Cardiorespiratory Impact of Intrathoracic Pressure Overshoot During Artificial Carbon Dioxide Pneumothorax: a Randomized Controlled Study

Background: The aim of this study is to evaluate cardiovascular and respiratory effects of intrathoracic pressure overshoot (higher than insufflation pressure) in patients who underwent thoracoscopic esophagectomy with carbon dioxide (CO2) pneumothorax.Methods: This prospective research included 200 patients who were scheduled for esophagectomy. The patients were randomly divided into the Stryker insufflator (STR) group and the Storz insufflator (STO) group. We recorded the changes of intrathoracic pressure, cardiopulmonary function and recovery time, and compared these indexes between the two groups.Results: We found that during the artificial pneumothorax, intrathoracic pressure overshoot occurred in both the STR group (8.9 mmHg, 38 times per hour) and the STO group (9.8 mmHg, 32 times per hour). The recorded maximum intrathoracic pressures were up to 58 mmHg in the STR group and 51 mmHg in the STO group. The average duration of intrathoracic pressure overshoot was significantly longer in the STR group (5.3 ± 0.86 s) vs. the STO group (1.2 ± 0.31 s). During intrathoracic pressure overshoot, a greater reduction in systolic blood pressure (SBP) (5.6 mmHg vs 1.1 mmHg), a higher elevation in airway peak pressure (4.8 ± 1.17 cmH2O vs 0.9 ± 0.41 cmH2O), and a larger increase in CVP (8.2 ± 2.86 cmH2O vs 4.9 ± 2.35 cmH2O) were observed in the STR group than in the STO group. Vasopressors were also applied more frequently in the STR group than in the STO group (68% vs 43%, P < 0.01). The reduction of SBP caused by thoracic pressure overshoot was significantly correlated with the duration of overshoot (R = 0.76) while not with the maximum overshoot pressure.Conclusion: Intrathoracic pressure overshoot can occur during thoracoscopic surgery with artificial CO2 pneumothorax and may lead to cardiovascular adverse effects which highly depend on the duration of the pressure overshoot.

Valve Plate Structural Optimal Design and Flow Field Analysis for the Aviation Bidirectional Three-Port Piston Pump

This paper designed and optimized a bidirectional three-port valve plate structure for solving the matching problem of flow rate and pressure in the aerospace pump-controlled differential hydraulic cylinder. This design aims to make the valve plate work well under the bidirectional high-speed condition. The model was set up using dynamic mesh and sliding mesh, and the simulation is conducted by FLUENT. In addition, the flow field of inlet and outlet flow rate pulsations, pressure pulsation in cylinder, and non-dead-point transition zone of four cases are analyzed to optimize the valve plate in this work. The numerical results show that different angles of non-dead-point transition zones of the valve plate have a big impact on the performance of the piston pump. For example, the flow rate pulsation reaches the minimum when the angle of non-dead point transition zone is greater than or equal to the angle of a cylinder port. However, at this time, the closed compression would occur and the pressure inside the cylinder would rise rapidly as the piston moves to the non-dead point zone, thus resulting in serious pressure overshoot. In addition, if the angle of non-dead point transition zone is reduced within a certain range, the pressure overshoot will be reduced drastically, and the flow pulsation rate will rise a bit. The study suggests that it is necessary to adjust the angle of non-dead point transition zone to balance the pressure overshoot and flow pulsation of the pump to obtain the optimal kidney structure of the valve plate.

Dynamic Characteristics of a Pressure-Compensated Inlet-Metered Pump

Pressure-compensated pumps are routinely used for supplying fluid power for hydraulic control systems. These pumps traditionally exhibit significant overshoot and oscillation before reaching a steady-state pressure condition, thus requiring the use of downstream safety valves to prevent over pressurization. In addition to over pressurizing the hydraulic control system, the response of the traditional pressure-compensated pump often induces excessive noise and creates instability for other components within the system. In this paper, a nontraditional pressure-compensated hydraulic pump is studied based upon the paradigm that has been offered by diesel-engine technology. This technology uses an inlet-metered pump to provide pressurized fuel for the high-pressure, fuel-injector rail. The analysis of this paper shows that a system of this type may be used to produce a first-order pressure response with no overshoot and oscillation, and that the characteristic time constant and settling time may be designed by specifying parameters that are identified in this research. The problem of cavitation damage is also discussed based upon preliminary testing done at the University of Missouri, and it is suggested that by using hardened machine parts cavitation damage may be prevented in these machines. In conclusion, this paper shows that continued development of the inlet-metered pump may be warranted for those applications where pressure overshoot and oscillation cannot be tolerated due to safety, noise, or other dynamical considerations.

