Noninvasive evaluation of left ventricular force-frequency relationships by measuring carotid arterial wave intensity during exercise stress

Leisure-Time Physical Activity Has a More Favourable Impact on Carotid Artery Stiffness Than Vigorous Physical Activity in Hypertensive Human Beings

Aim. To assess the effect of leisure time versus vigorous long-term dynamic physical activity (PA) on carotid stiffness in normotensive versus hypertensive subjects. Methods. The study was conducted on 120 leisure-time exercisers and 120 competitive athletes. One hundred and twenty sedentary subjects served as controls. In addition, participants were classified according to whether their systolic blood pressure was ≥130 mmHg (hypertensives, n = 120) or normal (normotensives, n = 240) according to the ACC/AHA 2017 definition. Carotid artery stiffness was assessed with an echo-tracking ultrasound system, using the pressure-strain elastic modulus (EP) and one-point pulse wave velocity (PWVβ) as parameters of stiffness. Results. The effect of the two levels of PA differed in the normotensives and the hypertensives. Among the normotensives, there was an ongoing, graded reduction in EP and PWVβ from the sedentary subjects to the athletes. By contrast, among the hypertensives, the lowest levels of EP and PWVβ were found among the leisure-time PA participants. EP and PWVβ did not differ between the hypertensive sedentary subjects and the athletes. A significant interaction was found between PA and BP status on EP (p = 0.03) and a borderline interaction on PWVβ (p = 0.06). In multiple regression analyses, PA was a negative predictor of EP (p = 0.001) and PWVβ (p = 0.0001). The strength of the association was weakened after the inclusion of heart rate in the models (p = 0.04 and 0.007, respectively). Conclusions. These data indicate that in people with hypertension, leisure-time PA has beneficial effects on carotid artery stiffness, whereas high-intensity chronic PA provides no benefit to vascular functions.

Measurement, Analysis and Interpretation of Pressure/Flow Waves in Blood Vessels

The optimal performance of the cardiovascular system, as well as the break-down of this performance with disease, both involve complex biomechanical interactions between the heart, conduit vascular networks and microvascular beds. ‘Wave analysis’ refers to a group of techniques that provide valuable insight into these interactions by scrutinizing the shape of blood pressure and flow/velocity waveforms. The aim of this review paper is to provide a comprehensive introduction to wave analysis, with a focus on key concepts and practical application rather than mathematical derivations. We begin with an overview of invasive and non-invasive measurement techniques that can be used to obtain the signals required for wave analysis. We then review the most widely used wave analysis techniques—pulse wave analysis, wave separation and wave intensity analysis—and associated methods for estimating local wave speed or characteristic impedance that are required for decomposing waveforms into forward and backward wave components. This is followed by a discussion of the biomechanical phenomena that generate waves and the processes that modulate wave amplitude, both of which are critical for interpreting measured wave patterns. Finally, we provide a brief update on several emerging techniques/concepts in the wave analysis field, namely wave potential and the reservoir-excess pressure approach.

Changes in cardiac contractility during graded exercise are greater in subjects with smaller body mass index, and greater in men than women: analyses using wave intensity and force-frequency relations

INTRODUCTION AND PURPOSE

Estimation of the contractility of the left ventricle during exercise is an important part of the rehabilitation protocol. It is known that cardiac contractility increases with an increase in heart rate. This phenomenon is called the force-frequency relation (FFR). Using wave intensity, we aimed to evaluate FFR noninvasively during graded exercise.

METHODS

We enrolled 83 healthy subjects. Using ultrasonic diagnostic equipment, we measured wave intensity (WD), which was defined in terms of blood velocity and arterial diameter, in the carotid artery and heart rate (HR) before and during bicycle ergometer exercise. FFRs were constructed by plotting the maximum value of WD (WD₁) against HR. We analyzed the variation among FFR responses of individual subjects.

RESULTS

WD₁ increased linearly with an increase in HR during exercise. The average slope of the FFR was 1.0 ± 0.5 m/s³ bpm. The slope of FFR decreased with an increase in body mass index (BMI). The slopes of FFRs were steeper in men than women, although there were no differences in BMI between men and women.

CONCLUSIONS

The FFR was obtained noninvasively by carotid arterial wave intensity (WD₁) and graded exercise. The slope of the FFR decreased with an increase in BMI, and was steeper in men than women.

Novel wave power analysis linking pressure-flow waves, wave potential, and the forward and backward components of hydraulic power

Wave intensity analysis provides detailed insights into factors influencing hemodynamics. However, wave intensity is not a conserved quantity, so it is sensitive to diameter variations and is not distributed among branches of a junction. Moreover, the fundamental relation between waves and hydraulic power is unclear. We, therefore, propose an alternative to wave intensity called “wave power,” calculated via incremental changes in pressure and flow (dPdQ) and a novel time-domain separation of hydraulic pressure power and kinetic power into forward and backward wave-related components (ΠP± and ΠQ±). Wave power has several useful properties: 1) it is obtained directly from flow measurements, without requiring further calculation of velocity; 2) it is a quasi-conserved quantity that may be used to study the relative distribution of waves at junctions; and 3) it has the units of power (Watts). We also uncover a simple relationship between wave power and changes in ΠP± and show that wave reflection reduces transmitted power. Absolute values of ΠP± represent wave potential, a recently introduced concept that unifies steady and pulsatile aspects of hemodynamics. We show that wave potential represents the hydraulic energy potential stored in a compliant pressurized vessel, with spatial gradients producing waves that transfer this energy. These techniques and principles are verified numerically and also experimentally with pressure/flow measurements in all branches of a central bifurcation in sheep, under a wide range of hemodynamic conditions. The proposed “wave power analysis,” encompassing wave power, wave potential, and wave separation of hydraulic power provides a potent time-domain approach for analyzing hemodynamics.

Noninvasive assessment of exercise tolerance using mitral annular velocities

PURPOSE

To investigate the feasibility of evaluating exercise tolerance using lateral and septal mitral annular velocities in patients with preserved left ventricular ejection fraction (LVEF) and those with reduced LVEF.

METHOD

We studied 36 patients with LVEF ≥50% and 36 with LVEF <50%. We measured peak early diastolic velocity of transmitral flow (E) and peak early diastolic velocities of the lateral (LEa) and septal (SEa) mitral annulus. The ratios of E to LEa (E/LEa) and E to SEa (E/SEa) were calculated. We measured peak oxygen consumption [Formula: see text] and anaerobic threshold (AT) by cardiopulmonary exercise testing.

RESULTS

In patients with LVEF ≥50%, E/LEa correlated well with [Formula: see text] and AT (r = -0.69 and r = -0.74, respectively; p < 0.001); E/SEa correlated modestly (r = -0.59 and r = -0.60, respectively; p < 0.001). In patients with LVEF <50%, E/LEa correlated well with [Formula: see text] and AT (r = -0.72 and r = -0.76; respectively, p < 0.001); E/SEa correlated modestly (r = -0.63 and r = -0.63, respectively; p < 0.001).

CONCLUSION

E/LEa may be more useful than E/SEa for the noninvasive estimation of exercise tolerance, throughout a wide range of LVEF.