Influence Of Mechanical Ventilation Research Articles

Study on moving fire smoke characteristics and mechanical ventilation system of tunnel

Limited by the narrow space of the tunnel, fire has become one of the important factors threatening the safe operation of subway especially the fire on a moving vehicle. Researches on moving fire through the large length-width ratio of tunnels are extremely lacking at present. This study investigates the characteristics of moving fire and the influence of mechanical ventilation under different conditions. First, a three-dimensional model of the tunnel with the moving train is established, and the dynamic mesh simulation is conducted and validated by the experiments. Then, the variation of smoke temperature distribution under different fire source intensities, train speeds, and blocking ratios are studied. Based on the smoke flow characteristics, the mechanical ventilation with different layouts of draught fans is investigated. It is found that the maximum growth rate of smoke spread is 70.90% with an increase of two fans. Finally, the influence of the tunnel shaft on the smoke characteristics under different fire source locations is discussed. When the fire source is under the shaft, the smoke discharge efficiency reaches the highest, almost 5.89% and 21.91% higher than other conditions. This study provides the basis and reference for the research and control of the tunnel moving fire.

Influence of mechanical wind heated by ground temperature on ambient temperature in tunnels: Numerical modeling, case study and analysis

A numerical heat transfer model of a tunnel in a cold region is proposed, and the accuracy of the model is verified by a laboratory model tunnel and field test. The effects of natural airflow velocity, natural airflow temperature, mechanical airflow velocity and jet fan operation time on ambient temperature in tunnels with high ground temperature are investigated. The result shows that mechanical ventilation can effectively reduce the range of ambient temperature below 0 °C in tunnels (RATB) with high ground temperature in a cold area. The lower the natural airflow temperature, the better the temperature control effect of mechanical ventilation. The RATB of Zilashan tunnel will exceed 5000 m without considering the influence of mechanical ventilation with natural airflow velocity at 3.0 m/s. The RATB decreases linearly with mechanical ventilation under different natural airflow velocities, natural airflow temperatures and jet fan operation time. Increasing the mechanical airflow velocity cannot effectively reduce the RATB considering the influence of mechanical ventilation with natural airflow velocity higher than 2.0 m/s. When considering mechanical ventilation to prevent freezing injury to the tunnel, the jet fan operation time shall not be less than 3.0 h. The longer the operation time of the jet fan, the faster the attenuation rate of RATB. When the jet fan operation time is 5.0 h, the attenuation rate of RATB is 8.6 times greater than when the jet fan operation time is 1.0 h with natural airflow velocity at 1.50 m/s. The existence of an insulation layer will greatly increase the antifreeze length of rock and antifreeze length can be controlled within 650 m under proper ventilation conditions in the Zilashan tunnel.

Association between Respiratory Failure and Clinical Outcomes in Patients with Acute Heart Failure: Analysis of 5 Pooled Clinical Trials

BackgroundDespite a temporal increase in respiratory failure in patients hospitalized with acute heart failure (HF), clinical trials have largely not reported the incidence or associated clinical outcomes for patients requiring mechanical ventilation. Methods and ResultsAfter pooling 5 acute HF clinical trials, we used multivariable logistic regression adjusted for demographics, comorbidities, examinations, and laboratory findings to assess associations between mechanical ventilation and clinical outcomes. Among the 8296 patients, 210 (2.5%) required mechanical ventilation. Age, sex, smoking history, baseline ejection fraction, HF etiology, and the proportion of patients randomized to treatment or placebo in the original clinical trial were similar between groups (all, P > 0.05). Baseline diabetes mellitus was more common in the mechanical ventilation group (P = 0.02), but other comorbidities, including chronic lung disease, were otherwise similar (all P > 0.05). HF rehospitalization at 30 days (12.7% vs 6.6%, P < 0.001) and all-cause 60-day mortality (33.3% vs 6.1%, P < 0.001) was higher among patients requiring mechanical ventilation. After multivariable adjustment, mechanical ventilation use was associated with an increased 30-day HF rehospitalization (odds ratio 2.03; 95% confidence interval, 1.29-3.21, P = 0.002), 30-day mortality (odds ratio 10.40; 95% confidence interval, 7.22-14.98, P < 0.001), and 60-day mortality (odds ratio 7.68; 95% confidence interval, 5.50-10.74, P < 0.001). The influence of mechanical ventilation did not differ by HF etiology or baseline ejection fraction (both, interaction P > 0.20). ConclusionsRespiratory failure during an index hospitalization for acute HF was associated with increased rehospitalization and all-cause mortality. The development of respiratory failure during an acute HF admission identifies a particularly vulnerable population, which should be identified for closer monitoring.

