Effects of acute intrathoracic pressure changes on left ventricular geometry and filling

Acute changes in intrathoracic pressure (ITP) affect left ventricular (LV) function. It has been suggested that this functional impairment could be the result of an alteration in LV filling caused by a reduction in LV compliance induced by the rearrangement of biventricular geometry that occurs under these conditions. Therefore, to evaluate the effects of an acute increase or decrease in ITP on LV geometry and filling, we used two-dimensional and Doppler echocardiography to study 25 normal volunteers both during the Müller maneuver (acute decrease in ITP induced by a forced inspiration against a closed airway) and during continuous positive airway pressure breathing. During both maneuvers LV geometry was altered as demonstrated by the significant increase in the normalized curvature radius of the interventricular septum and the unchanged curvature radius of the LV free wall. LV filling was altered during both maneuvers as demonstrated by significant decreases in early peak flow velocity, early-to-late peak flow velocity ratio, and early deceleration rate. Thus, during maneuvers that acutely decrease or increase ITP, alterations in LV geometry occur. These acute distortions of LV geometry may be one of the mechanisms responsible for alterations in LV filling.