Ventriculoarterial coupling during exercise in normal human subjects

Heat-related changes in the velocity and kinetic energy of flowing blood influence the human heart's output during hyperthermia

Passive whole-body hyperthermia increases limb blood flow and cardiac output (Q ̇ $\dot Q$ ), but the interplay between peripheral and central thermo-haemodynamic mechanisms remains unclear. Here we tested the hypothesis that local hyperthermia-induced alterations in peripheral blood flow and blood kinetic energy modulate flow to the heart andQ ̇ $\dot Q$ . Body temperatures, regional (leg, arm, head) and systemic haemodynamics, and left ventricular (LV) volumes and functions were assessed in eight healthy males during: (1) 3 h control (normothermic condition); (2) 3 h of single-leg heating; (3) 3 h of two-leg heating; and (4) 2.5 h of whole-body heating. Leg, forearm, and extracranial blood flow increased in close association with local rises in temperature while brain perfusion remained unchanged. Increases in blood velocity with small to no changes in the conduit artery diameter underpinned the augmented limb and extracranial perfusion. In all heating conditions,Q ̇ $\dot Q$ increased in association with proportional elevations in systemic vascular conductance, related to enhanced blood flow, blood velocity, vascular conductance and kinetic energy in the limbs and head (all R2 ≥ 0.803; P < 0.001), but not in the brain. LV systolic (end-systolic elastance and twist) and diastolic functional profiles (untwisting rate), pulmonary ventilation and systemic aerobic metabolism were only altered in whole-body heating. These findings substantiate the idea that local hyperthermia-induced selective alterations in peripheral blood flow modulate the magnitude of flow to the heart andQ ̇ $\dot Q$ through changes in blood velocity and kinetic energy. Localised heat-activated events in the peripheral circulation therefore affect the human heart's output. KEY POINTS: Local and whole-body hyperthermia increases limb and systemic perfusion, but the underlying peripheral and central heat-sensitive mechanisms are not fully established. Here we investigated the regional (leg, arm and head) and systemic haemodynamics (cardiac output:Q ̇ $\dot Q$ ) during passive single-leg, two-leg and whole-body hyperthermia to determine the contribution of peripheral and central thermosensitive factors in the control of human circulation. Single-leg, two-leg, and whole-body hyperthermia induced graded increases in leg blood flow andQ ̇ $\dot Q$ . Brain blood flow, however, remained unchanged in all conditions. Ventilation, extracranial blood flow and cardiac systolic and diastolic functions only increased during whole-body hyperthermia. The augmentedQ ̇ $\dot Q$ with hyperthermia was tightly related to increased limb and head blood velocity, flow and kinetic energy. The findings indicate that local thermosensitive mechanisms modulate regional blood velocity, flow and kinetic energy, thereby controlling the magnitude of flow to the heart and thus the coupling of peripheral and central circulation during hyperthermia.

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.

Mild hypothermia attenuates ischaemia/reperfusion injury: insights from serial non-invasive pressure-volume loops

AIMS

Mild hypothermia, 32-35°C, reduces infarct size in experimental studies, potentially mediating reperfusion injuries, but human trials have been ambiguous. To elucidate the cardioprotective mechanisms of mild hypothermia, we analysed cardiac performance in a porcine model of ischaemia/reperfusion, with serial cardiovascular magnetic resonance (CMR) imaging throughout 1 week using non-invasive pressure-volume (PV) loops.

METHODS AND RESULTS

Normothermia and Hypothermia group sessions (n = 7 + 7 pigs, non-random allocation) were imaged with Cardiovascular magnetic resonance (CMR) at baseline and subjected to 40 min of normothermic ischaemia by catheter intervention. Thereafter, the Hypothermia group was rapidly cooled (mean 34.5°C) for 5 min before reperfusion. Additional CMR sessions at 2 h, 24 h, and 7 days acquired ventricular volumes and ischaemic injuries (unblinded analysis). Stroke volume (SV: -24%; P = 0.029; Friedmans test) and ejection fraction (EF: -20%; P = 0.068) were notably reduced at 24 h in the Normothermia group compared with baseline. In contrast, the decreases were ameliorated in the Hypothermia group (SV: -6%; P = 0.77; EF: -6%; P = 0.13). Mean arterial pressure remained stable in Normothermic animals (-3%, P = 0.77) but dropped 2 h post-reperfusion in hypothermic animals (-18%, P = 0.007). Both groups experienced a decrease and partial recovery pattern for PV loop-derived variables over 1 week, but the adverse effects tended to attenuate in the Hypothermia group. Infarct sizes were 10 ± 8% in Hypothermic and 15 ± 8% in Normothermic animals (P = 0.32). Analysis of covariance at 24 h indicated that hypothermia has cardioprotective properties incremental to reducing infarct size, such as higher external power (P = 0.061) and lower arterial elastance (P = 0.015).