Reducing Fatigue Loading due to Pressure Shift in Discrete Fluid Power Force Systems

Discrete Fluid Power Force Systems is one of the topologies gaining focus in the pursuit of lowering energy losses in fluid power transmission systems. The cylinder based Fluid Power Force System considered in this article is constructed with a multi-chamber cylinder, a number of constant pressure lines and a valve manifold. The valve manifold is used to control the connections between the cylinder chambers and the pressure lines and hereby the resulting force form the cylinder. The valve manifold is equipped with fast on/off valves. However, shifting between pressure lines may yield pressure oscillations in the cylinder chamber, especially for systems with long connections between the cylinder and the valve manifold. Hose pressure oscillations will induce oscillations in the produced piston force. Hence, pressure oscillations may increase the fatigue loading on systems employing a discrete fluid power force system. The current paper investigates the correlation between pressure oscillations in the cylinder chambers and valve flow in the manifold. Furthermore, the correlation between the pressure shifting time and the pressure overshoot is investigated. The study therefore focus on how to shape the valve flow in the manifold to reduce the added fatigue loads. A simple transmission line model is developed for the analysis. Two inputs are given in the Laplace domain and the time domain solution of the cylinder pressure to the given inputs are derived through inverse Laplace transformation. Based on the time domain solutions the pressure overshoot for various pressure shifting times is investigated. With the two input functions defined by the pressure shifting time, T, the main results of the current paper show the correlation between the minimum shifting time and the pressure overshoot in a given cylinder chamber with a given line connection.

High Performance Pressure Control for the Hydraulic Press Based on the Soft Relief Fuzzy PID Controller

A soft relief controller is proposed to solve the pressure overshoot problem of the hydraulic press. Whose basic idea is to make the proportional relief valve open in advance to limit the pressure rise rate to reduce the pressure overshoot. What’s more, the fuzzy PID controller is introduced to improve the control performance. Based on the mechanism modeling method, the complete mathematical model of the hydraulic press is established to conduct the simulation research. The correctness of the mathematical model is proved through experiments. Simulation and experiment results demonstrate that the soft relief fuzzy PID controller which combines the soft relief controller and the fuzzy PID controller can guarantee the hydraulic press has no overshoot during the pressure building-up process. Furthermore, a high steady precision is achieved and the adjust time can meet the demands of most hydraulic presses.

A BREATHING SYNCHRONIZATION STRATEGY FOR THE NON-INVASIVE VENTILATOR SYSTEM

The study presents a method to achieve a subject-ventilator synchronic pressure supply for a non-invasive ventilator (NIV) used for obstructive sleep apnea syndrome (OSAS), solely through controlling the blower instead of using expiratory relief valves. The controller used air flow signal to distinguish inspiratory and expiratory phases, and used a fast auto-forecast (AF) algorithm to predict the current inspiratory duration based on respiration periods distinguished previously. Then in a patient's late inspiration the mechanical expiratory state was triggered to release pressure in advance. Afterward, when the beginning of a patient's actual expiration was detected, a timer was used to trigger the end-expiratory state. As the index of patient-ventilator synchrony, subject's chest movement was detected by electrical impedance signal in experiments. The experimental results indicated that the previous state transition based on the prediction of inspiratory duration can eliminate the pressure overshoot spike, and then avoid excessive expiratory pressure to subjects. The fast auto-forecast with end expiratory positive airway pressure (AF-EEPAP) controlling strategy presented in this paper provided a mild pressure curve, which is consistent with the subject's respiratory physiology, and thus improved respiratory synchrony between subject and ventilator.