Biomedical subjects

Demetra D Christou

Publications and source records attributed to Demetra D Christou.

7 recordsLinked to original sources

PubMed2005

Fatness is a better predictor of cardiovascular disease risk factor profile than aerobic fitness in healthy men.

BACKGROUND: The prevalence of cardiovascular disease (CVD) is partly attributable to an inactive and/or overweight population. However, the independent association of body fatness and aerobic fitness with CVD risk factors is uncertain. We sought to determine whether fatness or fitness better predicted traditional CVD risk factors in men with broad fatness, aerobic fitness, and age ranges using 3 expressions of adiposity. METHODS AND RESULTS: In 135 carefully screened healthy men, we measured 18 established CVD risk factors, body mass index, total percent body fat, waist circumference, and maximal aerobic capacity. Body mass index, percent body fat, and waist circumference were consistently associated with all metabolic risk factors (r=-0.44 to 0.51, P<0.05) after partialling out the effects of aerobic fitness and age. Body mass index and waist circumference were also independently associated with selective hemodynamic risk factors (r=0.20 to 0.30, P< or =0.01). In contrast, aerobic fitness was independently associated with only selective metabolic risk factors (r=-0.21 to 0.19, P<0.05) and was not associated with any hemodynamic risk factors (P>0.05). Both aerobic fitness and body fatness were independently associated with selective hemostatic risk factors (r=-0.22 to -0.26, P< or =0.01; r=-0.32 to 0.48, P<0.05, respectively). Overall, fatness was more strongly and consistently associated with CVD risk factors than aerobic fitness. CONCLUSIONS: Body fatness is a better predictor of CVD risk factor profile than aerobic fitness in healthy men. Although habitual physical activity is an effective strategy for preventing CVD, elevated body fatness is associated with an adverse CVD risk factor profile independently of aerobic fitness.

Adipose Tissue↗

PubMed2005

Women have lower tonic autonomic support of arterial blood pressure and less effective baroreflex buffering than men.

BACKGROUND: Short-term and tonic regulation of arterial blood pressure (BP) differ in premenopausal women and men of similar age. The autonomic nervous system (ANS) plays a critical role in BP regulation. METHODS AND RESULTS: To test the hypothesis that women have lower tonic ANS support of BP (reduction in intra-arterial BP during acute ganglionic blockade [GB] with intravenous trimethaphan) and less effective baroreflex buffering (BRB) of BP (potentiation of the systolic BP [SBP] response to bolus phenylephrine during versus before GB) than men, 51 healthy adults, 22 premenopausal women (aged 28+/-1 years, mean+/-SE) and 29 men (aged 27+/-1 years), were studied. Women had lower baseline SBP and plasma catecholamine concentrations than men (P<0.05). Tonic ANS support of BP was approximately 50% to 65% lower in the women (P<0.001). The reductions in BP during GB were related to baseline plasma catecholamine concentrations (r=-0.31 to -0.41, P<0.05). Acute BRB of BP was 47% smaller in the women (3.3+/-0.5 versus 6.3+/-0.9, P=0.006) and was related to the SBP responses to phenylephrine before GB (R2=0.71, P<0.0001). Systemic alpha1-adrenergic vascular responsiveness (SBP response to bolus phenylephrine during GB) was not different (women 21.5+/-2 mm Hg versus men 18.6+/-2 mm Hg, P=0.3). CONCLUSIONS: Premenopausal women have lower tonic sympathoadrenal activity-related ANS support of BP and less effective BRB of BP than men of similar age. The lower tonic ANS support of BP could contribute to the lower chronic BP levels of premenopausal women, whereas attenuated BRB of BP may help explain less effective BP regulation in women in response to vasoactive drugs and acute stress.

Adaptation, Physiological↗

PubMed2004

Increased abdominal-to-peripheral fat distribution contributes to altered autonomic-circulatory control with human aging.

