Biomedical subjects

D R Seals

Publications and source records attributed to D R Seals.

At least 73 records · Page 4Linked to original sources

PubMed1997

Age-related increase in muscle sympathetic nerve activity is associated with abdominal adiposity.

Tonic sympathetic nerve activity (SNA) increases with age, but the mechanisms are unknown. There is evidence that SNA is positively related to total and abdominal body fat, which also increase with age. We tested the hypotheses that 1) the elevation in SNA with age is partially accounted for by higher abdominal and/or total body fat and 2) skeletal muscle is a target of the adiposity-related sympathetic effects. Direct microneurographic recordings of skeletal muscle SNA (MSNA) were obtained during supine rest in 16 older (64 +/- 1 yr, means +/- SE) and 16 young (24 +/- 1 yr) adult males. Central body fat was estimated by waist circumference (WC) and fat mass (FM) by hydrostatic weight. MSNA, WC, and FM were higher in the older vs. young males (44 +/- 2 vs. 22 +/- 2 bursts/min, 91 +/- 2 vs. 79 +/- 1 cm, and 19 +/- 2 vs. 9 +/- 1 kg, respectively; all P < 0.0001). Although univariate correlations were high for MSNA and both WC (r = 0.77) and FM (r = 0.75), stepwise multiple regression analysis revealed WC to be the best predictor of MSNA (R2 = 0.60, P < 0.0001), with FM explaining only an additional 2% of the variance (not significant). Statistically covarying for WC reduced but did not eliminate the difference in adjusted age-group means for MSNA (39 +/- 3 vs. 26 +/- 2 bursts/min, P = 0.003). We conclude that 1) the elevated SNA in older adults is partially related to higher body fat, particularly in the abdominal region, and 2) skeletal muscle is a target of the adiposity-related sympathetic effects observed with aging.

Abdomen↗

PubMed1997

Absence of age-related decline in total blood volume in physically active females.

Total blood volume (TBV) is an important determinant of cardiovascular functional capacity and the ability to maintain homeostasis during acute thermal and orthostatic stress. The primary aim of the present study was to test the hypotheses that TBV is 1) decreased with age in healthy, sedentary females, 2) not decreased with age in physically active females, and 3) directly related to maximal aerobic activity [maximal O2 consumption (VO2max)] in women of different ages and physical activity levels. An additional aim was to determine whether the use of hormone-replacement therapy in postmenopausal women is associated with altered TBV. Resting supine plasma volume (modified Evans blue dye technique) was measured in 25 postmenopausal women [12 sedentary (post-S), 13 physically active (post-PA; mean values, respectively, age 60 and 58 yr, and VO2max = 23 and 40 ml.kg-1.min-1)] and 27 premenopausal women [12 sedentary (pre-S), 15 physically active (pre-PA; mean values, respectively, age 29 and 31 yr, and VO2max = 35 and 54 ml.kg-1.min-1)]. TBV was lower in post-S (61 ml/kg) compared with pre-S (73 ml/kg) but not in post-PA (82 ml/kg) compared with pre-PA (87 ml/kg). It was also lower in post-S compared with post-PA. The lower TBV in post-S relative to pre-S and post-PA was related to lower plasma and estimated red blood cell volumes. Volumes did not differ between users and nonusers of hormone replacement. TBV was directly related to VO2max among all subjects (r = 0.65). It is concluded that 1) aging is associated with a decrease in TBV due to reductions in both plasma and erythrocyte cell volumes in healthy, sedentary females; 2) total blood, plasma, and red blood cell volumes are maintained with age in physically active females; 3) TBV is directly related to maximal aerobic capacity in females; and 4) TBV is not different in postmenopausal women using versus not using hormone-replacement therapy.

Adult↗

PubMed1997

Systemic hemodynamic determinants of blood pressure in women: age, physical activity, and hormone replacement.