Influence of mechanical ventilation and loading modifications on left ventricular global longitudinal strain in patients undergoing general anesthesia: a pilot study

The modifications of left ventricular systolic function assessed with global longitudinal strain (GLS) after general anesthesia and invasive mechanical ventilation are poorly described. This was a single-center observational study. ASA I-II patients undergoing routine surgical procedures requiring anesthesia with invasive mechanical ventilation had serial trans-thoracic speckle-tracking echocardiography: at baseline, five minutes after anesthesia and invasive mechanical ventilation, one minute after passive leg raising and after extubation. The primary objective was to evaluate the modification of left ventricular systolic function, assessed with GLS, under anesthesia and mechanical ventilation. Secondary objectives were to evaluate the alterations of GLS after pre-load modifications with passive leg raising and after extubation. From November 2016 to July 2017, 27 patients were included. Baseline left ventricular ejection fraction (LVEF: 60% [56-63]) and GLS (-20.6% [-23.2/-19.2]) were within normal ranges. After anesthesia, LVEF was not altered but GLS showed a significant decrease (-18.2% [-20.4/-17.1], P<0.05). After passive leg raising, GLS was significantly impaired compared with baseline (-17.6% [-19.7/-15], P<0.05) and seven (26%) patients presented systolic function impairment (GLS >-16%). GLS was similar to baseline after extubation (-21.7% [-23.1/-19.5], P>0.05). Systolic function assessed with GLS is impaired after general anesthesia and invasive mechanical ventilation in patients without cardiovascular co-morbidities but remains within normal range.

Influence of mechanical ventilation and cooling systems on vibrations of high precision machines

The aim of the research was to describe the effects that air and water cooling systems can have on the dynamic behaviour of precise machines. Although much thought is paid to vibration isolation of the ground and isolation of individual effects of machines operating close to each other, it is often forgotten to model or to measure the effects that the ventilation or the machines cooling systems have on the machine itself. This can be especially important for high precision machines used for experimental research and medical equipment. The article shows the effects of ventilation and cooling system on the induction of additional resonant frequencies of the system for the high precision machine like a linear collider. This kind of machine requires special environmental conditions to assure proper beam stability. Due to the dynamic behaviour of typical machines, the presence of the new high amplitude frequencies in the 0-100 Hz range is very dangerous for its stability of work. In the case of high precision machines, it is not only a cause of not optimal working conditions but very often is a cause of serious problems.

A study on variation laws of infiltration rate with mechanical ventilation rate in a room

Mechanical ventilation system is commonly used or recommended to supply the outdoor fresh air for both centralized and non-centralized air-conditioning buildings. ASHRAE requires a positive pressure (i.e., zero infiltration rate) for mechanically ventilated rooms. In fact, positive pressure is difficult to be maintained under poor building airtightness or low mechanical ventilation rates. When the positive pressure is not achieved, the existence of air infiltration brings two problems—the outdoor air pollutants infiltrating indoors and the excessive fresh air cooling/heating load. In order to solve the above problems, air purifiers can be used to remove the indoor pollutants, and the mechanical ventilation rate should be reduced to prevent the excessive ventilation. Therefore, in order to determine the Clean Air Delivery Rate (CADR) for the air purifier and to calculate the amount of mechanical ventilation that should be reduced, the influence of mechanical ventilation on the room infiltration rates must be figured out. This study investigates the variation laws of the infiltration rate with the mechanical ventilation rate, and then theoretically deduces the relational expressions between the two rates for stack effect and wind dominant ventilation models. The theoretical derivations were validated by tests in actual rooms. From a practical perspective, this study can be used to improve the indoor environment and ventilation rates for mechanically ventilated rooms, demonstrated by the case study.

Influence of Mechanical Ventilation on the Pharmacokinetics of Vancomycin Administered by Continuous Infusion in Critically Ill Patients.

