Monitoring of false lumen thrombosis in type B aortic dissection by impedance cardiography - A multiphysics simulation study.

Aortic dissection is caused by a tear on the aortic wall that allows blood to flow through the wall layers. Usually, this tear involves the intimal and partly the medial layer of the aortic wall. As a result, a new false lumen develops besides the original aorta, denoted then as the true lumen. The local hemodynamic conditions such as flow disturbances, recirculations and low wall shear stress may cause thrombus formation and growth in the false lumen. Since the false lumen status is a significant predictor for late-dissection-related deaths, it is of great importance in the medical management of patients with aortic dissection. The hemodynamic changes in the aorta also alter the electrical conductivity of blood. Since the blood is much more conductive than other tissues in the body, such changes can be identified with non-invasive methods such as impedance cardiography. Therefore, in this study, the capability of impedance cardiography in monitoring thrombosis in the false lumen is studied by multiphysics simulations to assist clinicians in the medical management of patients under treatment. To tackle this problem, a 3D computational fluid dynamics simulation has been set up to model thrombosis in the false lumen and its impact on the blood flow-induced conductivity changes. The electrical conductivity changes of blood have been assigned as material properties of the blood-filled aorta in a 3D finite element electric simulation model to investigate the impact of conductivity changes on the measured impedance from the body's surface. The results show remarkable changes in the electrical conductivity distribution in the measurement region due to thrombosis in the false lumen, which significantly impacts the morphology of the impedance cardiogram. Thus, frequent monitoring of impedance cardiography signals may allow tracking the thrombus formation and growth in the false lumen.

[Current status of noninvasive hemodynamics in hypertension]. / Estado actual de la hemodinamia no invasiva en hipertensión arterial.

Hypertension is a haemodynamic disorder resulting from a persistent mismatch between cardiac output and peripheral resistance. Hypertension undergoes haemodynamic progression during its natural history. Impedance cardiography is a method of evaluating the cardiovascular system that obtains haemodynamic information from beat to beat through the analysis of variations in the impedance of the thorax on the passage of an electric current. Impedance cardiography unmasks the haemodynamic deterioration underlying the increase in blood pressure as age and systolic blood pressure increases. This method may help to improve blood pressure control through individualized treatment with reduction of peripheral resistance, maintenance of cardiac output or its increase, improvement of arterial compliance and preservation of organ-tissue perfusion. It is useful in the management of patients with resistant hypertension, since a greater percentage of patients controlled with changes in the treatment in relation to the haemodynamic measurements are obtained. Impedance cardiography is important and has prognostic utility in relation to a haemodynamic deterioration pattern and increased cardiovascular events.

Casting doubt on the value of assessing the cardiac index in pregnancy.

OBJECTIVES: The objective of this study is to assess the reliability of the cardiac index (CI) in healthy pregnant women at term by investigating the correlation between the cardiac output (CO) and the body surface area (BSA) using a novel non-invasive cardiography technique (NICaS™). METHODS: Sixty-one healthy, normotensive women with a singleton pregnancy at term (≥37 gestational weeks) participated in this prospective observational study between 1/2015 and 6/2015 L. Each woman was assessed for CO by the NICaS™, an impedance device that non-invasively measures the CO and its derivatives. The NICaS™ demonstrated a very good correlation with the gold standard Swan-Ganz catheter. BSA was determined by the Dubois nomogram. RESULTS: The mean ± standard deviation maternal age was 34.2 ± 5.3 years, mean height 166 ± 6 cm, and mean body mass index 23.9 ± 4.9 kg/m2. The mean gestational age was 38.8 ± 0.7 weeks. The correlation between the CO and the BSA was poor (Pearson r = 0.254, p < .005). CONCLUSIONS: The current study demonstrated poor correlation between the CO and the BSA in pregnant women, therefore, making the CI a non-reliable variable for assessing CO in pregnant women. We, therefore, suggest that the CO rather than the CI is the preferred parameter for hemodynamic measurements in this population.