Fig. 2

Examples of transesophageal echocardiographic (TEE) determination of two primary study outcome variables. Upper panel: determination of the right-to-left ventricular end-diastolic area ratio (RVEDA/LVEDA). Lower panel: determination of the end-diastolic eccentricity index (EDECCIx). The left vertical pair of images was obtained from study participant no. 12 during conventional ventilation (CV), the middle pair of images was obtained from participant no. 7 during 7-Hz high-frequency oscillation (HFO), and the right pair of images was obtained from participant no. 13 during 4-Hz HFO. In the lower panel (short-axis, transgastric views), “2” corresponds to the diameter of the left ventricle (LV) that was perpendicular to and bisecting the interventricular septum, whereas “1” corresponds to the diameter that was perpendicular to “2.” TEE measurements were repeated and averaged over 2–4 consecutive cardiac cycles (see also Additional file 1); EDECCIx was calculated as diameter “1”/diameter “2.” Description of figure modifications performed with Photoshop CC (Adobe Systems): upper panel, enhancement of the periphery of the right ventricle (RV) and LV using the “pen” tool and the “stroke path” command and enhancement of contrast of the middle image using the “adjust levels” command; lower panel, enhancement of diameter “1”/diameter “2” using the “line” tool. The original versions of the stored pairs of images are also provided in Additional file 1: Figure S1