'Dynamic' Starling mechanism: effects of ageing and physical fitness on ventricular-arterial coupling

Effects of aging and endurance exercise training on cardiorespiratory fitness and cardiac structure and function in healthy midlife and older women

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in women in developed societies. Unfavorable structural and functional adaptations within the heart and central blood vessels with sedentary aging in women can act as the substrate for the development of debilitating CVD conditions such as heart failure with preserved ejection fraction (HFpEF). The large decline in cardiorespiratory fitness, as indicated by maximal or peak oxygen uptake (V̇o2max and V̇o2peak, respectively), that occurs in women as they age significantly affects their health and chronic disease status, as well as the risk of cardiovascular and all-cause mortality. Midlife and older women who have performed structured endurance exercise training for several years or decades of their adult lives exhibit a V̇o2max and cardiac and vascular structure and function that are on par or even superior to much younger sedentary women. Therefore, regular endurance exercise training appears to be an effective preventative strategy for mitigating the adverse physiological cardiovascular adaptations associated with sedentary aging in women. Herein, we narratively describe the aging and short- and long-term endurance exercise training adaptations in V̇o2max, cardiac structure, and left ventricular systolic and diastolic function at rest and exercise in midlife and older women. The role of circulating estrogens on cardiac structure and function is described for consideration in the timing of exercise interventions to maximize beneficial adaptations. Current research gaps and potential areas for future investigation to advance our understanding in this critical knowledge area are highlighted.

Running away from cardiovascular disease at the right speed: The impact of aerobic physical activity and cardiorespiratory fitness on cardiovascular disease risk and associated subclinical phenotypes

Higher levels of physical activity (PA) and cardiorespiratory fitness (CRF) are associated with lower risk of incident cardiovascular disease (CVD). However, the relationship of aerobic PA and CRF with risk of atherosclerotic CVD outcomes and heart failure (HF) seem to be distinct. Furthermore, recent studies have raised concerns of potential toxicity associated with extreme levels of aerobic exercise, with higher levels of coronary artery calcium and incident atrial fibrillation noted among individuals with very high PA levels. In contrast, the relationship between PA levels and measures of left ventricular structure and function and risk of HF is more linear. Thus, personalizing exercise levels to optimal doses may be key to achieving beneficial outcomes and preventing adverse CVD events among high risk individuals. In this report, we provide a comprehensive review of the literature on the associations of aerobic PA and CRF levels with risk of adverse CVD outcomes and the preceding subclinical cardiac phenotypes to better characterize the optimal exercise dose needed to favorably modify CVD risk.

The effect of lifelong endurance exercise on cardiovascular structure and exercise function in women

KEY POINTS

The beneficial effects of sustained or lifelong (>25 years) endurance exercise on cardiovascular structure and exercise function have been largely established in men. The current findings indicate that committed (≥4 weekly exercise sessions) lifelong exercise results in substantial benefits in exercise capacity ( V ̇ O 2 max ), cardiovascular function at submaximal and maximal exercise, left ventricular mass and compliance, and blood volume compared to similarly aged or even younger (middle-age) untrained women. Endurance exercise training should be considered a key strategy to prevent cardiovascular disease with ageing in women as well as men.

ABSTRACT

This study was a retrospective, cross-sectional analysis of exercise performance and left ventricular (LV) morphology in 70 women to examine whether women who have performed regular, lifelong endurance exercise acquire the same beneficial adaptations in cardiovascular structure and function and exercise performance that have been reported previously in men. Three groups of women were examined: (1) 35 older (>60 years) untrained women (older untrained, OU), (2) 13 older women who had consistently performed four or more endurance exercise sessions weekly for at least 25 years (older trained, OT), and (3) 22 middle-aged (range 35-59 years) untrained women (middle-aged untrained, MU) as a reference control for the appropriate age-related changes. Oxygen uptake ( V ̇ O 2 ) and cardiovascular function (cardiac output ( Q ̇ ); stroke volume (SV) acetylene rebreathing) were examined at rest, steady-state submaximal exercise and maximal exercise (maximal oxygen uptake, V ̇ O 2 max ). Blood volume (CO rebreathing) and LV mass (cardiac magnetic resonance imaging), plus invasive measures of static and dynamic chamber compliance were also examined. V ̇ O 2 max (p < 0.001) and maximal exercise Q ̇ and SV were larger in older trained women compared to the two untrained groups (∼17% and ∼27% for Q ̇ and SV, respectively, versus MU; ∼40% and ∼38% versus OU, all p < 0.001). Blood volume (mL kg^-1 ) and LV mass index (g m^-2 ) were larger in OT versus OU (∼11% and ∼16%, respectively, both P ≤ 0.015) Static LV chamber compliance was greater in OT compared to both untrained groups (median (25-75%): MU: 0.065 (0.049-0.080); OU: 0.085 (0.061-0.138); OT: 0.047 (0.031-0.054), P ≤ 0.053). Collectively, these findings indicate that lifetime endurance exercise appears to be extremely effective at preserving or even enhancing cardiovascular structure and function with advanced age in women.

