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The minimization of mechanical work in vibrated granular matter.

ABSTRACT: Experiments and computer simulations are carried out to investigate phase separation in a granular gas under vibration. The densities of the dilute and the dense phase are found to follow a lever rule and obey an equation of state. Here we show that the Maxwell equal-areas construction predicts the coexisting pressure and binodal densities remarkably well, even though the system is far from thermal equilibrium. This construction can be linked to the minimization of mechanical work associated with density fluctuations without invoking any concept related to equilibrium-like free energies.

SUBMITTER: Clewett JP

PROVIDER: S-EPMC4931499 | biostudies-other | 2016

REPOSITORIES: biostudies-other

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The minimization of mechanical work in vibrated granular matter.

Clewett James P D JP Wade Jack J Bowley R M RM Herminghaus Stephan S Swift Michael R MR Mazza Marco G MG

Scientific reports 20160704

Experiments and computer simulations are carried out to investigate phase separation in a granular gas under vibration. The densities of the dilute and the dense phase are found to follow a lever rule and obey an equation of state. Here we show that the Maxwell equal-areas construction predicts the coexisting pressure and binodal densities remarkably well, even though the system is far from thermal equilibrium. This construction can be linked to the minimization of mechanical work associated wit ...[more]

PMID: 27373719

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Project description:BACKGROUND:Adaptive mechanical ventilation automatically adjusts respiratory rate (RR) and tidal volume (VT) to deliver the clinically desired minute ventilation, selecting RR and VT based on Otis' equation on least work of breathing. However, the resulting VT may be relatively high, especially in patients with more compliant lungs. Therefore, a new mode of adaptive ventilation (adaptive ventilation mode 2, AVM2) was developed which automatically minimizes inspiratory power with the aim of ensuring lung-protective combinations of VT and RR. The aim of this study was to investigate whether AVM2 reduces VT, mechanical power, and driving pressure (?Pstat) and provides similar gas exchange when compared to adaptive mechanical ventilation based on Otis' equation. METHODS:A prospective randomized cross-over study was performed in 20 critically ill patients on controlled mechanical ventilation, including 10 patients with acute respiratory distress syndrome (ARDS). Each patient underwent 1 h of mechanical ventilation with AVM2 and 1 h of adaptive mechanical ventilation according to Otis' equation (adaptive ventilation mode, AVM). At the end of each phase, we collected data on VT, mechanical power, ?P, PaO2/FiO2 ratio, PaCO2, pH, and hemodynamics. RESULTS:Comparing adaptive mechanical ventilation with AVM2 to the approach based on Otis' equation (AVM), we found a significant reduction in VT both in the whole study population (7.2?±?0.9 vs. 8.2?±?0.6?ml/kg, p?<? 0.0001) and in the subgroup of patients with ARDS (6.6?±?0.8?ml/kg with AVM2 vs. 7.9?±?0.5?ml/kg with AVM, p?<? 0.0001). Similar reductions were observed for ?Pstat (whole study population: 11.5?±?1.6 cmH2O with AVM2 vs. 12.6?±?2.5 cmH2O with AVM, p?<? 0.0001; patients with ARDS: 11.8?±?1.7 cmH2O with AVM2 and 13.3?±?2.7 cmH2O with AVM, p?=?0.0044) and total mechanical power (16.8?±?3.9?J/min with AVM2 vs. 18.6?±?4.6?J/min with AVM, p?=?0.0024; ARDS: 15.6?±?3.2?J/min with AVM2 vs. 17.5?±?4.1?J/min with AVM, p?=?0.0023). There was a small decrease in PaO2/FiO2 (270?±?98 vs. 291?±?102?mmHg with AVM, p?=?0.03; ARDS: 194?±?55 vs. 218?±?61 with AVM, p?=?0.008) and no differences in PaCO2, pH, and hemodynamics. CONCLUSIONS:Adaptive mechanical ventilation with automated minimization of inspiratory power may lead to more lung-protective ventilator settings when compared with adaptive mechanical ventilation according to Otis' equation. TRIAL REGISTRATION:The study was registered at the German Clinical Trials Register ( DRKS00013540 ) on December 1, 2017, before including the first patient.

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The minimization of mechanical work in vibrated granular matter.

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The minimization of mechanical work in vibrated granular matter.

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