We tested the hypothesis that the age-related changes in systemic hemodynamic determinants of arterial blood pressure in healthy women are related to physical activity and hormone replacement status. We studied 66 healthy, normotensive premenopausal (21-35 yr) and postmenopausal (50-72 yr) sedentary and endurance-trained women under supine resting conditions. Mean blood pressure was 7 mmHg higher in sedentary post- compared with premenopausal women, which was associated with an 11-mmHg higher systolic blood pressure, a 25% lower stroke volume and cardiac output, and a 50% higher systemic vascular resistance (all P < 0.05). Absolute (ml) levels of total blood volume did not differ across age, but resting oxygen consumption was approximately 35% lower in the postmenopausal women (P < 0.05). The elevations in mean and systolic blood pressures with age were similar in endurance-trained runners, but, in contrast to the sedentary women, the elevations were not associated with significant age-related differences in cardiac output, stroke volume, or oxygen consumption, and only a modest (15%) increase in systemic vascular resistance (P = 0.06). Postmenopausal swimmers demonstrated the same systemic hemodynamic profile as that of postmenopausal runners, indicating a nonspecific influence of the endurance-trained state. Blood pressure and its systemic hemodynamic determinants did not differ in postmenopausal users compared with those of nonusers of hormone replacement therapy. Resting oxygen consumption was the strongest physiological correlate of cardiac output in the overall population (r = 0.65, P < 0.001). We conclude that 1) the increases in arterial blood pressure at rest with age in healthy normotensive women are not obviously related to habitual physical activity status; 2) the systemic hemodynamic determinants of the age-related elevations in blood pressure are fundamentally different in sedentary vs. active women, possibly due, in part, to an absence of decline in resting oxygen consumption in the latter; and 3) systemic hemodynamics at rest are not different in healthy normotensive postmenopausal users vs. nonusers of estrogen-based hormone replacement.

Adult↗

PubMed1997

Influence of age on the sympathetic neural adjustments to alterations in systemic oxygen levels in humans.

We tested the hypothesis that aging influences the regulation of sympathetic nervous system activity (SNA) and arterial blood pressure during alterations in systemic O2 levels in humans. To accomplish this, we performed direct (intraneural) measurements of SNA to skeletal muscle (MSNA) in 10 young and 7 older healthy normotensive men during room air breathing (normoxic-control), moderate isocapnic hypoxemia [15 min of 10% fractional inspired O2 (FIO2)], and hyperoxemia (10 min of 50% FIO2). After hypoxemia, arterial O2 saturation (SaO2) declined similarly in the young and older men. MSNA (burst frequency and total minute activity) increased significantly (P < 0.05) in both groups. The magnitudes of the absolute increases in MSNA and the delta MSNA/delta SaO2 were not significantly different in the young and older men; however, because of higher normoxic baseline levels, the percentage increases in burst frequency were smaller (P = 0.02) and those for total minute activity tended to be smaller (P = 0.11) in the older men. Arterial blood pressure increased modestly (P < 0.05) and similarly in both groups, although the older men demonstrated a smaller increase in heart rate. After hyperoxemia [corrected], SaO2 increased and MSNA decreased (both P < 0.05) similarly in the young and older men. Arterial blood pressure did not change significantly from normoxic control levels in either group; however, a small (P < 0.05) reduction in heart rate was observed in both groups. In conclusion, aging does not obviously influence the regulation of absolute levels of MSNA or arterial blood pressure during alterations in systemic O2 levels in healthy men, although older men demonstrate a smaller percentage increase in MSNA from their elevated baseline levels, as well as an attenuated tachycardia in response to acute hypoxemia. As such, the present results are consistent with our previous findings on aging and sympathocirculatory control during other types of acute stress in humans.

Adaptation, Physiological↗

PubMed1997

Blood pressure risks factors in healthy postmenopausal women: physical activity and hormone replacement.

The prevalence of cardiovascular disease (CVD) increases with advancing age in women, particularly after menopause. CVD risk is lower in physically active women relative to their sedentary peers, but the responsible mechanisms are not well understood. The aims of this study were to test the hypotheses that 1) physically active postmenopausal women demonstrate more favorable blood pressure (BP)-related risk factors for CVD than do sedentary healthy women and 2) women on hormone replacement therapy (HRT) also have more favorable levels of these CVD risk factors. BP-related CVD risk factors were measured in physically active women (n = 18; age 55 +/- 1 yr; n = 8 on HRT) and in healthy less-active controls (n = 34; age 59 +/- 1 yr; n = 17 on HRT). Maximal oxygen consumption was higher in the active group, whereas waist-to-hip ratio and waist circumference were lower (all P < 0.005). The active women demonstrated marginally lower (5-8 mmHg; P < or = 0.10) levels of casual, 24-h, and daytime systolic BP (SBP). They also tended to have lower (P = 0.11) daytime SBP loads (percentage of BP recordings > 140/90 mmHg) and lower daytime and nighttime BP variabilities (P = 0.04) and a reduced (P < 0.007) SBP response to submaximal exercise. Women on HRT tended to have lower (3-4 mmHg; P = 0.07) levels of 24-h and nighttime diastolic BP (DBP) relative to the nonusers and smaller (P < 0.04) daytime and 24-h DBP loads. Stepwise multiple regression indicated that waist circumference was the primary predictor of most of the SBP-related CVD risk factors while HRT use was the best predictor for DBP loads. These findings indicate that, in general, physically active postmenopausal women demonstrate more favorable SBP-related CVD risk factors relative to their less-active healthy peers, which may be mediated, in party, by their lower levels of abdominal adiposity. In addition, HRT use tends to be associated with lower levels of DBP-related CVD risk factors.

