Biomedical subjects

Keith George

Publications and source records attributed to Keith George.

25 records · Page 2Linked to original sources

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

Combined oral contraceptives do not influence post-exercise hypotension in women.

The aim of the present study was to examine the pattern of cardiovascular recovery from exercise in 15 women (age, 20.3 +/- 1.4 years; body mass, 61.5 +/- 4.3 kg) across two phases of oral contraceptive (OC) use: 21 days of consumption and 7 days of withdrawal. Cardiovascular recovery was measured in the supine position for 60 min following 30 min of exercise at 60% maximal rate of oxygen consumption (VO2,max). Central and peripheral haemodynamics were assessed during consumption and withdrawal of the OC pill using occlusion plethysmography, Doppler flowmetry and echocardiography. Significant hypotension occurred following exercise (P < 0.05), returning to baseline values after 60 min. The peak hypotension occurred 5 min into recovery. Cardiac output and heart rate were elevated for 60 min following exercise (P < 0.05), whilst stroke volume remained at baseline values. Heart rate was greater throughout recovery during consumption compared to withdrawal (P < 0.05); however, although there was a trend for greater responses during consumption, phase of OC use did not affect the other central cardiovascular variables (P > 0.05). Post-exercise blood flow parameters were not significantly affected by exercise or OC phase; however, calf blood flow was greater, and resistance to flow lower during consumption (P > 0.05). The pattern of post-exercise fluctuations in cardiovascular parameters may differ from those seen in men, whilst oestrogen variation may influence research findings.

Adult↗

PubMed1999

Interacting Constraints and the Emergence of Postural Behavior in ACL-Deficient Subjects.

In this study, the authors examined how task, informational, and sensorimotor system constraints influence postural control. Postural behavior of subjects with (n = 15) and without (n = 15) a key sensorimotor system constraint, anterior cruciate ligaments (ACLs) in 1 knee, was examined during 1- and 2-legged stance with and without vision. Postural control was assessed on a commonly used postural sway meter and on a dynamic stabilometer. Data on postural sway characteristics were obtained for 30 s under 6 different conditions: standing, with eyes open and closed, on both legs, on the injured leg, and on the noninjured leg. The interaction of task, informational, and sensorimotor constraints was observed only on the dynamic stabilometer and not the postural sway meter. Vision was the most important informational constraint on postural control for subjects on the dynamic stabilometer, particularly for the ACL-deficient group standing on the injured leg. Under more static task constraints, ACL deficiency did not prove a significant disadvantage, because vision was confirmed as a significant source of exproprioceptive information. The results support the functionality of using dynamic tasks such as a stabilometer in assessing postural behavior of subjects with sensorimotor system constraints.

Journal Article↗

PubMedDate not supplied

Effect of weightlifting upon left ventricular function and markers of cardiomyocyte damage.

The purpose of this study was to assess left ventricular (LV) function and biochemical markers of myocyte after prolonged weightlifting activity. Seventeen male subjects (age range 20-34 years) performed a 90-min bout of weightlifting exercise consisting of three sets of 8-10 repetitions at 70% one-repetition maximum. Body mass, heart rate, systolic blood pressure (SBP) and echocardiographically determined indices of LV loading (LV internal diameter during diastole, LV meridonial wall stress), systolic function (stroke volume (SV), ejection fraction (EF), end-systolic pressure volume relationship; SBP/ESV) and diastolic filling (ratio of early to late; E:A) were obtained pre-exercise, immediately after and 24 h post-exercise. A 5-ml venous blood sample was obtained for the assessment of cardiac troponin T (cTnT) via third generation electrochemiluminescence assay. Data were assessed via one-way ANOVA and Pearson's correlation. Although SV declined (80.9 +/- 18.3 vs. 66.9 +/- 17.2, p < 0.05) there was no alteration in LV contractility (EF 62 +/- 6 vs. 59 +/- 7; SBP/ESV 3.51 +/- 1.4 vs. 3.51 +/- 1.4, p > 0.05). The E:A ratio was significantly decreased following exercise (1.78 +/- 0.41 vs. 1.33 +/- 0.37, p < 0.05). This decrease was not fully explained by loading conditions (r2 = 0.05 to 0.24). All values returned to baseline 24 h post-exercise. No cTnT was reported in any of the blood samples. In conclusion, there was no significant evidence of any LV contractile depression and no cTnT was observed post exercise. The small reduction in diastolic filling could not be explained by changes in haemodynamic loading or the post-exercise elevation in heart rate.

Adult↗