Sexual dimorphism in the complexity of cardiac pacemaker activity

This study explored the effects of gender and aging on the complexity of cardiac pacemaker activity. Electrocardiogram signals were studied in normal women (n = 240) and men (n = 240) ranging in age from 40 to 79 yr. Nonlinear analysis of short-term resting R-R intervals was performed using the correlation dimension (CD), approximate entropy (ApEn), and largest Lyapunov exponent (LLE). Evidence of nonlinear structure was obtained by the surrogate data test. CD, ApEn, and LLE were negatively correlated with age. Despite similar means and SDs of the R-R intervals, women had a significantly higher CD, ApEn, and LLE compared with men in the age strata of 40-44 and 45-49 yr. CD and ApEn were strongly (r > 0.71) correlated with low- and high-frequency components. We conclude that the resting cardiac pacemaker activity of women is more complex than that of men in middle age, and the gender-related difference diminishes after the age of 50 yr. The higher complexity implies a more comprehensive neural modulation.     

Determinants and interindividual variation of R-R interval dynamics in healthy middle-aged subjects

Determinants and intersubject variations of fractal and complexity measures of R-R interval variability were studied in a random population of 200 healthy middle-aged women (age 51 +/- 6 yr) and 189 men (age 50 +/- 6 yr) during controlled conditions in the supine and sitting positions. The short-term fractal exponent (alpha(1)) was lower in women than men in both the supine (1.18 +/- 0.20 vs. 1.12 +/- 0.17, P < 0.01) and sitting position (P < 0.001). Approximate entropy (ApEn), a measure of complexity, was higher in women in the sitting position (1.16 +/- 0.17 vs. 1.07 +/- 0.19, P < 0.001), but no gender-related differences were observed in ApEn in the supine position. Fractal and complexity measures were not related to any other demographic, laboratory, or lifestyle factors. Intersubject variations in a fractal measure, alpha(1) (e.g., 1.15 +/- 0.20 in the supine position, z value 1.24, not significant), and in a complexity measure, ApEn (e.g., 1.14 +/- 0.18 in the supine position, z value 1.44, not significant), were generally smaller and more normally distributed than the variations in the traditional measures of heart rate variability (e.g., standard deviation of R-R intervals 49 +/- 21 ms in the supine position, z value 2.53, P < 0.001). These results in a large random population sample show that healthy subjects express relatively little interindividual variation in the fractal and complexity measures of heart rate behavior and, unlike the traditional measures of heart rate variability, they are not related to lifestyle, metabolic, or demographic variables. However, subtle gender-related differences are also present in fractal and complexity measures of heart rate behavior.     

Fractal scale-invariant and nonlinear properties of cardiac dynamics remain stable with advanced age: a new mechanistic picture of cardiac control in healthy elderly

Heart beat fluctuations exhibit temporal structure with robust long-range correlations, fractal and nonlinear features, which have been found to break down with pathologic conditions, reflecting changes in the mechanism of neuroautonomic control. It has been hypothesized that these features change and even break down also with advanced age, suggesting fundamental alterations in cardiac control with aging. Here we test this hypothesis. We analyze heart beat interval recordings from the following two independent databases: 1) 19 healthy young (average age 25.7 yr) and 16 healthy elderly subjects (average age 73.8 yr) during 2 h under resting conditions from the Fantasia database; and 2) 29 healthy elderly subjects (average age 75.9 yr) during approximately 8 h of sleep from the sleep heart health study (SHHS) database, and the same subjects recorded 5 yr later. We quantify: 1) the average heart rate (); 2) the SD sigma(R-R) and sigma(DeltaR-R) of the heart beat intervals R-R and their increments DeltaR-R; 3) the long-range correlations in R-R as measured by the scaling exponent alpha(R-R) using the Detrended Fluctuation Analysis; 4) fractal linear and nonlinear properties as represented by the scaling exponents alpha(sgn) and alpha(mag) for the time series of the sign and magnitude of DeltaR-R; and 5) the nonlinear fractal dimension D(k) of R-R using the fractal dimension analysis. We find: 1) No significant difference in (P > 0.05); 2) a significant difference in sigma(R-R) and sigma(DeltaR-R) for the Fantasia groups (P < 10(-4)) but no significant change with age between the elderly SHHS groups (P > 0.5); and 3) no significant change in the fractal measures alpha(R-R) (P > 0.15), alpha(sgn) (P > 0.2), alpha(mag) (P > 0.3), and D(k) with age. Our findings do not support the hypothesis that fractal linear and nonlinear characteristics of heart beat dynamics break down with advanced age in healthy subjects. Although our results indeed show a reduced SD of heart beat fluctuations with advanced age, the inherent temporal fractal and nonlinear organization of these fluctuations remains stable. This indicates that the coupled cascade of nonlinear feedback loops, which are believed to underlie cardiac neuroautonomic regulation, remains intact with advanced age.     

