effect of oxygen inhalation on microembolic signals in patients with mechanical aortic valve

microembolic signals (mes) are frequently observed in transcranial ‎doppler (tcd) recordings of patients with mechanical heart valve (mhv). if gaseous bubbles are the underlying cause, number of mes produced by mhv could be reduced with oxygen ‎inhalation. from september 2003 to september ‎2004, a consecutive series of 14 patients ‎with st jude aortic valve visited in the cardiology clinic were referred to ‎neurosonology unit, valie asr hospital, khorasan. tcd monitoring of mes was performed with an ultrasound device and a 2 mhz probe. the mes counts were recorded during 30 ‎minutes breathing room air and thereafter 30 minutes breathing through a facial mask ‎with reservoir bag (6 liter o2 per minute). the criteria of mes detection were ‎characteristic chirping sound, unidirectional signal, random appearance within cardiac ‎cycle and intensity increase ≥ 3db above background. the mes counts in two periods ‎of monitoring were compared with paired t test and significance was declared at p ‎