CONCLUSION

Using non-invasive PV loops by CMR, we observed that mild hypothermia at reperfusion alleviates the heart's work after ischaemia/reperfusion injuries during the first week and preserves short-term cardiac performance. This hypothesis-generating study suggests hypothermia to have cardioprotective properties, incremental to reducing infarct size. The primary cardioprotective mechanism was likely an afterload reduction acutely unloading the left ventricle.

Endurance-trained subjects and sedentary controls increase ventricular contractility and efficiency during exercise: Feasibility of hemodynamics assessed by non-invasive pressure-volume loops

INTRODUCTION

Pressure-volume (PV) loops can be used to assess both load-dependent and load-independent measures of cardiac hemodynamics. However, analysis of PV loops during exercise is challenging as it requires invasive measures. Using a novel method, it has been shown that left ventricular (LV) PV loops at rest can be obtained non-invasively from cardiac magnetic resonance imaging (CMR) and brachial pressures. Therefore, the aim of this study was to assess if LV PV loops can be obtained non-invasively from CMR during exercise to assess cardiac hemodynamics.

METHODS

Thirteen endurance trained (ET; median 48 years [IQR 34-60]) and ten age and sex matched sedentary controls (SC; 43 years [27-57]) were included. CMR images were acquired at rest and during moderate intensity supine exercise defined as 60% of expected maximal heart rate. Brachial pressures were obtained in conjunction with image acquisition.

RESULTS

Contractility measured as maximal ventricular elastance (Emax) increased in both groups during exercise (ET: 1.0 mmHg/ml [0.9-1.1] to 1.1 mmHg/ml [0.9-1.2], p<0.01; SC: 1.1 mmHg/ml [0.9-1.2] to 1.2 mmHg/ml [1.0-1.3], p<0.01). Ventricular efficiency (VE) increased in ET from 70% [66-73] at rest to 78% [75-80] (p<0.01) during exercise and in SC from 68% [63-72] to 75% [73-78] (p<0.01). Arterial elastance (EA) decreased in both groups (ET: 0.8 mmHg/ml [0.7-0.9] to 0.7 mmHg/ml [0.7-0.9], p<0.05; SC: 1.0 mmHg/ml [0.9-1.2] to 0.9 mmHg/ml [0.8-1.0], p<0.05). Ventricular-arterial coupling (EA/Emax) also decreased in both groups (ET: 0.9 [0.8-1.0] to 0.7 [0.6-0.8], p<0.01; SC: 1.0 [0.9-1.1] to 0.7 [0.7-0.8], p<0.01).

CONCLUSIONS

This study demonstrates for the first time that LV PV loops can be generated non-invasively during exercise using CMR. ET and SC increase ventricular efficiency and contractility and decrease afterload and ventricular-arterial coupling during moderate supine exercise. These results confirm known physiology. Therefore, this novel method is applicable to be used during exercise in different cardiac disease states, which has not been possible non-invasively before.

Levosimendan versus dobutamine for sepsis-induced cardiac dysfunction: a systematic review and meta-analysis

Levosimendan and dobutamine are extensively used to treat sepsis-associated cardiovascular failure in ICU. Nevertheless, the role and mechanism of levosimendan in patients with sepsis-induced cardiomyopathy remains unclear. Moreover, previous studies on whether levosimendan is superior to dobutamine are still controversial. More importantly, these studies did not take changes (before-after comparison to the baseline) in quantitative parameters such as ejection fraction into account with the baseline level. Here, we aimed to determine the pros and cons of the two medicines by assessing the changes in cardiac function and blood lactate, mortality, with the standardized mean difference used as a summary statistic. Relevant studies were obtained by a thorough and disciplined literature search in several notable academic databases, including Google Scholar, PubMed, Cochrane Library and Embase until November 2020. Outcomes included changes in cardiac function, lactic acid, mortality and length of hospital stay. A total of 6 randomized controlled trials were included in this study, including 192 patients. Compared with dobutamine, patients treated with levosimendan had a greater improvement of cardiac index (ΔCI) (random effects, SMD = 0.90 [0.20,1.60]; I2 = 76%, P < 0.01) and left ventricular stroke work index (ΔLVSWI) (random effects, SMD = 1.56 [0.90,2.21]; I2 = 65%, P = 0.04), a significant decrease of blood lactate (Δblood lactate) (random effects, MD =  - 0.79 [- 1.33, - 0.25]; I2 = 68%, P < 0.01) at 24-h after drug intervention, respectively. There was no significant difference between levosimendan and dobutamine on all-cause mortality in ICU (fixed effect, OR = 0.72 [0.39,1.33]; I2 = 0%, P = 0.99). We combine effect sizes related to different measurement parameters to evaluate cardiac function, which implied that septic patients with myocardial dysfunction might have a better improvement of cardiac function by levosimendan than dobutamine (random effects, SMD = 1.05 [0.69,1.41]; I2 = 67%, P < 0.01). This study suggested a significant improvement of CI, LVSWI, and decrease of blood lactate in septic patients with myocardial dysfunction in ICU after 24-h administration of levosimendan than dobutamine. However, the administration of levosimendan has neither an impact on mortality nor LVEF. Septic patients with myocardial dysfunction may partly benefit from levosimendan than dobutamine, mainly embodied in cardiac function improvement.

