Relationship between Stroke Volume and Pulse Wave Velocity

Continuous Monitoring of Blood Pressure and Vascular Hemodynamic Properties With Miniature Extravascular Hall-Based Magnetic Sensor

Continuous measurement of vascular and hemodynamic parameters could improve monitoring of disease progression and enable timely clinical decision making and therapy surveillance in patients suffering from cardiovascular diseases. However, no reliable extravascular implantable sensor technology is currently available. Here, we report the design, characterization, and validation of an extravascular, magnetic flux sensing device capable of capturing the waveforms of the arterial wall diameter, arterial circumferential strain, and arterial pressure without restricting the arterial wall. The implantable sensing device, comprising a magnet and a magnetic flux sensing assembly, both encapsulated in biocompatible structures, has shown to be robust, with temperature and cyclic-loading stability. Continuous and accurate monitoring of arterial blood pressure and vascular properties was demonstrated with the proposed sensor in vitro with a silicone artery model and validated in vivo in a porcine model mimicking physiologic and pathologic hemodynamic conditions. The captured waveforms were further used to deduce the respiration frequency, the duration of the cardiac systolic phase, and the pulse wave velocity. The findings of this study not only suggest that the proposed sensing technology is a promising platform for accurate monitoring of arterial blood pressure and vascular properties, but also highlight the necessary changes in the technology and the implantation procedure to allow the translation of the sensing device in the clinical setting.

Remote Ischaemic Preconditioning Attenuates Cardiac Biomarkers During Vascular Surgery: A Randomised Clinical Trial

OBJECTIVE

The main aim of this study was to evaluate the effect of remote ischaemic preconditioning (RIPC) on preventing the leakage of cardiac damage biomarkers in patients undergoing vascular surgery.

METHODS

This is a randomised, sham-controlled, double-blinded, single-centre study. Patients undergoing open abdominal aortic aneurysm repair, surgical lower limb revascularisation surgery or carotid endarterectomy were recruited non-consecutively. The RIPC protocol consisting of 4 cycles of 5 minutes of ischaemia, followed by 5 minutes of reperfusion, was applied. A RIPC or a sham procedure was performed noninvasively along with preparation for anaesthesia. High sensitivity troponin T level was measured preoperatively and 2, 8 and 24 hours after surgery and pro b-type natriuretic peptide was measured preoperatively and 24 hours after surgery.

RESULTS

There was significantly higher leakage of high sensitivity troponin T (peak change median 2 ng/L, IQR 0.9-6.2 ng/L vs 0.6 ng/L, IQR 0.7-2.1 ng/L, p = .0002) and pro b-type natriuretic peptide (change median 144 pg/mL, IQR 17-318 pg/mL vs 51 pg/mL, IQR 12-196 pg/mL, p = .02) in the sham group compared to the RIPC group.

CONCLUSION

RIPC reduces the leakage of high sensitivity troponin T and pro b-type natriuretic peptide. Therefore, it may offer cardioprotection in patients undergoing non-cardiac vascular surgery. The clinical significance of RIPC has to be evaluated in larger studies excluding the factors known to influence its effect.

A review on low-dimensional physics-based models of systemic arteries: application to estimation of central aortic pressure

The physiological processes and mechanisms of an arterial system are complex and subtle. Physics-based models have been proven to be a very useful tool to simulate actual physiological behavior of the arteries. The current physics-based models include high-dimensional models (2D and 3D models) and low-dimensional models (0D, 1D and tube-load models). High-dimensional models can describe the local hemodynamic information of arteries in detail. With regard to an exact model of the whole arterial system, a high-dimensional model is computationally impracticable since the complex geometry, viscosity or elastic properties and complex vectorial output need to be provided. For low-dimensional models, the structure, centerline and viscosity or elastic properties only need to be provided. Therefore, low-dimensional modeling with lower computational costs might be a more applicable approach to represent hemodynamic properties of the entire arterial system and these three types of low-dimensional models have been extensively used in the study of cardiovascular dynamics. In recent decades, application of physics-based models to estimate central aortic pressure has attracted increasing interest. However, to our best knowledge, there has been few review paper about reconstruction of central aortic pressure using these physics-based models. In this paper, three types of low-dimensional physical models (0D, 1D and tube-load models) of systemic arteries are reviewed, the application of three types of models on estimation of central aortic pressure is taken as an example to discuss their advantages and disadvantages, and the proper choice of models for specific researches and applications are advised.

