Diastolic suction in heart failure: Impact of left ventricular geometry, untwist, and flow mechanics

Graded lower body negative pressure induces intraventricular negative pressures and incremental diastolic suction: a pressure volume study in a porcine model

Lower body negative pressure (LBNP) has been a tool to study compensatory mechanisms to central hypovolemia for decades. However, underlying hemodynamic mechanisms were mostly assessed non-invasively and remain unclear. We hypothesized that incremental LBNP reduces diastolic filling and thereby affects left ventricular (LV) diastolic suction (DS). Here, we investigated the impact of graded LBNP at 3 different levels of seal as well as during beta-adrenergic stimulation by invasive pressure-volume (PV) analysis. Eight Landrace pigs were instrumented closed-chest for PV assessment. LBNP was applied at three consecutive locations: I) cranial, 10cm below xiphoid process; II) medial, half-way between cranial and caudal; III) caudal, at the iliac spine. Level III) was repeated under dobutamine infusion. At each level, baseline measurements were followed by application of incremental LBNP of -15, -30 and -45 mmHg. LBNP induced varying degrees of preload-dependent hemodynamic changes, with cranial LBNP inducing more pronounced effects than caudal. According to the Frank-Starling mechanism, graded LBNP progressively reduced LV stroke volume (LV SV) following a decrease in LV end-diastolic volume. Negative intraventricular minimal pressures were observed during dobutamine-infusion as well as higher levels of LBNP. Of note, incremental LV negative pressures were accompanied by increasing DS volumes, derived by extrapolating the volume at zero transmural pressure, the so-called equilibrium volume (V0), related to LV SV. In conclusion, graded preload reduction shifts the PV loop to smaller volumes and end-systolic volume below V0, which induces negative LV pressures and increases LV suction. Accordingly, LBNP induced central hypovolemia is associated with increased DS.

Noninvasive assessment of intraventricular pressure difference in left ventricular dyssynchrony using vector flow mapping

Diastolic intraventricular pressure difference (IVPD) reflects left ventricular (LV) diastolic function. The relative pressure imaging (RPI) enables the noninvasive quantification of IVPD based on vector flow mapping (VFM) and visualization of regional pressure distribution. LV dyssynchrony causes deterioration of cardiac performance. However, it remains unclear how IVPD is modulated by LV dyssynchrony. LV dyssynchrony was created in ten open-chest dogs by right ventricular (RV) pacing. The other ten dogs undergoing right atrial (RA) pacing set at the similar heart rate with RV pacing were used as controls. Echocardiographic images were acquired at baseline and during pacing simultaneously with LV pressure measurement by a micromanometer. Pressure difference (ΔP) was computed between the apex and the base of the LV inflow tract during a cardiac cycle by RPI and ΔP during isovolumic relaxation time (ΔP_IRT), a parameter of diastolic suction, and that during early filling phase (ΔP_E) were measured. During RV pacing, stroke volume (SV) and ΔP_IRT decreased significantly, while ΔP_E did not change compared to the baseline. During RA pacing, SV, ΔP_IRT and ΔP_E did not change significantly. ΔP_IRT tended to correlate with -dP/dt_min and end-systolic volume, and significantly correlated with ejection fraction. IVPD during isovolumic relaxation time was decreased by LV dyssynchrony, while IVPD during early filling phase was not. A reduction of diastolic suction is observed in LV dyssynchrony and is significantly related to a decrease in SV.