Easy-to-use preload stress echocardiography by using combined dynamic postural stress can identify high-risk patients with heart failure with reduced ejection fraction

Aims

Haemodynamic assessment during stress testing is not commonly performed in patients with heart failure with reduced ejection fraction (HFrEF) because of its invasiveness, lower feasibility, and safety concerns. This study aimed to assess the haemodynamic characteristics of patients with HFrEF in response to non‐invasive preload stress during dynamic postural alterations achieved by combining both semi‐sitting position and passive leg‐lifting and to evaluate whether combined postural stress could be used for risk stratification in these patients.

Methods and results

For this study, 101 patients with HFrEF and 35 age‐matched and sex‐matched healthy controls were prospectively recruited. After all standard echocardiographic measurements were obtained in the left decubitus position, all subjects underwent postural stress testing, which consisted of changing from semi‐sitting position to passive leg‐lifting. During a median follow‐up period of 12.2 months, 21 (21%) patients developed adverse cardiovascular events. In patients without adverse cardiovascular events, the stroke volume index (SVi) significantly changed from 28 ± 8 to 35 ± 10 mL/m² (P < 0.001) during combined postural stress. By contrast, ΔSVi during combined dynamic postural stress was significantly smaller in patients with cardiovascular events than in those without events (ΔSVi 3.4 ± 4.0 vs. 6.4 ± 3.8 mL/m², P = 0.002), which indicated severely diseased heart operated on a relatively flat portion of the Frank–Starling curve. In a multivariate Cox proportional hazard analysis, ΔSVi (hazard ratio 0.81, P = 0.02) was an independent predictor of future adverse cardiovascular events.

Conclusions

The combined assessment of dynamic postural stress is a non‐invasive, simple, quick, and easy‐to‐use clinical tool for assessing preload reserve and risk stratification in HFrEF patients.

Ventricular-Vascular Coupling at Rest and after Exercise Is Associated with Heart Failure Hospitalizations in Patients With Coronary Artery Disease

BACKGROUND

The ventricular-vascular coupling ratio, defined as the ratio of arterial elastance (E_a) to left ventricular end-systolic elastance (E_es), has not been examined in populations with coronary artery disease (CAD), and its association with heart failure (HF) in this population is unknown.

METHODS

Ventricular-vascular coupling was measured at rest and after exercise using echocardiography and cuff blood pressure in 815 patients with stable CAD enrolled in the Heart and Soul Study. Adjusted Cox proportional-hazard models were used to evaluate the association between ventricular-vascular coupling and future HF hospitalizations.

RESULTS

After a median of 8.9 years, 144 patients (18%) were hospitalized for HF. After multivariate adjustment, patients in the highest tertile of E_es (rest: hazard ratio [HR], 0.31 [95% CI, 0.17-0.57; P < .001]; exercise: HR, 0.26 [95% CI, 0.13-0.50; P < .001]) were at decreased risk for HF hospitalization, while patients in the highest tertile of the E_a/E_es ratio (rest: HR, 3.36 [95% CI, 1.91-5.93; P < .001]; exercise: HR, 4.09; [95% CI, 2.22-7.51; P < .001]) were at increased risk, compared with the lowest tertiles. E_a and the relative change observed in E_es and the E_a/E_es ratio with exercise were not associated with HF hospitalizations.

CONCLUSIONS

The E_a/E_es ratio and E_es, at rest and after exercise, are strongly associated with future HF hospitalizations in patients with stable CAD and low rates of baseline HF. Ventricular-vascular coupling obtained from echocardiography shows promise as a risk assessment tool for HF in patients with CAD.

A predictor of aerobic threshold for patients with heart failure with reduced ejection fraction

[Purpose] The initial cardiopulmonary response to exercise is hypothesized to be a useful predictor of aerobic threshold in patients with heart failure. This study aimed to evaluate the correlation between aerobic threshold and cardiopulmonary responses to exercise onset by comparing patients with heart failure using preserved (≥50%) and reduced (<50%) left ventricular ejection fractions. [Participants and Methods] Twenty-eight males (age, 36-82 years; 12 with preserved and 16 with reduced left ventricular ejection fractions) underwent a progressive submaximal cardiopulmonary exercise test using a cycle ergometer. The aerobic threshold, time constant, and area under the oxygen uptake curve for the first 4 min (V̇O₂AUC) were determined. [Results] A significant association was observed between aerobic threshold and V̇O₂AUC in the reduced group but not in the preserved group. No significant correlations were found between time constant and V̇O₂AUC or between aerobic threshold and time constant in either group. [Conclusion] The results suggest that V̇O₂AUC measured from exercise onset to an initial 4-min period could provide an easily and safely obtained predictor to assess aerobic capacity in people with reduced left ventricular ejection fractions.

