Effects of Progressive Hypoventilation on Left Ventricular Appearance: An Alternative Etiology of Acute Sonographic Short-Axis D-Shaping.

ObjectivesThe purpose of this study was to evaluate the effects of progressive hypoventilation on echocardiographic measures of the left ventricular (LV) appearance in a porcine model. MethodsTen piglets were included in the experimental group, and 5 served as controls. The experimental group underwent 3 interventions of progressive hypoventilation (baseline: tidal volume, 240mL; respiratory frequency, 16 minutes(-1); first intervention: tidal volume, 240mL; respiratory frequency, 8 minutes-1; second intervention: tidal volume, 240mL; respiratory frequency, 4 minutes(-1); and third intervention: tidal volume, 120mL; respiratory frequency, 4 minutes(-1)). Respiratory resuscitation was initiated if the MAP decreased to 50% of the baseline level or at the end of the third intervention. Transthoracic sonography and invasive measurements were obtained throughout. The primary end point was the LV end-diastolic eccentricity index, a measure of LV D-shaping. ResultsThe median LV end-diastolic eccentricity index increased from 1.1 (interquartile range, 1.0-1.1) at baseline to 1.4 (1.3-1.4) 3 minutes after the third intervention (P<.001) and returned to baseline after resuscitation (P=.093). The MAP declined from 87mm Hg (81-92mm Hg) to 50 mmHg (33-66mm Hg) after initiation of the third intervention (P<.001). The mean pulmonary arterial pressure increased from 20mm Hg (15-21mm Hg) to 39mm Hg (38-40mm Hg) during the second intervention (P<.001). ConclusionsProgressive hypoventilation led to a marked D-configuration of the LV and a sharp decrease in systemic blood pressure. After respiratory resuscitation, sonographic measures normalized. These findings were explainable by the pressure changes observed within the left and right ventricles.