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Biomedical subjects

D R Seals

Publications and source records attributed to D R Seals.

At least 19 recordsLinked to original sources
PubMed1999

Cardiopulmonary baroreflex inhibition of sympathetic nerve activity is preserved with age in healthy humans.

1. We tested the hypothesis that the ability of the cardiopulmonary baroreflex to produce sympathoinhibition is reduced with age in humans. Eleven young (23 +/- 1 years, mean +/- s.e.m.) and ten older (64 +/- 1) healthy adult males were studied under supine conditions (control) and in response to cardiopulmonary baroreflex stimulation evoked by acute central circulatory hypervolaemia (10 deg head-down tilt). The two groups were normotensive and free of overt cardiovascular disease. 2. Supine baseline (control) levels of efferent muscle sympathetic nerve activity (MSNA) burst frequency were twice as high in the older men (41 +/- 2 vs. 21 +/- 2 bursts min-1, P < 0.05). In both groups in response to head-down tilt arterial blood pressure and heart rate were unchanged, peripheral venous pressure (PVP) increased (P < 0.05), MSNA total activity decreased (P < 0.05), antecubital venous plasma noradrenaline concentrations did not change significantly, and forearm blood flow and vascular conductance increased (vascular resistance decreased) (all P < 0.05). The mean absolute DeltaMSNA/DeltaPVP was similar in the young and older men, although the higher control levels of MSNA in the older men resulted in a smaller percentage DeltaMSNA/DeltaPVP (P < 0.05). Per DeltaPVP, the reduction in forearm vascular resistance was smaller in the older men, but there were no age group differences when expressed as increases in forearm vascular conductance. 3. These results indicate that the ability of the cardiopulmonary baroreflex to inhibit MSNA is well preserved with age in healthy adult humans. As such, these findings are not consistent with the concept that this mechanism plays a role in the age-associated elevation in basal MSNA.

Adult↗
PubMed1998

Hemodynamic sequelae of age-related increases in arterial stiffness in healthy women.

Stiffening of central arteries is believed to contribute to the increase in the incidence of cardiovascular disease with age, presumably through its adverse influence on arterial blood pressure. We found that (1) the physiologic link between age-related increases in arterial stiffness and blood pressure appears to be elevated systemic vascular resistance, and (2) increased arterial stiffness and systemic vascular resistance with age were inversely related to blood volume, stroke volume, and cardiac output.

Adult↗
PubMed1998

Influence of body fatness on the coronary risk profile of physically active postmenopausal women.

We have shown previously that endurance-trained postmenopausal runners demonstrate more favorable coronary heart disease (CHD) risk factors compared with age-matched sedentary women. However, the runners exhibited higher levels of physical activity and lower levels of body fatness, both of which can influence CHD risk factors. To gain insight into the influence of body fatness per se, we studied 38 postmenopausal healthy women: 10 swimmers, 10 runners, and nine obese and nine leaner sedentary subjects matched for age, hormone replacement use, and years postmenopause. Swimmers and runners were further matched for exercise training volume (4.5+/-0.2 v 4.6+/-0.6 h/wk) and relative competitive performance (79%+/-5% v 77+/-3% of age-adjusted world record). Maximal oxygen consumption (VO2max) on the treadmill was lower (P < .01) in swimmers versus runners. Body mass (65.0+/-2.0 v 59.0+/-1.3 kg), percent body fat (29%+/-2% v 23%+/-2%), and waist circumference (79+/-3 v 71+/-1 cm) were greater (P < .01) in swimmers than in runners. There were no significant differences in total caloric intake or dietary composition between swimmers and runners. Insulin sensitivity (via Bergman's minimal model) and fasting plasma concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), glucose, and plasminogen activator inhibitor-1 (PAI-1) activity were not different between the groups. However, plasma high-density lipoprotein cholesterol (HDL-C), HDL2-C, HDL-C/TC, insulin, fibrinogen, fibrin D-dimer, PAI antigen, tissue plasminogen activator (t-PA) activity, and t-PA antigen levels all were less favorable (P < .05) in swimmers versus runners. Daytime, nighttime, and 24-hour systolic blood pressure (SBP) was 6 to 10 mm Hg higher in swimmers compared with runners, but resting blood pressure, 24-hour blood pressure load, and blood pressure variability were not significantly different. Stepwise regression showed that measures of body fatness were the primary independent determinants of most of the metabolic CHD risk factors. When analysis of covariance (ANCOVA) was performed with body fatness as a covariate, differences in CHD risk factors between swimmers and runners were abolished (P=.18 to .90). We conclude that among endurance-trained postmenopausal women matched for training volume and competitive eliteness, higher total and abdominal body fatness is, in general, associated with a less favorable metabolic CHD risk profile. Thus, high levels of habitual aerobic exercise do not appear to negate the deleterious effects of adiposity on the coronary risk profile of healthy middle-aged and older women.