Pathophysiological changes involved in drug disposition in critically ill patients should be considered in order to optimize the dosing of vancomycin administered by continuous infusion, and certain strategies must be applied to reach therapeutic targets on the first day of treatment. The aim of this study was to develop a population pharmacokinetic model of vancomycin to determine clinical covariates, including mechanical ventilation, that influence the wide variability of this antimicrobial. Plasma vancomycin concentrations from 54 critically ill patients were analyzed simultaneously by a population pharmacokinetic approach. A nomogram for dosing recommendations was developed and was internally evaluated through stochastic simulations. The plasma vancomycin concentration-versus-time data were best described by a one-compartment open model with exponential interindividual variability associated with vancomycin clearance and the volume of distribution. Residual error followed a homoscedastic trend. Creatinine clearance and body weight significantly dropped the objective function value, showing their influence on vancomycin clearance and the volume of distribution, respectively. Characterization based on the presence of mechanical ventilation demonstrated a 20% decrease in vancomycin clearance. External validation (n = 18) was performed to evaluate the predictive ability of the model; median bias and precision values were 0.7 mg/liter (95% confidence interval [CI], -0.4, 1.7) and 5.9 mg/liter (95% CI, 5.4, 6.4), respectively. A population pharmacokinetic model was developed for the administration of vancomycin by continuous infusion to critically ill patients, demonstrating the influence of creatinine clearance and mechanical ventilation on vancomycin clearance, as well as the implications for targeting dosing rates to reach the therapeutic range (20 to 30 mg/liter).

Speckle-Tracking analysis of left ventricular systolic function in the intensive care unit.

Speckle-tracking analysis is a new available tool in order to assess left ventricular function in cardiology. Its novelty relies on the technological ability to track natural acoustic markers (known as speckle) within the myocardium during the cardiac cycle. This technology allows the evaluation of myocardium strain during systole and diastole. To date, global longitudinal strain (GLS) has been extensively studied in cardiology. It is now well established that GLS is more sensitive than left ventricular ejection fraction with 2D echocardiography in detecting systolic function impairment. It is also superior to left ventricular ejection fraction in the prediction of major cardio-vascular events. In the intensive care unit (ICU) setting, data are scarce. In experimental model and human studies in septic shock, speckle-tracking analysis suggests that GSL is impaired along with preserved left ventricular ejection fraction. Recent data also suggest that GLS impairment could predict in-ICU mortality in septic shock. In severe subarachnoid haemorrhage patients, speckle-tracking analysis could be more sensitive in detecting stress cardiomyopathy. However, there are many gaps to fill in the critically ill patient. For instance, the influence of mechanical ventilation on GLS is not fully elucidated, and there are, to date, too few data to exactly assess potential GLS alterations on the patient's outcome. Nonetheless, this new tool provides objective and sensitive data with acceptable intra and inter-observer variability and may be of primary interest in the evaluation of left-ventricular systolic function in the ICU.

Time influence of mechanical ventilation on functional independence in patients submitted to cardiac surgery: literature review

Abstract Introduction: Patients submitted to cardiovascular surgery present motor and respiratory complications mainly due to high surgery manipulation and the use of mechanical ventilation. Reducing the weaning start time and disconnecting patient's ventilation system prematurely can decrease the pulmonary complications and hospitalization time. Motor complications are the most relevant as they have a direct effect on functional independence provoked by immobility time. Objectives : Identify if mechanical ventilation time has an impact on functional capacity on patients submitted to cardiac surgery in order to contribute to the establishment of reliable evidence to practice through this patient's profile. Materials and methods : Original articles were analyzed, published between 2000 and 2014, which focused on the influence of mechanical ventilation time concerning the functional independence on patients submitted to cardiac surgery, contained in the following electronic database: Scielo, BIREME (LILACS), PubMed e CAPES. Results : It was observed that the length of stay in the intensive care unit in cardiac surgery was influenced directly by CPB, VM and pulmonary dysfunction. Functional independence was compromised in patients with longer duration of mechanical ventilation, postoperative pain and prolonged bed rest. It was also found that there is no consensus on the protocol for improved functional capacity. Conclusion : There is a functional decline in patients undergoing cardiac surgery, especially those at increased length of stay in mechanical ventilation, reflecting a direct and negative impact on their functional independence and quality of life.

Development of an integrated model of cardiovascular and pulmonary physiology for the evaluation of mechanical ventilation strategies.

