Blood pressure threshold confines stroke volume responsiveness to passive leg raising in healthy individuals.

Passive leg raising (PLR) is a common maneuver to assess fluid responsiveness in the emergency department. The effect of blood pressure (BP) on PLR-induced left ventricular (LV) stroke volume (SV) response was examined in normotensive (CON, n = 100), hypotensive (HOTN, n = 51) and hypertensive (HTN, n = 16) individuals. Limb BP and Echo measurements were completed within 1 min when the participants were transitioned from the semi-recumbent position to bilateral leg elevation at 45° and lower limb BP was reduced at PLR in all three groups. LV end-diastolic diameter (LVDD), LV end-systolic diameter (LVDS), end-systolic or end-diastolic volume (ESV, EDV) were comparable at baseline among three groups, whereas E, E/A ratio, and deceleration time were significantly lower and A was significantly greater in the HOTN and HTN groups compared with the CON group (p < 0.05). Notably, EDV, LVDD and SV, cardiac output, ejection fraction, and fractional shortening were increased significantly after PLR only in HOTN group (p < 0.05). EDV and SV were positively correlated with E and the E/A ratio in HOTN (p < 0.05), whereas a negative correlation was observed in CON group (p < 0.05). Receiver operating characteristic (ROC) analysis demonstrated that baseline E < 0.77 m/s and systolic BP < 101 mmHg effectively predicted an SV increase of > 15% at PLR with good sensitivity and specificity. Mean arterial pressure, diastolic BP and E wave velocity confine SV responsiveness to PLR even in CON individuals. These findings indicate inherent physiological thresholds for SV augmentation via the Frank-Starling mechanism even in the general population.