Adipose Tissue↗
PubMed1998

Elevated heart rate variability in physically active young and older adult women.

1. Low heart rate variability is associated with an increased risk of cardiac sudden death, coronary heart disease and all-cause mortality. We have previously shown that physically active postmenopausal women demonstrate higher levels of heart rate variability and cardiac baroreflex sensitivity compared to their sedentary peers. The purpose of the present prospective study was to test the hypothesis that heart rate variability and cardiac baroreflex sensitivity would be reduced with age in sedentary but not physically active women. To accomplish this, we measured heart rate variability (both time and frequency domain) and spontaneous cardiac baroreflex sensitivity (SBRS, sequence method) in the sitting posture in 23 sedentary women [11 premenopausal and 12 postmenopausal (age, 28 +/- 1 and 61 +/- 2 years; VO2max, 35.3 +/- 1.4 and 21.7 +/- 1.5 ml.min-1.kg-1 respectively] and in 22 physically active women [12 premenopausal and 10 postmenopausal (age, 31 +/- 1 and 59 +/- 2 years; VO2max, 52.5 +/- 1.4 and 39.7 +/- 1.8 ml.min-1.kg-1)]. 2. The S.D. of the R-R interval (time domain) was reduced (P < 0.05) with age in both sedentary (52 +/- 6 versus 33 +/- 4 ms) and physically active women (72 +/- 8 versus 49 +/- 9 ms). The high-frequency power (3740 +/- 1527 versus 915 +/- 188 and 9516 +/- 2849 versus 2803 +/- 1083 ms2/Hz), total power of heart rate variability and SBRS (11 +/- 2 versus 7 +/- 2 and 19 +/- 3 versus 13 +/- 2 ms/mmHg) also demonstrated similar age-related reductions in sedentary and physically active women, respectively (all P < 0.05). The S.D. of the R-R interval, high-frequency and total power of heart rate variability, and SBRS were higher (all P < 0.05) in the physically active compared with the sedentary women at any age. There was no significant influence of age or physical activity status on the low-frequency power of heart rate variability. In addition, no significant differences in any of the time or frequency domain measures of heart rate variability or SBRS were observed in users compared with non-users of hormone replacement therapy. 3. The results of the present study suggest that heart rate variability and cardiac baroreflex sensitivity decline similarly with age in healthy sedentary and physically active women. However, physically active women demonstrate higher levels of heart rate variability and cardiac baroreflex sensitivity compared with their sedentary peers, regardless of age.

Adult↗
PubMed1998

Arterial stiffness and hormone replacement use in healthy postmenopausal women.

BACKGROUND: Arterial stiffness has been shown to be positively related to cardiovascular disease risk. Little, however, is known about the influence of hormone replacement use on arterial stiffness in females. METHODS: Arterial pulse wave velocity (PWV) and carotid augmentation index (AI, applanation tonometry) were measured in 34 healthy postmenopausal women, including users (n = 18) and nonusers (n = 16) of hormone replacement. RESULTS: There were no significant group differences in any of the physical characteristics including resting blood pressure. None of the measures of arterial stiffness differed between user and nonusers of hormone replacement. CONCLUSIONS: The present cross-sectional study indicates that reduced arterial stiffness does not appear to be a likely mechanism contributing to the lower incidence of cardiovascular disease in postmenopausal women taking hormone replacement.

Aged↗
PubMed1998

Regular walking increases peak limb vasodilatory capacity of older hypertensive humans: implications for arterial structure.

