Towards continuous non-invasive blood pressure measurements—interpretation of the vasculature response to cuff inflation

Blood pressure (BP) surrogates, such as pulse transit time (PTT) or pulse arrival time (PAT), have been intensively explored with the goal of achieving cuffless, continuous, and accurate BP inference. In order to estimate BP, a one-point calibration strategy between PAT and BP is typically used. Recent research focuses on advanced calibration procedures exploiting the cuff inflation process to improve calibration robustness by active and controlled modulation of peripheral PAT, as measured via plethysmograph (PPG) and electrocardiogram (ECG) combination. Such methods require a detailed understanding of the mechanisms behind the vasculature’s response to cuff inflation; for this, a model has recently been developed to infer the PAT-BP calibration from measured cuff-induced vasculature changes. The model, while promising, is still preliminary and only partially validated; in-depth analysis and further developments are still needed. Therefore, this work aims to improve our understanding of the cuff-vasculature interaction in this model; we seek to define potential opportunities and to highlight which aspects may require further study. We compare model behaviors with clinical data samples based on a set of observable characteristics relevant for BP inference and calibration. It is found that the observed behaviors are qualitatively well represented with the current simulation model and complexity, with limitations regarding the prediction of the onset of the distal arm dynamics and behavior changes at high cuff pressures. Additionally, a sensitivity analysis of the model’s parameter space is conducted to show the factors that influence the characteristics of its observable outputs. It was revealed that easily controllable experimental variables, such as lateral cuff length and inflation rate, have a significant impact on cuff-induced vasculature changes. An interesting dependency between systemic BP and cuff-induced distal PTT change is also found, revealing opportunities for improved methods for BP surrogate calibration. However, validation via patient data shows that this relation does not hold for all patients, indicating required model improvements to be validated in follow up studies. These results provide promising directions to improve the calibration process featuring cuff inflation towards accurate and robust non-invasive blood pressure estimation

Modulation of Pulse Propagation and Blood Flow via Cuff Inflation—New Distal Insights

In standard critical care practice, cuff sphygmomanometry is widely used for intermittent blood pressure (BP) measurements. However, cuff devices offer ample possibility of modulating blood flow and pulse propagation along the artery. We explore underutilized arrangements of sensors involving cuff devices which could be of use in critical care to reveal additional information on compensatory mechanisms. In our previous work, we analyzed the response of the vasculature to occlusion perturbations by means of observations obtained non-invasively. In this study, our aim is to (1) acquire additional insights by means of invasive measurements and (2) based on these insights, further develop cuff-based measurement strategies. Invasive BP experimental data is collected downstream from the cuff in two patients monitored in the OR. It is found that highly dynamic processes occur in the distal arm during cuff inflation. Mean arterial pressure increases in the distal artery by 20 mmHg, leading to a decrease in pulse transit time by 20 ms. Previous characterizations neglected such distal vasculature effects. A model is developed to reproduce the observed behaviors and to provide a possible explanation of the factors that influence the distal arm mechanisms. We apply the new findings to further develop measurement strategies aimed at acquiring information on pulse arrival time vs. BP calibration, artery compliance, peripheral resistance, artery-vein interaction

Feasibility of in-vivo estimation of the brachial artery area-pressure relation from CINE and real-time MRI during upper arm cuff inflations

Objective: We investigate the basic feasibility of estimating the brachial artery area-pressure relationship from MRI data obtained during pressure cuff inflations in-vivo. Methods: We acquired cross-sectional real-time MR images and cardiac-gated CINE MR images from the upper arm of a single male subject at rest during supra-systolic pressure cuff inflations and deflations. We estimate from the MR images the lumen area changes of the brachial artery, and, simultaneously, from the cuff pressure the systemic blood pressure of the subject. We reconstruct the area-pressure curve from two real-time and three CINE independent measurements. Results: The area-pressure curve can be reconstructed, and it is plausible and appears largely consistent with the literature using other methods. Conclusion: MR imaging during pressure cuff inflations is an easy to use, non-invasive candidate method to estimate the brachial artery pressure-area curve