In vitro validation of measurement of volume elastic modulus using photoplethysmography

Arterial stiffness (AS) is one of the earliest detectable symptoms of cardiovascular diseases and their progression. Current AS measurement methods provide an indirect and qualitative estimation of AS. The purpose of this study is to explore the utilisation of Photoplethysmography (PPG) as a measure of volumetric strain in providing a direct quantification of the Volume Elastic modulus (E_v). An in vitro experimental setup was designed using an arterial model to simulate the human circulation in health (Model 2) and disease (Model 1). Flow, pressure, and PPG signals were recorded continuously under varied conditions of flow dynamics. The obtained E_v values were validated with the gold standard mechanical testing techniques. Values obtained from both methods had no significant difference for both models with a percent error of 0.26% and 1.9% for Model 1 and Model 2, respectively. This study shows that PPG and pressure signals can provide a direct measure of AS in an in vitro setup. With emerging noninvasive pressure measurement methods, this research paves the way for the direct quantification of AS in vivo.

Pilot Study: Estimation of Stroke Volume and Cardiac Output from Pulse Wave Velocity

Background

Transesophageal echocardiography (TEE) is increasingly replacing thermodilution pulmonary artery catheters to assess hemodynamics in patients at high risk for cardiovascular morbidity. However, one of the drawbacks of TEE compared to pulmonary artery catheters is the inability to measure real time stroke volume (SV) and cardiac output (CO) continuously. The aim of the present proof of concept study was to validate a novel method of SV estimation, based on pulse wave velocity (PWV) in patients undergoing cardiac surgery.

Methods

This is a retrospective observational study. We measured pulse transit time by superimposing the radial arterial waveform onto the continuous wave Doppler waveform of the left ventricular outflow tract, and calculated SV (SV_PWV) using the transformed Bramwell-Hill equation. The SV measured by TEE (SV_TEE) was used as a reference.

Results

A total of 190 paired SV were measured from 28 patients. A strong correlation was observed between SV_PWV and SV_TEE with the coefficient of determination (R²) of 0.71. A mean difference between the two (bias) was 3.70 ml with the limits of agreement ranging from -20.33 to 27.73 ml and a percentage error of 27.4% based on a Bland-Altman analysis. The concordance rate of two methods was 85.0% based on a four-quadrant plot. The angular concordance rate was 85.9% with radial limits of agreement (the radial sector that contained 95% of the data points) of ± 41.5 degrees based on a polar plot.

Conclusions

PWV based SV estimation yields reasonable agreement with SV measured by TEE. Further studies are required to assess its utility in different clinical situations.

The Effects of Hemodynamic Changes on Pulse Wave Velocity in Cardiothoracic Surgical Patients

The effect of blood pressure on pulse wave velocity (PWV) is well established. However, PWV variability with acute hemodynamic changes has not been examined in the clinical setting. The aim of the present study is to investigate the effect of hemodynamic changes on PWV in patients who undergo cardiothoracic surgery. Using data from 25 patients, we determined blood pressure (BP), heart rate (HR), and the left ventricular outflow tract (LVOT) velocity-time integral. By superimposing the radial arterial waveform on the continuous wave Doppler waveform of the LVOT, obtained by transesophageal echo, we were able to determine pulse transit time and to calculate PWV, stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR). Increases in BP, HR, and SVR were associated with higher values for PWV. In contrast increases in SV were associated with decreases in PWV. Changes in CO were not significantly associated with PWV.