BACKGROUND: Although regular aerobic exercise has been shown to lower arterial blood pressure in older adult humans with essential hypertension, the mechanisms responsible for this hypotensive effect remain largely unknown. OBJECTIVE: To examine the hypothesis that the reduction in arterial blood pressure in older hypertensive humans with regular exercise is accompanied by evidence of a change in arterial structure. METHODS: We measured peak limb vascular conductance, a well-established noninvasive measure of arterial structure, both in the forearm (untrained limb) and in the calf (exercise-trained limb) of 22 older adults (aged 51-74 years) with stage 1 or 2 essential hypertension. Eleven subjects walked 3-4 days/week at a mild exercise intensity (45% of heart rate reserve) for 6 months. Eleven other subjects served as nonexercising controls. RESULTS: Maximal oxygen consumption of subjects in the exercise group increased by 17% (P < 0.05) with no change in body mass and body fat. Systolic and diastolic arterial blood pressures at rest were reduced by 7 +/- 4 and 5 +/- 2 mmHg, respectively (P < 0.05). There were roughly 20% increases in peak forearm blood flow and peak forearm vascular conductance (both P < 0.05). Similar increases in peak calf blood flow and vascular conductance were observed (both P < 0.01). There were no significant changes in any of these variables over the same time period for the nonexercising controls. CONCLUSIONS: The decrease in resting blood pressure in older adults with stage 1 or 2 essential hypertension in response to regular aerobic exercise is associated with an increase in peak limb vascular conductance, which could be due in part to favorable changes in arterial structure. These exercise-induced functional and, possibly, structural changes are not confined to the exercise-trained limbs, but rather are more systemic in nature. These apparent beneficial changes in limb vasodilatory capacity and vascular structure can be produced with a mode, intensity, and frequency of aerobic exercise that can be tolerated and is commonly performed by older adults.

Aged↗
PubMed1998

Smaller differences in total and regional adiposity with age in women who regularly perform endurance exercise.

Our aim was to determine if women who regularly perform endurance exercise demonstrate age-related elevations in body mass and adiposity. Ninety-five healthy females were studied: premenopausal (n = 28; mean +/- SE age 30 +/- 1 yr) and postmenopausal (n = 31; 56 +/- 1 yr) endurance-trained runners and premenopausal (n = 17; 29 +/- 1 yr) and postmenopausal (n = 19; 61 +/- 1 yr) sedentary controls. In the runners, body mass did not differ across age, but percent fat and fat mass were higher (P < 0.05) in the postmenopausal women. The age-related difference in total body fat, however, was only approximately 50% as great (P < 0.01) as that observed in the sedentary controls due in part to smaller age-related differences in central (truncal) fat. The higher fat mass in the postmenopausal runners was modestly (inversely) related to both exercise volume (r = -0.44, P < 0.01) and maximal oxygen consumption (r = -0.41, P < 0.01). The present findings provide experimental support for the hypothesis that women who regularly engage in vigorous endurance exercise may not gain body weight, undergo only a modest increase in total body fat, and do not demonstrate a significant elevation in central adiposity with age.

Adipose Tissue↗
PubMed1998

Low-frequency arterial pressure fluctuations do not reflect sympathetic outflow: gender and age differences.

Low-frequency arterial pressure oscillations (Mayer waves) have been proposed as an index of vascular sympathetic outflow. However, cross-sectional differences in these pressure oscillations may not reflect different levels of sympathetic nervous outflow in humans. Three groups of healthy subjects with characteristically different sympathetic nervous outflow were studied: young females (n = 10, 18-28 yr), young males (n = 11, 18-29 yr), and older males (n = 13, 60-72 yr). Average R-R interval, arterial pressures, and systolic pressure variability at the Mayer wave frequency (0.05-0.15 Hz) did not differ among the three groups. Diastolic pressure Mayer wave variability was similar in young females vs. young males (39 +/- 10 vs. 34 +/- 5 mmHg2) and lower in older males vs. young males (14 +/- 2 mmHg2; P < 0.05). In contrast, muscle sympathetic activity was lowest in young females (892 +/- 249 total activity/min) and highest in older males (3,616 +/- 528 total activity/min; both P < 0.05 vs. young males: 2,505 +/- 285 total activity/min). Across the three groups, arterial pressure Mayer wave variability did not correlate with any index of sympathetic activity. Our results demonstrate that arterial pressure Mayer wave amplitude is not a surrogate measure of vascular sympathetic outflow.