Gender Differences in Ventricular-vascular Coupling Following Exercise

OBJECTIVE

To study the differences of cardiovascular system between men and women in response to exercise stress.

METHODS

Forty healthy youth were tested according to Bruce protocol of exercise stress. They were detected by ultrasonography during the rest, peak exercise, and recovery stages, respectively. The left ventricular diastolic elastance (Ed), effective arterial elastance (Ea), left ventricular end-systolic elatance (Ees), ventricular-vascular coupling index (VVI), and total stiffness index (TSI) were measured and calculated according to the formulas. The results of all stages were compared according to genders.

RESULTS

All stages, the Ed, TSI, and VVI of women were higher than those of men, but the Ees was lower than that of men (all P<0.05); there was no significant difference in Ea between men and women. The Ed, Ees, Ea, and TSI were closely related with left ventricular oxygen consumption and heart function, and women showed more closely. Before and after exercise, the changes were different in Ed, Ees, Ea, TSI, and VVI (all P<0.05), and VVI changed least.

CONCLUSIONS

Before and after exercise, the ventricular stiffness matched well with arterial stiffness and maintained within a narrow range. For women, the tolerance of exercise was lower than that of men.

The relationship between ventricular-vascular uncoupling during exercise and impaired left ventricular longitudinal functional reserve in hypertensive patients

Uncoupling between heart and vessel may be accompanied by left ventricular (LV) dysfunction during exercise. We investigated the association between ventricular-vascular uncoupling during exercise and impaired LV longitudinal functional reserve in hypertensive subjects. Supine bicycle exercise echocardiography (25-watt, 3-minute increments) was performed in 216 hypertensive patients (106 male; mean age, 58 ± 9 years). Arterial elastance (Ea), end-systolic ventricular elastance (Ees), and ventricular-vascular interaction (VVI) index (Ea/Ees) were calculated at rest and at each stage of exercise. The patients were divided into three groups according to the tertile value of VVI ratio. The VVI ratio was defined as the ratio of VVI index at 50 W exercise over VVI index at rest; normal VVI response (n = 72); borderline VVI response (n = 72); and abnormal VVI response (n = 72). There were no significant differences in conventional echo parameters, mitral inflow velocities, mitral annular early diastolic (E') velocity, and mitral annular systolic velocity (S') at rest among the three groups. However, E' velocities and S' velocities at 25 W and 50 W were significantly lower in patients with abnormal VVI response compared with those in the other groups (P = .010 at 25 W, P = .008 at 50 W in E' velocity; P = .022 at 25 W, P = .043 at 50 W in S' velocity). Longitudinal diastolic functional reserve index from rest to 50 W was significantly lower in patients with abnormal VVI response compared with the other groups. Ventricular-vascular uncoupling during exercise was related to impaired LV longitudinal functional reserve in hypertensive patients.

Arterial-ventricular coupling with aging and disease

Age is the dominant risk factor for cardiovascular diseases. Understanding the coupling between the left ventricle (LV) and arterial system, termed arterial-ventricular coupling (E(A)/E(LV)), provides important mechanistic insights into the complex cardiovascular system and its changes with aging in the absence and presence of disease. E(A)/E(LV) can be indexed by the ratio of effective arterial elastance (E(A); a measure of the net arterial load exerted on the LV) to left ventricular end-systolic elastance (E(LV); a load-independent measure of left ventricular chamber performance). Age-associated alterations in arterial structure and function, including diameter, wall thickness, wall stiffness, and endothelial dysfunction, contribute to a gradual increase in resting E(A) with age. Remarkably there is a corresponding increase in resting E(LV) with age, due to alterations to LV remodeling (loss in myocyte number, increased collagen) and function. These age-adaptations at rest likely occur, at least, in response to the age-associated increase in E(A) and ensure that E(A)/E(LV) is closely maintained within a narrow range, allowing for optimal energetic efficiency at the expense of mechanical efficacy. This optimal coupling at rest is also maintained when aging is accompanied by the presence of hypertension, and obesity, despite further increases in E(A) and E(LV) in these conditions. In contrast, in heart failure patients with either reduced or preserved ejection fraction, E(A)/E(LV) at rest is impaired. During dynamic exercise, E(A)/E(LV) decreases, due to an acute mismatch between the arterial and ventricular systems as E(LV) increases disproportionate compared to E(A) (≈200 vs. 40%), to ensure that sufficient cardiac performance is achieved to meet the increased energetic requirements of the body. However, with advancing age the reduction in E(A)/E(LV) during acute maximal exercise is blunted, due to a blunted increase E(LV). This impaired E(A)/E(LV) is further amplified in the presence of disease, and may explain, in part, the reduced cardiovascular functional capacity with age and disease. Thus, although increased stiffness of the arteries itself has important physiological and clinical relevance, such changes also have major implications on the heart, and vice versa, and the manner in the way they interact has important ramifications on cardiovascular function both at rest and during exercise. Examination of the alterations in arterial-ventricular coupling with aging and disease can yield mechanistic insights into the pathophysiology of these conditions and increase the effectiveness of current therapeutic interventions.