Unexpected course of nonlinear cardiac interbeat interval dynamics during childhood and adolescence

The fluctuations of the cardiac interbeat series contain rich information because they reflect variations of other functions on different time scales (e.g., respiration or blood pressure control). Nonlinear measures such as complexity and fractal scaling properties derived from 24 h heart rate dynamics of healthy subjects vary from childhood to old age. In this study, the age-related variations during childhood and adolescence were addressed. In particular, the cardiac interbeat interval series was quantified with respect to complexity and fractal scaling properties. The R-R interval series of 409 healthy children and adolescents (age range: 1 to 22 years, 220 females) was analyzed with respect to complexity (Approximate Entropy, ApEn) and fractal scaling properties on three time scales: long-term (slope β of the power spectrum, log power vs. log frequency, in the frequency range 10(-4) to 10(-2) Hz) intermediate-term (DFA, detrended fluctuation analysis, α(2)) and short-term (DFA α(1)). Unexpectedly, during age 7 to 13 years β and ApEn were higher compared to the age <7 years and age >13 years (β: -1.06 vs. -1.21; ApEn: 0.88 vs. 0.74). Hence, the heart rate dynamics were closer to a 1/f power law and most complex between 7 and 13 years. However, DFA α(1) and α(2) increased with progressing age similar to measures reflecting linear properties. In conclusion, the course of long-term fractal scaling properties and complexity of heart rate dynamics during childhood and adolescence indicates that these measures reflect complex changes possibly linked to hormonal changes during pre-puberty and puberty.     

Nonlinear fractal dynamics of human colonic pressure activity based upon the box-counting method

The computational fractal dimension of human colonic pressure activity acquired by a telemetric capsule robot under normal physiological conditions was studied using the box-counting method. The fractal dimension is a numeric value that quantifies to measure how rough the signal is from nonlinear dynamics, rather than its amplitude or other linear statistical features. The colonic pressure activities from the healthy subject during three typical periods were analysed. The results showed that the activity might be fractal with a non-integer fractal dimension after it being integrated over time using the cumsum method, which was never revealed before. Moreover, the activity (after it being integrated) acquired soon after wakening up was the roughest (also the most complex one) with the largest fractal dimension, closely followed by that acquired during sleep with that acquired long time after awakening up (in the daytime) ranking third with the smallest fractal dimension. Fractal estimation might provide a new method to learn the nonlinear dynamics of human gastrointestinal pressure recordings.     

Fractal and periodic heart rate dynamics in fetal sheep: comparison of conventional and new measures based on fractal analysis

The physiological significance of spectral and fractal components of spontaneous heart rate (HR) variability in the fetus remains unclear. To examine the relationship between circadian rhythms in different measures of HR variability, R-R interval time series obtained by fetal ECGs were recorded continuously over 24 h in five pregnant sheep at 116-125 days gestation. Conventional measures of short-term (STV) and long-term variability (LTV), low-frequency (LF; 0.025-0.15 cycles/beat) and high-frequency (HF; 0.2-0.5 cycles/beat) spectral powers, the LF-to-HF ratio, and fractal dimension values were calculated from 24-h ECG recordings and quantified every 60 min. STV, LTV, and LF and HF spectral powers were minimal during the day but increased significantly to their highest values at night. We found a significant positive correlation between these measures, whereas the cosinor method showed significant similarity between their circadian rhythm patterns. Fetal R-R intervals also exhibited fractal structures. Fetal HR variability had a fractal structure, which was similar between day and night. These results suggested that the circadian rhythms exhibited by STV and LTV during the day were mainly due to changes in frequency components rather than to fractal components of fetal HR fluctuation.     