Autonomic nervous system (ANS) control of the circulation is altered with aging in adult humans. Similar changes are observed in obesity, particularly abdominal obesity. To determine whether age-associated differences in ANS-circulatory function can be partially explained by increased body fatness, we examined ANS function and three expressions of adiposity (total body fat, abdominal body fat, and abdominal-to-peripheral body fat distribution; dual-energy X-ray absorptiometry) in 43 healthy men: 27 young (25 +/- 1 yr) and 16 older (65 +/- 1). ANS functions assessed included 1) autonomic support of arterial blood pressure (BP; radial artery catheter), i.e., the reduction in BP during versus before acute ganglionic blockade (GB; intravenous trimethaphan); 2) baroreflex buffering, i.e., the increase in systolic BP with continuous incremental and bolus infusions of phenylephrine during versus before GB; 3) cardiovagal baroreflex sensitivity (Oxford technique); and 4) heart rate variability (time- and frequency-domain analyses). Covarying for abdominal-to-peripheral fat distribution reduced or abolished age-related differences in ANS support of BP, cardiovagal baroreflex sensitivity, and heart rate variability but did not affect age-related differences in baroreflex buffering. Covarying for abdominal and total fat had small selective or no effects on age-associated differences in autonomic-circulatory control. Abdominal-to-peripheral fat distribution explains a significant portion of the variance in a number of autonomic-circulatory functions attributable to aging. Therefore, the development of this fat pattern may contribute to several changes in ANS-cardiovascular function observed with aging. These results may help explain how changes in body fat distribution with advancing age are linked to impairments in circulatory control.

Abdomen↗

PubMed2004

High energy flux mediates the tonically augmented beta-adrenergic support of resting metabolic rate in habitually exercising older adults.

The sympathetic nervous system contributes to resting metabolic rate (RMR) via beta-adrenergic receptor (beta-AR) stimulation of energy metabolism. RMR and beta-AR support of RMR are greater in habitually exercising compared with sedentary older adults possibly due to greater energy flux (magnitude of energy intake and energy expenditure during energy balance). In 10 older adults regularly performing aerobic endurance exercise (mean +/- se, 66 +/- 1 yr) compared with baseline, a reduction in energy flux (via abstention of exercise and proportional reduction in dietary intake) decreased (P < 0.05) energy expenditure (7746 +/- 440 vs. 9630 +/- 662 kJ.d(-1)), caloric intake (7808 +/- 431 vs. 9433 +/- 528 kJ.d(-1)), RMR (5192 +/- 167 vs. 5401 +/- 209 kJ.d(-1)), and skeletal muscle sympathetic nervous system activity (36 +/- 2 vs. 42 +/- 2 bursts.min(-1)). Significant beta-AR support of RMR was observed at baseline (167 +/- 42 kJ.d(-1)) but not during reduced energy flux. The change in RMR from baseline to reduced energy flux was related to the corresponding change in beta-AR support of RMR (r = 0.77, P = 0.009). No changes were observed in seven time controls (69 +/- 3 yr) who maintained energy flux. High energy flux is a key mechanism contributing to the elevated RMR and beta-AR support of RMR in habitually exercising older adults. Maintenance of high energy flux via regular exercise may be an effective strategy for maintaining energy expenditure and preventing age-associated obesity.

Aged↗

PubMed2003

Baroreflex buffering in sedentary and endurance exercise-trained healthy men.

Baroreflex buffering plays an important role in arterial blood pressure control. Previous reports suggest that baroreflex sensitivity may be altered in endurance exercise-trained compared with untrained subjects. It is unknown, however, if in vivo baroreflex buffering is altered in the endurance exercise-trained state in humans. Baroreflex buffering was determined in 36 healthy normotensive men (18 endurance exercise-trained, 41+/-5 [SEM] years; 18 untrained, 41+/-4 years) by measuring the potentiation of the systolic blood pressure responses to a phenylephrine bolus and to incremental phenylephrine infusion during compared with before ganglionic blockade with trimethaphan. The exercise-trained men had a lower resting heart rate and higher maximal oxygen consumption and heart rate variability than the sedentary control subjects (all P=0.01). Mean levels and variability of blood pressure, cardiovagal baroreflex sensitivity (change in heart rate/change in systolic blood pressure), and basal muscle sympathetic nerve activity were not different in the two groups. The systolic blood pressure responses to phenylephrine were not different in the endurance-trained and untrained men before or during ganglionic blockade (P>0.6). Measures of baroreflex buffering with the use of a phenylephrine bolus (3.9+/-0.8 versus 4.0+/-0.7, trained versus untrained, P=0.85) and incremental infusion (2.8+/-0.4 versus 2.5+/-0.6, P=0.67) were similar in the two groups. Baroreflex buffering does not differ in endurance exercise-trained compared with untrained healthy men. These results support the concept that habitual vigorous endurance exercise does not modulate in vivo baroreflex buffering in healthy humans.

