Global end-diastolic volume increases to maintain fluid responsiveness in sepsis-induced systolic dysfunction.

BACKGROUND: Sepsis-induced cardiac dysfunction may limit fluid responsiveness and the mechanism thereof remains unclear. Since cardiac function may affect the relative value of cardiac filling pressures, such as the recommended central venous pressure (CVP), versus filling volumes in guiding fluid loading, we studied these parameters as determinants of fluid responsiveness, according to cardiac function. METHODS: A delta CVP-guided, 90 min colloid fluid loading protocol was performed in 16 mechanically ventilated patients with sepsis-induced hypotension and three 30 min consecutive fluid loading steps of about 450 mL per patient were evaluated. Global end-diastolic volume index (GEDVI), cardiac index (CI) and global ejection fraction (GEF) were assessed from transpulmonary dilution. Baseline and changes in CVP and GEDVI were compared among responding (CI increase ≥10% and ≥15%) and non-responding fluid loading steps, in patient with low (<20%, n = 9) and near-normal (≥20%) GEF (n = 7) at baseline. RESULTS: A low GEF was in line with other indices of impaired cardiac (left ventricular) function, prior to and after fluid loading. Of 48 fluid loading steps, 9 (of 27) were responding when GEF <20% and 6 (of 21) when GEF ≥20. Prior to fluid loading, CVP did not differ between responding and non-responding steps and levels attained were 23 higher in the latter, regardless of GEF (P = 0.004). Prior to fluid loading, GEDVI (and CI) was higher in responding (1007 ± 306 mL/m(2)) than non-responding steps (870 ± 236 mL/m(2)) when GEF was low (P = 0.002), but did not differ when GEF was near-normal. Increases in GEDVI were associated with increases in CI and fluid responsiveness, regardless of GEF (P < 0.001). CONCLUSIONS: As estimated from transpulmonary dilution, about half of patients with sepsis-induced hypotension have systolic cardiac dysfunction. During dysfunction, cardiac dilation with a relatively high baseline GEDVI maintains fluid responsiveness by further dilatation (increase in GEDVI rather than of CVP) as in patients without dysfunction. Absence of fluid responsiveness during systolic cardiac dysfunction may be caused by diastolic dysfunction and/or right ventricular dysfunction.

A novel compliance-pressure loop approach to quantify arterial compliance in systole and in diastole.

Arterial compliance has been recognized as a critical parameter in governing pulsatile flow dynamics. It has traditionally been assumed constant throughout the cardiac cycle and its computation has been based either on the classic Windkessel model (C) in diastole or the stroke volume over pulse pressure (Cv) method in systole. Other methods using area (Cam) or two-area (Ctam) and exponential (C(P)exp1) methods were used for the cardiac cycle. We proposed a novel compliance-pressure loop (CPP loop) approach for the quantification of arterial compliance and compared it to existing linear and nonlinear methods. Experimental data were gathered in 5 dogs and blood pressure levels were varied (systolic pressure of 100 mmHg-185 mmHg) with induced hypertension and vasodilation. Results showed the limited regime of validity of C (Control:0.4681 ±â€¯0.1270 ml/mmHg, MTX:0.3015 ±â€¯0.1264 ml/mmHg and NTP:1.8323 ±â€¯0.7207 ml/mmHg) and Cv (Control:0.3583 ±â€¯0.0158 ml/mmHg, MTX:0.2602 ±â€¯0.1275 ml/mmHg and NTP:0.4131 ±â€¯0.0589 ml/mmHg), Cam (Control:0.4175 ±â€¯0.0505, MTX:0.3086 ±â€¯0.1568 and NTP:1.4181 ±â€¯0.4812) and Ctam (Control: 0.2064 ±â€¯0.0228 ml/mmHg, MTX:0.1967 ±â€¯0.0884 ml/mmHg, NTP:0.0881 ±â€¯0.0375 ml/mmHg) and that C(P)exp1 underestimates the arterial compliance compared to our method (Control:0.2233 ±â€¯0.0168 ml/mmHg vs 0.4481 ±â€¯0.0515 ml/mmHg, MTX:0.1976 ±â€¯0.0964 ml/mmHg vs 0.3273 ±â€¯0.1443 ml/mmHg and NTP: 0.2177 ±â€¯0.0273 ml/mmHg vs 1.9990 ±â€¯1.8221 ml/mmHg at mean arterial pressure). The CPP method based on the exponential method is superior, as it provides continuous compliance variations and CPP loop area can be readily visualized from hypotension to hypertension conditions. We conclude that the concept of using compliance-pressure loop is advantageous as it can afford continuous and accurate tracking of the dynamic arterial behavior despite greatly varying blood pressure levels.

Simultaneous pressure-volume measurements using optical sensors and MRI for left ventricle function assessment during animal experiment.

Simultaneous pressure and volume measurements enable the extraction of valuable parameters for left ventricle function assessment. Cardiac MR has proven to be the most accurate method for volume estimation. Nonetheless, measuring pressure simultaneously during MRI acquisitions remains a challenge given the magnetic nature of the widely used pressure transducers. In this study we show the feasibility of simultaneous in vivo pressure-volume acquisitions with MRI using optical pressure sensors. Pressure-volume loops were calculated while inducing three inotropic states in a sheep and functional indices were extracted, using single beat loops, to characterize systolic and diastolic performance. Functional indices evolved as expected in response to positive inotropic stimuli. The end-systolic elastance, representing the contractility index, the diastolic myocardium compliance, and the cardiac work efficiency all increased when inducing inotropic state enhancement. The association of MRI and optical pressure sensors within the left ventricle successfully enabled pressure-volume loop analysis after having respective data simultaneously recorded during the experimentation without the need to move the animal between each inotropic state.