An Experimental Study on the Blood Pressure Cuff as a Transducer for Oscillometric Blood Pressure Measurements

Noninvasive blood pressure (BP) measurements still rely on empirical interpretation of arterial oscillations recorded via cuff-based oscillometric methods. Extensive effort has dedicated to establishing a theoretical basis for oscillometry, aiming at more accurate BP estimations and measurement of additional hemodynamic parameters. However, oscillometry is still a heuristic method for BP inference. Goal: This study is focused on improving our understanding of the expression of arm volume pulsations in oscillometric signals. The aim is to identify the main factors that determine the transfer function of arm volume to cuff pressure oscillations for existing cuff devices—this being an essential step in establishing a theoretical basis for oscillometry. Methods: The effects of air compression within the cuff and the influence of viscoelastic cuff material properties on the transfer function are studied by an experimental setup. Mechanical numerical modeling is used to interpret the results. Results: Air compression is found to be of adiabatic nature in the frequency range of interest. The cuff material exhibits viscous characteristics which is the cause of cuff response dependence on inflation speed, tightness of wrapping, time passed since previous measurement, and heart rate. Conclusion: It was found that typical cuffs used in clinical practice exhibit complex behavior. Cuff hardware needs to be improved to enable practical translation of pressure to arm volume oscillations. The presented characterization method contributes to standardized development of new cuff prototypes and to identification of designs, techniques, and materials with improved properties for enabling BP measurement accuracy and extraction of additional hemodynamic information

Nanostructuring Effect of Nano-CeO2 Particles Reinforcing Cobalt Matrix during Electrocodeposition Process

The electrodeposition method was used to obtain nanostructured layers of Co/nano-CeO2 on 304L stainless steel, from a cobalt electrolyte in which different concentrations of CeO2 nanoparticles (0, 10, 20, and 30 g/L) were dispersed. The electrodeposition was performed at room temperature using three current densities (23, 48, and 72 mA cm−2), and the time was kept constant at 90 min. The influence of current densities and nanoparticle concentrations on the characteristics of the obtained nanostructured layers is also discussed. An X-ray diffractometer (XRD) was used to investigate the phase structure and cobalt crystallite size of the nanostructured layers, and a contact angle (sessile drop method) was used to assess the wettability of the electrodeposited layers. The roughness of the surfaces was also studied. The results show that the nanostructured layers became more hydrophilic with increasing nanoparticle concentration and increasing current density. In the case of pure cobalt deposits, an increase in the current density led to an increase in the size of the cobalt crystallites in the electrodeposited layer, while for the Co/nano-CeO2 nanostructured layers, the size of the crystallites decreased with increasing current density. This confirms the nanostructuring effect of nano-CeO2 electrocodeposited with cobalt

Insights into oscillometry: An Experimental Study for Improvement of Cuff-Based Blood Pressure Measurement Technology

Non-invasive blood pressure (BP) measurements are usually performed by means of an empirical interpretation of arterial oscillations recorded via cuff based oscillometic methods. Extensive effort has been put into development of a theoretical treatment of oscillometry aiming at more accurate BP estimations and measurement of additional hemodynamic parameters. However, oscillometry is still basically a heuristic method for BP inference.This study introduces an experimental setup and discusses experimental results to improve understanding of cuff characteristics and the process by which oscillometric signals are produced, with the aim of improving cuff-based non-invasive BP measurement technology relevant in clinical practice. The work focuses on mechanical simulations of arm volume pulsations in cuff pressure signals. The effects of air compression within the cuff and the influence of viscoelastic properties of exterior cuff material are also investigated. Additionally, arm volume changes and compressibility of arm tissue due to external cuff pressure were studied with an MRI system. Our results reveal novel insights into oscillometry and enable understanding of transducer design for cuffs including the importance of viscoelastic material properties and effects of cuff inflation on arm tissue