Aged↗

PubMed1997

Age and gender interactions in physiological functional capacity: insight from swimming performance.

One experimental approach to studying the effects of aging on physiological functional capacity in humans is to analyze the peak exercise performance of highly trained athletes with increasing age. To gain insight into the relationships among age, gender, and exercise task duration with use of this model, we performed a 5-yr (1991-1995) retrospective analysis of top freestyle performance times from the US Masters Swimming Championships. Regression analysis showed that in both men and women endurance swimming performance (i.e., 1,500 m) declined linearly from peak levels at age 35-40 yr until approximately 70 yr of age, whereupon performance declined exponentially thereafter. In both genders, the variability among the top 10 winning times in each 5-yr age interval increased markedly with advancing age. Compared with the 1,500-m freestyle, performance in the 50-m freestyle (short-duration task) showed only a modest decline until ages 75 and 80 yr in women and men, respectively. The rate and magnitude of the declines in both short- and long-duration swimming performance with age were significantly (P < 0.05) greater in women than in men. In the women, the percent decline in swimming performance over a 50-yr age period from the 19- to 24-yr to the 69- to 74-yr age groups became progressively greater from the shortest distance (50 m) to the two longest distances (800 and 1,500 m), whereas in men, no differences were observed in the magnitude of performance decline with age among the five longest distance events (i.e., 100-1,500 m). The percent gender difference in performance throughout the age range studied became progressively smaller (P < 0.05) with increasing distance from 50 m (19 +/- 1%) to 1,500 m (11 +/- 1%). The findings in this cross-sectional study indicate that from peak levels at age 35-40 yr, physiological functional capacity, as assessed by swimming performance, decreases linearly until approximately 70-80 yr of age, whereupon the decline becomes exponential. Moreover, the rate of decline with advancing age appears to be associated with event duration and gender.

Adolescent↗

PubMed1997

Age-related declines in maximal aerobic capacity in regularly exercising vs. sedentary women: a meta-analysis.

Our purpose was to determine the relationship between habitual aerobic exercise status and the rate of decline in maximal aerobic capacity across the adult age range in women. A meta-analytic approach was used in which mean maximal oxygen consumption (VO2 max) values from female subject groups (ages 18-89 yr) were obtained from the published literature. A total of 239 subject groups from 109 studies involving 4,884 subjects met the inclusion criteria and were arbitrarily separated into sedentary (groups = 107; subjects = 2,256), active (groups = 69; subjects = 1, 717), and endurance-trained (groups = 63; subjects = 911) populations. VO2 max averaged 29.7 +/- 7.8, 38.7 +/- 9.2, and 52.0 +/- 10.5 ml . kg-1 . min-1, respectively, and was inversely related to age within each population (r = -0.82 to -0.87, all P < 0.0001). The rate of decline in VO2 max with increasing subject group age was lowest in sedentary women (-3.5 ml . kg-1 . min-1 . decade-1), greater in active women (-4.4 ml . kg-1 . min-1 . decade-1), and greatest in endurance-trained women (-6.2 ml . kg-1 . min-1 . decade-1) (all P < 0.001 vs. each other). When expressed as percent decrease from mean levels at age approximately 25 yr, the rates of decline in VO2 max were similar in the three populations (-10.0 to -10.9%/decade). There was no obvious relationship between aerobic exercise status and the rate of decline in maximal heart rate with age. The results of this cross-sectional study support the hypothesis that, in contrast to the prevailing view, the rate of decline in maximal aerobic capacity with age is greater, not smaller, in endurance-trained vs. sedentary women. The greater rate of decline in VO2 max in endurance-trained populations may be related to their higher values as young adults (baseline effect) and/or to greater age-related reductions in exercise volume; however, it does not appear to be related to a greater rate of decline in maximal heart rate with age.