AORTOVENTRICULAR MECHANICAL MATCHING: SIMULATION OF NORMAL AND PATHOLOGICAL CONDITIONS

A mechanical mock of the cardiovascular system was used to simulate different conditions of ventricular-arterial mechanical matching. Four ventricles and four aortas with different elastances were set up, and all possible connection combinations tested by sampling ventricular and aortic pressures and flows. The mechanical energy produced by the simulated ventricles and the amount transferred to the aorta in the different connection conditions were calculated. The results demonstrate a clear dependence between the mechanical work production of the ventricles and the ventricular elastance (slope of the end-systolic pressure–volume relation) (from 20.42 ± 0.02 mJ/beat to 12.10 ± 0.02 mJ/beat), and an efficiency of energy transfer to the aorta strongly dependent on ventricular-aortic mechanical matching (from 56% to 20.7%). These results show that, even in optimal simulated conditions, only 56% of the energy produced is transferred to the load; and highlight the important role of mechanical aspects in conditions of very limited cardiovascular performance (i.e. final stages of heart failure), where energy transfer efficiency may be as low as 20.7%. This evidence emphasizes that the mechanical aspects must also be entertained in the evolution of complex cardiovascular pathologies, evaluating the possibility of combining mechanical and pharmaceutical interventions.

Use of the Frank-Starling mechanism during exercise is linked to exercise-induced changes in arterial load

Effective arterial elastance(E(A)) is a measure of the net arterial load imposed on the heart that integrates the effects of heart rate(HR), peripheral vascular resistance(PVR), and total arterial compliance(TAC) and is a modulator of cardiac performance. To what extent the change in E(A) during exercise impacts on cardiac performance and aerobic capacity is unknown. We examined E(A) and its relationship with cardiovascular performance in 352 healthy subjects. Subjects underwent rest and exercise gated scans to measure cardiac volumes and to derive E(A)[end-systolic pressure/stroke volume index(SV)], PVR[MAP/(SV*HR)], and TAC(SV/pulse pressure). E(A) varied with exercise intensity: the ΔE(A) between rest and peak exercise along with its determinants, differed among individuals and ranged from -44% to +149%, and was independent of age and sex. Individuals were separated into 3 groups based on their ΔE(A)I. Individuals with the largest increase in ΔE(A)(group 3;ΔE(A)≥0.98 mmHg.m(2)/ml) had the smallest reduction in PVR, the greatest reduction in TAC and a similar increase in HR vs. group 1(ΔE(A)<0.22 mmHg.m(2)/ml). Furthermore, group 3 had a reduction in end-diastolic volume, and a blunted increase in SV(80%), and cardiac output(27%), during exercise vs. group 1. Despite limitations in the Frank-Starling mechanism and cardiac function, peak aerobic capacity did not differ by group because arterial-venous oxygen difference was greater in group 3 vs. 1. Thus the change in arterial load during exercise has important effects on the Frank-Starling mechanism and cardiac performance but not on exercise capacity. These findings provide interesting insights into the dynamic cardiovascular alterations during exercise.

Arterial-cardiac interaction: the concept and implications

Vascular stiffening of the large arteries is a common feature of human aging. Increased aortic stiffness with age may contribute to pathological changes in the left ventricle and this can induce ventricular stiffening. Vascular-ventricular stiffening combined with abnormal arterial-cardiac interaction is considered an important pathophysiology of heart failure with a preserved ejection fraction. Here, I briefly review the concept and implications of arterial-cardiac interaction and this will pave the way to understanding and controlling heart failure with a preserved ejection fraction, which is more prevalent in the elderly.

Arterial-ventricular coupling: mechanistic insights into cardiovascular performance at rest and during exercise

