Shear stress, energy losses, and costs: a resolved dilemma of pulsatile cardiac assist devices

Endothelial shear stress enhancements: a potential solution for critically ill Covid-19 patients

Most critically ill Covid-19 patients succumb to multiple organ failure and/or sudden cardiac arrest (SCA) as a result of comorbid endothelial dysfunction disorders which had probably aggravated by conventional mechanical assist devices. Even worse, mechanical ventilators prevent the respiratory pump from performing its crucial function as a potential generator of endothelial shear stress (ESS) which controls microcirculation and hemodynamics since birth. The purpose of this work is to bring our experience with ESS enhancement and pulmonary vascular resistance (PVR) management as a potential therapeutic solution in acute respiratory distress syndrome (ARDS). We propose a non-invasive device composed of thoracic and infradiaphragmatic compartments that will be pulsated in an alternating frequency (20/40 bpm) with low-pressure pneumatic generator (0.1–0.5 bar). Oxygen supply, nasogastric with, or without endotracheal tubes are considered.

Endothelial Function in Patients With Continuous-Flow Left Ventricular Assist Devices

The endothelium plays a crucial role in maintaining cardiovascular homeostasis. Shear stress generated by flowing blood regulates the release of substances that provide adequate tissue perfusion. The extent of damage to endothelial cells depends on locally disturbed shear stress caused by the deteriorated flow. Patients with heart failure have reduced cardiac output, which results in reduced blood flow and negative shear stress. Reduced shear stress also affects microcirculation and reduces tissue perfusion. Consequently, the production of free oxygen radicals is increased and bioavailability of nitric oxide is additionally decreased. Therefore, endothelial dysfunction is involved in the progression of heart failure and cardiovascular events. Left ventricular assist devices (LVAD) are used for the treatment of patients with advanced heart failure. Older pulsatile flow LVADs were mostly substituted by continuous-flow LVADs (cf-LVADs). Despite the advantages of the cf-LVADs, the loss of pulsatility leads to different complications on the micro- and macrovascular levels. One of the pathogenetic mechanisms of cardiovascular complications with cf-LVADs may be endothelial dysfunction, which after the implantation of the device does not improve and may even deteriorate. In contrast, the pulsatile pattern of LVADs on blood flow could preserve endothelial function.

Circulatory Flow Restoration Versus Cardiopulmonary Resuscitation: New Therapeutic Approach in Sudden Cardiac Arrest

Sudden cardiac arrest (SCA) remains a major problem for health authorities worldwide. Insufficiencies of current cardiopulmonary resuscitation (CPR) are most probably related to an inappropriate concept and applied methods that still concentrate on heartbeat as priority, instead of blood circulation to maintain organs' perfusions. The aim of this works is to propose a new therapeutic approach for SCA in a more effective and secure manner compared with current CPR methods. It correlates to a non-invasive circulatory flow restoration (CFR) device composed of a multilayered thoracic and infradiaphragmatic compartments that will be pulsated alternatively and in fixed frequencies using a low-pressure pneumatic generator. Proof-of-concept studies with different prototypes and methods of SCA, showed restoration of hemodynamics (BP ≥ 100 mm Hg) and increased urine output after 20 min of cardiac arrest in pediatric dogs and piglets. In summary, a CFR device can induce shear stress-mediated endothelial function to restore microcirculation and cellular metabolism. This represents a cost-effective method, predisposes to return of spontaneous circulation in case of SCA, adaptable for all age groups, in public and hospital environments.