We describe the development of an integrated cardiovascular and pulmonary model for use in the investigation of novel mechanical ventilation strategies in the intensive care unit. The cardiac model includes the cardiac chambers, the pulmonary circulation and the systemic circulation. The modeling of complex mechanisms for vascular segments, time varying elastance functions of cardiovascular components and the effect of vascular resistances, in health and disease under the influence of mechanical ventilation is investigated. The resulting biomedical simulator can aid in understanding the underlying pathophysiology of critically-ill patients and facilitate the development of more effective therapeutic strategies for evaluation in clinical trials.

Influence of mechanical ventilation and sepsis on redox balance in diaphragm, myocardium, limb muscles, and lungs

Mechanical ventilation (MV), using high tidal volumes (V(T)), causes lung (ventilator-induced lung injury [VILI]) and distant organ injury. Additionally, sepsis is characterized by increased oxidative stress. We tested whether MV is associated with enhanced oxidative stress in sepsis, the commonest underlying condition in clinical acute lung injury. Protein carbonylation and nitration, antioxidants, and inflammation (immunoblotting) were evaluated in diaphragm, gastrocnemius, soleus, myocardium, and lungs of nonseptic and septic (cecal ligation and puncture 24 hours before MV) rats undergoing MV (n = 7 per group) for 150 minutes using 3 different strategies (low V(T) [V(T) = 9 mL/kg], moderate V(T) [V(T) = 15 mL/kg], and high V(T) [V(T) = 25 mL/kg]) and in nonventilated control animals. Compared with nonventilated control animals, in septic and nonseptic rodents (1) diaphragms, limb muscles, and myocardium of high-V(T) rats exhibited a decrease in protein oxidation and nitration levels, (2) antioxidant levels followed a specific fiber-type distribution in slow- and fast-twitch muscles, (3) tumor necrosis factor α (TNF-α) levels were higher in respiratory and limb muscles, whereas no differences were observed in myocardium, and (4) in lungs, protein oxidation was increased, antioxidants were rather decreased, and TNF-α remained unmodified. In this model of VILI, oxidative stress does not occur in distant organs or skeletal muscles of rodents after several hours of MV with moderate-to-high V(T), whereas protein oxidation levels were increased in the lungs of the animals. Inflammatory events were moderately expressed in skeletal muscles and lungs of the MV rats. Concomitant sepsis did not strongly affect the MV-induced effects on muscles, myocardium, or lungs in the rodents.

Influence of mechanical ventilation with Chest Compression Synchronized ventilation (CCSV) or Intermitted Positive Pressure Ventilation (IPPV) on haemodynamics in a pig model

Objective: Guidelines recommend mechanical ventilation with Intermitted Positive Pressure Ventilation (IPPV) during resuscitation.1,2 Positive pressure ventilation might influence the effects of chest compressions on haemodynamics. We investigated the influence of the novel ventilator mode Chest Compression Synchronized Ventilation (CCSV) on arterial blood pressure compared with IPPV in a cross-over pig model.3

Mechanical ventilation in neurosurgery

The mechanical ventilation in neurological patients indicates some aspects related to the techniques used, such as hyperventilation and the application of positive end-expiratory pressure (PEEP). The measures generally adopted for lung protective ventilation, such as high levels of PEEP, low tidal volume, elevated respiratory frequency, and permissive hypercapnia can be damaging for patients with neurological disesases. The influence of mechanical ventilation on hemodynamic parameters, such as intracranial pressure (ICP) and cerebral perfusion pressure (CPP) has been the focus of many studies, even though the results are still controversial. The role of PEEP and its implications in neurological patients is in evidence. Based on data available in the literature, albeit controversial, there is a tendency to infer that the use of PEEP at low to moderate levels is unlikely to cause a significantincrease in ICP. While cerebral vasoconstriction induced by hypocapnia reduces effectively ICP, the risk of reducing cerebral blood flow (CBF) to a critical condition level was always a clinical concern and a subject of scientific investigation. There are few data about lung recruitment maneuver in this patient population.Lung protection strategiesshould alwaysbe respected, butsimultaneouslyoptimizeCPPandICP. Monitoring ofventilationisof paramountimportance, since there is a stronginfluenceof respiratory parametersin brainphysiology.