Understanding the performance of the left ventricle (LV) requires not only examining the properties of the LV itself, but also investigating the modulating effects of the arterial system on left ventricular performance. The interaction of the LV with the arterial system, termed arterial-ventricular coupling (E(A)/E(LV)), is a central determinant of cardiovascular performance and cardiac energetics. E(A)/E(LV) can be indexed by the ratio of effective arterial elastance (E(A); a measure of the net arterial load exerted on the left ventricle) to left ventricular end-systolic elastance (E(LV); a load-independent measure of left ventricular chamber performance). At rest, in healthy individuals, E(A)/E(LV) is maintained within a narrow range, which allows the cardiovascular system to optimize energetic efficiency at the expense of mechanical efficacy. During exercise, an acute mismatch between the arterial and ventricular systems occurs, due to a disproportionate increase in E(LV) (from an average of 4.3 to 13.2, and 4.7 to 15.5 mmHg.ml(-1).m(-2) in men and women, respectively) vs. E(A) (from an average of 2.3 to 3.2, and 2.3 to 2.9 mmHg.ml(-1).m(-2) in men and women, respectively), to ensure that sufficient cardiac performance is achieved to meet the increased energetic requirements of the body. As a result E(A)/E(LV) decreases from an average of 0.58 to 0.34, and 0.52 to 0.27 in men and women, respectively. In this review, we provide an overview of the concept of E(A)/E(LV), and examine the effects of age, hypertension, and heart failure on E(A)/E(LV) and its components (E(A) and E(LV)) in men and women. We discuss these effects both at rest and during exercise and highlight the mechanistic insights that can be derived from studying E(A)/E(LV).

Effect of levosimendan on ventriculo-arterial coupling in patients with ischemic cardiomyopathy

BACKGROUND

Levosimendan, a novel calcium sensitizer, enhances myocardial contractility without affecting intracellular calcium concentration. It also dilates peripheral arterial vessels by acting on ATP-dependent K(+) channels. Ventriculo-arterial coupling, the relationship between myocardial contractility and the arterial system, describes the efficiency of the cardiovascular system by analysing the relationship between myocardial contractility expressed by ventricular elastance (E(es)) and arterial elastance (E(a)). The aim of this prospective clinical investigation was to evaluate the effects of levosimendan on ventriculo-arterial coupling in patients with ischemic cardiomyopathy.

METHODS

Fifteen patients with stable angina and left ventricular dysfunction underwent elective coronary surgery. Before surgery started, ventriculo-arterial coupling and several variables of cardiovascular performance were assessed by invasive monitoring and transoesophageal echocardiography before and after administration of levosimendan (12 mug/kg bolus) in coronary patients under general anesthesia.

RESULTS

The cardiac index and ejection fraction increased significantly [from 1.92 +/- 0.4 to 2.1 +/- 0.4 l/min/m(2) (P = 0.0004) and from 31% +/- 6 to 40% +/- 9 (P = 0.001), respectively], while mean arterial pressure and systemic vascular resistances decreased significantly [from 83 +/- 10 to 72 +/- 5 mmHg (P = 0.0016) and from 997 +/- 341 to 855 +/- 324 dyne s/cm(5) (P = 0.0002), respectively]. After administration of levosimendan, E(a) decreased significantly (from 4.3 +/- 1.8 to 3.2 +/- 1.3 mmHg/ml/m(2), P= 0.005), while E(es) significantly increased (from 2.8 +/- 1.6 to 4.4 +/- 2.3 mmHg/ml/m(2), P= 0.05); as a result, E(a)/E(es) decreased significantly (from 1.76 +/- 1 to 0.83 +/- 0.2, P= 0.002).

CONCLUSION

Levosimendan improves ventriculo-arterial coupling and cardiovascular performance in coronary patients with left ventricular dysfunction by enhancing myocardial contractility and reducing arterial elastance.

Cardiovascular Function in Multi-Ethnic Study of Atherosclerosis: Normal Values by Age, Sex, and Ethnicity

OBJECTIVE

MRI provides accurate and high-resolution measurements of cardiac anatomy and function. The purpose of this study was to describe the imaging protocol and normal values of left ventricular (LV) function and mass in the Multi-Ethnic Study of Atherosclerosis (MESA).

SUBJECTS AND METHODS

Eight hundred participants (400 men, 400 women) in four age strata (45-54, 55-64, 65-74, 75-84 years) were chosen at random. Participants with the following known cardiovascular risk factors were excluded: current smoker, systolic blood pressure > 140 mm Hg, diastolic blood pressure > 90 mm Hg, fasting glucose > 110 mg/dL, total cholesterol > 240 mg/dL, and high-density lipoprotein (HDL) cholesterol < 40 mg/dL. Cardiac MR images were analyzed using MASS software (version 4.2). Mean values, SDs, and correlation coefficients in relationship to patient age were calculated.

RESULTS

There were significant differences in LV volumes and mass between men and women. LV volumes were inversely associated with age (p < 0.05) for both sexes except for the LV end-systolic volume index. For men, LV mass was inversely associated with age (slope = -0.72 g/year, p = 0.0021), but LV mass index was not associated with age (slope = -0.179 g/m2/year, p = 0.075). For women, LV mass (slope = -0.15 g/year, p = 0.30) and LV mass index (slope = 0.0044 g/m2/year, p = 0.95) were not associated with age. LV mass was the largest in the African-American group (men, 181.6 +/- 35.8 [SD] g; women, 128.8 +/- 28.1 g) and was smallest in the Asian-American group (men, 129.1 +/- 20.0 g; women, 89.4 +/- 13.3 g).