Cortisol and GH secretory dynamics, and their interrelationships, in healthy aged women and men

We studied 130 healthy aged women (n = 57) and men (n = 73), age 65-88 yr, with age-related reductions in insulin-like growth factor I and gonadal steroid levels to assess the interrelationships between cortisol and growth hormone (GH) secretion and whether these relationships differ by sex. Blood was sampled every 20 min from 8:00 PM to 8:00 AM; cortisol was measured by RIA and GH by immunoradiometric assay, followed by deconvolution analyses of hormone secretory parameters and assessment of approximate entropy (ApEn) and cross-ApEn. Cortisol mass/burst, cortisol production rate, and mean and integrated serum cortisol concentrations (P < 0.0005), and overnight basal GH secretion (P < 0.05), were elevated in women vs. men. Integrated cortisol concentrations were directly related to most measures of GH secretion in women (P < 0.01) and with mean and integrated GH concentrations in men (P < 0.05). Integrated GH concentrations were directly related to mean and integrated cortisol levels in women (P < 0.005) and men (P < 0.05), with no sex differences. There were no sex differences in cortisol or GH ApEn values; however, the cross-ApEn score was greater in women (P < 0.05), indicating reduced GH-cortisol pattern synchrony in aged women vs. men. There were no significant relationships of integrated cortisol secretion with GH ApEn, or vice versa, in either sex. Thus postmenopausal women appear to maintain elevated cortisol production in patterns that are relatively uncoupled from those of GH, whereas mean hormone outputs remain correlated.     

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

Tanaka, Hirofumi, and Douglas R. Seals. Age and genderinteractions in physiological functional capacity: insight from swimming performance. J. Appl.Physiol. 82(3): 846-851, 1997.One experimentalapproach to studying the effects of aging on physiological functionalcapacity in humans is to analyze the peak exercise performance ofhighly trained athletes with increasing age. To gain insight into therelationships among age, gender, and exercise task duration with use ofthis model, we performed a 5-yr (1991-1995) retrospective analysisof top freestyle performance times from the US Masters SwimmingChampionships. Regression analysis showed that in both men and womenendurance swimming performance (i.e., 1,500 m) declined linearly frompeak levels at age 35-40 yr until ~70 yr of age, whereuponperformance declined exponentially thereafter. In both genders, thevariability among the top 10 winning times in each 5-yr age intervalincreased markedly with advancing age. Compared with the 1,500-mfreestyle, 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- andlong-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 a50-yr age period from the 19- to 24-yr to the 69- to 74-yr age groupsbecame progressively greater from the shortest distance (50 m) to thetwo longest distances (800 and 1,500 m), whereas in men, no differenceswere observed in the magnitude of performance decline with age amongthe five longest distance events (i.e., 100-1,500 m). The percentgender difference in performance throughout the age range studiedbecame 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 functionalcapacity, as assessed by swimming performance, decreases linearly until ~70-80 yr of age, whereupon the decline becomes exponential.Moreover, the rate of decline with advancing age appears to beassociated with event duration and gender.

     

Longitudinal changes in aerobic power in older men and women.

