Echocardiographic assessment of aortic elastic properties with automated border detection in an ICU: in vivo application of the arctangent Langewouters model

Abstract

We studied whether combined pressure and transesophageal ultrasound monitoring is feasible in the intensive care unit (ICU) setting for global cardiovascular hemodynamic monitoring [systemic vascular resistance (SVR) and total arterial compliance (C PPM)] and direct estimation of local ascending and descending aortic mechanical properties, i.e., distensibility and compliance coefficients (DC and CC). Pressurearea data were fitted to the arctangent Langewouters model, with aortic cross-sectional area obtained via automated border detection. Data were measured in 19 subjects at baseline, during infusion of sodium nitroprusside (SNP), and after washout. SNP infusion lowered SVR from 1.15 Ϯ 0.40 to 0.80 Ϯ 0.32 mmHg ⅐ ml Ϫ1 ⅐ s (P Ͻ 0.05), whereas C PPM increased from 0.87 Ϯ 0.46 to 1.02 Ϯ 0.42 ml/mmHg (P Ͻ 0.05). DC and CC increased from 0.0018 Ϯ 0.0007 to 0.0025 Ϯ 0.0009 l/mmHg (P Ͻ 0.05) and from 0.0066 Ϯ 0.0028 to 0.0083 Ϯ 0.0026 cm 2 /mmHg (P Ͻ 0.05), respectively, at the descending, but not ascending, aorta. The Langewouters model fitted the descending aorta data reasonably well. Assessment of local mechanical properties of the human ascending aorta in a clinical setting by automated border detection remains technically challenging.afterload; large artery function; nitroprusside; coronary artery bypass grafting; intensive care unit LEFT VENTRICULAR SYSTOLIC function and cardiac output are determined by left ventricular preload, contractility, afterload, and heart rate (HR). Therefore, assessment of cardiovascular hemodynamic function should include these determinants. Transesophageal echocardiography is increasingly being used for patient monitoring in the operating room and intensive care unit (ICU). Interestingly, these patients often have a pressure catheter in the aorta for pressure monitoring. The simultaneous availability of ultrasound imaging modalities and intra-arterial pressure potentially allows for the online and in situ assessment of most determinants of cardiovascular function.The main determinants of arterial afterload are systemic vascular resistance (SVR) and total arterial compliance, reflecting the steady and main pulsatile component of arterial load, respectively (18,21,24). Both are derived from aortic pressure and flow; therefore, they can be monitored in the clinical setting as described above.In addition to the aforementioned global afterload parameters, transesophageal echocardiography in conjunction with arterial pressure monitoring has the potential to assess local mechanical characteristics of central vessels via the construction and analysis of pressure-area or pressure-diameter curves (3, 4). It is well established that large artery elastic dysfunction is an important cardiovascular risk factor (1, 28). Reduced arterial compliance leads to an increased systolic pressure and pulse pressure (PP) and, consequently, an increased load to the heart. Because Ͼ60% of the total arterial compliance resides in the ascending and thoracic aorta, determining the regional compliance of the thorac...

Asymmetric time-dependent model for the dynamic finger arterial pressure–volume relationship

“…This gives an opportunity to study the structure of the vascular wall, in which mechanical properties are determined by elastin, collagen and smooth muscle [3]. Changes in the smooth muscle tone can be traced [10]. The function used to describe the nonlinearity of the P-V relationship is free from contradiction, namely that different mechanical events for positive and negative transmural pressures are modelled symmetrically for both sides, as done by the Langewouters arctangent model.…”

“…In special experiments, certain properties can be selectively detected. For example, it was found when investigating the smooth muscle tone in the descending aorta [10], that P 0 decreased by 18.3 mmHg and P 1 increased by 7.3 mmHg (or, in other words by 107%) after sodium nitroprusside infusion. Those P-C curves had essentially different positions and shapes.…”

“…The volumetric PPG signal was uncalibrated, and this made the quantitative model-based compliance estimation, as done in [10], impossible. However, the model parameters allowed the quantification of other artery properties, such as the inflection point position (P 0 ), elasticity changes in the bending and compression regions (P 1n ), transition and high stiffness regions (P 1p ) and also dynamics (s).…”

Non-invasive quantification of peripheral arterial volume distensibility and its non-linear relationship with arterial pressure

“…To obtain arterial volume compliance, in practice, both arterial pressure change and the simultaneous blood volume change are recorded by different invasive or non-invasive techniques (Buntin and Silver, 1990;Mackenzie et al, 2002;McVeigh et al, 2002;Pannier et al, 2002), but these techniques cannot yet give an accurate measurement of the blood volume (or artery radius) and arterial pressure changes in clinical use. Furthermore, most studies focused mainly on a relatively large single artery (Heerman et al, 2005;Laurent et al, 1994), rather than the total peripheral arterial system. Determining peripheral arterial properties can contribute to studying the development and progression of hypertension.…”

Novel method for early signs of clinical shock detection by monitoring blood capillary/vessel spatial pattern

“…Due to its speed and real-time information, hemodynamic monitoring is currently a popular and reliable technique for all kinds of shock detection in ICU patients. Various techniques, such as arterial catheter [5][6][7], central venous catheter [7], echocardiography [8][9][10][11], esophageal Doppler monitor [9], Foley catheter, gastric tonometry [12][13][14], pulmonary artery catheter [6,15,16], pulse oximetry [17,18], and DOCT (Doppler Optical Coherence Tomography) [19] are used for shock monitoring. Each has its own merits and demerits.…”