Adolescent↗
PubMed1998

Role of central circulatory factors in the fat-free mass-maximal aerobic capacity relation across age.

Fat-free mass (FFM) (primarily skeletal muscle mass) is related to maximal aerobic capacity among healthy humans across the adult age range. The basis for this physiological association is assumed to be a direct relation between skeletal muscle mass and its capacity to consume oxygen. We tested the alternative hypothesis that FFM exerts its influence on maximal aerobic capacity in part via an association with central circulatory function. To do so, we analyzed data from 103 healthy sedentary adults aged 18-75 yr. FFM was strongly and positively related to maximal oxygen consumption (r = 0.80, P < 0. 001). FFM was also strongly and positively related to supine resting levels of blood volume (r = 0.79, P < 0.001) and stroke volume (r = 0.75, P < 0.001). Statistically controlling for the collective influences of blood volume and stroke volume abolished the tight relation between FFM and maximal oxygen consumption (r = 0.12, not significant). These results indicate that 1) FFM may be an important physiological determinant of blood volume and stroke volume among healthy sedentary adult humans of varying age; and 2) this relation between FFM and central circulatory function appears to represent the primary physiological basis for the strong association between FFM and maximal aerobic capacity in this population. Our findings suggest that sarcopenia (loss of skeletal muscle mass with aging) may contribute to the age-related decline in maximal aerobic capacity primarily via reductions in blood volume and stroke volume rather than a direct effect on the oxygen-consuming potential of muscle per se.

Adipose Tissue↗
PubMed1998

Influence of age on arterial baroreflex inhibition of sympathetic nerve activity in healthy adult humans.

Resting levels of muscle sympathetic nerve activity (MSNA) increase markedly with age in healthy adult humans. An age-related reduction in arterial baroreflex inhibition of MSNA could contribute to these elevations. To test this hypothesis, we measured MSNA using peroneal microneurography in young (age, 25 +/- 1 yr; n = 8) and older (69 +/- 1 yr; n = 7) healthy normotensive men before (baseline control) and during graded constant infusion of phenylephrine hydrochloride (0.5-2.0 microgram . kg-1. min-1) that produced a sustained approximately 10-mmHg increase in arterial blood pressure. Central venous pressure was controlled at baseline levels (+/-1 mmHg) using lower body negative pressure. Resting MSNA was approximately 95% higher in the older compared with the young subjects (43 +/- 5 vs. 22 +/- 3 bursts/min; P < 0.05). However, arterial baroreflex MSNA inhibitory responsiveness was similar in the older compared with the young subjects (254 +/- 112 vs. 259 +/- 40 arbitrary integration units/mmHg, respectively), although the percent reduction in MSNA was smaller in the older men (8.9 +/- 0.7 vs. 5.2 +/- 1.1%/mmHg), due to their elevated baseline levels. The reflex increase in the R-R interval was not different in the two groups (13 +/- 10 vs. 16 +/- 7 ms/mmHg). In summary, our findings suggest that arterial baroreflex inhibition of MSNA is preserved with age in healthy normotensive adult humans. As such, this mechanism does not appear to contribute to the age-related rise in tonic MSNA.

Adult↗
PubMed1998

Absence of age-related increase in central arterial stiffness in physically active women.

