Dilated blood vessels in the lung provides possible explanation for low oxygen levels in severe COVID-19 cases

Mechanical ventilation equipment

Findings from a pilot study partly-funded by NHLBI suggest that COVID-19 causes significant dilation of the blood vessels in the lung, specifically in the capillaries. This vasodilation could contribute to the very low levels of oxygen seen in COVID-19 respiratory failure. It could also explain why the disease behaves differently than traditional cases of acute respiratory distress syndrome (ARDS).

Researchers initially sought out to assess cerebral blood flow in mechanically ventilated COVID-19 patients to detect abnormalities consistent with stroke. They administered saline injections with tiny microbubbles into the veins of 18 mechanically ventilated patients with severe COVID-19 pneumonia. Researchers then used a non-invasive ultrasound technique called transcranial Doppler (TCD) to determine if the microbubbles appeared in the blood vessels of the brain.

Microbubbles detected in the blood vessels of the brain imply that there is a hole in the heart or that the capillaries in the lungs are abnormally dilated, allowing the microbubbles to pass through.

Fifteen of the 18 patients had detectable microbubbles that indicated abnormally dilated blood vessels in the lungs. The number of microbubbles detected by TCD also correlated with the severity of hypoxemia. The findings indicate that vasodilation of the lungs might explain the disproportionate hypoxemia seen in many patients with COVID-19 pneumonia. Study results were published in the American Journal of Respiratory and Critical Care Medicine.