The purpose of this study was to describe the longitudinal (10 yr) decline in aerobic power [maximal O(2) uptake (Vo(2 max))] and anaerobic threshold [ventilatory threshold (T(Ve))] of older adults living independently in the community. Ten years after initial testing, 62 subjects (34 men, mean age 73.5 +/- 6.4 yr; 28 women, 72.1 +/- 5.3 yr) achieved Vo(2 max) criteria during treadmill walking tests to the limit of tolerance, with T(Ve) determined in a subset of 45. Vo(2 max) in men showed a rate of decline of -0.43 ml.kg(-1).min(-1).yr(-1), and the decline in Vo(2 max) was consequent to a lowered maximal heart rate with no change in the maximum O(2) pulse. The women showed a slower rate of decline of Vo(2 max) of -0.19.ml.kg(-1).min(-1).yr(-1) (P < 0.05), again with a lowered HR(max) and unchanged O(2) pulse. In this sample, lean body mass was not changed over the 10-yr period. Changes in Vo(2 max) were not significantly related to physical activity scores. T(Ve) showed a nonsignificant decline in both men and women. Groupings of young-old (65-72 yr at follow-up) vs. old-old (73-90 yr at follow-up) were examined. In men, there were no differences in the rate of Vo(2 max) decline. The young-old women showed a significant decline in Vo(2 max), whereas old-old women, initially at a Vo(2 max) of 19.4 +/- 3.1 ml.kg(-1).min(-1), showed no loss in Vo(2 max). The longitudinal data, vs. cross-sectional analysis, showed a greater decline for men but similar estimates of the rates of change in women. Thus the 10-yr longitudinal study of the cohort of community-dwelling older adults who remained healthy, ambulatory, and independent showed a 14% decline in Vo(2 max) in men, and a smaller decline of 7% in women, with the oldest women showing little change over the 10-yr period.     

Greater rate of decline in maximal aerobic capacity with age in endurance-trained than in sedentary men.

To determine the relation between habitual endurance exercise status and the age-associated decline in maximal aerobic capacity [i.e., maximal O(2) consumption (Vo(2 max))] in men, we performed a well-controlled cross-sectional laboratory study on 153 healthy men aged 20-75 yr: 64 sedentary and 89 endurance trained. Vo(2 max) (ml. kg(-1). min(-1)), measured by maximal treadmill exercise, was inversely related to age in the endurance-trained (r = -0.80) and sedentary (r = -0.74) men but was higher in the endurance-trained men at any age. The rate of decline in Vo(2 max) with age (ml. kg(-1). min(-1)) was greater (P < 0.001) in the endurance-trained than in the sedentary men. Whereas the relative rate of decline in Vo(2 max) (percent decrease per decade from baseline levels in young adulthood) was similar in the two groups, the absolute rate of decline in Vo(2 max) was -5.4 and -3.9 ml. kg(-1). min(-). decade(-1) in the endurance-trained and sedentary men, respectively. Vo(2 max) declined linearly across the age range in the sedentary men but was maintained in the endurance-trained men until approximately 50 yr of age. The accelerated decline in Vo(2 max) after 50 yr of age in the endurance-trained men was related to a decline in training volume (r = 0.46, P < 0.0001) and was associated with an increase in 10-km running time (r = -0.84, P < 0.0001). We conclude that the rate of decline in maximal aerobic capacity during middle and older age is greater in endurance-trained men than in their sedentary peers and is associated with a marked decline in O(2) pulse.     

Night work and mortality: prospective study among Finnish employees over the time span 1984 to 2008

There is considerable evidence showing that night work is associated with increased morbidity, but only a few studies have focused on its relation to mortality. This study investigates the relationship between the type of working-time arrangement (weekly night work/daytime work) and total and cause-specific mortality among men and women. The data consist of a representative working conditions survey of Finnish employees conducted in 1984 (2286 men/2216 women), which has been combined with register-based follow-up data from Statistics Finland covering the years 1985-2008. In the 1984 survey, the employees were asked if they worked during the night (23:00-06:00 h) and if so, how often. In this study, the authors compare employees who worked at night (121 men/89 women) to daytime employees who did not do night work (1325 men/1560 women). The relative risk of death was examined by Cox proportional hazards analyses adjusted for background (age, level of education, family situation, and county), health (longstanding illness, pain symptoms, smoking status, and psychological symptoms), and work-related factors (weekly working hours, physical and psychological demands, demands of learning at work, and perceived job insecurity). Female employees working at night had a 2.25-fold higher risk of mortality than female dayworkers (95% confidence interval [CI] 1.20-4.20) after adjustment for background and health- and work-related factors. In addition to total mortality, night work was also associated with tumor mortality. Female night workers had a 2.82-fold higher risk of tumor mortality than female dayworkers (95% CI 1.20-6.65) in the adjusted model. Among men, no such significant association was observed. The present study indicated that female night workers had a higher risk of both total and tumor mortality compared to female daytime employees. Additional research on the potential factors and mechanisms behind the association between night work and mortality is required.     