Increased arterial stiffness is thought to contribute to the increased incidence of cardiovascular disease with age. Little, however, is known about the influence of aging on central and peripheral arterial stiffness in females. Moreover, it is unknown whether physical activity status influences age-related increases in arterial stiffness in females. Arterial pulse wave velocity (PWV) and augmentation index (AI, applanation tonometry) were measured in 53 healthy females, including 10 premenopausal (Pre-S) and 18 postmenopausal (Post-S) sedentary women, and 9 premenopausal (Pre-PA) and 16 postmenopausal (Post-PA) physically active women. In the sedentary women, there were no age-related differences in arterial blood pressure, but aortic PWV and carotid AI (measures of central arterial stiffness) were higher (P<.01) in Post-S versus Pre-S (1065+/-110 versus 690+/-80 cm/sec and 16.5%+/-1.8% versus 0.3%+/-1.6%, respectively); however, there were no significant differences in leg and arm PWV (measures of peripheral arterial stiffness). Systolic and mean arterial blood pressures were higher (P<.05) in Post-PA versus Pre-PA. Despite this and in contrast to the sedentary women, aortic PWV and AI were not different in Post-PA versus Pre-PA. Stepwise multiple regression indicated that maximal oxygen consumption, plasma total cholesterol, and plasma LDL-cholesterol were significant independent predictors and together explained up to 50% of the variability in central arterial stiffness. We concluded that (1) central, but not peripheral, arterial stiffness increases with age in sedentary healthy females in the absence of age-related increases in arterial blood pressure; (2) significant age-related increases in central arterial stiffness are not observed in highly physically active women; and (3) aerobic fitness and plasma total cholesterol and LDL-cholesterol levels are significant independent physiological correlates of central arterial stiffness in this population.

Adult↗
PubMed1998

Physical activity status and adverse age-related differences in coagulation and fibrinolytic factors in women.

Adverse changes in coagulation and fibrinolytic factors are thought to contribute to the increased risk of cardiovascular disease and atherothrombosis with age. We tested the hypothesis that such age-related changes in specific coagulation and fibrinolytic factors are absent in physically active women. Resting levels of plasma fibrinogen, tissue-type plasminogen activator (t-PA) antigen and activity, plasminogen activator inhibitor-1 (PAI-1) antigen and activity, and fibrin D-dimer were measured in 24 healthy premenopausal women: 11 sedentary (aged 28+/-1 years; Pre-S) and 13 physically active (aged 30+/-1 years; Pre-PA) and in 27 healthy postmenopausal women: 14 sedentary (aged 61+/-1 years; Post-S) and 13 physically active (aged 58+/-1 years; Post-PA). Post-S had higher (P<.05) fibrinogen, t-PA antigen, PAI-1 antigen, PAI-1 activity, and fibrin D-dimer levels and lower t-PA activity than Pre-S. Post-PA demonstrated lower (P<.01) plasma fibrinogen, t-PA antigen, PAI-1 antigen, and PAI-1 activity and higher (P<.01) t-PA activity levels than Post-S. In addition, plasma fibrin D-dimer levels tended (P=.06) to be lower in Post-PA than in Post-S. Although plasma levels of fibrinogen and fibrin D-dimer in Post-PA were lower than in Post-S, they were higher (P<.05) than in Pre-PA. Importantly, however, the fibrinolytic profile of Post-PA did not differ from that of Pre-PA. The results of the present study demonstrate that the adverse age-associated differences in plasma fibrinogen concentrations and the endogenous fibrinolytic system in sedentary healthy women are either attenuated or absent in highly physically active women. The smaller or absent age-related differences in coagulation and fibrinolytic factors in women who habitually exercise may represent an important mechanism contributing to their lower age-related increase in both cardiovascular disease and atherothrombotic events. Future studies need to determine whether women who are moderately active would demonstrate the same favorable hemostatic profile.

Adult↗
PubMed1998

Augmented cardiopulmonary and integrative sympathetic baroreflexes but attenuated peripheral vasoconstriction with age.