Exercise and Coronary Atherosclerosis: Observations, Explanations, Relevance, and Clinical Management

Physical activity and exercise training are effective strategies for reducing the risk of cardiovascular events, but multiple studies have reported an increased prevalence of coronary atherosclerosis, usually measured as coronary artery calcification, among athletes who are middle-aged and older. Our review of the medical literature demonstrates that the prevalence of coronary artery calcification and atherosclerotic plaques, which are strong predictors for future cardiovascular morbidity and mortality, was higher in athletes compared with controls, and was higher in the most active athletes compared with less active athletes. However, analysis of plaque morphology revealed fewer mixed plaques and more often only calcified plaques among athletes, suggesting a more benign composition of atherosclerotic plaques. This review describes the effects of physical activity and exercise training on coronary atherosclerosis in athletes who are middle-aged and older and aims to contribute to the understanding of the potential adverse effects of the highest doses of exercise training on the coronary arteries. For this purpose, we will review the association between exercise and coronary atherosclerosis measured using computed tomography, discuss the potential underlying mechanisms for exercise-induced coronary atherosclerosis, determine the clinical relevance of coronary atherosclerosis in middle-aged athletes and describe strategies for the clinical management of athletes with coronary atherosclerosis to guide physicians in clinical decision making and treatment of athletes with elevated coronary artery calcification scores.

Increased Myocardial Stiffness in Patients With High-Risk Left Ventricular Hypertrophy: The Hallmark of Stage-B Heart Failure With Preserved Ejection Fraction

BACKGROUND

Individuals with left ventricular hypertrophy (LVH) and elevated cardiac biomarkers in middle age are at high risk for the development of heart failure with preserved ejection fraction (HFpEF). However, it is unknown what the pathophysiological underpinnings of this high-risk state may be. We tested the hypothesis that patients with LVH and elevated cardiac biomarkers would demonstrate elevated left ventricular (LV) myocardial stiffness in comparison with healthy controls as a key marker for future HFpEF.

METHODS

Forty-six patients with LVH (LV septum >11 mm) and elevated cardiac biomarkers (N-terminal pro-B-type natriuretic peptide [>40 pg/mL] or troponin T [>0.6 pg/mL]) were recruited, along with 61 age- and sex-matched (by cohort) healthy controls. To define LV pressure-volume relationships, right heart catheterization and 3-dimensional echocardiography were performed while preload was manipulated using lower body negative pressure and rapid saline infusion.

RESULTS

There were significant differences in body size, blood pressure, and baseline pulmonary capillary wedge pressure between groups (eg, pulmonary capillary wedge pressure: LVH, 13.4±2.7 versus control, 11.7±1.7 mm Hg, P<0.0001). The LV was less distensible in LVH than in controls (smaller volume for the same filling pressure). When preload was expressed as transmural filling pressure (pulmonary capillary wedge pressure - right atrial pressure), LV myocardial stiffness was nearly 30% greater in LVH than in controls (LVH stiffness constant, 0.053±0.027 versus controls, 0.042±0.020, P=0.028).

CONCLUSIONS

LV myocardial stiffness in patients with LVH and elevated biomarkers (stage-B HFpEF) is greater than in age- and sex-matched controls and thus appears to represent a transitional state from a normal healthy heart to HFpEF. Although the LV myocardial stiffness of patients with LVH is greater than that of healthy controls at this early stage, further studies are required to clarify whether interventions such as exercise training to improve LV compliance may prevent the full manifestation of the HFpEF syndrome in these high-risk individuals.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifiers: NCT03476785 and NCT02039154.

The impact of 2 years of high-intensity exercise training on a model of integrated cardiovascular regulation

KEY POINTS

Heart rate variability, a common and easily measured index of cardiovascular dynamics, is the output variable of complicated cardiovascular and respiratory control systems. Both neural and non-neural control mechanisms may contribute to changes in heart rate variability. We previously developed an innovative method using transfer function analysis to assess the effect of prolonged exercise training on integrated cardiovascular regulation. In the present study, we modified and applied this to investigate the effect of 2 years of high-intensity training on circulatory components to tease out the primary effects of training. Our method incorporated the dynamic Starling mechanism, dynamic arterial elastance and arterial-cardiac baroreflex function. The dynamic Starling mechanism gain and arterial-cardiac baroreflex gain were significantly increased in the exercise group. These parameters remained unchanged in the controls. Conversely, neither group experienced a change in dynamic arterial elastance. The integrated cardiovascular regulation gain in the exercise group was 1.34-fold larger than that in the control group after the intervention. In these previously sedentary, otherwise healthy, middle-aged adults, 2 years of high-intensity exercise training improved integrated cardiovascular regulation by enhancing the dynamic Starling mechanism and arterial-cardiac baroreflex sensitivity.

