Pulmonary Vascular Dilatation Detected by Automated Transcranial Doppler in COVID-19 Pneumonia

Some patients with coronavirus disease (COVID-19) pneumonia demonstrate severe hypoxemia despite having near normal lung compliance, a combination not commonly seen in typical acute respiratory distress syndrome (ARDS). The disconnect between gas exchange and lung mechanics in COVID-19 pneumonia has raised the question of whether the mechanisms of hypoxemia in COVID-19 pneumonia differ from those in classical ARDS. Dual-energy computed tomographic imaging has demonstrated pulmonary vessel dilatation and autopsies have shown pulmonary capillary deformation in patients with COVID-19 pneumonia. These data suggest that pulmonary vasodilatations may explain the disproportionate hypoxemia in some patients with COVID-19 pneumonia and, somewhat surprisingly, track with poor lung compliance. Our detection of transpulmonary bubbles may be analogous to hepatopulmonary syndrome, a pulmonary vascular disorder of chronic liver disease characterized by pulmonary vascular dilatations with increased blood flow to affected lung units, which results in ventilation-perfusion mismatch and hypoxemia. The normal lung filters microbubbles from the injection of agitated saline as the bubble diameter is larger.