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

Abstract

The 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. Ten piglets were included in the experimental group, and 5 served as controls. The experimental group underwent 3 interventions of progressive hypoventilation (baseline: tidal volume, 240 mL; respiratory frequency, 16 minutes-1 ; first intervention: tidal volume, 240 mL; respiratory frequency, 8 minutes-1; second intervention: tidal volume, 240 mL; respiratory frequency, 4 minutes-1 ; and third intervention: tidal volume, 120 mL; 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. The 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 87 mm Hg (81-92 mm Hg) to 50 mmHg (33-66 mm Hg) after initiation of the third intervention (P < .001). The mean pulmonary arterial pressure increased from 20 mm Hg (15-21 mm Hg) to 39 mm Hg (38-40 mm Hg) during the second intervention (P < .001). Progressive 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.