OXYGEN INHALATION CAN DIFFERENTIATE GASEOUS FROM NONGASEOUS MICROEMBOLI DETECTED BY TRANSCRANIAL DOPPLER ULTRASOUND

Background and Purpose Clinically silent circulating microemboli can b e detected by transcranial Doppler sonography. The composition of thes e emboli in different clinical conditions is unclear. Methods We perfo rmed 1-hour transcranial Doppler sonographic recordings from the middl e cerebral or posterior cerebral artery in 20 patients with mechanical prosthetic heart valves, in 78 patients with an arterial embolic sour ce, and in 20 control subjects. During 30 minutes of this recording, t he patients inspired room air and 6 L of oxygen per minute via a loose ly fitting facial mask; during the remaining 30 minutes, they breathed room air only. Results There was a significant decline of embolic sig nals (ES) under oxygen in the patients with mechanical prosthetic card iac valves (144 ES without oxygen versus 63 ES with oxygen; P = .002) but not in the patients with arterial embolic sources (145 ES without oxygen versus 135 ES with oxygen; P = NS). In the control subjects, no ES were found. Conclusions ES in patients with mechanical prosthetic cardiac valves correspond mainly to gas bubbles. Oxygen inhibits the c avitation process of mechanical prosthetic heart valves or speeds up r edissolution of gas bubbles generated by cavitation. In contrast, soli d microemboli originating from thrombus or atheroma cannot be suppress ed by oxygen inhalation. This simple method of oxygen inhalation shoul d help to clarify the composition of microemboli in various clinical a nd experimental settings.