Ecological implications of a latitudinal gradient in inter-annual climatic variability: a test using fractal and chaos theories

Although measures of seasonality are common, ecologists have seldom measured inter-annual variation or tested for the presence of a latitudinal gradient. Yet, species diversity and range size may be influenced by latitudinal gradients in climatic variability. Fractal and chaos theories offer new techniques to measure climatic unpredictability by analyzing the dynamics of nonlinear time-series data. We analyzed data on the number of freezing degree-days and date of first permanent ice from 12 weather stations (43–83°N) in Canada to describe latitudinal gradients in the timing of seasonal events. Time-series (ca 30 yr) of climatic variables were found to be nonlinear dynamic systems that were neither stochastic nor cyclic. The analyses reveal a latitudinal gradient in system memory length, with high latitude locations displaying shorter memory length (R/S fractal analysis and Lyapunov exponent). This latitudinal gradient is also characterized by more random and irregular fractal patterns (Hurst exponent) associated with higher latitudes. Both of these patterns may be due to the simpler climatic systems in high latitudes as indicated by fewer dynamic variables (lower correlation dimension). Application of fractal and chaos theories show that the timing of seasonal events (i.e. inter-annual variation) comprises a chaotic-dynamic system of comparatively low dimension.     

Fractal dimension in health and heart failure.

BACKGROUND: Non-linear analysis of heart rate variability (HRV) can give additional information about autonomic control of the heart rate. This study applied the fractal dimension (FD) in a congestive heart failure (CHF) population. METHODS: FD and HRV were evaluated in a healthy population (n=21) and an end-stage heart failure population (n=21) using 1-h segments during the day and night from Holter recordings. RESULTS: CHF patients presented a loss of circadian variation in both FD and conventional time- and frequency-domain HRV indices. FD was higher in the CHF population both during the day and night. In the CHF population the correlation between FD and high-frequency power of HRV was lost. CONCLUSION: Day-night variations of heart rate fluctuations are lost in heart failure. Changes in FD reflecting physiological and pathophysiological changes were observed.     

Age-related decline in handgrip strength differs according to gender

It is well-established that at old age there is a significant decline in muscle strength. Reference values for muscle strength might be useful for assessment of muscle impairment and of physiological adaptations. However, it is still unclear whether gender affects the rate of decline. Therefore, the aim of this study is to investigate the effect of gender and age on handgrip strength and to establish reference values for this variable. Reviewing medical charts collected from 1994 to 2005, a convenience sample of 2,648 subjects (1,787 men and 861 women), aged between 18 and 90 years, was obtained. Our results show higher handgrip strength for men compared with women (36.8 +/- 0.20 vs. 21.0 +/- 0.18 kg; p < 0.001). The regression analysis with a quadratic model shows that aging accounts for 30% of the variance in handgrip strength (r(2) = 0.30; p < 0.001) in men and 28% (r(2) = 0.28; p < 0.001) in women. In addition, the bent linear regression with multiple regressors show that a faster decline in handgrip strength occurs at the age of 30 years for men and 50 years for women. We conclude that handgrip strength decline with age differs between genders, making useful the existence of distinct male and female normative age group data.     

Gender differences in the decline in aerobic capacity and its physiological determinants during the later decades of life.

