Although this new index is a strong candidate for an aortic stiffness index independent from ambient pressure, its validity has not been examined in humans. Importantly, the Modelflow aortic age, which reflects age-related changes in the aortic pressure-area relationship, is theoretically not influenced by the ambient blood pressure, because it considers the entire aortic compliance curve in its calculations. We have recently developed a new concept of the “Modelflow aortic age” by inversely applying the original Modelflow method, in which the arterial pressure waveform and stroke volume are required as input variables (see Supplemental Appendix the online version of this article contains supplemental data). Since the aortic input impedance used in the Modelflow calculation is generated from the known age-related changes in the aortic pressure-area relationship, the Modelflow system requires both the arterial pressure waveform and subject chronological age as input variables to estimate stroke volume ( 49). The Modelflow method has been utilized in clinical settings and/or physiological studies to estimate aortic flow and thus stroke volume from the arterial blood pressure waveform via aortic input impedance ( 5). At present, among commonly used indexes for arterial stiffness, only the β-stiffness index considers the curvilinear relationship of arterial compliance curve using a simple exponential correction ( 20). Therefore, an index for aortic stiffness that is not affected by the ambient blood pressure is warranted. Therefore, it is virtually impossible to distinguish between conditions in which high blood pressure causes functionally stiffer arteries by changing the operational point on the same compliance curve, from one in which mechanically stiff arteries (changes in the compliance curve itself) lead to high blood pressure due to impaired buffering of the arterial pressure waveform. For example, higher blood pressures shift the operational point of the arterial compliance curve to the flatter portion, resulting in functionally stiffer arteries on the same arterial compliance curve. However, all of these approaches are, by their nature, influenced by the ambient blood pressure due to the curvilinear nature of arterial compliance (arterial pressure-area relationship) ( 38). Large arterial stiffness is an independent predictor of mortality and morbidity from cardiovascular disease in the elderly population ( 3, 4, 7, 11, 33, 37, 39, 44, 50).Ĭentral aortic stiffness can be evaluated by several methods, such as pulse-wave velocity (PWV) of the central aorta, systemic arterial compliance (ratio of stroke volume to pulse pressure), or aortic impedance (dynamic relationship between aortic flow and pressure) ( 34, 41).
( 49) showed that structural properties of the thoracic and abdominal aortas are altered linearly with age in humans and are clinically relevant. This process is characterized primarily by the development of fibrosis and degeneration of elastin, which result in structural changes in the arterial wall ( 28, 29). The Modelflow aortic age can more precisely and reliably estimate aortic stiffening with aging and modifiers, such as life-long exercise training compared with the pressure-dependent index of static systemic arterial stiffness, and provides a physiologically relevant and clinically compelling context for such measurements.Īrteriosclerosis with aging leads to large-vessel arterial stiffening in humans. The typical error was very small and two times smaller in the Modelflow aortic age (13%) during cardiac unloading by lower body negative pressure.
The coefficient of variation of sedentary subjects was three times smaller with the Modelflow aortic age (21%) than with other indexes, such as static systemic arterial stiffness (61%), central pulse wave velocity (61%), or carotid β-stiffness index (58%). In contrast, Masters athletes showed younger Modelflow aortic ages than their chronological ages. Modelflow aortic ages were comparable with chronological ages in both sedentary groups, indicating that healthy sedentary individuals have age-appropriate aortas. Twelve sedentary elderly (65–77 yr), 11 Masters athletes (65–73 yr), and 12 sedentary young individuals (20–42 yr) were studied. The purpose of the present study was to validate this pressure-independent index for aortic stiffness in humans. chronological age) for measures of arterial stiffness. We developed a new concept of the “Modelflow aortic age,” which is, theoretically, not influenced by the ambient blood pressure and provides an easily understood context (biological vs. Indexes for arterial stiffness are, by their nature, influenced by the ambient blood pressure due to the curvilinear nature of arterial compliance.
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