Stroke volume variation as a predictor of fluid responsiveness in patients undergoing airway pressure release ventilation.

We investigated the effectiveness of stroke volume variation (SVV) shown by the Vigileo-FloTrac™ system (Edwards Lifesciences, Irvine, CA) to predict fluid responsiveness in patients undergoing airway pressure release ventilation (APRV). All 80 patients mechanically ventilated in the intensive care unit of our hospital from April to November 2010 were included in this study. After starting APRV, Ringer's lactate solution was administered for 30 minutes. Haemodynamic variables including heart rate, mean arterial pressure, cardiac index (CI), stroke volume index (SVI) and SVV were measured before and after volume loading. SVV before volume loading was significantly correlated with absolute change in SVV (ΔSVV) and percentage change in stroke volume index (ΔSVI) after volume loading (ΔSVV: P<0.05, r2=0.534; ΔSVI: P<0.05, r2=0.217). Of the 80 patients, 38 (47.5%) were responders to intravascular volume expansion (increase in CI≥15%) and 42 (52.5%) were non-responders (increase in CI<15%). Receiver operating characteristic (ROC) curves were generated for SVV and central venous pressure by varying the discriminating threshold of the variable and areas under the ROC curves were calculated. The areas under the ROC curves were 0.793 for SVV (95% confidence interval: 0.709-0.877) and 0.442 for central venous pressure (95% confidence interval: 0.336-0.549), which were significantly different (P<0.05). The optimal threshold value of SVV to discriminate between responders and nonresponders was 14% (sensitivity: 78.9%; specificity: 64.3%). We found that SVV was able to predict fluid responsiveness in patients undergoing APRV with acceptable levels of sensitivity and specificity.

Analyses of adenosine and adenine nucleotides in biological materials by fluorescence reaction-high-performance liquid chromatography.

A previous method of determination of adenine compounds by high-performance liquid chromatography, using bromoacetaldehyde as a fluorescent reagent and a column of Hitachi gel No. 3012-N, was improved and extended to biological materials, especially to measure enzyme activities. A column packed with finer beads, Hitachi gel No. 3013-N, was found to be better than that of No. 3012-N, judging from the analysis time and resolution. ADP, from the hydrolysis of ATP by Na, K-ATPase, was determined quantitatively, and the enzyme activity was inhibited with ouabain. cAMP obtained from ATP by reaction with adenylate cyclase was also determined in the presence of various concentrations of L-epinephrine or sodium fluoride. The ATP levels in human blood were determined, and the cellular levels of ATP and ADP in neuroblastoma N1E 115 were examined as a function of cell growth.

ATP synthesis in cell envelope vesicles of Halobacterium halobium driven by membrane potential and/or base-acid transition.

Cell envelope vesicles active in ATP synthesis were prepared from Halobacterium halobium cells, which genetically lack bacteriorhodopsin, by sonication in the presence of substrates. ATP was synthesized when vesicles were illuminated to build up membrane potential through the action of halorhodopsin. The threshold value of membrane potential for ATP synthesis was about -100 mV relative to the external medium, i.e., inside-negative. ATP synthesis also occurred in the dark upon acidification of the external medium of a suspension of cell envelope vesicles. This base-acid transition ATP synthesis took place when the pH difference was greater than 1.6 units. The threshold pH difference was lowered when the base-acid transition was carried out under dim light which induced a membrane potential of about -100 mV. Regardless of the sort of driving force, ATP synthesis was optimum at the intravesicular pH of around 6.5 and almost nil at 8, where ATP syntheses by F0F1 type ATPases in other organisms are most active. The synthesis could be inhibited by N,N'-dicyclohexylcarbodiimide (DCCD) with a half-maximum inhibition at around 25 microM/2 mg protein/ml. These results strongly suggest that in halobacteria a DCCD-sensitive H+-translocating ATP synthase is in operation which is driven by membrane potential and/or pH gradient, and obeys chemiosmotic energetics. The results also suggest that the ATP synthase may not be identical to F0F1 type H+-translocating ATPases found in mitochondria, chloroplasts and eubacteria.