ABSTRACT

Assessing the effects of exercise training on cardiovascular variability is challenging because of the complexity of multiple mechanisms. In a prospective, parallel-group, randomized controlled study, we examined the effect of 2 years of high-intensity exercise training on integrated cardiovascular function, which incorporates the dynamic Starling mechanism, dynamic arterial elastance and arterial-cardiac baroreflex function. Sixty-one healthy participants (48% male, aged 53 years, range 52-54 years) were randomized to either 2 years of exercise training (exercise group: n = 34) or control/yoga group (controls: n = 27). Before and after 2 years, subjects underwent a 6 min recording of beat-by-beat pulmonary artery diastolic pressure (PAD), stroke volume index (SV index), systolic blood pressure (sBP) and RR interval measurements with controlled respiration at 0.2 Hz. The dynamic Starling mechanism, dynamic arterial elastance and arterial-cardiac baroreflex function were calculated by transfer function gain between PAD and SV index; SV index and sBP; and sBP and RR interval, respectively. Fifty-three participants (controls: n = 25; exercise group: n = 28) completed the intervention. After 2 years, the dynamic Starling mechanism gain (Group × Time interaction: P = 0.008) and the arterial-cardiac baroreflex gain (P = 0.005) were significantly increased in the exercise group but remained unchanged in the controls. There was no change in dynamic arterial elastance in either of the two groups. The integrated cardiovascular function gain in the exercise group increased 1.34-fold, whereas there was no change in the controls (P = 0.02). In these previously sedentary, otherwise healthy middle-aged adults, a 2 year programme of high-intensity exercise training improved integrated cardiovascular regulation by enhancing the dynamic Starling mechanism and arterial-cardiac baroreflex sensitivity, without changing dynamic arterial elastance.

Preload-corrected dynamic Starling mechanism in patients with heart failure with preserved ejection fraction

The beat-to-beat dynamic Starling mechanism (DSM), the dynamic modulation of stroke volume (SV) because of breath-by-breath changes in left-ventricular end-diastolic pressure (LVEDP), reflects ventricular-arterial coupling. The purpose of this study was to test whether the LVEDP-SV relationship remained impaired in heart failure with preserved ejection fraction (HFpEF) patients after normalization of LVEDP. Right heart catheterization and model-flow analysis of the arterial pressure waveform were performed while preload was manipulated using lower-body negative pressure to alter LVEDP. The DSM was compared at similar levels of LVEDP between HFpEF patients ( n = 10) and age-matched healthy controls ( n = 12) (HFpEF vs. controls: 10.9 ± 3.8 vs. 11.2 ± 1.3 mmHg, P = 1.00). Transfer function analysis between diastolic pulmonary artery pressure (PAD) representing dynamic changes in LVEDP vs. SV index was applied to obtain gain and coherence of the DSM. The DSM gain was significantly lower in HFpEF patients than in the controls, even at a similar level of LVEDP (0.46 ± 0.19 vs. 0.99 ± 0.39 ml·m−2·mmHg−1, P = 0.0018). Moreover, the power spectral density of PAD, the input variability, was greater in the HFpEF group than the controls (0.75 ± 0.38 vs. 0.28 ± 0.26 mmHg2, P = 0.01). Conversely, the power spectral density of SV index, the output variability, was not different between the groups ( P = 0.97). There was no difference in the coherence, which confirms the reliability of the linear transfer function between the two groups (0.71 ± 0.13 vs. 0.77 ± 0.19, P = 0.87). The DSM gain in HFpEF patients is impaired compared with age-matched controls even at a similar level of LVEDP, which may reflect intrinsic LV diastolic dysfunction and incompetence of ventricular-arterial coupling.

NEW & NOTEWORTHY The beat-to-beat dynamic Starling mechanism (DSM), the dynamic modulation of stroke volume because of breath-by-breath changes in left-ventricular end-diastolic pressure (LVEDP), reflects ventricular-arterial coupling. Although the DSM gain is impaired in heart failure with preserved ejection fraction (HFpEF) patients, it is not clear whether this is because of higher LVEDP or left-ventricular diastolic dysfunction. The DSM gain in HFpEF patients is severely impaired, even at a similar level of LVEDP, which may reflect intrinsic left-ventricular diastolic dysfunction.

Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association

Mounting evidence has firmly established that low levels of cardiorespiratory fitness (CRF) are associated with a high risk of cardiovascular disease, all-cause mortality, and mortality rates attributable to various cancers. A growing body of epidemiological and clinical evidence demonstrates not only that CRF is a potentially stronger predictor of mortality than established risk factors such as smoking, hypertension, high cholesterol, and type 2 diabetes mellitus, but that the addition of CRF to traditional risk factors significantly improves the reclassification of risk for adverse outcomes. The purpose of this statement is to review current knowledge related to the association between CRF and health outcomes, increase awareness of the added value of CRF to improve risk prediction, and suggest future directions in research. Although the statement is not intended to be a comprehensive review, critical references that address important advances in the field are highlighted. The underlying premise of this statement is that the addition of CRF for risk classification presents health professionals with unique opportunities to improve patient management and to encourage lifestyle-based strategies designed to reduce cardiovascular risk. These opportunities must be realized to optimize the prevention and treatment of cardiovascular disease and hence meet the American Heart Association's 2020 goals.

The effect of 1 year of Alagebrium and moderate-intensity exercise training on left ventricular function during exercise in seniors: a randomized controlled trial

Sedentary aging leads to left ventricular (LV) and vascular stiffening due in part to advanced glycation end-products (AGEs) cross-linking of extracellular matrix proteins. Vigorous lifelong exercise ameliorates age-related cardiovascular (CV) stiffening and enhances exercise LV function, although this effect is limited when exercise is initiated later in life. We hypothesized that exercise training might be more effective at improving the impact of age-related CV stiffening during exercise when combined with an AGE cross-link breaker (Alagebrium). Sixty-two seniors (≥60 yr) were randomized into four groups: sedentary + placebo, sedentary + Alagebrium, exercise + placebo, and exercise + Alagebrium for 1 yr. Moderate-intensity aerobic exercise was performed 3-4 sessions/wk; controls underwent similar frequency of yoga/balance training. Twenty-four similarly-aged, lifelong exercisers (4-5 sessions/wk) served as a comparator for the effect of lifelong exercise on exercising LV function. Oxygen uptake (Douglas bags), stroke index (SI; acetylene rebreathing), and effective arterial elastance (Ea) were collected at rest and submaximal and maximal exercise. Maximum O2 uptake (23 ± 5 to 25 ± 6 ml·kg(-1)·min(-1)) increased, while SI (35 ± 11 to 39 ± 12 ml/m(2)) and Ea (4.0 ± 1.1 to 3.7 ± 1.2 mmHg·ml(-1)·m(-2)) were improved across all conditions with exercise, but remained unchanged in controls (exercise × time, P ≤ 0.018). SI or Ea were not affected by Alagebrium (medication × time, P ≥ 0.468) or its combination with exercise (interaction P ≥ 0.252). After 1 yr of exercise plus Alagebrium, exercise SI and Ea remained substantially below that of lifelong exercisers (15-24 and 9-22%, respectively, P ≤ 0.415). In conclusion, Alagebrium plus exercise had no synergistic effect on exercise LV function and failed to achieve levels associated with lifelong exercise, despite a similar exercise frequency.

Spectral transfer function analysis of respiratory hemodynamic fluctuations predicts end-diastolic stiffness in preserved ejection fraction heart failure

Preserved ejection fraction heart failure (HFpEF) diagnosis remains controversial, and invasive left ventricular (LV) hemodynamic evaluation and/or exercise testing is advocated by many. The stiffer HFpEF myocardium may show impaired stroke volume (SV) variation induced by fluctuating LV filling pressure during ventilation. Our aim was to investigate spectral transfer function (STF) gain from end-diastolic pressure (EDP) to indexed SV (SVi) in experimental HFpEF. Eighteen-week-old Wistar-Kyoto (WKY) and ZSF1 lean (ZSF1 Ln) and obese rats (ZSF1 Ob) randomly underwent LV open-chest (OC, n = 8 each group) or closed-chest hemodynamic evaluation (CC, n = 6 each group) under halogenate anesthesia and positive-pressure ventilation at constant inspiratory pressure. Beat-to-beat fluctuations in hemodynamic parameters during ventilation were assessed by STF. End-diastolic stiffness (βi) and end-systolic elastance (Eesi) for indexed volumes were obtained by inferior vena cava occlusion in OC (multibeat) or single-beat method estimates in CC. ZSF1 Ob showed higher EDP spectrum (P < 0.001), higher STF gain between end-diastolic volume and EDP, and impaired STF gain between EDP and SVi compared with both hypertensive ZSF1 Ln and normotensive WKY controls (P < 0.001). Likewise βi was only higher in ZSF1 Ob while Eesi was raised in both ZSF1 groups. On multivariate analysis βi and not Eesi correlated with impaired STF gain from EDP to SVi (P < 0.001), and receiver-operating characteristics analysis showed an area under curve of 0.89 for higher βi prediction (P < 0.001). Results support further clinical testing of STF analysis from right heart catheterization-derived EDP surrogates to noninvasively determined SV as screening/diagnostic tool to assess myocardial stiffness in HFpEF.

