Background and purpose: Microembolic signals (MES) are frequently observed by transcranial Doppler ultrasound after prosthetic heart valve implantation. Whether these MES are due to solid or gaseous particles is uncertain. We hypothesized that MES are gaseous and that if they are due to cavitation effects, their occurrence should respond to changes of dissolved oxygen concentration in the blood.
Methods: Transcranial monitoring of MES was performed in five patients with prosthetic aortic valves, who inspired 100% oxygen through a facial mask. In one patient 100% oxygen was administered under hyperbaric (2.5 kPa) conditions in a hyperbaric chamber.
Results: Inspiration of 100% oxygen reduced the total number of MES from 96/30 min to 2/30 min. Increasing the concentration of dissolved oxygen in the hyperbaric chamber led to an increase from 0.3 MES per minute (1.0 kPa) to 0.9 MES per minute (2.5 kPa).
Conclusions: The dependence of occurrence of MES in patients with prosthetic cardiac valves on the oxygen partial pressure in blood provides strong evidence that these microemboli are gaseous.