CLINICALLY SILENT MICROEMBOLI IN PATIENTS WITH ARTIFICIAL PROSTHETIC AORTIC VALVES ARE PREDOMINANTLY GASEOUS AND NOT SOLID

Background and Purpose Microembolic signals (MES) are frequently obser ved by transcranial Doppler ultrasound after prosthetic heart valve im plantation. 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 m onitoring 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 concent ration of dissolved oxygen in the hyperbaric chamber led to an increas e from 0.3 MES per minute (1.0 kPa) to 0.9 MES per minute (2.5 kPa). C onclusions The dependence of occurrence of MES in patients with prosth etic cardiac valves on the oxygen partial pressure in blood provides s trong evidence that these microemboli are gaseous.