Adolescent↗

PubMed1997

Greater rate of decline in maximal aerobic capacity with age in physically active vs. sedentary healthy women.

Using a meta-analytic approach, we recently reported that the rate of decline in maximal oxygen uptake (VO2 max) with age in healthy women is greatest in the most physically active and smallest in the least active when expressed in milliliters per kilogram per minute per decade. We tested this hypothesis prospectively under well-controlled laboratory conditions by studying 156 healthy, nonobese women (age 20-75 yr): 84 endurance-trained runners (ET) and 72 sedentary subjects (S). ET were matched across the age range for age-adjusted 10-km running performance. Body mass was positively related with age in S but not in ET. Fat-free mass was not different with age in ET or S. Maximal respiratory exchange ratio and rating of perceived exertion were similar across age in ET and S, suggesting equivalent voluntary maximal efforts. There was a significant but modest decline in running mileage, frequency, and speed with advancing age in ET. VO2 max (ml . kg-1 . min-1) was inversely related to age (P < 0.001) in ET (r = -0.82) and S (r = -0.71) and was higher at any age in ET. Consistent with our meta-analysic findings, the absolute rate of decline in VO2 max was greater in ET (-5.7 ml . kg-1 . min-1 . decade-1) compared with S (-3.2 ml . kg-1 . min-1 . decade-1; P < 0. 01), but the relative (%) rate of decline was similar (-9.7 vs -9. 1%/decade; not significant). The greater absolute rate of decline in VO2 max in ET compared with S was not associated with a greater rate of decline in maximal heart rate (-5.6 vs. -6.2 beats . min-1 . decade-1), nor was it related to training factors. The present cross-sectional findings provide additional evidence that the absolute, but not the relative, rate of decline in maximal aerobic capacity with age may be greater in highly physically active women compared with their sedentary healthy peers. This difference does not appear to be related to age-associated changes in maximal heart rate, body composition, or training factors.

Adult↗

PubMed1997

Regular exercise and the age-related decline in resting metabolic rate in women.

A low resting metabolic rate (RMR) is a risk factor for future weight gain. We tested the hypothesis that the age-related decline in RMR in sedentary women is not observed in women who exercise regularly. Sixty-five healthy, weight-stable women, aged 21-35 or 50-72 yr, were studied: 12 premenopausal and 15 postmenopausal sedentary women, 13 premenopausal and 15 postmenopausal distance runners, and 10 endurance-trained postmenopausal swimmers. RMR was measured by indirect calorimetry (ventilated hood system) after an overnight fast, and values were adjusted for fat mass and fat-free mass (RMRadj). The RMRadj was approximately 10% lower in the postmenopausal vs. premenopausal sedentary women (52 +/- 2 vs. 57 +/- 2 Cal/h; P < 0.002). In contrast, RMRadj was not significantly different in the premenopausal (59 +/- 2 Cal/h) and postmenopausal (57 +/- 1 Cal/h) distance runners. The postmenopausal swimmers had a RMRadj (57 +/- 2 Cal/h) identical to that of the postmenopausal runners, suggesting a generalized influence of the endurance exercise-trained state in postmenopausal women. Group differences in RMRadj were not associated with differences in total energy intake or composition or with plasma concentrations of norepinephrine, T3, or T4. However, maximal oxygen consumption (aerobic fitness) accounted for 35% of the individual variance in RMRadj in the overall population (r = 0.59; P < 0.001). Our results are consistent with the concept that the age-related decline in RMR in sedentary women is not observed in women who regularly perform endurance exercise. The elevated level of RMR observed in middle-aged and older exercising women may play a role in their lower levels of body weight and fatness compared to those in sedentary women.

Adult↗

PubMed1996

Gender does not influence sympathetic neural reactivity to stress in healthy humans.

