Novel non-invasive techniques for hemodynamic monitoring

The monitoring of hemodynamic parameters is crucial for optimal patient management and treatment. However, established methods are often invasive and possibly inapplicable to sensitive age groups. Novel, non-invasive techniques have the potential to transform cardiovascular (CV) assessment, offering reduced hospitalization periods, lower infection risk and decreased staff-to-patient ratio. Cardiac output (CO) monitoring provides valuable insight on global tissue perfusion. To overcome limitations of traditional methods, a novel technique was proposed. Taking into account the basic principles of CV physiology we derived an equation where the required variables can be extracted non-invasively. The novel technique was validated in a controlled, in silico, environment against previously established wave analysis methods. Subsequent data analysis showed that the new method yielded superior accuracy and precision. The new method was further evaluated in vivo using a 2D transthoracic echocardiography protocol for CO estimation. The corresponding comparison showed that the SVB method provides highly reproducible and accurate estimates of CO when compared to ultrasound. The estimation of pulse transit time (PTT) affects critically the accuracy and precision of pulse wave velocity (PWV) measurements. We proposed the "€œDiastole-Patching"€ method (DPm), which estimates PTT based on a signal region in the diastolic foot of the wave and is more robust against noisy arterial waveforms. DPm and previously established techniques were tested with a computational model of the arterial tree where the "real"€ values of PWV are known. The novel method yielded the highest agreement, accuracy and precision even when the waves were distorted with noise. The technique was further evaluated against the corresponding â€"reference"€ algorithm of a commercially available device with in vivo acquired waves. DPm yielded more precise and reproducible measurements of PWV. Total Systemic Compliance (CT) expresses the ability of the arterial system to dilate and store blood during cardiac ejection. Our aim was to develop a relationship between aPWV and CT. The proposed, generalized Bramwell-Hill model of the systemic arterial tree estimates CT by a single non-invasive measurement of PWV. The proposed scheme was found to accurately estimate CT from aPWV. The mechanical properties of woven Dacron grafts differ significantly from the human aorta. As a result, aortic graft implantation changes the aortic geometry and mechanical properties, thus affecting blood pressure and wave reflections. A dedicated cardiovascular model was developed to include graft geometry and in vitro measured Dacron properties. It was found that aortic reconstruction affected aortic hemodynamics. For the proximal graft, the primary reason for pulse pressure rise is augmentation of the forward wave. For the distal graft, the pulse pressure rise is associated with augmented wave reflections resulting from the compliance mismatch between the aorta and the distal graft. To conclude, this body of work has shown that given the current computational tools and biosensors, it is possible to design and validate a set of non-invasive techniques that will provide valuable clinical insight for a wide gamut of cardiovascular diseases.


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