Acute respiratory distress syndrome (ARDS) remains an important clinical challenge with a mortality rate of 35–45%. It is being increasingly demonstrated that the improvement of outcomes requires a tailored, individualized approach to therapy, guided by a detailed understanding of each patient’s pathophysiology. In patients with ARDS, disturbances in the physiological matching of alveolar ventilation (V) and pulmonary perfusion (Q) (V/Q mismatch) are a hallmark derangement. The perfusion of collapsed or consolidated lung units gives rise to intrapulmonary shunting and arterial hypoxemia, whereas the ventilation of non-perfused lung zones increases physiological dead-space, which potentially necessitates increased ventilation to avoid hypercapnia. Beyond its impact on gas exchange, V/Q mismatch is a predictor of adverse outcomes in patients with ARDS; more recently, its role in ventilation-induced lung injury and worsening lung edema has been described. Innovations in bedside imaging technologies such as electrical impedance tomography readily allow clinicians to determine the regional distributions of V and Q, as well as the adequacy of their matching, providing new insights into the phenotyping, prognostication, and clinical management of patients with ARDS. The purpose of this review is to discuss the pathophysiology, identification, consequences, and treatment of V/Q mismatch in the setting of ARDS, employing experimental data from clinical and preclinical studies as support.

Purpose Personalized positive end-expiratory pressure (PEEP) might foster lung and diaphragm protection in patients with acute respiratory distress syndrome (ARDS) who are undergoing pressure support ventilation (PSV). We aimed to compare the physiologic effects of personalized PEEP set according to synchronized electrical impedance tomography (EIT) and driving transpulmonary pressure (∆PL) monitoring against a classical lower PEEP/FiO₂ table in intubated ARDS patients undergoing PSV. Methods A cross-over randomized multicenter study was conducted in 30 ARDS patients with simultaneous recording of the airway, esophageal and transpulmonary pressure, together with EIT during PSV. Following a decremental PEEP trial (18 cmH₂O to 4 cmH₂O), PEEP_EIT-∆PL was identified as the level with the smallest difference between lung overdistension and collapse. A low PEEP/FiO₂ table was used to select PEEP_TABLE. Each PEEP strategy was applied for 20 min, and physiologic data were collected at the end of each step. Results The PEEP trial was well tolerated. Median PEEP_EIT-∆PL was higher than PEEP_TABLE (10 [8–12] vs. 8 [5–10] cmH₂O; P = 0.021) and, at the individual patient level, PEEP_EIT-∆PL level differed from PEEP_TABLE in all patients. Overall, PEEP_EIT-∆PL was associated with lower dynamic ∆PL (P < 0.001) and pressure–time product (P < 0.001), but there was variability among patients. PEEP_EIT-∆PL also decreased respiratory drive and effort (P < 0.001), improved regional lung mechanics (P < 0.05) and reversed lung collapse (P = 0.007) without increasing overdistension (P = 0.695). Conclusion Personalized PEEP selected using synchronized EIT and transpulmonary pressure monitoring could be associated with reduced dynamic lung stress and metabolic work of breathing in ARDS patients undergoing PSV.

Monitoring with electrical impedance tomography (EIT) during a decremental PEEP trial has been used to identify the PEEP that yields the optimal balance of pulmonary overdistension and collapse. This method is based on pixel-level changes in respiratory system compliance and depends on fixed or measured airway driving pressure. We developed a novel approach to quantify overdistension and collapse during pressure support ventilation (PSV) by integrating transpulmonary pressure and EIT monitoring and performed pilot tests in three hypoxemic patients. We report that our experimental approach is feasible and capable of identifying a PEEP that balances overdistension and collapse in intubated hypoxemic patients undergoing PSV.

Funding Acknowledgements: Type of funding sources: None. Background: Heart disease is a major determinant of prognosis in type 1 myotonic dystrophy (DM1), second only to respiratory complications. Cardiac imaging, possibly including cardiac magnetic resonance (CMR), is recommended in patients with DM1. However, limited information is available on CMR findings and their prognostic significance in DM1. Methods: We identified all patients with DM1 evaluated from 2009 to 2020 in a CMR laboratory with an established collaboration with a Neuromuscular Disorder Unit. Results: Thirty-four patients were retrieved (21 males, aged 45 ± 12). At the time of CMR examination, 97% had neuromuscular symptoms (mean duration 16 ± 13 years), 12 (35%) presented with atrioventricular block (n = 11 1st degree, n = 1 2nd degree type 1), 15 (44%) with intraventricular conduction disturbances (n = 5 left bundle branch block, n = 5 right bundle branch block, n = 3 left anterior fascicular block, n = 2 other non-specific intraventricular conduction delay), 4 (12%) with atrial fibrillation or flutter. No patient had a device. At CMR, 5 (15%) patients had left ventricular (LV) systolic dysfunction (LV ejection fraction [LVEF] <50%) and 5 (15%) a depressed right ventricular (RV) function (RVEF <50%). Compared to age- and sex-specific reference values for our laboratory, 12 (35%) patients showed a decreased LV end-diastolic volume index (LVEDVi), 7 (21%) a decreased LV mass index (LVMi), and 29 (83%) a decreased LVMi/LVEDVi ratio. Nine (26%) patients had mid-wall late gadolinium enhancement (LGE, mean extent 4.5 ± 2.0% of LVM; n = 8 septal, n = 4 inferolateral, n = 2 inferior, n = 1 anterolateral), and 14 (40%) some areas of fatty infiltration (n = 9 involving the LV, n = 13 the RV). Native T1 in the interventricular septum (1,041 ± 53 ms) approached the upper reference limit (1,089 ms), and the extracellular volume was slightly increased (33 ± 2%, reference values <30%). Over a median follow-up of 3.3 years (interquartile interval 1.6-4.7), 2 (6%) patients died, one for infectious and respiratory complications and the other for unknown causes, 5 (15%) patients underwent pacemaker implantation for conduction disturbances, and 4 (12%) had a documentation of high-risk (Lown class ≥4) ventricular ectopic beats (VEBs). Among all CMR variables collected, higher values of LVMi/LVEDVi ratio emerged as univariate predictor of all-cause death (p = 0.044). At logistic regression analysis, anteroseptal wall thickness was associated with the need for pacemaker implantation (p = 0.028), while LGE mass was associated with high-risk VEBs (p = 0.026). Conclusions: Patients with DM1 display several structural and functional cardiac abnormalities, with variable degrees of cardiac muscle hypotrophy, fibrosis and fatty infiltration. The possibility to predict the need for pacemaker implantation, ventricular arrhythmias and all-cause or cardiovascular mortality should be verified in larger cohorts.