Sympathetic neural regulation of blood pressure: influences of sex and aging

Sex and age have important influences on sympathetic neural control of blood pressure in humans. Young women are relatively protected against risk of hypertension due to greater peripheral vasodilator influences compared with young men and older people. This protective effect is lost at menopause. Older men and women have higher sympathetic nerve activity and tighter coupling between SNA and blood pressure, contributing to the increased risk of hypertension with aging.

Sex differences in ventricular-vascular coupling following endurance training

Introduction

Ventricular and vascular coupling is defined as the ratio of arterial elastance (Ea) to ventricular elastance (Elv) and describes the interaction between the heart and arterial system. There are sex differences in both arterial and ventricular function in response to both acute exercise and aerobic exercise training.

Purpose

To examine the effects of aerobic exercise training on elastances and the coupling ratio in young adult men and women. We hypothesized a reduction in the coupling ratio in both sexes due to a decrease in Ea that would be more pronounced in men and an increase in Elv that would be larger in women.

Methods

Fifty-three healthy, young adults completed the study. Central pulse wave velocity and heart volumes were measured before and after an 8-week aerobic training intervention. Elastances were calculated as Ea = end-systolic pressure/stroke volume and Elv = end-systolic pressure/end-systolic volume and indexed to body surface area.

Results

After the intervention, women augmented indexed and un-indexed Elv from 2.09 ± 0.61 to 2.52 ± 0.80 mmHg/ml, p < 0.05, and reduced the coupling ratio from 0.72 ± 18 to 0.62 ± 15, p < 0.05, while men maintained their pre-training ratio (from 0.66 ± 0.20 to 0.74 ± 0.21, p > 0.05). Women also reduced end-systolic pressure (from 91 ± 10 to 87 ± 10 mmHg), and both groups reduced central pulse wave velocity (from 6.0 ± 1.0 to 5.6 ± 0.6 m/s, p < 0.05).

Conclusion

We conclude that after 8 weeks of aerobic training, only women reduced their coupling ratio due to an increase in Elv. This suggests that aerobic exercise training elicits sex-dependent changes in the coupling ratio in young, healthy individuals.

Causes of exercise intolerance in heart failure with preserved ejection fraction: searching for consensus

Exercise intolerance is one of the cardinal symptoms of heart failure with preserved ejection fraction (HFpEF). We review its mechanistic basis using evidence from exercise studies. One barrier to a consensus understanding of the pathophysiology is heterogeneity of the patient population. Therefore, we pay special attention to varying study definitions of the disease and their possible impact on the causal factors that are implicated. We then discuss the role of exercise testing and its potential to subtype HFpEF in to more homogeneous mechanism-based subclasses.

The effect of lifelong exercise dose on cardiovascular function during exercise

An increased "dose" of endurance exercise training is associated with a greater maximal oxygen uptake (Vo2max), a larger left ventricular (LV) mass, and improved heart rate and blood pressure control. However, the effect of lifelong exercise dose on metabolic and hemodynamic response during exercise has not been previously examined. We performed a cross-sectional study on 101 (69 men) seniors (60 yr and older) focusing on lifelong exercise frequency as an index of exercise dose. These included 27 who had performed ≤ 2 exercise sessions/wk (sedentary), 25 who performed 2-3 sessions/wk (casual), 24 who performed 4-5 sessions/wk (committed) and 25 who performed ≥ 6 sessions/wk plus regular competitions (Masters athletes) over at least the last 25 yr. Oxygen uptake and hemodynamics [cardiac output, stroke volume (SV)] were collected at rest, two levels of steady-state submaximal exercise, and maximal exercise. Doppler ultrasound measures of LV diastolic filling were assessed at rest and during LV loading (saline infusion) to simulate increased LV filling. Body composition, total blood volume, and heart rate recovery after maximal exercise were also examined. Vo2max increased in a dose-dependent manner (P < 0.05). At maximal exercise, cardiac output and SV were largest in committed exercisers and Masters athletes (P < 0.05), while arteriovenous oxygen difference was greater in all trained groups (P < 0.05). At maximal exercise, effective arterial elastance, an index of ventricular-arterial coupling, was lower in committed exercisers and Masters athletes (P < 0.05). Doppler measures of LV filling were not enhanced at any condition, irrespective of lifelong exercise frequency. These data suggest that performing four or more weekly endurance exercise sessions over a lifetime results in significant gains in Vo2max, SV, and heart rate regulation during exercise; however, improved SV regulation during exercise is not coupled with favorable effects on LV filling, even when the heart is fully loaded.