The influence of mechanical ventilation in a hemorrhagic shock model

Journal of Trauma and Acute Care Surgery: August 2013 - Volume 75 - Issue 2 - p 344-354 doi: 10.1097/TA.0b013e3182995604

Mechanical ventilation with positive end-expiratory pressure in critically ill patients: comparison of CW-Doppler ultrasound cardiac output monitoring (USCOM) and thermodilution (PiCCO)

Background Aggressive mechanical ventilation can markedly and unpredictably aff ect cardiac function. The fall in cardiac output (CO) is due to a reduction in left ventricular stroke volume (SV). The aim of the present pilot study was to assess the eff ects of diff erent positive end-expiratory pressure (PEEP) levels on circulatory function and to compare them with continuous wave (CW)-Doppler ultrasound cardiac output monitoring (USCOM) and a thermodilution-based haemodynamic monitoring system (PiCCO).Methods Twenty mechanically ventilated (PEEP ≤10 mbar) adult patients (female n = 6, male n = 14, mean age 62 years, mean SAPS II-score 48.5), the majority with pneumonia and septic shock) were followed with USCOM and PiCCO at stepwise increased PEEP-levels from 0-10 mbar (1 mbar steps). The changes in CO/SV were recorded.Results With both methods, an increase of PEEP resulted in a decrease of SV and CO. Although the absolute decrease was consistently higher by USCOM, the changes of the parameters were qualitatively comparable. CO fell from 8.83 L/min (± 2.39) by 0.4 L/min to 8.49 L/min (± 2.48) with PiCCO and from 9.3 L/min (± 3.43) by 1.0 L/min to 8.3 L/min (± 3.2) with USCOM. The median CO/SV fell by 4.5%/5.2% with PiCCO and 10.8%/9% with USCOM, respectively. Correlation of CO values with the two methods by Bland-Altman yielded comparable results (mean percentage error at PEEP 0 mbar 13%, PEEP 10 mbar 18%). An adequate fl ow signal with USCOM was achieved in all patients.Conclusions A signifi cant infl uence of mechanical ventilation with PEEP on haemodynamic parameters was evident both with USCOM and PiCCO. While thermodilution methods like PiCCO are well established but time-consuming and invasive, CW-Doppler based USCOM constitutes an important tool for easy, rapid and reliable diagnosis and haemodynamic monitoring of critically ill patients.

Echographic evaluation of ICU patients with tissue Doppler imaging: more studies and more consensus are still needed

In many intensive care units (ICUs), cardiac transthoracic echocardio graphy (TTE) has replaced invasive monitoring in routine evaluation of acutely ill patients. Since the mid ’80s, there have been many studies of ICU patients, most of whom were receiving mechanical ventilation (MV). With the emergence of new TTE modalities such as tissue Doppler imaging (TDI) and strain rate or threedimensional imaging, new studies are currently available. TDI is now widely used in cardiology and is a powerful tool in the assessment of left ventricular fi lling pressures (LVFPs), relaxation, or right ventricular function. It was suggested that the ratio of pulsed Doppler mitral fl ow in early diastole (E wave) over early diastolic mitral annulus velocity (E a with TDI), known as E/E a , was closely related to LVFP. However, in many clinical situations, a lack of correlation between E/E a and LVFP was observed, even in patients with spontaneous breathing [1]. Th ree studies focusing on TDI and left ventricular function in ICU patients were recently published [2-4], two of them in Critical Care [2,4]. Th ese studies provide new approaches in the assessment of systolic or diastolic function during septic shock and weaning from MV. In all studies, patients were mechanically ventilated, adding complexity to the TTE examination. For years, invasive pressure measurements in patients under MV have been performed at the end-expiratory time, when intra-thoracic pressure is closer to atmospheric pressure in most cases. For TTE study, things are slightly diff erent. Doppler study (such as E wave) aims to determine direction and velocity of blood fl ow. Th at fl ow, as intra-cardiac pressure, depends of the respiratory cycle. By contrast, TDI determines the velocity of the myocardium and is considered relatively load-independent. So the necessity to perform measure ments (E a ) at a certain time of the respiratory cycle may be questioned. Moreover, methodo logical diff erences between studies may be confusing (Table 1). Th ese diff erences may lead to a loss of information in some cases and eventually may explain the diff erences observed between TTE and invasive monitoring. At the bedside, the clinician may be tempted to use a simple beat measurement and disregard the res pira tory time. Further studies focusing on the feasibility and infl uence of MV on TDI parameters are needed [5]. Guidelines regarding the methods and designs of future trials in the ICU will be valuable, as these studies demon strate that a quantitative assessment of cardiovascular parameters over a simple qualitative approach is possible with TTE in patients on MV. As in the study by Moschietto and colleagues [2], evolution of these values may provide crucial information for the clinician.