CONCLUSION

The normal LV differs in volume and mass between sexes and among certain ethnic groups. When indexed by body surface area, LV mass was independent of age for both sexes. Studies that assess cardiovascular risk factors in relationship to cardiac function and structure need to account for these normal variations in the population.

Ventriculo-arterial coupling and mechanical efficiency with remifentanil in patients with coronary artery disease

BACKGROUND

Optimum transfer of energy from the left ventricle to the arterial circulation requires appropriate matching of these mechanical systems. Left ventricular-arterial coupling describes this relationship between the ventricular elastance (Ees) and arterial elastance (Ea). The ratio of these elastances defines the efficiency of myocardium and provides in our study a useful technique for assessment of the actions of remifentanil. The purpose of this study was to evaluate the effects of remifentanil on ventriculo-arterial coupling in cardiac surgery in patients with coronary artery disease.

METHODS

Fourteen patients with coronary artery disease, submitted intraoperatively to cardiac anesthesia for myocardial revascularization, were examined prospectively. With the use of transesophageal echocardiography (TEE) and different dicrotic arterial pressures, we determined the ventricle elastance (Ees), the arterial elastance (Ea) and myocardial efficiency before and after administration of a slow-bolus of remifentanil (1 micro kg(-1)).

RESULTS

Remifentanil decreases significantly the ventricular elastance (from 6.09 mmHg ml-1 m(-2) to 4.88) (P < 0.05), with a less, but however, significant decrease of arterial elastance (from 3.68 mmHg ml(-1) m(-2) to 3.13) (P < 0.05). Despite causing simultaneous declines, maintains a good myocardial efficiency (0.64-0.68) with no significant difference.

CONCLUSION

Although remifentanil depresses ventricular and arterial elastance, preserves a good left ventricular-arterial coupling and mechanical efficiency, despite a little increase of coupling. However, these effects are maintained only during a slow intravenous infusion and are dose-dependent with impairment of coupling, that may contribute to decline in overall cardiovascular performance, at higher anesthetic dose and rapid infusion in patients with a severe myocardial dysfunction.

Verapamil acutely reduces ventricular-vascular stiffening and improves aerobic exercise performance in elderly individuals

OBJECTIVES

We tested the hypothesis that acute intravenous verapamil acutely enhances aerobic exercise performance in healthy older individuals in association with a combined reduction of ventricular systolic and arterial vascular stiffnesses.

BACKGROUND

Age-related vascular stiffening coupled with systolic ventricular stiffening may limit cardiovascular reserve and, thus, exercise performance in aged individuals.

METHODS

Nineteen healthy volunteers with mean age 70 +/- 10 years underwent maximal-effort upright ergometry tests on two separate days after receiving either 0.15 mg/kg i.v. verapamil or 0.5 N saline in a double-blind, randomized, crossover study.

RESULTS

Baseline vascular stiffness, indexed by arterial pulse-wave velocity (Doppler) and augmentation index (carotid tonometry) declined with verapamil (-5.9 +/- 2.1% and -31.7 +/- 12.8%, respectively, both p < 0.05). Preload-adjusted maximal ventricular power, a surrogate for ventricular end-systolic stiffness, also declined by -9.5 +/- 3.6%. Peripheral resistance and peak filling rate were unchanged. With verapamil, exercise duration prior to the anaerobic threshold (AT) increased by nearly 50% (260 +/- 129 to 387 +/- 176 s) with a corresponding 13.4 +/- 4.7% rise in oxygen consumption (VO2) at that time (both p < 0.01). Total exercise duration prolonged by +6 +/- 2.7% (p < 0.05) with no change in maximal VO2. Baseline cardiodepression from verapamil reversed by peak exercise with net increases in stroke volume and cardiac output (p < 0.05).

CONCLUSIONS

Acute intravenous verapamil reduces ventriculovascular stiffening and improves aerobic exercise performance in healthy aged individuals. This highlights a role for heart-arterial coupling in modulating exertional capacity in the elderly, suggesting a potentially therapeutic target for aged individuals with exertional limitations.

Left ventricular-arterial system coupling at peak exercise in dilated nonischemic cardiomyopathy

We assessed the ventricular-arterial coupling at peak exercise in 20 patients with dilated cardiomyopathy (ejection fraction, 27+/-12%) and 7 normal subjects by radionuclide ventriculography during exercise, coupled with respiratory gas analysis. The end-systolic pressure-volume ratio, taken as an index of contractility, and the effective arterial elastance were calculated at rest and at peak exercise. The end-systolic pressure/volume ratio increased from 3.7+/-2.7 to 6.9+/-4.0 mm Hg/mL at peak exercise in the normal subjects, but did not change significantly (from 0.9+/-0.5 to 1.0+/-0.6 mm Hg/mL) in the patients. Arterial elastance did not change significantly in the patients (+17+/-32%, not significant [NS] vs rest) or in the normal subjects (+22+/-28%, NS vs rest). The change in ejection fraction during exercise correlated both with the end-systolic pressure/volume ratio and with effective arterial elastance changes (r=0.60 and 0.68, respectively). We conclude that ventricular arterial coupling is further altered at peak exercise in these patients because of the lack of increase in contractility and not of altered effective arterial elastance response.