Previous data support the idea of heightened sympathetically mediated cardiovascular reactivity in males. However, definitive conclusions cannot be made because of inconsistent reports, possibly stemming from imprecise measurement of sympathetic activity and/or failure to equate the stress stimuli between genders. The present study tested the hypothesis that males exhibit heightened sympathetic reactivity that is associated with heightened cardiovascular and plasma catecholamine responses. In 37 healthy adults (20 males, 17 females: age = 20-42 yr), direct recordings of skeletal muscle sympathetic nerve activity (MSNA), plasma catecholamines, heart rate, blood pressure, and perceived stress were measured before and during three laboratory stressors (isometric handgrip, cold pressor, and mental arithmetic). MSNA, catecholamine, and cardiovascular reactivity (defined as change from rest) were not consistently different between genders. For the isometric handgrip, when expressed as absolute unit changes, males had larger MSNA responses (P < 0.01), which were partially explained by greater contraction force; they did not differ in terms of percent change from baseline or in perceived stress. The responses to the cold pressor and mental arithmetic tasks were similar between genders. These findings indicate that stress-evoked vasoconstrictor neural excitation and the associated increases in blood pressure are not consistently influenced by gender.

Adult↗

PubMed1996

Elevated heart rate variability in physically active postmenopausal women: a cardioprotective effect?

Coronary heart disease (CHD) and cardiac sudden death (CSD) incidence accelerates after menopause, but the incidence is lower in physically active versus less active women. Low heart rate variability (HRV) is a risk factor for CHD and CSD. The purpose of the present investigation was to test the hypothesis that HRV at rest is greater in physically active compared with less active postmenopausal women. If true, we further hypothesized that the greater HRV in the physically active women would be closely associated with an elevated spontaneous cardiac baroreflex sensitivity (SBRS). HRV (both time and frequency domain measures) and SBRS (sequence method) were measured during 5-min periods of controlled frequency breathing (15 breaths/min) in the supine, sitting, and standing postures in 9 physically active postmenopausal women (age = 53 +/- 1 yr) and 11 age-matched controls (age = 56 +/- 2 yr). Body weight, body mass index, and body fat percentage were lower (P < 0.01) and maximal oxygen uptake was higher (P < 0.01) in the physically active group. The standard deviation of the R-R intervals (time domain measure) was higher in all postures in the active women (P < 0.05) as were the high-frequency, low-frequency, and total power of HRV. SBRS also was higher (P < 0.05) in the physically active women in all postures and accounted for approximately 70% of the variance in the high-frequency power of HRV (P < 0.05). The results of the present investigation indicate that physically active postmenopausal women demonstrate higher levels of HRV compared with age-matched, less active women. Furthermore, SBRS accounted for the majority of the variance in the high-frequency power of HRV, suggesting the possibility of a mechanistic link with cardiac vagal modulation of heart rate. Our findings may provide insight into a possible cardioprotective mechanism in physically active postmenopausal women.

Baroreflex↗

PubMed1996

Adiposity and regional body fat distribution in physically active young and middle-aged women.

OBJECTIVE: To test the hypothesis that age does not directly influence body composition or regional body fat distribution throughout middle age in women. DESIGN: Cross-sectional. SUBJECTS: Thirty female endurance athletes of similar competitive ranking ranging in age from 23-56 years. MEASUREMENTS: Body composition (hydrodensitometry and skinfolds) and regional body fat distribution (waist and hip circumference and tricep, subscapular, suprailiac, abdomen and thigh skinfolds); maximal oxygen uptake. RESULTS: In contrast to the age-related increases in total and regional body fat levels and decreases in fat-free mass in the general population of women, there were no significant trends for changes in body composition or regional body fat distribution in our cross-section of highly physically active subjects with age. CONCLUSION: These findings suggest that age-related increases in total body fat and decreases in fat-free mass may be a result of reduced chronic physical activity levels with age rather than an inevitable consequence of the aging process.

Adipose Tissue↗

PubMed1995

Effects of aging on the responsiveness of the human cardiac sympathetic nerves to stressors.