Influence of mechanical ventilation on intestinal microcirculation and inflammation in septic rats

Although the adverse effects of mechanical ventilation on circulation and intestinal organ perfusion are well known, the influence of assisted breathing versus controlled ventilation has not been investigated. We hypothesized that pressure support ventilation causes less decrease in gut perfusion and less neutrophil adhesion than controlled ventilation.

Mechanical ventilation aggravates transfusion-related acute lung injury induced by MHC class I antibodies

Transfusion-related acute lung injury (TRALI) occurs more often in critically ill patients than in a general hospital population, possibly due to the presence of underlying inflammatory conditions that may prime pulmonary neutrophils. Mechanical ventilation (MV) may be a risk factor for developing TRALI. We determined the influence of MV on the development of TRALI, combining a murine MV model causing ventilator-induced lung injury with a model of antibody-induced TRALI [1,2].

Total Body Response to Mechanical Ventilation of Healthy Lungs: an Experimental Study in Piglets

The objective of our study was to assess the influence of mechanical ventilation on healthy body organs. Fifteen piglets (aged 6 weeks, 19-27 kg) were anesthetized, instrumented, and divided into three groups: Group A - spontaneously breathing, group B - mechanically ventilated with tidal volume 6 ml/kg, and group C - ventilated with tidal volume 10 ml/kg for 12 hours. The parameters of lung, heart, liver and kidney functions neurohumoral regulation and systemic inflammatory reaction were recorded initially (time-1) and after 12 hours (time-12) of mechanical ventilation. At the onset of experiment (time-1) the levels of soluble adhesive molecules were higher (CAM; P<0.01), glomerular filtration index and free water clearance were lower (P<0.05) in both ventilated groups than in group A. Right ventricle myocardial performance index was higher (RIMP; P<0.05) in group C when compared with group A. Levels of CAM (P<0.05) and creatinine clearance (P<0.01) were higher, free water clearance was lower (P<0.05) in group C when compared to group B. At time-12 the RIMP (P<0.05) and levels of CAM were increased (P<0.01), creatinine clearance was decreased (P<0.05) in both ventilated groups compared to the same parameter at time-1. Ventilation index was higher (P<0.05), and hypoxemic index was lower (P<0.01) in group C when compared to group B. In conclusion, this study showed that mechanical ventilation induced changes compatible with early inflammatory response in healthy animals. Higher tidal volumes had detrimental effect on ventilatory parameters, reduced myocardial performance and potentiated adverse reaction of other organs.

The Impact of Rotary Blood Pump in Conjunction with Mechanical Ventilation on Ventricular Energetic Parameters

Aim of this work is to study the impact of left ventricular rotary blood pump assistance, on energetic variables, when mechanical ventilation (MV) of the lungs is applied. Computer simulation was used to perform this study. Lumped parameter models reproduce the circulatory system. Variable elastance models reproduce the Starling's law of the heart for each ventricle. After the reproduction of ischemic heart disease left ventricular assistance was applied using a model of rotary blood pump. The pump speed was changed in steps and was assumed to be constant during each step. The influence of mechanical ventilation was introduced by different values of positive mean thoracic pressure. The increase of the rotational speed has a significant influence on some ventricular energetic variables. In fact it decreased left ventricular external work, left and right ventricular pressure-volume area and the left ventricular efficiency. Finally, it increased the right ventricular efficiency but had no influence on the right ventricular external work. The increase of thoracic pressure from -2 to +5 mmHg caused a significant decrease of external work, pressure-volume area (right ventricular pressure-volume area dropped up to 50%) and an increase of right ventricular efficiency (by 40%) while left ventricular efficiency remained almost stable. Numerical simulation is a very suitable tool to predict changes of not easily measurable parameters such as energetic ventricular variables when mechanical assistance of heart and/or lungs is applied independently or simultaneously.