The large arteries, especially the aorta, are known to play a major role in the circulation of blood flow both during ventricular ejection and during diastole, thus providing the blood supply required by the organs. Additionally, the damping function exercised by the aorta plays a fundamental role in central hemodynamics, providing adequate ventricular-arterial coupling during the cardiac cycle.The loss of this function due to increased arterial stiffness plays a role in the development of hypertension and left ventricular hypertrophy and has been associated with the development of atherosclerosis and myocardial ischemia. Noninvasive methods for assessing the function of large arteries, such as pulse wave velocity (PWV) measurement, have provided a better understanding of the correlations of arterial stiffness with cardiovascular disease, and have been used as prognostic markers in different populations.However, due to methodological limitations, all studies have been performed in the supine position, and the impact of postural changes, especially orthostasis, has not been evaluated on these vascular properties. Thus, the study by Elias Neto et al. published in this issue, as the first to evaluate the effect of orthostasis on the aortic functional properties in normotensive and hypertensive individuals not treated by the aortic PWV measurement in humans, provides important information to understand the role of these properties in the physiological adaptation of central hemodynamics in relation to the gravity effects. The authors evaluated nearly 100 individuals with no evident cardiovascular disease by measuring carotid-femoral PWV performed in the supine and standing positions after the 70° tilt test and demonstrated a significant and sustained increase in PWV throughout the tilt test, in both young and older individuals. Interestingly, although there was a direct and significant association between baseline and post-orthostasis PWV values and systolic blood pressure (SBP ), SBP remained unaltered or showed a slight decrease during the tilt test and, therefore, the increase in PWV during inclination occurred by other mechanisms of circulatory adaptation, including an increase in peripheral arterial resistance (indirectly suggested by the observed increase in mean BP ) and changes in circulatory dynamics promoted by the gravitational force, which are related to the differential structural and geometric characteristics of the aorta throughout its trajectory. In a study with a smaller number of individuals and another methodology for PWV assessment, the authors also found an increase in PWV with the tilt test and attributed this increase to increased hydrostatic pressure and greater sympathetic activity.
Due to gravitational effect, blood flow increases in the more distal arterial segments, which have smaller diameter and less elasticity, causing an increase in PWV and also in BP in the infradiaphragmatic territories. The consequence of this increase in carotid-femoral PWV would be the early return of the retrograde wave to the heart, increasing pulse pressure at the aortic root, which could contribute to maintaining a more adequate cerebral blood flow with the biped position assumed by humans. It is noteworthy that this same mechanism of early wave reflection in the aortic root is one of the main factors responsible for SBP increase in the elderly, as a consequence of the increase in arterial stiffness observed with aging. Evaluating the results of the study by Elias Neto et al., the PWV of young individuals after orthostasis showed values similar to those found in the elderly in the dorsal position, corroborating the role of increased PWV with increased retrograde wave in the individual’s adaptation to the orthostatic position.
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