BACKGROUND: Aging increases human sympathetic nervous activity at rest. Beause of the probable importance of neural stress responses in the heart as triggers for clinical end points of coronary artery disease, it is pertinent to investigate whether sympathetic nervous responses to stresses are increased by aging. METHODS AND RESULTS: We applied kinetic methods for measuring the fluxes to plasma of neurochemicals relevant to sympathetic neurotransmission in younger (aged 20 to 30 years) and older (aged 60 to 75 years) healthy men during mental stress (difficult mental arithmetic), isometric exercise (sustained handgrip), and dynamic exercise (supine cycling). The increase in total norepinephrine spillover to plasma with mental stress was unaffected by age. In contrast, the increase in cardiac norepinephrine spillover was two to three times higher in the older subjects (P < .05). The probable mechanism of this higher cardiac norepinephrine spillover was reduced neuronal reuptake of the transmitter, because age had no influence on the overflow of the norepinephrine precursor, dihydroxyphenylalanine, or intraneuronal metabolite, dihydroxyphenylglycol (levels of these two substances reflect rates of cardiac norepinephrine synthesis and intraneuronal metabolism), and the transcardiac extraction of plasma radiolabeled norepinephrine was lower in the older subjects (P < .05). An almost identical pattern of neurochemical response was seen with isometric exercise. During cycling, total norepinephrine spillover was 16% lower in the older men, but cardiac norepinephrine spillover was 53% higher. CONCLUSIONS: Reduced norepinephrine reuptake increases the overflow of the neurotransmitter to plasma from the aging heart during stimulation of the cardiac sympathetic outflow. Failure of transmitter inactivation at postjunctional receptors with aging would amplify the neural signal, and in the presence of myocardial disease could trigger adverse stress-induced cardiovascular events, particularly when accompanied by an age-dependent reduction in vagal tone. Reduction of postsynaptic adrenergic responsiveness with aging, however, might protect against this, as indicated by our finding that in no case was the heart rate increase during stress greater in older men, despite their having larger increases in cardiac norepinephrine spillover.

Adult↗

PubMed1995

Muscle sympathetic nerve activity during postural change in healthy young and older adults.

Recent evidence suggests that during orthostatic stress the reflex increase in muscle sympathetic nerve activity may be diminished in older adults. To test this hypothesis, we measured muscle sympathetic nerve activity, plasma noradrenaline concentrations, heart rate, and arterial blood pressure in twelve young (mean, 25 years; range, 19-29 years) adults and 14 older (mean 64 years; range, 60-74 years) healthy adults, while supine and during upright sitting. Supine control levels of muscle sympathetic nerve activity were higher in the older subjects (35 +/- 1 vs. 25 +/- 1 bursts/min, p < 0.05), but there were no differences in plasma noradrenaline concentrations, heart rate or arterial pressure. Despite higher supine control levels in the older group, the absolute unit increases in muscle sympathetic nerve activity in response to upright sitting (p < 0.05 vs. control) were not different in the two groups (7 +/- 1 vs. 7 +/- 1 bursts/min), nor were the increases in plasma noradrenaline concentrations. Heart rate did not increase above supine control in response to sitting in either group. Arterial pressure increased slightly (p < 0.05, supine vs. control), but there were no age-related differences. These results indicate that, contrary to recent findings, the reflex increases in muscle sympathetic nerve activity and plasma noradrenaline concentrations and regulation of arterial pressure during this natural orthostatic stress are well preserved in older healthy men and women.

Adult↗

PubMed1995

Cardiovascular, plasma norepinephrine, and thermal adjustments to prolonged exercise in young and older healthy humans.

We tested the hypothesis that the whole body energy expenditure, plasma norepinephrine, cardiovascular, and internal body temperature adjustments to prolonged submaximal exercise (i.e., 'cardiovascular drift') performed at the same per cent of peak oxygen uptake (per cent VO2peak) under thermoneutral ambient conditions would be smaller in older compared to young non-physically trained men. Healthy young (25 +/- 1 years; VO2max = 49.3 +/- 1.6 ml kg-1 min-1; n = 6) and older (66 +/- 2 years; VO2max = 31.5 +/- 2.3 ml kg-1 min-1; n = 6) untrained men with similar levels of chronic physical activity were studied during pre-exercise standing rest and serially during 45 min of constant load treadmill walking at approximately 65% VO2peak (Ta = approximately 23 degrees C; approximately 40 RH). There were no group differences at rest. From rest to 5 min of exercise, the increases in heart rate were less (P < 0.05), the changes in arterial blood pressure and per cent delta blood volume were not different, and the rise in plasma norepinephrine concentration was greater (P < 0.05) in the older men vs. young controls. Consistent with our hypothesis, the increases in rectal temperature and plasma norepinephrine concentrations from 5 to 45 min of exercise were smaller in the older men (1.06-0.18 vs. 1.46 +/- 0.16 degrees C and 110 +/- 132 vs. 443 +/- 189%, respectively, P < 0.05). In contrast, the progressive increases in VO2, heart rate, and perceived effort, as well as the time-dependent reductions in systolic, mean and diastolic arterial blood pressure and per cent delta blood volume, were not different in the two groups. Thus, the whole body energy expenditure and selected cardiovascular adjustments to prolonged submaximal treadmill exercise performed at the same per cent VO2peak under comfortable ambient conditions are not different in healthy, physical activity-matched young and older men, despite a smaller elevation in internal body temperature in the latter.

