations, free radicals and beta-adrenoceptor down-regulation. In summary, whilst some descriptive evidence of EICF is available, there are large gaps in our knowledge of what specific factors related to exercise might facilitate functional changes. These topics present interesting but complex challenges to future research in this field.

Cardiomyopathies↗

PubMed2002

The cardiospecificity of the third-generation cTnT assay after exercise-induced muscle damage.

PURPOSE: The purpose of the present study was to examine the cardiospecificity of cTnI and the new third-generation cTnT assay, in the presence of exercise-induced muscle damage in highly trained individuals, and to examine the impact of a maximal-ramping treadmill test on cardiac function. METHODS: Eight highly trained male triathletes (mean +/- SD; age: 29 +/- 9 yr; height: 1.79 +/- 0.10 m; body mass: 77 +/- 10 kg; .VO(2max): 67.4 +/- 6.3 mL.kg(-1).min(-1)) completed two bouts of exercise. On the first occasion, subjects completed a maximal-ramping treadmill test. On a separate occasion, the subjects completed 30 min of downhill running (15% gradient) at a speed equivalent to 70% of maximal running velocity attained during the maximal-ramping treadmill test. All subjects were assessed using ECG, echocardiography, and blood analysis. Measurements were taken at rest, immediately after, and 48 h postexercise for each bout of exercise. Echocardiographic analysis was used to determine left ventricular systolic and diastolic function. Blood samples were analyzed for markers of myocyte damage. RESULTS: Echocardiographic results indicated normal left ventricular function before and after both exercise bouts. Total CK and CKMB were significantly elevated 48 h after the downhill run. cTnT and cTnI were not elevated at any stage of the study. CONCLUSIONS: Neither the maximal-ramping treadmill test nor the 30-min downhill run produced cardiac dysfunction or myocardial damage in young, healthy trained subjects. The elevated total CK and CKMB within the downhill study are noncardiac in origin as demonstrated by the lack of cTnT and cTnI. The cTnI and new third-generation cTnT assays may be used to detect cardiac damage in the presence of elevated total CK and CKMB associated with exercise-induced skeletal muscle damage.

Adult↗

PubMed2002

Evaluation of a cardiac prevention and rehabilitation programme for all patients at first presentation with coronary artery disease.

BACKGROUND: A cardiac prevention and rehabilitation (CP&R) programme was established for patients following their first clinical episode of coronary heart disease and 1-year outcomes were evaluated against British targets for coronary prevention. METHODS: Patients were evaluated 1 year after participation and outcomes compared with patients in the same health district registered with a random half of general practitioners not eligible for the programme (internal reference group) and patients identified in other English centres which participated in the EUROASPIRE II survey (external reference group). RESULTS: Three hundred and eighteen patients (76% of 417 incident cases) attended for 1-year screening. Of those who participated in the programme 96/113 (85%) attended (Group 1); 152/194 (78%) attended from all those eligible for the programme (Group 2); 166/223 (74%) attended from those receiving usual care in the same health district (Group 3 - internal reference group). In the EUROASPIRE II survey (Group 4 - external reference group) 362/744 (58%) patients were screened. Current smoking at follow-up was Group 1, 8%, Group 2, 11%, Group 3, 13% and Group 4, 18%. Proportions with a BMI < 25 kg/m were 29%, 25%, 32%, 18%; BP < 140/90 mmHg 58%, 56%, 49%, 48%; total cholesterol < 5.0 mmol/l 60%, 54%, 43%, 46%; antiplatelet therapy 88%, 87%, 86%, 81%; beta-blocker therapy 48%, 46%, 46%, 44%; and lipid lowering therapy 56%, 51%, 36%, 69% respectively. CONCLUSIONS: A CP&R programme was associated with a majority of coronary patients, whether attending the programme or not, achieving the Joint British Society's recommended prevention targets within the same health district. Specifically, a higher proportion of programme patients reached the cholesterol target of <5.0 mmol/l compared with both usual care and other centres elsewhere. This was achieved by using more lipid lowering therapy compared with usual care in the same health district, but less than other centres outside the health district. The overall results for the whole health district show a higher standard of preventive care compared with contemporary EUROASPIRE II results from other health districts in England.

Body Mass Index↗