Cardiovascular effects of 1 year of progressive endurance exercise training in patients with heart failure with preserved ejection fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is a disease of the elderly with cardiovascular stiffening and reduced exercise capacity. Exercise training appears to improve exercise capacity and cardiovascular function in heart failure with reduced ejection fraction. However, it is unclear whether exercise training could improve cardiovascular stiffness, exercise capacity, and ventricular-arterial coupling in HFpEF.

METHODS

Eleven HFpEF patients and 13 healthy controls underwent invasive measurements with right heart catheterization to define Starling and left ventricular (LV) pressure-volume curves; secondary functional outcomes included Doppler echocardiography, arterial stiffness, cardiopulmonary exercise testing with cardiac output measurement, and ventricular-arterial coupling assessed by the dynamic Starling mechanism. Seven of 11 HFpEF patients (74.9 ± 6 years; 3 men/4 women) completed 1 year of endurance training followed by repeat measurements. Pulmonary capillary wedge pressures and LV end-diastolic volumes were measured at baseline during decreased and increased cardiac filling. LV compliance was assessed by the slope of the pressure-volume curve. Beat-to-beat LV end-diastolic pressure (estimated from pulmonary arterial diastolic pressure) and stroke volume index were obtained, and spectral transfer function analysis was used to assess the dynamic Starling mechanism.

RESULTS

Before training, HFpEF patients had reduced exercise capacity, distensibility and dynamic Starling mechanism but similar LV compliance and end-diastolic volumes compared to controls albeit with elevated filling pressure and increased wall stress. One year of training had little effect on LV compliance and volumes, arterial stiffness, exercise capacity or ventricular-arterial coupling.

CONCLUSION

Contrary to our hypothesis, 1 year of endurance training failed to impart favorable effects on cardiovascular stiffness or function in HFpEF.

Sex, ageing and resting blood pressure: gaining insights from the integrated balance of neural and haemodynamic factors

Young women tend to have lower blood pressure, and less risk of hypertension, compared to young men. As people age, both blood pressure and the risk of hypertension increase in both sexes; this occurs most strikingly in women after menopause. However, the mechanisms for these influences of sex and age remain incompletely understood. In this review we are specifically interested in the interaction between neural (sympathetic nerve activity; SNA) and haemodynamic factors (cardiac output, blood pressure and vascular resistance) and how these change with sex and age. While peripheral vascular SNA can vary 7- to 10-fold among normotensive young men and women, it is reproducible in a given individual. Surprisingly, higher levels of SNA are not associated with higher blood pressures in these groups. In young men, high SNA is associated with higher total peripheral vascular resistance (TPR), and appears to be balanced by lower cardiac output and less peripheral vascular responsiveness to adrenergic stimulation. Young women do not exhibit the SNA-TPR relationship. Recent evidence suggests that β-adrenergic vasodilatation offsets the vasoconstrictor effects of α-adrenergic vasoconstriction in young women, which may contribute to the generally lower blood pressures in this group. Sympathetic nerve activity increases with age, and in groups over 40, levels of SNA are more tightly linked to levels of blood pressure. The potentially protective β-adrenergic effect seen in young women appears to be lost after menopause and probably contributes to the increased blood pressure and increased risk of hypertension seen in older women.

Effect of exercise training on biologic vascular age in healthy seniors

Arteriosclerosis with aging leads to central arterial stiffening in humans, which could be a prime cause for increased cardiac afterload in the elderly. The purpose of the present study was to assess the effects of 1 yr of progressive exercise training on central aortic compliance and left ventricular afterload in sedentary healthy elderly volunteers. Ten healthy sedentary seniors and 11 Masters athletes (>65 yr) were recruited. The sedentary seniors underwent 1 yr of progressive exercise training so that at the end of the year, they were exercising ∼200 min/wk. Central aortic compliance was assessed by the Modelflow aortic age, which reflects the intrinsic structural components of aortic compliance. Cardiac afterload was assessed by effective arterial elastance (Ea) with its contributors of peripheral vascular resistance (PVR) and systemic arterial compliance (SAC). After exercise training, Ea, PVR, and SAC were improved in sedentary seniors and became comparable with those of Masters athletes although the Modelflow aortic age was not changed. Moreover, after exercise training, when stroke volume was restored with lower body negative pressure back to pretraining levels, the exercise training-induced improvements in Ea, PVR, and SAC were eliminated. Aortic stiffening with aging was not improved even after 1 yr of progressive endurance exercise training in the previously sedentary elderly, while left ventricular afterload was reduced. This reduced afterload after exercise training appeared to be attributable to cardiovascular functional modulation to an increase in stroke volume rather than to intrinsic structural changes in the arterial wall.

