Postural dependency of right to left shunt: role of contrast-enhanced transcranial Doppler and its potential clinical implications.

BACKGROUND AND PURPOSE Right to left shunt is involved in conditions in which postural changes may be pathogenically relevant. The aim of this work was to assess the frequency of posturally dependent right to left shunt. METHODS In 109 consecutive right to left shunt-positive subjects (male/female=40/69, age 43+/-12 years), we assessed with contrast-enhanced transcranial Doppler the bubble load during normal breathing and after the Valsalva maneuver in both standing and recumbent position randomizing the order of testing. RESULTS During normal breathing, the average bubble count was 11+/-20 in the recumbent and 26+/-60 in the standing position. After the Valsalva maneuver, it was 40+/-38 and 42+/-37, respectively. The increase of bubble load in standing position occurred in 42% of patients and was independent of the order of testing. CONCLUSIONS The amount of permanent right to left shunt is posture-dependent in 40% of patients. Testing in the sitting position may thus be warranted in doubtful or inconclusive results obtained with the subject in the horizontal position.