Based on observations of smaller increases in limb vascular resistance during acute incremental hypovolemia in older adults, cardiopulmonary and integrative (combined cardiopulmonary and arterial) baroreflex control of sympatho-circulatory function is thought to be impaired with aging in humans. We tested this hypothesis directly by making intraneural measurements of skeletal muscle sympathetic nerve activity (MSNA; peroneal microneurography) in groups of young (23+/-1 years; n=11) and older (64+/-1 years; n=12) healthy adult men during progressive hypovolemia produced by graded (-5 to -40 mm Hg) lower body negative pressure (LBNP). Baseline levels of MSNA and arterial blood pressure were higher and heart rate was lower in the older subjects (P<0.05). Lower levels of LBNP (-5 to -20 mm Hg) did not affect arterial blood pressure or heart rate in either group; systolic and pulse pressures declined during higher levels of LBNP (-30 and -40 mm Hg) but only in the young subjects (P<0.05). Graded LBNP evoked progressive, linear reductions in peripheral venous pressure (PVP) and increases in MSNA, plasma norepinephrine concentration (PNE), and forearm vascular resistance (FVR) in both groups (all P<0.05). DeltaMSNA/ deltaPVP was approximately 150% greater in the older versus young men during both lower and higher levels of hypovolemia (P<0.01); however, deltaFVR/deltaPVP was approximately 50% smaller in the older men (P<0.05). There was no difference in the MSNA-PNE relation with age, but deltaFVR/deltaMSNA was approximately 65% to 70% smaller in the older subjects (P<0.05). Our findings indicate that cardiopulmonary and integrative baroreflex control of central sympathetic outflow during hypovolemia is augmented, not impaired, with age in healthy humans. However, the reflex-mediated increases in limb vascular resistance during hypovolemia are smaller in older adults because of attenuated vasoconstrictor responsiveness to sympathetic stimulation.

Adult↗
PubMed1997

Effect of regular aerobic exercise on elevated blood pressure in postmenopausal women.

The efficacy of aerobic exercise for lowering arterial blood pressure (BP) in postmenopausal women with elevations of 130 to 159/85 to 99 mm Hg has not been established. To determine this, 10 postmenopausal women with high normal resting BP or stage I essential hypertension were studied throughout a 12-week lead-in period (no exercise, n = 5) and/or 12 weeks of moderate-intensity aerobic exercise (walking, n = 9). There were no significant time effects during the lead-in period (all p >0.4). Maximal aerobic capacity (as assessed by maximal oxygen consumption) was unchanged after 12 weeks of exercise, but exercise tolerance (treadmill walking time) increased by approximately 10% (p <0.05). Body weight, dietary intake and composition, and urinary sodium excretion were unchanged before versus after exercise training. After 12 weeks of exercise, systolic and diastolic BP at rest were significantly lowered by 10/7 and 12/5 mm Hg, respectively, in the sitting and standing positions (p <0.001); some (> or = 3 to 5 mm Hg) decrease in BP was observed in every subject. On average, subjects with stage I hypertension had a reduction in BP into the high normal range, whereas subjects with high-normal initial levels had a reduction in BP into the normal range. Borderline significant (p = 0.06 to 0.07) reductions in systolic and diastolic BP were observed by the end of the second and tenth weeks of training, respectively. Ambulatory determined 24-hour levels of BP were unchanged with training, but significant reductions in BP during submaximal exercise occurred. Our results demonstrate that regular aerobic exercise can produce clinically important reductions in resting BP in Caucasian postmenopausal women with mild to moderately elevated initial levels. This effect of exercise is observed in the absence of changes in maximal aerobic capacity, body weight, or dietary intake.

Body Mass Index↗
PubMed1997

Elevated levels of circulating cell adhesion molecules in uncomplicated essential hypertension.

Elevated levels of circulating soluble cell adhesion molecules are associated with the development of cardiovascular disease. We tested the hypothesis that circulating levels of soluble cell adhesion molecules are elevated in older men with uncomplicated essential hypertension, which may contribute to the increased risk of atherosclerosis in this population. Circulating levels of soluble intercellular adhesion molecule-1, vascular adhesion molecule-1, and E-selectin were measured in 11 hypertensive (69+/-1 years) and ten normotensive (65+/-1 years) older men who were free of overt atherosclerotic disease, diabetes, and dyslipidemia. The hypertensive subjects had higher (P < .05) circulating levels of soluble intercellular adhesion molecule-1 (232.4+/-16.5 v 189.8+/-11.1 ng/mL) and vascular adhesion molecule-1 (737.3+/-65.6 v 565.7+/-46.8 ng/mL) compared with their normotensive peers. However, there was no difference in the levels of soluble E-selectin between the hypertensive (51.1+/-3.9 ng/ mL) and normotensive (48.8+/-6.6 ng/mL) subjects. Univariate analysis revealed a positive correlation between soluble intercellular adhesion molecule-1 and both systolic (r = 0.50, P = .02) and diastolic (r = 0.49, P = .03) blood pressure. In addition, soluble vascular adhesion molecule-1 was positively correlated with age (r = 0.60, P = .004) and systolic blood pressure (r = 0.43, P = .05). The results of this study support the hypothesis that circulating levels of soluble cell adhesion molecules are elevated in older men with uncomplicated essential hypertension.