Adult↗

PubMed1995

Aging effects on human sympathetic neuronal function.

To study the effect of aging on human sympathetic nervous function, we applied kinetic methods for measuring the fluxes to plasma of neurochemicals relevant to sympathetic neurotransmission in younger (aged 20-30 yr) and older (aged 60-75 yr) healthy men. Mean plasma norepinephrine concentration was 66% higher in older men, attributable to 22% lower norepinephrine plasma clearance (P < 0.05) and 29% higher norepinephrine spillover to plasma (difference not statistically significant). Regional venous sampling disclosed that sympathetic outflow to all organs was not activated by aging. Renal norepinephrine spillover was normal in older men. Although spillover of norepinephrine from the heart was increased in older men, 21.1 +/- 11.4 ng/min compared with 11.4 +/- 8.6 ng/min (P < 0.05), diminished norepinephrine reuptake rather than increased cardiac sympathetic nerve firing was the most likely cause, although somewhat reduced intracardiac methylation of norepinephrine with aging also possibly contributed. The extraction of tritiated norepinephrine from plasma during transit through the heart was reduced, suggesting neuronal norepinephrine reuptake was lowered and overflow of the norepinephrine precursor dihydroxyphenylalanine and metabolites dihydroxyphenylglycol and 3-methoxy-4-hydroxy phenylglycol was normal, indicating that norepinephrine synthesis and release were not increased.

Adult↗

PubMed1995

Physiological determinants of 10-km performance in highly trained female runners of different ages.

Endurance exercise performance declines with age; however, there is little information on the mechanisms responsible, especially in women. We tested the hypothesis that this performance decline in women is associated with decreases in maximal O2 consumption (VO2max), blood lactate threshold (LT), and running economy (RE). We determined a 10-km race pace, VO2max, LT, and RE in 31 highly trained female runners aged 23-56 yr with similar relative (i.e., age-adjusted) competitive performances. Absolute 10-km race pace declined with age (r = -0.83). Both 10-km performance and age were correlated with VO2max (P < 0.05) and with the running velocity and O2 consumption at LT but not with RE. The runners then were divided into three age groups: group I (23-35 yr), group II (37-47 yr), and group III (49-56 yr). Stepwise regression analyses performed on subjects pooled from groups I and II and from groups II and III indicated that the majority (60%) of the variability in performance for runners aged 23-47 yr was explained by the running velocity at which LT occurred, whereas VO2max explained the majority (74%) of the variability for the runners aged 37-56 yr. We conclude that decreases in VO2max and running velocity at LT are the two physiological phenomena most closely associated with declines in 10-km performance with age in highly trained female runners. However, the contributions of these two mechanisms to the declines in performance are not uniform with advancing age.

Adult↗

PubMed1995

Lesser vagal withdrawal during isometric exercise with age.

The tachycardia that accompanies isometric exercise decreases with age in humans; however, the mechanism of this decline is unknown. To determine whether less cardiac vagal withdrawal is associated with the age-related decrease in this response, we assessed high-frequency R-R interval variability (0.15-0.40 Hz), an index of cardiac vagal tone, before (control) and during isometric exercise to exhaustion in healthy young (21-29 yr; n = 12) and older (61-72 yr; n = 11) men. During control, the two groups did not differ in respiratory rate, mean arterial pressure, or heart rate, although the older subjects had a lower high-frequency amplitude (12.2 +/- 1.1 vs. 29.4 +/- 4.6 ms/Hz; P < 0.05). During isometric exercise, the respiratory rate and arterial pressure responses did not differ; however, the older men had a lower absolute heart rate and a smaller increase in heart rate, and only the young men demonstrated a significant decline in high-frequency amplitude. The heart rate responses to exercise were correlated with the declines in high-frequency amplitude (initial, r = -0.808; midpoint, r = -0.714; peak, r = -0.632; all P < 0.005), which were, in turn, correlated with the control high-frequency amplitude (initial, r = -0.727; midpoint, r = -0.643; peak, r = -0.610; all P < 0.01). Thus smaller declines in high-frequency amplitude, related to lower baseline amplitude, corresponded to smaller increases in heart rate throughout isometric exercise. Therefore, we conclude that the smaller tachycardiac response to isometric exercise in older humans is associated with an inability to decrease cardiac vagal tone below an already reduced baseline level.

Adult↗