Adrenergic alpha-Agonists↗

PubMed2003

Baroreflex buffering is reduced with age in healthy men.

BACKGROUND: Baroreflex buffering is an important mechanism in arterial blood pressure control. The effect of healthy (physiological) aging on tonic baroreflex buffering in humans is unknown. METHODS AND RESULTS: Baroreflex buffering was determined in 27 young (aged 25+/-1 years) and 16 older (aged 65+/-1 years) healthy normotensive men by measuring the potentiation of the systolic blood pressure (SBP) responses to a phenylephrine bolus (BRBbolus) and incremental infusion (BRBslope) during compared with before ganglionic blockade with trimethaphan. The SBP responses to phenylephrine either were not different or greater in the older men before ganglionic blockade, but smaller during ganglionic blockade. BRBbolus (2.1+/-0.4 versus 5.1+/-0.7, P<0.001) and BRBslope (1.6+/-0.2 versus 3.5+/-0.4, P<0.0001) were approximately 115% smaller in the older men. Baroreflex buffering was not consistently related to mean levels or variability of blood pressure or heart rate, or to cardiovagal baroreflex sensitivity, but correlated with muscle sympathetic nerve activity (BRBbolus: r=-0.55, BRBslope: r=-0.69, P<0.005) and the SBP responses to phenylephrine during ganglionic blockade (BRBbolus: r=0.53; BRBslope: r=0.98, P<0.0001). BRBbolus was also inversely related to the SBP response to phenylephrine before ganglionic blockade (r=-0.78, P<0.0001). CONCLUSIONS: Physiological aging in men is associated with a marked reduction in baroreflex buffering. The decrease in baroreflex buffering with aging is related to increases in basal sympathetic nerve activity and reductions in systemic alpha1-adrenergic vascular responsiveness. These findings are helpful for interpreting changes in baroreflex buffering in older patients with cardiovascular disease, as well as changes in responsiveness to vasoactive drugs with aging.

Adult↗

PubMed2003

Adiposity contributes to differences in left ventricular structure and diastolic function with age in healthy men.

We sought to examine the influence of adiposity in age-associated changes in the left ventricle (LV) in a cohort of 113 healthy men, aged 20-79 yr, by measuring LV structure and diastolic function (echocardiography), whole body composition, and regional adiposity (dual energy x-ray absorptiometry). Aging was associated with increased levels of adiposity, greater wall thickness to chamber radius ratio, LV concentric remodeling, and reduced LV diastolic function (all P < 0.05). Bivariate correlation analysis showed that mean LV wall thickness, a concentric LV morphology, and diastolic function were related to adiposity (r = -0.63 to 0.51; all P < 0.05). The relation between age and both mean LV wall thickness and concentric remodeling was reduced after controlling for percentage total body fat (by 38% and 54%, respectively), percentage abdominal fat (by 42% and 62%), and the abdominal/thigh fat ratio (by 35% and 46%). The diastolic function-age relation was reduced after controlling for percentage total body fat (by 35%), percentage abdominal fat (by 39%), and the abdominal/thigh fat ratio (by 29%). There were no apparent differences in the contribution of percentage total body fat, percentage abdominal fat, or abdominal/thigh fat to the association between age and LV structure/diastolic function. We conclude that increasing adiposity contributes to the LV remodeling/reduced diastolic function that occurs with aging in healthy men.

Abdomen↗