Monitoring the Evolution of Asynchrony between Mean Arterial Pressure and Mean Cerebral Blood Flow via Cross-Entropy Methods.

Cerebrovascular control is carried out by multiple nonlinear mechanisms imposing a certain degree of coupling between mean arterial pressure (MAP) and mean cerebral blood flow (MCBF). We explored the ability of two nonlinear tools in the information domain, namely cross-approximate entropy (CApEn) and cross-sample entropy (CSampEn), to assess the degree of asynchrony between the spontaneous fluctuations of MAP and MCBF. CApEn and CSampEn were computed as a function of the translation time. The analysis was carried out in 23 subjects undergoing recordings at rest in supine position (REST) and during active standing (STAND), before and after surgical aortic valve replacement (SAVR). We found that at REST the degree of asynchrony raised, and the rate of increase in asynchrony with the translation time decreased after SAVR. These results are likely the consequence of the limited variability of MAP observed after surgery at REST, more than the consequence of a modified cerebrovascular control, given that the observed differences disappeared during STAND. CApEn and CSampEn can be utilized fruitfully in the context of the evaluation of cerebrovascular control via the noninvasive acquisition of the spontaneous MAP and MCBF variability.

Respiration is a Confounder of the Closed Loop Relationship Between Mean Arterial Pressure and Mean Cerebral Blood Flow.

This study tested the hypothesis that respiration (RESP) is a confounder or suppressor of the closed loop relationship responsible for the cerebrovascular dynamical interactions as assessed from spontaneous variability of mean arterial pressure (MAP) and mean cerebral blood flow (MCBF). The evaluation was carried out in the information domain via transfer entropy (TE) estimated through a linear model-based approach comparing TE markers computed solely over MAP and MCBF series with TE indexes accounting for the eventual action of RESP over MAP and MCBF. We considered 11 patients (age: 76±5 yrs, 7 males) undergoing surgical aortic valve replacement (SAVR) at supine resting (REST) and during active standing (STAND) before and after SAVR surgery. The decrease of the predictive ability of MCBF to MAP when accounting for RESP compared to the one assessed when disregarding RESP suggested that RESP is a confounder of the link from MCBF to MAP along the Cushing reflex instead of being a suppressor. This result was more evident in POST when autonomic control was dramatically depressed and in an unchallenged condition such as REST. RESP did not affect significantly the link from MAP to MCBF along the pressure-to-flow relationship. Clarification of the type of RESP influence on the MAP-MCBF closed loop relationship could favor a deeper characterization of cerebrovascular interactions and the comprehension of cerebral autoregulation mechanisms.Clinical Relevance- This study suggests that respiration is a confounder of the closed loop relationship between MAP and MCBF, especially of the flow-to-pressure causal link. This result might open new possibilities in elucidating the mechanisms of cerebral autoregulation in healthy and pathological populations.

Clinical Course of COVID-19 Infection in Patients Urgently Operated of Cardiac Surgical Procedures.

OBJECTIVE: The aim of this study was to describe the clinical course of a consecutive series of patients operated of urgent cardiac surgery during COVID-19 outbreak. BACKGROUND: In Italy, COVID outbreak has mostly occurred in the metropolitan area of Milan, and in the surrounding region of Lombardy, and previously "conventional" hospitals were converted into COVID spokes to increase ICU beds availability, and to allow only urgent CS procedures. METHODS: Among urgent CS patients (left main stenosis with unstable angina, acute endocarditis, valvular regurgitation with impending heart failure), 10 patients (mean age = 57 ± 9 years), despite a negative admission triage, developed COVID-pneumonia postoperatively, at a median of 7 days after CS. RESULTS: Patients showed typical lymphopenia, higher prothrombotic profile, and higher markers of inflammation (ferritin and interleukin-6 values). At the zenith of pulmonary distress, patients presented with severe hypoxia (median PaO2/FIO2 ratio = 116), requiring advanced noninvasive ventilation (Venturi mask and continuous positive airway pressure) in the majority of cases. All patients were treated with hydroxychloroquine, azithromycin, and low-molecular-weight heparin at anticoagulant dose. Overall in-hospital mortality was 10% (1/10), peaking 25% in patients who developed COVID pneumonia immediately after CS. The remaining patients, with late infection, were all discharged home without oxygen support, at a median of 25 days after symptom onset. CONCLUSIONS: As postoperative mortality in case of COVID pneumonia is not negligible, meticulous rules (precise triage, safe hospital path, high level of protection for health-care teams, prompt diagnosis of suspicious symptoms) should be strictly followed in patients undergoing CS during COVID pandemic. The role of therapies alternative to CS should be further assessed.