Schematic of the 3-compartment model used to describe the observed kinetics of ¹³C-methacetin (M), paracetamol (P) and ¹³CO₂ (C) (quantified in the breath as DOB).

<p>(1) Injection of M into the blood, (2) reversible exchange of M between blood and liver, (3) hepatic metabolization of M to P and C, (4) reversible exchange of P between blood and other body compartments, (5) reversible exchange of CO₂ between blood and other body compartments, (6) respiratory removal of M, (7) injection of H¹³CO₃ (in the proposed novel 2DOB-method). Ω_B, Ω_L and Ω_X denote the volume of the three compartments.</p

DOB_B curves initiated by the direct injection of 1 mmol/l 13C-bicarbonate into the plasma at time t = 0.

<p>Thin lines represent simulated DOB curves based on the kinetic model parameters k_+C and k_−C determined for the 25 subjects (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone-0070780-t001" target="_blank">Table 1</a>). Bold lines indicate DOB curves fitted to experimental data measured in 6 patients [20]. The DOB values are normalized to the DOB value at t = 0 (100%).</p

Typical time-course of plasma ¹³C-methacetin (triangles), paracetamol (circles) and DOB (squares) after intravenous injection of ¹³C-methacetin (2 mg/kg).

<p>The thin dotted lines represent best-fit curves constructed by means of an exponential regression function (1) to estimate numerical values of the characteristic parameters M_o.5, DOB_max, DOB_maxT and DOB20 (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone-0070780-t001" target="_blank">Table 1</a>). The solid lines represent best-fit curves obtained by fitting <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone.0070780.e002" target="_blank">equation system (2)</a> to the measured data (numerical parameter values for the shown data are for patient PX, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone-0070780-t001" target="_blank">Table 1</a>). The bold grey curve represents the computed time-course of the variable (Ω_L/Ω_B) [¹³C-methacetin] (see transformation (3)) in the liver compartment.</p

Relation between the hepatic metabolization capacity (represented by the parameter FHMC being the % share 13C-methacetin metabolized within 3 minutes) and the DOB curve parameter DOB_max (triangles), DOB_maxT (circles) and DOB20 (squares).

<p>Numerical values of these parameters for the 25 subjects are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone-0070780-t001" target="_blank">Table 1</a>. DOB_max and DOB20 are given in ‰.</p

Simulated DOB (values in ‰) curves of a ‘generic’ patient at different degrees of liver impairment.

<p>The value of the metabolization rate was successively reduced in steps of 10% from the initial 100%-value (k_L = 0.09 min⁻¹).</p

Correlation between plasma endothelin-1 levels and severity of septic liver failure quantified by maximal liver function capacity (LiMAx test). A prospective study

<div><p>Aim</p><p>To investigate the relationship between the degree of liver dysfunction, quantified by maximal liver function capacity (LiMAx test) and endothelin-1, TNF-α and IL-6 in septic surgical patients.</p><p>Methods</p><p>28 septic patients (8 female, 20 male, age range 35–80y) were prospectively investigated on a surgical intensive care unit. Liver function, defined by LiMAx test, and measurements of plasma levels of endothelin-1, TNF-α and IL-6 were carried out within the first 24 hours after onset of septic symptoms, followed by day 2, 5 and 10. Patients were divided into 2 groups (group A: LiMAx ≥100 μg/kg/h, moderate liver dysfunction; group B: LiMAx <100 μg/kg/h, severe liver dysfunction) for analysis and investigated regarding the correlation between endothelin-1 and the severity of liver failure, quantified by LiMAx test.</p><p>Results</p><p>Group B showed significant higher results for endothelin-1 than patients in group A (P = 0.01, d5; 0.02, d10). For TNF-α, group B revealed higher results than group A, with a significant difference on day 10 (P = 0.005). IL-6 showed a non-significant trend to higher results in group B. The Spearman's rank correlation coefficient revealed a significant correlation between LiMAx and endothelin-1 (-0.434; P <0.001), TNF-α (-0.515; P <0.001) and IL-6 (-0.590; P <0.001).</p><p>Conclusions</p><p>Sepsis-related hepatic dysfunction is associated with elevated plasma levels of endothelin-1, TNF-α and IL-6. Low LiMAx results combined with increased endothelin-1 and TNF-α and a favourable correlation between LiMAx and cytokine values support the findings of a crucial role of Endothelin-1 and TNF-α in development of septic liver failure.</p></div

Figure 8

<p><b><i>A</i></b><i> Conventional breath test</i>: Relation between the true value of the liver function parameter FHMC and the characteristic parameter DOB_max of DOB curves. DOB curves were simulated at various degrees of liver impairment by reducing the value of the model parameter k_L in steps of 10%. For each degree of liver function impairment, we used the 25 different parameters pairs k_+C, k_−C for systemic CO₂/bicarbonate kinetics obtained in the 25 investigated subjects. Note that for the liver-healthy ‘generic’ patient ( = 100% metabolization capacity) the variance of DOB_max is 8.1 thus being 25% of the mean (36.7). <b><i>B</i></b><i> 2DOB breath test:</i> Relation between true and estimated values of the liver function parameter FHMC. Estimation of FHMC values was performed by fitting the compartment model to the 2-phasic DOB curve resulting from injection of ¹³C- bicarbonate followed by injection of ¹³C-methacetin (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone-0070780-g006" target="_blank">Fig. 6</a>).</p

Relationship between FMHC and the severity of liver function impairment assessed by the LIMAX score FHMC values were estimated for 30 patients with different severity of liver function failure by fitting the model equation system (2) to conventional DOB curve data while fixing the values of the kinetic parameters k_+C, k_−C for systemic CO₂/bicarbonate kinetics at the mean value obtained in the 25 investigated subjects.

<p>Based on the LIMAX score the patients were arranged into three different groups of liver function failure (indicated by the colors green, blue and red) and within each group ranked with their FMHC value. The inset shows experimental and fitted DOB curves for three patients belonging to different classes of liver function impairment (indicated by a circle in the FHMC versus patient no. plot).</p

Model parameters for individual test subjects.

<p>Model parameters for individual test subjects.</p

Simulated DOB (values in ‰) curves for the conventional breath test and the proposed novel 2DOB method.

<p>The conventional breath tests was simulated by generating DOB curves with the mean values of the kinetic model parameters determined in the 25 subjects (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone-0070780-t001" target="_blank">Table 1</a>). We imposed a random error of 15% to the simulated DOB data (open circles) and approximated these data by the exponential regression function (thin line) from which the characteristic parameters of the DOB were derived. Simulation of 2DOB breath test was done in a similar way but with the exception that first at time t = 0 a bolus of 0.1 mmol/l ¹³C-bicarbonate followed by the injection of 2 mg ¹³C-methacetin/kg bodyweight at time t = 15 min. A random error of 15% was imposed to the simulated 2-phasic DOB data (closed circles). Fitting of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070780#pone.0070780.e002" target="_blank">equation system (2)</a> to these data yielded the model parameters k_+C, k_−C, k_+M, k_−M and k_L and theoretical time-courses of DOB (bold line) and of 13C-methacetin (curve not shown) in the liver. Based on this information the numerical value of FHMC was estimated.</p