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The Physiological Genesis of Ballistocardiography and Seismocardiography and Their Clinical Applications in the Era of Digital Medicine

par Morra, Sofia
Président du jury Devière, Jacques
Promoteur Van De Borne, Philippe
Publication Non publié, 2021-05-04

Thèse de doctorat

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Résumé :

The 21st century brought tremendous changes in technologies, sweeping away every aspect of daily life, from social to private life, from education to professional world, at a breakneck pace. Medical science has not been spared by this colossal wave of changes: e-health, e-patients, e-physicians and e-medical students have already made their first appearance in the routine medical practice. Surgical robots, 3D printing, Artificial-Intelligence based imaging, smartwatches, wearable sensors are already used to improve diagnosis, personalize treatments and monitor patients’ health. Ballistocardiography (BCG) and seismocardiography (SCG) are ancient techniques which estimate the mechanical performance of the heart through measuring myocardial contraction-induced vibrations transmitted to the skin surface. They made their first appearance into clinic at the beginning of the 20th century to help in the diagnosis of cardiovascular diseases, but their popularity drastically declined in the middle of the 70s and they never had their place in clinical practice: cumbersome and complex equipment, ambiguity in the signal interpretation, unclear understanding of the physiological genesis of the signal, the advent of high-performing technologies (cardiac MRI, echocardiography) are a few of the reasons for their clinical failure. Thanks to the tremendous improvements in technologies, these techniques of the past came back to the medical world as wearable biosensors, first holding the promise of a remote and continuous monitoring of the cardiovascular status. Displacement, velocity and acceleration of blood mass flowing into cardiac chambers and main extracardiac vessels are recorded for each heartbeat along three cardinal axes and in two dimensions, a linear and a rotational one, by the renewed BCG and SCG, with 6 degrees-of-freedom (6D-BCG and 6D-SCG). By applying the Newtonian principles to the recorded signals, signal processing algorithms automatically compute the kinetic energy (KE) and its temporal integral (iK) for each cardiac cycle. This work first analyzed the influence of normal and pathological respiration as well as the effects of sympathetic overactivity on the genesis of the 6D-BCG and 6D-SCG signals and the iK parameters; secondary, it tested the usefulness of 6D-BCG and 6D-SCG techniques in the detection of cardiac dysfunction and hemodynamic impairment during acute myocardial infarction and reperfusion in an animal model for acute coronary syndrome. While breathing normally mildly affects cardiac iK parameters, pathological respiration profoundly alters them. During a sustained end-expiratory apnea, as it happens in patients suffering from central sleep apnea, the iK generated within a contractile cycle acutely increases at the end of the apnea, strictly depending on the magnitude of sympathetic activity; inspiring against a resistance, as it happens in patients suffering from obstructive sleep apnea, acutely increases the cardiac iK and this surge is related to the acute external force afterloading the left ventricle. So, whether it is a central apnea or an obstructive one, myocardial mechanical function as expressed in terms of iK is profoundly impaired, suggesting the myocardium is enduring a sustain endeavor during these pathological respirations. During an experimental acute myocardial infarction, in a context of mechanical ventilation without major respiratory events, iK parameters drastically drop during coronary occlusion and does not improve during reperfusion, along with systemic blood pressures and cardiac output, thus holding the promise to continuously monitor the cardiac contractile function and the hemodynamic profile both during acute coronary occlusion and reperfusion. Renewed and wearable 6D-BCG and 6D-SCG may prove useful in the detection and continuous monitoring of cardiac dysfunction and hemodynamic impairment in patients suffering from sleep disordered breathing and may be used in the mid-long-term follow-up of patients with myocardial dysfunction of ischemic origin. There is still a lot of work to do before validating these renewed technologies in the practice of cardiovascular medicine, but evidences are there to consider them as next generation medical devices.