Aged↗
PubMed1997

Relations of total and abdominal adiposity to muscle sympathetic nerve activity in healthy older males.

OBJECTIVES: We recently reported that skeletal muscle sympathetic nerve activity (MSNA) is related to total body and abdominal fatness in a pooled population of young and older males. Both MSNA and adiposity increase with age. Thus, it is not clear if the relation between MSNA and adiposity exists among older adults and if the age-related increase in MSNA is explained by increases in adiposity. We therefore tested the hypotheses that: 1) among older men, those with higher total body fatness and abdominal adiposity have higher MSNA and 2) MSNA is not different in healthy young and older men with similar total body and/or abdominal fatness. DESIGN: Older healthy men (63 +/- 1 y) were separated into higher and lower groups of body fat (26.9 +/- 0.8%, n = 9 vs 21.3 +/- 1.1, n = 10; P < 0.0001) and waist circumference (96.4 +/- 3.5 cm, n = 8 vs 86.2 +/- 1.5, n = 8; P < 0.01). Younger controls (26 +/- 1 y) were then matched with those in the older-lower groups for %body fat (21 +/- 1.1%, n = 10) or waist circumference (86.2 +/- 0.8 cm, n = 10). MEASUREMENTS: Total body fat was determined by hydrodensitometry, abdominal adiposity by waist circumference and resting MSNA by microneurography. RESULTS: Among the older subjects those in the higher %body fat and waist circumference groups had higher (P < 0.02) MSNA (47 +/- 3 and 48 +/- 4 bursts/min, respectively) than those in the lower groups (37 +/- 2 and 38 +/- 3 bursts/min). MSNA was directly related to %body fat (r = 0.52, P = 0.03) and waist circumference (r = 0.64, P = 0.007) in the older groups. MSNA was greater (P < 0.001) in the older-lower groups than in the young controls matched for %body fat (23 +/- 2 bursts/min) or waist circumference (24 +/- 3 bursts/min). CONCLUSIONS: 1) among healthy older men, higher levels of total body and/or abdominal adiposity are associated with higher levels of MSNA and 2) the age-related elevation in MSNA is reduced but not abolished when differences in adiposity are eliminated.

Abdomen↗
PubMed1997

Reproducibility of a semiautomated acetylene rebreathing technique for measuring cardiac output in humans at rest.

The specific aims of the present study were to determine: (1) the day-to-day reproducibility of a semiautomated acetylene rebreathing technique for measuring cardiac output under resting conditions; (2) the reproducibility of this technique among subjects differing in gender and age; and (3) the number of trials within a session necessary to maximize the day-to-day reproducibility of the technique. To address these aims, cardiac output was measured in 21 healthy men (n = 8) and women (n = 13) between the ages of 25 and 71 years in the supine posture on two separate days. Mean levels of cardiac output at rest were similar on day 1 vs. day 2 in the overall group. Cardiac output measured on day 1 was highly correlated (r = 0.98, P < 0.001) with cardiac output measured on day 2. The day 1 to day 2 mean difference in cardiac output for the individual subjects was < 4%. The mean levels of heart rate and stroke volume also were similar between day 1 and day 2. The relation between cardiac output measured on day 1 vs. day 2 in the gender and age subgroups was similar to that observed in the overall group. The mean absolute difference among the three rebreathing trials within a day was 360 ml min-1 in the overall group, with a coefficient of variation of 7%. The variability between rebreathing trials measured on day 1 vs. day 2 in the gender and age subgroups was similar to that observed in the overall group. The reliability of cardiac output measured on different days was excellent with a single rebreathing trial (r = 0.93) and improved significantly up to three trials (r = 0.98). In conclusion, the findings of the present study indicate that the acetylene rebreathing technique can be a highly reproducible method for measuring cardiac output under resting conditions. The reproducibility is consistently strong in healthy humans of varying age and in both genders, and is enhanced by the use of multiple trials.

Acetylene↗