We investigated the hemodynamic determinants of the age-associated decline in maximal oxygen uptake (V(O2 max)) and the influence of gender on the decline in V(O2 max) and its determinants in old and very old men and women. Sedentary, 60- to 92-yr-old women (n = 71) and men (n = 29), with no evidence of cardiovascular disease, underwent maximal treadmill exercise tests during which V(O2 max) and maximal cardiac output (Q(max)) were determined. V(O2 max) and age were inversely related in both women (-23 +/- 2 ml.min(-1).yr(-1); P < 0.0001) and men (-57 +/- 5 ml.min(-1).yr(-1); P < 0.0001). The absolute slope of the V(O2 max) vs. age relationship was twofold steeper in men than in women (P < 0.0001). Q(max) was also inversely related to age in a gender-specific manner (women = -87 +/- 25 ml.min(-1).yr(-1), P = 0.0009; men = -215 +/- 50 ml.min(-1).yr(-1), P = 0.0002; P = 0.01 women vs. men). Age-related changes in maximal exercise arteriovenous oxygen content difference (a-vD(O2)) were marginally different (P = 0.08) between women (-0.12 +/- 0.03 ml.dl(-1).yr(-1), P = 0.0003) and men (-0.22 +/- 0.04 ml.dl(-1).yr(-1), P < 0.0001). Age-associated decreases in Q(max) and a-vD(O2) contributed equally to the declines in V(O2 max) in both men and women. In the later stages of life, V(O2 max), Q(max), and a-vD(O2) decrease with age more rapidly in older men than they do in older women. As a result, the gender differences dissipate in the later decades of life. Declines in Q(max) and a-vD(O2) contribute equally to the age-related decrease in V(O2 max) in men and women.     

Entropies of short binary sequences in heart period dynamics

Dynamic aspects of R-R intervals have often been analyzed by means of linear and nonlinear measures. The goal of this study was to analyze binary sequences, in which only the dynamic information is retained, by means of two different aspects of regularity. R-R interval sequences derived from 24-h electrocardiogram (ECG) recordings of 118 healthy subjects were converted to symbolic binary sequences that coded the beat-to-beat increase or decrease in the R-R interval. Shannon entropy was used to quantify the occurrence of short binary patterns (length N = 5) in binary sequences derived from 10-min intervals. The regularity of the short binary patterns was analyzed on the basis of approximate entropy (ApEn). ApEn had a linear dependence on mean R-R interval length, with increasing irregularity occurring at longer R-R interval length. Shannon entropy of the same sequences showed that the increase in irregularity is accompanied by a decrease in occurrence of some patterns. Taken together, these data indicate that irregular binary patterns are more probable when the mean R-R interval increases. The use of surrogate data confirmed a nonlinear component in the binary sequence. Analysis of two consecutive 24-h ECG recordings for each subject demonstrated good intraindividual reproducibility of the results. In conclusion, quantification of binary sequences derived from ECG recordings reveals properties that cannot be found using the full information of R-R interval sequences.     

AGING AND THE CIRCADIAN RHYTHM OF MELATONIN: A CROSS-SECTIONAL STUDY OF CHINESE SUBJECTS 30–110 YR OF AGE

Although previous reports indicate that nocturnal plasma melatonin secretion declines with age, some recent findings do not support this point. In the present cross-sectional study, we documented serum melatonin concentrations at two time points, 02:00 and 08:00h, in 144 persons aged 30–110 yr and found a significant age-related decline. It began around the age of 60 and reached a very significantly lower level in subjects in their 70s and over 80 yr of age (P<0.01, when compared with age <60 yr). Nocturnal melatonin levels were higher among (post-menopausal only) women than men overall (P<0.05). In the older age-groups, nocturnal melatonin levels did not differ between healthy controls and subjects with high blood pressure or ischemic heart disease. To further check these results, we also assessed the circadian pattern of serum melatonin in four subgroups of healthy men, aged 30–39, 40–49, 50–59, and 60–69 yr: blood samples were taken at 2h intervals from 08:00 to 22:00h and hourly from 22:00 to 08:00h. Our results showed generally similar circadian melatonin patterns that peaked at night with very low levels during the daytime. No significant difference was found among the three younger groups, but nocturnal melatonin levels were significantly lower in the men in their 60s.     