Exercise-induced cognitive plasticity, implications for mild cognitive impairment and Alzheimer's disease

Lifestyle factors such as intellectual stimulation, cognitive and social engagement, nutrition, and various types of exercise appear to reduce the risk for common age-associated disorders such as Alzheimer’s disease (AD) and vascular dementia. In fact, many studies have suggested that promoting physical activity can have a protective effect against cognitive deterioration later in life. Slowing or a deterioration of walking speed is associated with a poor performance in tests assessing psychomotor speed and verbal fluency in elderly individuals. Fitness training influences a wide range of cognitive processes, and the largest positive impact observed is for executive (a.k.a. frontal lobe) functions. Studies show that exercise improves additional cognitive functions such as tasks mediated by the hippocampus, and result in major changes in plasticity in the hippocampus. Interestingly, this exercise-induced plasticity is also pronounced in APOE ε4 carriers who express a risk factor for late-onset AD that may modulate the effect of treatments. Based on AD staging by Braak and Braak (1991) and Braak et al. (1993) we propose that the effects of exercise occur in two temporo-spatial continua of events. The “inward” continuum from isocortex (neocortex) to entorhinal cortex/hippocampus for amyloidosis and a reciprocal “outward” continuum for neurofibrillary alterations. The exercise-induced hypertrophy of the hippocampus at the core of these continua is evaluated in terms of potential for prevention to stave off neuronal degeneration. Exercise-induced production of growth factors such as the brain-derived neurotrophic factor (BDNF) has been shown to enhance neurogenesis and to play a key role in positive cognitive effects. Insulin-like growth factor (IGF-1) may mediate the exercise-induced response to exercise on BDNF, neurogenesis, and cognitive performance. It is also postulated to regulate brain amyloid β (Aβ) levels by increased clearance via the choroid plexus. Growth factors, specifically fibroblast growth factor and IGF-1 receptors and/or their downstream signaling pathways may interact with the Klotho gene which functions as an aging suppressor gene. Neurons may not be the only cells affected by exercise. Glia (astrocytes and microglia), neurovascular units and the Fourth Element may also be affected in a differential fashion by the AD process. Analyses of these factors, as suggested by the multi-dimensional matrix approach, are needed to improve our understanding of this complex multi-factorial process, which is increasingly relevant to conquering the escalating and intersecting world-wide epidemics of dementia, diabetes, and sarcopenia that threaten the global healthcare system. Physical activity and interventions aimed at enhancing and/or mimicking the effects of exercise are likely to play a significant role in mitigating these epidemics, together with the embryonic efforts to develop cognitive rehabilitation for neurodegenerative disorders.

Congestive heart failure with preserved ejection fraction is associated with severely impaired dynamic Starling mechanism

Sedentary aging leads to increased cardiovascular stiffening, which can be ameliorated by sufficient amounts of lifelong exercise training. An even more extreme form of cardiovascular stiffening can be seen in heart failure with preserved ejection fraction (HFpEF), which comprises ~40~50% of elderly patients diagnosed with congestive heart failure. There are two major interrelated hypotheses proposed to explain heart failure in these patients: 1) increased left ventricular (LV) diastolic stiffness and 2) increased arterial stiffening. The beat-to-beat dynamic Starling mechanism, which is impaired with healthy human aging, reflects the interaction between ventricular and arterial stiffness and thus may provide a link between these two mechanisms underlying HFpEF. Spectral transfer function analysis was applied between beat-to-beat changes in LV end-diastolic pressure (LVEDP; estimated from pulmonary artery diastolic pressure with a right heart catheter) and stroke volume (SV) index. The dynamic Starling mechanism (transfer function gain between LVEDP and the SV index) was impaired in HFpEF patients (n = 10) compared with healthy age-matched controls (n = 12) (HFpEF: 0.23 ± 0.10 ml·m⁻²·mmHg⁻¹ and control: 0.37 ± 0.11 ml·m⁻²·mmHg⁻¹, means ± SD, P = 0.008). There was also a markedly increased (3-fold) fluctuation of LV filling pressures (power spectral density of LVEDP) in HFpEF patients, which may predispose to pulmonary edema due to intermittent exposure to higher pulmonary capillary pressure (HFpEF: 12.2 ± 10.4 mmHg² and control: 3.8 ± 2.9 mmHg², P = 0.014). An impaired dynamic Starling mechanism, even more extreme than that observed with healthy aging, is associated with marked breath-by-breath LVEDP variability and may reflect advanced ventricular and arterial stiffness in HFpEF, possibly contributing to reduced forward output and pulmonary congestion.

Normovolemia defined according to cardiac stroke volume in healthy supine humans

BACKGROUND

Both hypovolemia and a fluid overload are detrimental for outcome in surgical patients but the effort to establish normovolemia is hampered by the lack of an operational clinical definition. Manipulating the central blood volume on a tilt table demonstrates that the flat part of the Frank-Starling curve is reached when subjects are supine and that finding may be applicable for a clinical definition of normovolemia. However, it is unknown whether stroke volume (SV) responds to an increase in preload induced by fluid administration.