A new methodology for non-invasive clinical assessment of cardiovascular system performance and of ventricular-arterial coupling during stress

The objective of the study was to develop a non-invasive method for the quantitative evaluation of cardiovascular performance and ventricular-arterial (VA) coupling during varying physiological states. VA-coupling was represented by the ratio between the arterial and ventricular elastances-Ea/Ees. Approximate indices of the relative change of Ees and VA-coupling during stress were developed and tested. These indices can be evaluated directly from non-invasive measurements of ejection fraction values (for VA-coupling) and measurements of stroke volumes and systolic and diastolic arterial pressures (for Ees). Additional relative indices can be evaluated from these data (e.g., stroke work, cardiac output) to yield a complete representation of the cardiovascular response to stress. The present methodology was applied to assess the exercise stress response in healthy subjects (H, n = 8) and in patients with left ventricular dysfunction (n = 24). Left ventricular volumes were determined by nuclear angiography and arterial pressures were measured non-invasively by a new, validated method. Using published data obtained invasively, we found that the relative indices of Ees and VA-coupling showed a high correlation with the invasive ones (r > 0.8, P < 0.01). The patients were subgrouped by their maximal exercise capacitance (P2-50W, P3-75W). At rest, the two patient groups had similar ejection fraction values (45 +/- 15% and 48 +/- 16%), which were significantly different from those of the healthy subjects (66 +/- 7%, P < 0.05). During stress, a larger increase in stroke work and cardiac output was found in the healthy subjects. All three groups showed similar relative increases in Ees and heart rate, but relative Ea increased in P2 and decreased in H, while the opposite was found for the end-diastolic volume. The relative VA-coupling index in P2 was significantly larger than that in P3 and H (P < 0.05). The present non-invasively based indices can be used to quantitatively monitor the individual cardiovascular response to stress testing or drug interventions and to evaluate the importance of VA-coupling in the clinical setting.

Left ventricular end-systolic elastance is incorrectly estimated by the use of stepwise afterload variations in conscious, unsedated, autonomically intact dogs

BACKGROUND

End-systolic elastance (Ees), the slope parameter of the end-systolic pressure (ESP)-volume (ESV) relation (ESPVR), is usually estimated in patients by producing stepwise, steady-state pharmacological afterload variations and collecting one ESP-ESV point from each step. The ESPVR is then constructed by fitting a linear equation to these points. In sedated, autonomically blocked dogs, it has been shown that when one point from control, one point from a state of increased afterload, and one point from a state of decreased afterload are used, the resulting Ees incorrectly estimates true Ees, defined as the slope of the ESPVR obtained by transient vena caval occlusion. We investigated if this was also the case in unsedated, autonomically intact dogs when the points used belonged to steady states of progressively decreasing or progressively increasing afterload pressure.

METHODS AND RESULTS

In 10 conscious dogs instrumented with left ventricular (LV) endocardial sonomicrometers to measure LV volume, a LV pressure transducer, and an inferior vena caval (IVC) occluder, two protocols were carried out on separate days. In each protocol, an ESPVR was generated by IVC occlusion in the control state and in two steady-state levels of afterload change produced by stepwise infusion of nitroprusside (protocol 1, afterload decrease) and angiotensin II (protocol 2, afterload increase). In each protocol, steady-state ESP-ESV data points were averaged from the control state and from each level of afterload variation. Linear equations were fitted to the three steady-state points from each protocol, and the estimated Ees values obtained (EesEST) were compared with the Ees values of the control ESPVRs obtained by IVC occlusion (EesTRUE). In protocol 1, EesEST underestimated EesTRUE by about 16% (EesEST, 6.49 +/- 1.55 mm Hg/mL; EesTRUE, 7.48 +/- 1.29 mm Hg/mL; P < .02). In protocol 2, EesEST overestimated EesTRUE by about 37% (EesEST, 9.99 +/- 3.97 mm Hg/mL; EesTRUE, 6.43 +/- 3.88 mm Hg/mL; P < .007).

CONCLUSIONS

In conscious, autonomically intact dogs, the use of stepwise, steady-state afterload variations to obtain ESP-ESV data points to construct the ESPVR incorrectly estimates Ees. In the case of afterload reduction, EesTRUE is underestimated an average of 16.3%, and in the case of afterload increase, EesTRUE is overestimated an average of 37.1%. These errors should be taken into account when interpreting clinical studies using this methodology.