Night Work and Mortality: Prospective Study Among Finnish Employees Over the Time Span 1984 to 2008

There is considerable evidence showing that night work is associated with increased morbidity, but only a few studies have focused on its relation to mortality. This study investigates the relationship between the type of working-time arrangement (weekly night work/daytime work) and total and cause-specific mortality among men and women. The data consist of a representative working conditions survey of Finnish employees conducted in 1984 (2286 men/2216 women), which has been combined with register-based follow-up data from Statistics Finland covering the years 1985–2008. In the 1984 survey, the employees were asked if they worked during the night (23:00–06:00?h) and if so, how often. In this study, the authors compare employees who worked at night (121 men/89 women) to daytime employees who did not do night work (1325 men/1560 women). The relative risk of death was examined by Cox proportional hazards analyses adjusted for background (age, level of education, family situation, and county), health (longstanding illness, pain symptoms, smoking status, and psychological symptoms), and work-related factors (weekly working hours, physical and psychological demands, demands of learning at work, and perceived job insecurity). Female employees working at night had a 2.25-fold higher risk of mortality than female dayworkers (95% confidence interval [CI] 1.20–4.20) after adjustment for background and health- and work-related factors. In addition to total mortality, night work was also associated with tumor mortality. Female night workers had a 2.82-fold higher risk of tumor mortality than female dayworkers (95% CI 1.20–6.65) in the adjusted model. Among men, no such significant association was observed. The present study indicated that female night workers had a higher risk of both total and tumor mortality compared to female daytime employees. Additional research on the potential factors and mechanisms behind the association between night work and mortality is required. (Author correspondence: jouko.natti@uta.fi)     

Aging attenuates both the regularity and joint synchrony of LH and testosterone secretion in normal men: analyses via a model of graded GnRH receptor blockade

Testosterone (T) secretion declines in the aging male, albeit for unknown reasons. From an ensemble perspective, repeated incremental signaling among gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and T is required to maintain physiological androgen availability. Pattern-regularity statistics, such as univariate approximate entropy (ApEn) and bivariate cross-ApEn, provide specific and sensitive model-free measurement of altered multi-pathway control. The present study exploits partial muting of one pathway (GnRH drive) to appraise adaptive regulation of LH and T secretion in young and aging individuals. Analyses comprised 100 paired 18-h LH and T concentration time series obtained in 25 healthy men ages 20-72 yr each administered placebo and three graded doses of a specific GnRH-receptor antagonist. Graded blockade of GnRH drive increased the individual regularity of LH and T secretion and the synchrony of LH-T feedforward and T-LH feedback in the cohort as a whole (P<0.001 for each). However, age markedly attenuated ganirelix-induced enhancement of univariate T orderliness and bivariate LH-T feedback and T-LH feedback synchrony (P 相似文献   

Role of muscle loss in the age-associated reduction in VO2 max

A progressive decline in maximal O2 consumption (VO2max) expressed traditionally as per kilogram body weight generally occurs with advancing age. To investigate the extent to which this decline could be attributable to the age-associated loss of metabolically active tissue, i.e., muscle, we measured 24-h urinary creatinine excretion, an index of muscle mass, in 184 healthy nonobese volunteers, ages 22-87 yr, from the Baltimore Longitudinal Study of Aging who had achieved a true VO2max during graded treadmill exercise. A positive correlation was found between VO2max and creatinine excretion in both men (r = 0.64, P less than 0.001) and women (r = 0.47, P less than 0.001). As anticipated, VO2max showed a strong negative linear relationship with age in both men and women. Creatinine excretion also declined with age in men and women. When VO2max was normalized for creatinine excretion, the variance in the VO2max decline attributable to age declined from 60 to 14% in men and from 50 to 8% in women. Thus comparing the standard age regression of VO2max per kilogram body weight with that in which VO2max is normalized per milligram creatinine excretion, the decline in VO2max between a hypothetical 30 yr old and a 70 yr old was reduced from 39 to 18% in men and from 30 to 14% in women. We conclude that in both sexes, a large portion of the age-associated decline in VO2max in non-endurance-trained individuals is explicable by the loss of muscle mass, which is observed with advancing age.