METHODS

In 20 healthy subjects (23 +/- 2 years, mean +/- SD), SV was measured by esophageal Doppler before and after fluid administration to evaluate whether SV increases in healthy, non-fasting, supine subjects. Two hundred millilitres of a synthetic colloid (hydroxyethyl starch, HES 130/0.4) was provided and repeated if a >or=10% increment in SV was obtained.

RESULTS

None of the subjects increased SV >or=10% following fluid administration but there was a minor increase in mean arterial pressure (92 +/- 15 to 93 +/- 12 mmHg, P = 0.01), while heart rate (HR) (66 +/- 12 beats min(-1); P = 0.32), cardiac output (4.8 +/- 1.1 l min(-1); P = 0.25) and the length of the systole corrected to a HR of 60 beats/min (corrected flow time; 344 +/- 24 ms; P = 0.31) did not change.

CONCLUSION

Supporting the proposed definition of normovolemia, non-fasting, supine, healthy subjects are provided with a preload to the heart that does not limit SV suggesting that the upper flat part of the Frank-Starling relationship is reached.

Cardiac output and oxygen uptake relationship during physical effort in men and women over 60 years old

This study investigated the relationship between oxygen uptake (VO(2)), cardiac output (Q), stroke volume (SV), and heart rate (HR) in 54 men and 77 women (age = 69 +/- 5 years) during incremental effort. Subjects performed a maximal cycle-ergometer test and VO(2) was directly measured. HR and SV were assessed by ECG and cardiograph impedance. Regression equations were calculated for Q-VO(2), HR-VO(2), and Q-HR relationships. The equations obtained for women were (a) Q (l min(-1)) = 2.61 + 4.67 VO(2) (l min(-1))(r(2) = 0.84); (b) HR (bpm) = 62.03 + 46.55 VO(2) (l min(-1)) (r (2) = 0.72); (c) SV (ml) 100:6[1 - e(-2.6 VO2 (1 min-1))] (r (2) = 0.41); (d) HR (bpm) = 41.48 + 9.24 Q (l min(-1)) (r (2) = 0.73). Equations for men were (a) Q (l min(-1)) = 2.52 + 5.70 VO(2) (l min(-1)) (r (2) = 0.89); (b) HR (bpm) = 66.31 + 32.35 VO(2) (l min(-1)) (r (2) = 0.72); (c) [1 - e(-1.7 VO2 (1 min-1))] (r (2) = 0.47); (d) HR (bpm) = 56.33 + 5.25 Q (l min(-1)) (r (2) = 0.69). The intercepts for Q-VO(2) and HR-VO(2) equations were similar for both genders, but the slopes were different (P < 0.05). The SV increased from baseline to 50-60% of VO(2) peak in both groups. No gender effect was found in SV increasing pattern, but the absolute values were in general higher for men (P > 0.05). A significant difference between men and women was observed for both slopes and intercepts in the Q-HR relationship (P < 0.05). In conclusion, (a) Q-VO(2) relation was linear during progressive effort; (b) regression intercepts were similar, but the slopes were higher for men compared to women; (c) SV-VO(2) relationship was nonlinear and maximum SV was reached at very submaximal workload; (d) older men exhibited higher Q upward potential as well higher SV but lower HR for a given submaximal workload than women of similar age.

Decompression to altitude: assumptions, experimental evidence, and future directions

Although differences exist, hypobaric and hyperbaric exposures share common physiological, biochemical, and clinical features, and their comparison may provide further insight into the mechanisms of decompression stress. Although altitude decompression illness (DCI) has been experienced by high-altitude Air Force pilots and is common in ground-based experiments simulating decompression profiles of extravehicular activities (EVAs) or astronauts' space walks, no case has been reported during actual EVAs in the non-weight-bearing microgravity environment of orbital space missions. We are uncertain whether gravity influences decompression outcomes via nitrogen tissue washout or via alterations related to skeletal muscle activity. However, robust experimental evidence demonstrated the role of skeletal muscle exercise, activities, and/or movement in bubble formation and DCI occurrence. Dualism of effects of exercise, positive or negative, on bubble formation and DCI is a striking feature in hypobaric exposure. Therefore, the discussion and the structure of this review are centered on those highlighted unresolved topics about the relationship between muscle activity, decompression, and microgravity. This article also provides, in the context of altitude decompression, an overview of the role of denitrogenation, metabolic gases, gas micronuclei, stabilization of bubbles, biochemical pathways activated by bubbles, nitric oxide, oxygen, anthropometric or physiological variables, Doppler-detectable bubbles, and potential arterialization of bubbles. These findings and uncertainties will produce further physiological challenges to solve in order to line up for the programmed human return to the Moon, the preparation for human exploration of Mars, and the EVAs implementation in a non-zero gravity environment.