The cTTE study was performed using a Philips Epiq7c system fitted with an S5–1 probe (1–5 MHz). The TTE test was routinely performed to rule out cardiac shunt due to other reasons before the injection of mixture solution. The apical four-chamber view was used to record the count of microbubbles continuously. Following recordings in basal condition, it was repeated during a VM. The VM was performed by the patients blowing into a plastic tube connected to the manometer device [15 (link)]. We asked patients to carry out the VM a few seconds before the contrast injection and maintain until the right atrium was filled with the contrast agent. If the testing results with or without VM were positive, two more operations were needed to assess its reproducibility. The maximum number of bubbles recorded from the left ventricle was regarded as the ultimate result.
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